xref: /linux/fs/btrfs/extent_io.c (revision d6296cb65320be16dbf20f2fd584ddc25f3437cd)

// SPDX-License-Identifier: GPL-2.0

#include <linux/bitops.h>
#include <linux/slab.h>
#include <linux/bio.h>
#include <linux/mm.h>
#include <linux/pagemap.h>
#include <linux/page-flags.h>
#include <linux/sched/mm.h>
#include <linux/spinlock.h>
#include <linux/blkdev.h>
#include <linux/swap.h>
#include <linux/writeback.h>
#include <linux/pagevec.h>
#include <linux/prefetch.h>
#include <linux/fsverity.h>
#include "misc.h"
#include "extent_io.h"
#include "extent-io-tree.h"
#include "extent_map.h"
#include "ctree.h"
#include "btrfs_inode.h"
#include "bio.h"
#include "check-integrity.h"
#include "locking.h"
#include "rcu-string.h"
#include "backref.h"
#include "disk-io.h"
#include "subpage.h"
#include "zoned.h"
#include "block-group.h"
#include "compression.h"
#include "fs.h"
#include "accessors.h"
#include "file-item.h"
#include "file.h"
#include "dev-replace.h"
#include "super.h"
#include "transaction.h"

static struct kmem_cache *extent_buffer_cache;

#ifdef CONFIG_BTRFS_DEBUG
static inline void btrfs_leak_debug_add_eb(struct extent_buffer *eb)
{
	struct btrfs_fs_info *fs_info = eb->fs_info;
	unsigned long flags;

	spin_lock_irqsave(&fs_info->eb_leak_lock, flags);
	list_add(&eb->leak_list, &fs_info->allocated_ebs);
	spin_unlock_irqrestore(&fs_info->eb_leak_lock, flags);
}

static inline void btrfs_leak_debug_del_eb(struct extent_buffer *eb)
{
	struct btrfs_fs_info *fs_info = eb->fs_info;
	unsigned long flags;

	spin_lock_irqsave(&fs_info->eb_leak_lock, flags);
	list_del(&eb->leak_list);
	spin_unlock_irqrestore(&fs_info->eb_leak_lock, flags);
}

void btrfs_extent_buffer_leak_debug_check(struct btrfs_fs_info *fs_info)
{
	struct extent_buffer *eb;
	unsigned long flags;

	/*
	 * If we didn't get into open_ctree our allocated_ebs will not be
	 * initialized, so just skip this.
	 */
	if (!fs_info->allocated_ebs.next)
		return;

	WARN_ON(!list_empty(&fs_info->allocated_ebs));
	spin_lock_irqsave(&fs_info->eb_leak_lock, flags);
	while (!list_empty(&fs_info->allocated_ebs)) {
		eb = list_first_entry(&fs_info->allocated_ebs,
				      struct extent_buffer, leak_list);
		pr_err(
	"BTRFS: buffer leak start %llu len %lu refs %d bflags %lu owner %llu\n",
		       eb->start, eb->len, atomic_read(&eb->refs), eb->bflags,
		       btrfs_header_owner(eb));
		list_del(&eb->leak_list);
		kmem_cache_free(extent_buffer_cache, eb);
	}
	spin_unlock_irqrestore(&fs_info->eb_leak_lock, flags);
}
#else
#define btrfs_leak_debug_add_eb(eb)			do {} while (0)
#define btrfs_leak_debug_del_eb(eb)			do {} while (0)
#endif

/*
 * Structure to record info about the bio being assembled, and other info like
 * how many bytes are there before stripe/ordered extent boundary.
 */
struct btrfs_bio_ctrl {
	struct bio *bio;
	int mirror_num;
	enum btrfs_compression_type compress_type;
	u32 len_to_oe_boundary;
	btrfs_bio_end_io_t end_io_func;

	/*
	 * This is for metadata read, to provide the extra needed verification
	 * info.  This has to be provided for submit_one_bio(), as
	 * submit_one_bio() can submit a bio if it ends at stripe boundary.  If
	 * no such parent_check is provided, the metadata can hit false alert at
	 * endio time.
	 */
	struct btrfs_tree_parent_check *parent_check;

	/*
	 * Tell writepage not to lock the state bits for this range, it still
	 * does the unlocking.
	 */
	bool extent_locked;

	/* Tell the submit_bio code to use REQ_SYNC */
	bool sync_io;
};

static void submit_one_bio(struct btrfs_bio_ctrl *bio_ctrl)
{
	struct bio *bio;
	struct bio_vec *bv;
	struct inode *inode;
	int mirror_num;

	if (!bio_ctrl->bio)
		return;

	bio = bio_ctrl->bio;
	bv = bio_first_bvec_all(bio);
	inode = bv->bv_page->mapping->host;
	mirror_num = bio_ctrl->mirror_num;

	/* Caller should ensure the bio has at least some range added */
	ASSERT(bio->bi_iter.bi_size);

	if (!is_data_inode(inode)) {
		if (btrfs_op(bio) != BTRFS_MAP_WRITE) {
			/*
			 * For metadata read, we should have the parent_check,
			 * and copy it to bbio for metadata verification.
			 */
			ASSERT(bio_ctrl->parent_check);
			memcpy(&btrfs_bio(bio)->parent_check,
			       bio_ctrl->parent_check,
			       sizeof(struct btrfs_tree_parent_check));
		}
		bio->bi_opf |= REQ_META;
	}

	if (btrfs_op(bio) == BTRFS_MAP_READ &&
	    bio_ctrl->compress_type != BTRFS_COMPRESS_NONE)
		btrfs_submit_compressed_read(inode, bio, mirror_num);
	else
		btrfs_submit_bio(bio, mirror_num);

	/* The bio is owned by the end_io handler now */
	bio_ctrl->bio = NULL;
}

/*
 * Submit or fail the current bio in the bio_ctrl structure.
 */
static void submit_write_bio(struct btrfs_bio_ctrl *bio_ctrl, int ret)
{
	struct bio *bio = bio_ctrl->bio;

	if (!bio)
		return;

	if (ret) {
		ASSERT(ret < 0);
		btrfs_bio_end_io(btrfs_bio(bio), errno_to_blk_status(ret));
		/* The bio is owned by the end_io handler now */
		bio_ctrl->bio = NULL;
	} else {
		submit_one_bio(bio_ctrl);
	}
}

int __init extent_buffer_init_cachep(void)
{
	extent_buffer_cache = kmem_cache_create("btrfs_extent_buffer",
			sizeof(struct extent_buffer), 0,
			SLAB_MEM_SPREAD, NULL);
	if (!extent_buffer_cache)
		return -ENOMEM;

	return 0;
}

void __cold extent_buffer_free_cachep(void)
{
	/*
	 * Make sure all delayed rcu free are flushed before we
	 * destroy caches.
	 */
	rcu_barrier();
	kmem_cache_destroy(extent_buffer_cache);
}

void extent_range_clear_dirty_for_io(struct inode *inode, u64 start, u64 end)
{
	unsigned long index = start >> PAGE_SHIFT;
	unsigned long end_index = end >> PAGE_SHIFT;
	struct page *page;

	while (index <= end_index) {
		page = find_get_page(inode->i_mapping, index);
		BUG_ON(!page); /* Pages should be in the extent_io_tree */
		clear_page_dirty_for_io(page);
		put_page(page);
		index++;
	}
}

void extent_range_redirty_for_io(struct inode *inode, u64 start, u64 end)
{
	struct address_space *mapping = inode->i_mapping;
	unsigned long index = start >> PAGE_SHIFT;
	unsigned long end_index = end >> PAGE_SHIFT;
	struct folio *folio;

	while (index <= end_index) {
		folio = filemap_get_folio(mapping, index);
		filemap_dirty_folio(mapping, folio);
		folio_account_redirty(folio);
		index += folio_nr_pages(folio);
		folio_put(folio);
	}
}

/*
 * Process one page for __process_pages_contig().
 *
 * Return >0 if we hit @page == @locked_page.
 * Return 0 if we updated the page status.
 * Return -EGAIN if the we need to try again.
 * (For PAGE_LOCK case but got dirty page or page not belong to mapping)
 */
static int process_one_page(struct btrfs_fs_info *fs_info,
			    struct address_space *mapping,
			    struct page *page, struct page *locked_page,
			    unsigned long page_ops, u64 start, u64 end)
{
	u32 len;

	ASSERT(end + 1 - start != 0 && end + 1 - start < U32_MAX);
	len = end + 1 - start;

	if (page_ops & PAGE_SET_ORDERED)
		btrfs_page_clamp_set_ordered(fs_info, page, start, len);
	if (page_ops & PAGE_SET_ERROR)
		btrfs_page_clamp_set_error(fs_info, page, start, len);
	if (page_ops & PAGE_START_WRITEBACK) {
		btrfs_page_clamp_clear_dirty(fs_info, page, start, len);
		btrfs_page_clamp_set_writeback(fs_info, page, start, len);
	}
	if (page_ops & PAGE_END_WRITEBACK)
		btrfs_page_clamp_clear_writeback(fs_info, page, start, len);

	if (page == locked_page)
		return 1;

	if (page_ops & PAGE_LOCK) {
		int ret;

		ret = btrfs_page_start_writer_lock(fs_info, page, start, len);
		if (ret)
			return ret;
		if (!PageDirty(page) || page->mapping != mapping) {
			btrfs_page_end_writer_lock(fs_info, page, start, len);
			return -EAGAIN;
		}
	}
	if (page_ops & PAGE_UNLOCK)
		btrfs_page_end_writer_lock(fs_info, page, start, len);
	return 0;
}

static int __process_pages_contig(struct address_space *mapping,
				  struct page *locked_page,
				  u64 start, u64 end, unsigned long page_ops,
				  u64 *processed_end)
{
	struct btrfs_fs_info *fs_info = btrfs_sb(mapping->host->i_sb);
	pgoff_t start_index = start >> PAGE_SHIFT;
	pgoff_t end_index = end >> PAGE_SHIFT;
	pgoff_t index = start_index;
	unsigned long pages_processed = 0;
	struct folio_batch fbatch;
	int err = 0;
	int i;

	if (page_ops & PAGE_LOCK) {
		ASSERT(page_ops == PAGE_LOCK);
		ASSERT(processed_end && *processed_end == start);
	}

	if ((page_ops & PAGE_SET_ERROR) && start_index <= end_index)
		mapping_set_error(mapping, -EIO);

	folio_batch_init(&fbatch);
	while (index <= end_index) {
		int found_folios;

		found_folios = filemap_get_folios_contig(mapping, &index,
				end_index, &fbatch);

		if (found_folios == 0) {
			/*
			 * Only if we're going to lock these pages, we can find
			 * nothing at @index.
			 */
			ASSERT(page_ops & PAGE_LOCK);
			err = -EAGAIN;
			goto out;
		}

		for (i = 0; i < found_folios; i++) {
			int process_ret;
			struct folio *folio = fbatch.folios[i];
			process_ret = process_one_page(fs_info, mapping,
					&folio->page, locked_page, page_ops,
					start, end);
			if (process_ret < 0) {
				err = -EAGAIN;
				folio_batch_release(&fbatch);
				goto out;
			}
			pages_processed += folio_nr_pages(folio);
		}
		folio_batch_release(&fbatch);
		cond_resched();
	}
out:
	if (err && processed_end) {
		/*
		 * Update @processed_end. I know this is awful since it has
		 * two different return value patterns (inclusive vs exclusive).
		 *
		 * But the exclusive pattern is necessary if @start is 0, or we
		 * underflow and check against processed_end won't work as
		 * expected.
		 */
		if (pages_processed)
			*processed_end = min(end,
			((u64)(start_index + pages_processed) << PAGE_SHIFT) - 1);
		else
			*processed_end = start;
	}
	return err;
}

static noinline void __unlock_for_delalloc(struct inode *inode,
					   struct page *locked_page,
					   u64 start, u64 end)
{
	unsigned long index = start >> PAGE_SHIFT;
	unsigned long end_index = end >> PAGE_SHIFT;

	ASSERT(locked_page);
	if (index == locked_page->index && end_index == index)
		return;

	__process_pages_contig(inode->i_mapping, locked_page, start, end,
			       PAGE_UNLOCK, NULL);
}

static noinline int lock_delalloc_pages(struct inode *inode,
					struct page *locked_page,
					u64 delalloc_start,
					u64 delalloc_end)
{
	unsigned long index = delalloc_start >> PAGE_SHIFT;
	unsigned long end_index = delalloc_end >> PAGE_SHIFT;
	u64 processed_end = delalloc_start;
	int ret;

	ASSERT(locked_page);
	if (index == locked_page->index && index == end_index)
		return 0;

	ret = __process_pages_contig(inode->i_mapping, locked_page, delalloc_start,
				     delalloc_end, PAGE_LOCK, &processed_end);
	if (ret == -EAGAIN && processed_end > delalloc_start)
		__unlock_for_delalloc(inode, locked_page, delalloc_start,
				      processed_end);
	return ret;
}

/*
 * Find and lock a contiguous range of bytes in the file marked as delalloc, no
 * more than @max_bytes.
 *
 * @start:	The original start bytenr to search.
 *		Will store the extent range start bytenr.
 * @end:	The original end bytenr of the search range
 *		Will store the extent range end bytenr.
 *
 * Return true if we find a delalloc range which starts inside the original
 * range, and @start/@end will store the delalloc range start/end.
 *
 * Return false if we can't find any delalloc range which starts inside the
 * original range, and @start/@end will be the non-delalloc range start/end.
 */
EXPORT_FOR_TESTS
noinline_for_stack bool find_lock_delalloc_range(struct inode *inode,
				    struct page *locked_page, u64 *start,
				    u64 *end)
{
	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
	struct extent_io_tree *tree = &BTRFS_I(inode)->io_tree;
	const u64 orig_start = *start;
	const u64 orig_end = *end;
	/* The sanity tests may not set a valid fs_info. */
	u64 max_bytes = fs_info ? fs_info->max_extent_size : BTRFS_MAX_EXTENT_SIZE;
	u64 delalloc_start;
	u64 delalloc_end;
	bool found;
	struct extent_state *cached_state = NULL;
	int ret;
	int loops = 0;

	/* Caller should pass a valid @end to indicate the search range end */
	ASSERT(orig_end > orig_start);

	/* The range should at least cover part of the page */
	ASSERT(!(orig_start >= page_offset(locked_page) + PAGE_SIZE ||
		 orig_end <= page_offset(locked_page)));
again:
	/* step one, find a bunch of delalloc bytes starting at start */
	delalloc_start = *start;
	delalloc_end = 0;
	found = btrfs_find_delalloc_range(tree, &delalloc_start, &delalloc_end,
					  max_bytes, &cached_state);
	if (!found || delalloc_end <= *start || delalloc_start > orig_end) {
		*start = delalloc_start;

		/* @delalloc_end can be -1, never go beyond @orig_end */
		*end = min(delalloc_end, orig_end);
		free_extent_state(cached_state);
		return false;
	}

	/*
	 * start comes from the offset of locked_page.  We have to lock
	 * pages in order, so we can't process delalloc bytes before
	 * locked_page
	 */
	if (delalloc_start < *start)
		delalloc_start = *start;

	/*
	 * make sure to limit the number of pages we try to lock down
	 */
	if (delalloc_end + 1 - delalloc_start > max_bytes)
		delalloc_end = delalloc_start + max_bytes - 1;

	/* step two, lock all the pages after the page that has start */
	ret = lock_delalloc_pages(inode, locked_page,
				  delalloc_start, delalloc_end);
	ASSERT(!ret || ret == -EAGAIN);
	if (ret == -EAGAIN) {
		/* some of the pages are gone, lets avoid looping by
		 * shortening the size of the delalloc range we're searching
		 */
		free_extent_state(cached_state);
		cached_state = NULL;
		if (!loops) {
			max_bytes = PAGE_SIZE;
			loops = 1;
			goto again;
		} else {
			found = false;
			goto out_failed;
		}
	}

	/* step three, lock the state bits for the whole range */
	lock_extent(tree, delalloc_start, delalloc_end, &cached_state);

	/* then test to make sure it is all still delalloc */
	ret = test_range_bit(tree, delalloc_start, delalloc_end,
			     EXTENT_DELALLOC, 1, cached_state);
	if (!ret) {
		unlock_extent(tree, delalloc_start, delalloc_end,
			      &cached_state);
		__unlock_for_delalloc(inode, locked_page,
			      delalloc_start, delalloc_end);
		cond_resched();
		goto again;
	}
	free_extent_state(cached_state);
	*start = delalloc_start;
	*end = delalloc_end;
out_failed:
	return found;
}

void extent_clear_unlock_delalloc(struct btrfs_inode *inode, u64 start, u64 end,
				  struct page *locked_page,
				  u32 clear_bits, unsigned long page_ops)
{
	clear_extent_bit(&inode->io_tree, start, end, clear_bits, NULL);

	__process_pages_contig(inode->vfs_inode.i_mapping, locked_page,
			       start, end, page_ops, NULL);
}

static void end_page_read(struct page *page, bool uptodate, u64 start, u32 len)
{
	struct btrfs_fs_info *fs_info = btrfs_sb(page->mapping->host->i_sb);

	ASSERT(page_offset(page) <= start &&
	       start + len <= page_offset(page) + PAGE_SIZE);

	if (uptodate) {
		if (fsverity_active(page->mapping->host) &&
		    !PageError(page) &&
		    !PageUptodate(page) &&
		    start < i_size_read(page->mapping->host) &&
		    !fsverity_verify_page(page)) {
			btrfs_page_set_error(fs_info, page, start, len);
		} else {
			btrfs_page_set_uptodate(fs_info, page, start, len);
		}
	} else {
		btrfs_page_clear_uptodate(fs_info, page, start, len);
		btrfs_page_set_error(fs_info, page, start, len);
	}

	if (!btrfs_is_subpage(fs_info, page))
		unlock_page(page);
	else
		btrfs_subpage_end_reader(fs_info, page, start, len);
}

/* lots and lots of room for performance fixes in the end_bio funcs */

void end_extent_writepage(struct page *page, int err, u64 start, u64 end)
{
	struct btrfs_inode *inode;
	const bool uptodate = (err == 0);
	int ret = 0;

	ASSERT(page && page->mapping);
	inode = BTRFS_I(page->mapping->host);
	btrfs_writepage_endio_finish_ordered(inode, page, start, end, uptodate);

	if (!uptodate) {
		const struct btrfs_fs_info *fs_info = inode->root->fs_info;
		u32 len;

		ASSERT(end + 1 - start <= U32_MAX);
		len = end + 1 - start;

		btrfs_page_clear_uptodate(fs_info, page, start, len);
		btrfs_page_set_error(fs_info, page, start, len);
		ret = err < 0 ? err : -EIO;
		mapping_set_error(page->mapping, ret);
	}
}

/*
 * after a writepage IO is done, we need to:
 * clear the uptodate bits on error
 * clear the writeback bits in the extent tree for this IO
 * end_page_writeback if the page has no more pending IO
 *
 * Scheduling is not allowed, so the extent state tree is expected
 * to have one and only one object corresponding to this IO.
 */
static void end_bio_extent_writepage(struct btrfs_bio *bbio)
{
	struct bio *bio = &bbio->bio;
	int error = blk_status_to_errno(bio->bi_status);
	struct bio_vec *bvec;
	u64 start;
	u64 end;
	struct bvec_iter_all iter_all;

	ASSERT(!bio_flagged(bio, BIO_CLONED));
	bio_for_each_segment_all(bvec, bio, iter_all) {
		struct page *page = bvec->bv_page;
		struct inode *inode = page->mapping->host;
		struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
		const u32 sectorsize = fs_info->sectorsize;

		/* Our read/write should always be sector aligned. */
		if (!IS_ALIGNED(bvec->bv_offset, sectorsize))
			btrfs_err(fs_info,
		"partial page write in btrfs with offset %u and length %u",
				  bvec->bv_offset, bvec->bv_len);
		else if (!IS_ALIGNED(bvec->bv_len, sectorsize))
			btrfs_info(fs_info,
		"incomplete page write with offset %u and length %u",
				   bvec->bv_offset, bvec->bv_len);

		start = page_offset(page) + bvec->bv_offset;
		end = start + bvec->bv_len - 1;

		end_extent_writepage(page, error, start, end);

		btrfs_page_clear_writeback(fs_info, page, start, bvec->bv_len);
	}

	bio_put(bio);
}

/*
 * Record previously processed extent range
 *
 * For endio_readpage_release_extent() to handle a full extent range, reducing
 * the extent io operations.
 */
struct processed_extent {
	struct btrfs_inode *inode;
	/* Start of the range in @inode */
	u64 start;
	/* End of the range in @inode */
	u64 end;
	bool uptodate;
};

/*
 * Try to release processed extent range
 *
 * May not release the extent range right now if the current range is
 * contiguous to processed extent.
 *
 * Will release processed extent when any of @inode, @uptodate, the range is
 * no longer contiguous to the processed range.
 *
 * Passing @inode == NULL will force processed extent to be released.
 */
static void endio_readpage_release_extent(struct processed_extent *processed,
			      struct btrfs_inode *inode, u64 start, u64 end,
			      bool uptodate)
{
	struct extent_state *cached = NULL;
	struct extent_io_tree *tree;

	/* The first extent, initialize @processed */
	if (!processed->inode)
		goto update;

	/*
	 * Contiguous to processed extent, just uptodate the end.
	 *
	 * Several things to notice:
	 *
	 * - bio can be merged as long as on-disk bytenr is contiguous
	 *   This means we can have page belonging to other inodes, thus need to
	 *   check if the inode still matches.
	 * - bvec can contain range beyond current page for multi-page bvec
	 *   Thus we need to do processed->end + 1 >= start check
	 */
	if (processed->inode == inode && processed->uptodate == uptodate &&
	    processed->end + 1 >= start && end >= processed->end) {
		processed->end = end;
		return;
	}

	tree = &processed->inode->io_tree;
	/*
	 * Now we don't have range contiguous to the processed range, release
	 * the processed range now.
	 */
	unlock_extent(tree, processed->start, processed->end, &cached);

update:
	/* Update processed to current range */
	processed->inode = inode;
	processed->start = start;
	processed->end = end;
	processed->uptodate = uptodate;
}

static void begin_page_read(struct btrfs_fs_info *fs_info, struct page *page)
{
	ASSERT(PageLocked(page));
	if (!btrfs_is_subpage(fs_info, page))
		return;

	ASSERT(PagePrivate(page));
	btrfs_subpage_start_reader(fs_info, page, page_offset(page), PAGE_SIZE);
}

/*
 * Find extent buffer for a givne bytenr.
 *
 * This is for end_bio_extent_readpage(), thus we can't do any unsafe locking
 * in endio context.
 */
static struct extent_buffer *find_extent_buffer_readpage(
		struct btrfs_fs_info *fs_info, struct page *page, u64 bytenr)
{
	struct extent_buffer *eb;

	/*
	 * For regular sectorsize, we can use page->private to grab extent
	 * buffer
	 */
	if (fs_info->nodesize >= PAGE_SIZE) {
		ASSERT(PagePrivate(page) && page->private);
		return (struct extent_buffer *)page->private;
	}

	/* For subpage case, we need to lookup buffer radix tree */
	rcu_read_lock();
	eb = radix_tree_lookup(&fs_info->buffer_radix,
			       bytenr >> fs_info->sectorsize_bits);
	rcu_read_unlock();
	ASSERT(eb);
	return eb;
}

/*
 * after a readpage IO is done, we need to:
 * clear the uptodate bits on error
 * set the uptodate bits if things worked
 * set the page up to date if all extents in the tree are uptodate
 * clear the lock bit in the extent tree
 * unlock the page if there are no other extents locked for it
 *
 * Scheduling is not allowed, so the extent state tree is expected
 * to have one and only one object corresponding to this IO.
 */
static void end_bio_extent_readpage(struct btrfs_bio *bbio)
{
	struct bio *bio = &bbio->bio;
	struct bio_vec *bvec;
	struct processed_extent processed = { 0 };
	/*
	 * The offset to the beginning of a bio, since one bio can never be
	 * larger than UINT_MAX, u32 here is enough.
	 */
	u32 bio_offset = 0;
	int mirror;
	struct bvec_iter_all iter_all;

	ASSERT(!bio_flagged(bio, BIO_CLONED));
	bio_for_each_segment_all(bvec, bio, iter_all) {
		bool uptodate = !bio->bi_status;
		struct page *page = bvec->bv_page;
		struct inode *inode = page->mapping->host;
		struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
		const u32 sectorsize = fs_info->sectorsize;
		u64 start;
		u64 end;
		u32 len;

		btrfs_debug(fs_info,
			"end_bio_extent_readpage: bi_sector=%llu, err=%d, mirror=%u",
			bio->bi_iter.bi_sector, bio->bi_status,
			bbio->mirror_num);

		/*
		 * We always issue full-sector reads, but if some block in a
		 * page fails to read, blk_update_request() will advance
		 * bv_offset and adjust bv_len to compensate.  Print a warning
		 * for unaligned offsets, and an error if they don't add up to
		 * a full sector.
		 */
		if (!IS_ALIGNED(bvec->bv_offset, sectorsize))
			btrfs_err(fs_info,
		"partial page read in btrfs with offset %u and length %u",
				  bvec->bv_offset, bvec->bv_len);
		else if (!IS_ALIGNED(bvec->bv_offset + bvec->bv_len,
				     sectorsize))
			btrfs_info(fs_info,
		"incomplete page read with offset %u and length %u",
				   bvec->bv_offset, bvec->bv_len);

		start = page_offset(page) + bvec->bv_offset;
		end = start + bvec->bv_len - 1;
		len = bvec->bv_len;

		mirror = bbio->mirror_num;
		if (uptodate && !is_data_inode(inode) &&
		    btrfs_validate_metadata_buffer(bbio, page, start, end, mirror))
			uptodate = false;

		if (likely(uptodate)) {
			loff_t i_size = i_size_read(inode);
			pgoff_t end_index = i_size >> PAGE_SHIFT;

			/*
			 * Zero out the remaining part if this range straddles
			 * i_size.
			 *
			 * Here we should only zero the range inside the bvec,
			 * not touch anything else.
			 *
			 * NOTE: i_size is exclusive while end is inclusive.
			 */
			if (page->index == end_index && i_size <= end) {
				u32 zero_start = max(offset_in_page(i_size),
						     offset_in_page(start));

				zero_user_segment(page, zero_start,
						  offset_in_page(end) + 1);
			}
		} else if (!is_data_inode(inode)) {
			struct extent_buffer *eb;

			eb = find_extent_buffer_readpage(fs_info, page, start);
			set_bit(EXTENT_BUFFER_READ_ERR, &eb->bflags);
			eb->read_mirror = mirror;
			atomic_dec(&eb->io_pages);
		}

		/* Update page status and unlock. */
		end_page_read(page, uptodate, start, len);
		endio_readpage_release_extent(&processed, BTRFS_I(inode),
					      start, end, PageUptodate(page));

		ASSERT(bio_offset + len > bio_offset);
		bio_offset += len;

	}
	/* Release the last extent */
	endio_readpage_release_extent(&processed, NULL, 0, 0, false);
	bio_put(bio);
}

/*
 * Populate every free slot in a provided array with pages.
 *
 * @nr_pages:   number of pages to allocate
 * @page_array: the array to fill with pages; any existing non-null entries in
 * 		the array will be skipped
 *
 * Return: 0        if all pages were able to be allocated;
 *         -ENOMEM  otherwise, and the caller is responsible for freeing all
 *                  non-null page pointers in the array.
 */
int btrfs_alloc_page_array(unsigned int nr_pages, struct page **page_array)
{
	unsigned int allocated;

	for (allocated = 0; allocated < nr_pages;) {
		unsigned int last = allocated;

		allocated = alloc_pages_bulk_array(GFP_NOFS, nr_pages, page_array);

		if (allocated == nr_pages)
			return 0;

		/*
		 * During this iteration, no page could be allocated, even
		 * though alloc_pages_bulk_array() falls back to alloc_page()
		 * if  it could not bulk-allocate. So we must be out of memory.
		 */
		if (allocated == last)
			return -ENOMEM;

		memalloc_retry_wait(GFP_NOFS);
	}
	return 0;
}

/*
 * Attempt to add a page to bio.
 *
 * @bio_ctrl:       record both the bio, and its bio_flags
 * @page:	    page to add to the bio
 * @disk_bytenr:    offset of the new bio or to check whether we are adding
 *                  a contiguous page to the previous one
 * @size:	    portion of page that we want to write
 * @pg_offset:	    starting offset in the page
 * @compress_type:  compression type of the current bio to see if we can merge them
 *
 * Attempt to add a page to bio considering stripe alignment etc.
 *
 * Return >= 0 for the number of bytes added to the bio.
 * Can return 0 if the current bio is already at stripe/zone boundary.
 * Return <0 for error.
 */
static int btrfs_bio_add_page(struct btrfs_bio_ctrl *bio_ctrl,
			      struct page *page,
			      u64 disk_bytenr, unsigned int size,
			      unsigned int pg_offset,
			      enum btrfs_compression_type compress_type)
{
	struct bio *bio = bio_ctrl->bio;
	u32 bio_size = bio->bi_iter.bi_size;
	u32 real_size;
	const sector_t sector = disk_bytenr >> SECTOR_SHIFT;
	bool contig = false;

	ASSERT(bio);
	/* The limit should be calculated when bio_ctrl->bio is allocated */
	ASSERT(bio_ctrl->len_to_oe_boundary);
	if (bio_ctrl->compress_type != compress_type)
		return 0;


	if (bio->bi_iter.bi_size == 0) {
		/* We can always add a page into an empty bio. */
		contig = true;
	} else if (bio_ctrl->compress_type == BTRFS_COMPRESS_NONE) {
		struct bio_vec *bvec = bio_last_bvec_all(bio);

		/*
		 * The contig check requires the following conditions to be met:
		 * 1) The pages are belonging to the same inode
		 *    This is implied by the call chain.
		 *
		 * 2) The range has adjacent logical bytenr
		 *
		 * 3) The range has adjacent file offset
		 *    This is required for the usage of btrfs_bio->file_offset.
		 */
		if (bio_end_sector(bio) == sector &&
		    page_offset(bvec->bv_page) + bvec->bv_offset +
		    bvec->bv_len == page_offset(page) + pg_offset)
			contig = true;
	} else {
		/*
		 * For compression, all IO should have its logical bytenr
		 * set to the starting bytenr of the compressed extent.
		 */
		contig = bio->bi_iter.bi_sector == sector;
	}

	if (!contig)
		return 0;

	real_size = min(bio_ctrl->len_to_oe_boundary - bio_size, size);

	/*
	 * If real_size is 0, never call bio_add_*_page(), as even size is 0,
	 * bio will still execute its endio function on the page!
	 */
	if (real_size == 0)
		return 0;

	return bio_add_page(bio, page, real_size, pg_offset);
}

static void calc_bio_boundaries(struct btrfs_bio_ctrl *bio_ctrl,
				struct btrfs_inode *inode, u64 file_offset)
{
	struct btrfs_ordered_extent *ordered;

	/*
	 * Limit the extent to the ordered boundary for Zone Append.
	 * Compressed bios aren't submitted directly, so it doesn't apply to
	 * them.
	 */
	if (bio_ctrl->compress_type == BTRFS_COMPRESS_NONE &&
	    btrfs_use_zone_append(btrfs_bio(bio_ctrl->bio))) {
		ordered = btrfs_lookup_ordered_extent(inode, file_offset);
		if (ordered) {
			bio_ctrl->len_to_oe_boundary = min_t(u32, U32_MAX,
					ordered->file_offset +
					ordered->disk_num_bytes - file_offset);
			btrfs_put_ordered_extent(ordered);
			return;
		}
	}

	bio_ctrl->len_to_oe_boundary = U32_MAX;
}

static void alloc_new_bio(struct btrfs_inode *inode,
			  struct btrfs_bio_ctrl *bio_ctrl,
			  struct writeback_control *wbc, blk_opf_t opf,
			  u64 disk_bytenr, u32 offset, u64 file_offset,
			  enum btrfs_compression_type compress_type)
{
	struct btrfs_fs_info *fs_info = inode->root->fs_info;
	struct bio *bio;

	bio = btrfs_bio_alloc(BIO_MAX_VECS, opf, inode, bio_ctrl->end_io_func,
			      NULL);
	/*
	 * For compressed page range, its disk_bytenr is always @disk_bytenr
	 * passed in, no matter if we have added any range into previous bio.
	 */
	if (compress_type != BTRFS_COMPRESS_NONE)
		bio->bi_iter.bi_sector = disk_bytenr >> SECTOR_SHIFT;
	else
		bio->bi_iter.bi_sector = (disk_bytenr + offset) >> SECTOR_SHIFT;
	btrfs_bio(bio)->file_offset = file_offset;
	bio_ctrl->bio = bio;
	bio_ctrl->compress_type = compress_type;
	calc_bio_boundaries(bio_ctrl, inode, file_offset);

	if (wbc) {
		/*
		 * Pick the last added device to support cgroup writeback.  For
		 * multi-device file systems this means blk-cgroup policies have
		 * to always be set on the last added/replaced device.
		 * This is a bit odd but has been like that for a long time.
		 */
		bio_set_dev(bio, fs_info->fs_devices->latest_dev->bdev);
		wbc_init_bio(wbc, bio);
	}
}

/*
 * @opf:	bio REQ_OP_* and REQ_* flags as one value
 * @wbc:	optional writeback control for io accounting
 * @disk_bytenr: logical bytenr where the write will be
 * @page:	page to add to the bio
 * @size:	portion of page that we want to write to
 * @pg_offset:	offset of the new bio or to check whether we are adding
 *              a contiguous page to the previous one
 * @compress_type:   compress type for current bio
 *
 * The will either add the page into the existing @bio_ctrl->bio, or allocate a
 * new one in @bio_ctrl->bio.
 * The mirror number for this IO should already be initizlied in
 * @bio_ctrl->mirror_num.
 */
static int submit_extent_page(blk_opf_t opf,
			      struct writeback_control *wbc,
			      struct btrfs_bio_ctrl *bio_ctrl,
			      u64 disk_bytenr, struct page *page,
			      size_t size, unsigned long pg_offset,
			      enum btrfs_compression_type compress_type,
			      bool force_bio_submit)
{
	struct btrfs_inode *inode = BTRFS_I(page->mapping->host);
	unsigned int cur = pg_offset;

	ASSERT(bio_ctrl);

	ASSERT(pg_offset < PAGE_SIZE && size <= PAGE_SIZE &&
	       pg_offset + size <= PAGE_SIZE);

	ASSERT(bio_ctrl->end_io_func);

	if (force_bio_submit)
		submit_one_bio(bio_ctrl);

	while (cur < pg_offset + size) {
		u32 offset = cur - pg_offset;
		int added;

		/* Allocate new bio if needed */
		if (!bio_ctrl->bio) {
			alloc_new_bio(inode, bio_ctrl, wbc, opf, disk_bytenr,
				      offset, page_offset(page) + cur,
				      compress_type);
		}
		/*
		 * We must go through btrfs_bio_add_page() to ensure each
		 * page range won't cross various boundaries.
		 */
		if (compress_type != BTRFS_COMPRESS_NONE)
			added = btrfs_bio_add_page(bio_ctrl, page, disk_bytenr,
					size - offset, pg_offset + offset,
					compress_type);
		else
			added = btrfs_bio_add_page(bio_ctrl, page,
					disk_bytenr + offset, size - offset,
					pg_offset + offset, compress_type);

		/* Metadata page range should never be split */
		if (!is_data_inode(&inode->vfs_inode))
			ASSERT(added == 0 || added == size - offset);

		/* At least we added some page, update the account */
		if (wbc && added)
			wbc_account_cgroup_owner(wbc, page, added);

		/* We have reached boundary, submit right now */
		if (added < size - offset) {
			/* The bio should contain some page(s) */
			ASSERT(bio_ctrl->bio->bi_iter.bi_size);
			submit_one_bio(bio_ctrl);
		}
		cur += added;
	}
	return 0;
}

static int attach_extent_buffer_page(struct extent_buffer *eb,
				     struct page *page,
				     struct btrfs_subpage *prealloc)
{
	struct btrfs_fs_info *fs_info = eb->fs_info;
	int ret = 0;

	/*
	 * If the page is mapped to btree inode, we should hold the private
	 * lock to prevent race.
	 * For cloned or dummy extent buffers, their pages are not mapped and
	 * will not race with any other ebs.
	 */
	if (page->mapping)
		lockdep_assert_held(&page->mapping->private_lock);

	if (fs_info->nodesize >= PAGE_SIZE) {
		if (!PagePrivate(page))
			attach_page_private(page, eb);
		else
			WARN_ON(page->private != (unsigned long)eb);
		return 0;
	}

	/* Already mapped, just free prealloc */
	if (PagePrivate(page)) {
		btrfs_free_subpage(prealloc);
		return 0;
	}

	if (prealloc)
		/* Has preallocated memory for subpage */
		attach_page_private(page, prealloc);
	else
		/* Do new allocation to attach subpage */
		ret = btrfs_attach_subpage(fs_info, page,
					   BTRFS_SUBPAGE_METADATA);
	return ret;
}

int set_page_extent_mapped(struct page *page)
{
	struct btrfs_fs_info *fs_info;

	ASSERT(page->mapping);

	if (PagePrivate(page))
		return 0;

	fs_info = btrfs_sb(page->mapping->host->i_sb);

	if (btrfs_is_subpage(fs_info, page))
		return btrfs_attach_subpage(fs_info, page, BTRFS_SUBPAGE_DATA);

	attach_page_private(page, (void *)EXTENT_PAGE_PRIVATE);
	return 0;
}

void clear_page_extent_mapped(struct page *page)
{
	struct btrfs_fs_info *fs_info;

	ASSERT(page->mapping);

	if (!PagePrivate(page))
		return;

	fs_info = btrfs_sb(page->mapping->host->i_sb);
	if (btrfs_is_subpage(fs_info, page))
		return btrfs_detach_subpage(fs_info, page);

	detach_page_private(page);
}

static struct extent_map *
__get_extent_map(struct inode *inode, struct page *page, size_t pg_offset,
		 u64 start, u64 len, struct extent_map **em_cached)
{
	struct extent_map *em;

	if (em_cached && *em_cached) {
		em = *em_cached;
		if (extent_map_in_tree(em) && start >= em->start &&
		    start < extent_map_end(em)) {
			refcount_inc(&em->refs);
			return em;
		}

		free_extent_map(em);
		*em_cached = NULL;
	}

	em = btrfs_get_extent(BTRFS_I(inode), page, pg_offset, start, len);
	if (em_cached && !IS_ERR(em)) {
		BUG_ON(*em_cached);
		refcount_inc(&em->refs);
		*em_cached = em;
	}
	return em;
}
/*
 * basic readpage implementation.  Locked extent state structs are inserted
 * into the tree that are removed when the IO is done (by the end_io
 * handlers)
 * XXX JDM: This needs looking at to ensure proper page locking
 * return 0 on success, otherwise return error
 */
static int btrfs_do_readpage(struct page *page, struct extent_map **em_cached,
		      struct btrfs_bio_ctrl *bio_ctrl,
		      blk_opf_t read_flags, u64 *prev_em_start)
{
	struct inode *inode = page->mapping->host;
	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
	u64 start = page_offset(page);
	const u64 end = start + PAGE_SIZE - 1;
	u64 cur = start;
	u64 extent_offset;
	u64 last_byte = i_size_read(inode);
	u64 block_start;
	struct extent_map *em;
	int ret = 0;
	size_t pg_offset = 0;
	size_t iosize;
	size_t blocksize = inode->i_sb->s_blocksize;
	struct extent_io_tree *tree = &BTRFS_I(inode)->io_tree;

	ret = set_page_extent_mapped(page);
	if (ret < 0) {
		unlock_extent(tree, start, end, NULL);
		btrfs_page_set_error(fs_info, page, start, PAGE_SIZE);
		unlock_page(page);
		goto out;
	}

	if (page->index == last_byte >> PAGE_SHIFT) {
		size_t zero_offset = offset_in_page(last_byte);

		if (zero_offset) {
			iosize = PAGE_SIZE - zero_offset;
			memzero_page(page, zero_offset, iosize);
		}
	}
	bio_ctrl->end_io_func = end_bio_extent_readpage;
	begin_page_read(fs_info, page);
	while (cur <= end) {
		unsigned long this_bio_flag = 0;
		bool force_bio_submit = false;
		u64 disk_bytenr;

		ASSERT(IS_ALIGNED(cur, fs_info->sectorsize));
		if (cur >= last_byte) {
			iosize = PAGE_SIZE - pg_offset;
			memzero_page(page, pg_offset, iosize);
			unlock_extent(tree, cur, cur + iosize - 1, NULL);
			end_page_read(page, true, cur, iosize);
			break;
		}
		em = __get_extent_map(inode, page, pg_offset, cur,
				      end - cur + 1, em_cached);
		if (IS_ERR(em)) {
			unlock_extent(tree, cur, end, NULL);
			end_page_read(page, false, cur, end + 1 - cur);
			ret = PTR_ERR(em);
			break;
		}
		extent_offset = cur - em->start;
		BUG_ON(extent_map_end(em) <= cur);
		BUG_ON(end < cur);

		if (test_bit(EXTENT_FLAG_COMPRESSED, &em->flags))
			this_bio_flag = em->compress_type;

		iosize = min(extent_map_end(em) - cur, end - cur + 1);
		iosize = ALIGN(iosize, blocksize);
		if (this_bio_flag != BTRFS_COMPRESS_NONE)
			disk_bytenr = em->block_start;
		else
			disk_bytenr = em->block_start + extent_offset;
		block_start = em->block_start;
		if (test_bit(EXTENT_FLAG_PREALLOC, &em->flags))
			block_start = EXTENT_MAP_HOLE;

		/*
		 * If we have a file range that points to a compressed extent
		 * and it's followed by a consecutive file range that points
		 * to the same compressed extent (possibly with a different
		 * offset and/or length, so it either points to the whole extent
		 * or only part of it), we must make sure we do not submit a
		 * single bio to populate the pages for the 2 ranges because
		 * this makes the compressed extent read zero out the pages
		 * belonging to the 2nd range. Imagine the following scenario:
		 *
		 *  File layout
		 *  [0 - 8K]                     [8K - 24K]
		 *    |                               |
		 *    |                               |
		 * points to extent X,         points to extent X,
		 * offset 4K, length of 8K     offset 0, length 16K
		 *
		 * [extent X, compressed length = 4K uncompressed length = 16K]
		 *
		 * If the bio to read the compressed extent covers both ranges,
		 * it will decompress extent X into the pages belonging to the
		 * first range and then it will stop, zeroing out the remaining
		 * pages that belong to the other range that points to extent X.
		 * So here we make sure we submit 2 bios, one for the first
		 * range and another one for the third range. Both will target
		 * the same physical extent from disk, but we can't currently
		 * make the compressed bio endio callback populate the pages
		 * for both ranges because each compressed bio is tightly
		 * coupled with a single extent map, and each range can have
		 * an extent map with a different offset value relative to the
		 * uncompressed data of our extent and different lengths. This
		 * is a corner case so we prioritize correctness over
		 * non-optimal behavior (submitting 2 bios for the same extent).
		 */
		if (test_bit(EXTENT_FLAG_COMPRESSED, &em->flags) &&
		    prev_em_start && *prev_em_start != (u64)-1 &&
		    *prev_em_start != em->start)
			force_bio_submit = true;

		if (prev_em_start)
			*prev_em_start = em->start;

		free_extent_map(em);
		em = NULL;

		/* we've found a hole, just zero and go on */
		if (block_start == EXTENT_MAP_HOLE) {
			memzero_page(page, pg_offset, iosize);

			unlock_extent(tree, cur, cur + iosize - 1, NULL);
			end_page_read(page, true, cur, iosize);
			cur = cur + iosize;
			pg_offset += iosize;
			continue;
		}
		/* the get_extent function already copied into the page */
		if (block_start == EXTENT_MAP_INLINE) {
			unlock_extent(tree, cur, cur + iosize - 1, NULL);
			end_page_read(page, true, cur, iosize);
			cur = cur + iosize;
			pg_offset += iosize;
			continue;
		}

		ret = submit_extent_page(REQ_OP_READ | read_flags, NULL,
					 bio_ctrl, disk_bytenr, page, iosize,
					 pg_offset, this_bio_flag,
					 force_bio_submit);
		if (ret) {
			/*
			 * We have to unlock the remaining range, or the page
			 * will never be unlocked.
			 */
			unlock_extent(tree, cur, end, NULL);
			end_page_read(page, false, cur, end + 1 - cur);
			goto out;
		}
		cur = cur + iosize;
		pg_offset += iosize;
	}
out:
	return ret;
}

int btrfs_read_folio(struct file *file, struct folio *folio)
{
	struct page *page = &folio->page;
	struct btrfs_inode *inode = BTRFS_I(page->mapping->host);
	u64 start = page_offset(page);
	u64 end = start + PAGE_SIZE - 1;
	struct btrfs_bio_ctrl bio_ctrl = { 0 };
	int ret;

	btrfs_lock_and_flush_ordered_range(inode, start, end, NULL);

	ret = btrfs_do_readpage(page, NULL, &bio_ctrl, 0, NULL);
	/*
	 * If btrfs_do_readpage() failed we will want to submit the assembled
	 * bio to do the cleanup.
	 */
	submit_one_bio(&bio_ctrl);
	return ret;
}

static inline void contiguous_readpages(struct page *pages[], int nr_pages,
					u64 start, u64 end,
					struct extent_map **em_cached,
					struct btrfs_bio_ctrl *bio_ctrl,
					u64 *prev_em_start)
{
	struct btrfs_inode *inode = BTRFS_I(pages[0]->mapping->host);
	int index;

	btrfs_lock_and_flush_ordered_range(inode, start, end, NULL);

	for (index = 0; index < nr_pages; index++) {
		btrfs_do_readpage(pages[index], em_cached, bio_ctrl,
				  REQ_RAHEAD, prev_em_start);
		put_page(pages[index]);
	}
}

/*
 * helper for __extent_writepage, doing all of the delayed allocation setup.
 *
 * This returns 1 if btrfs_run_delalloc_range function did all the work required
 * to write the page (copy into inline extent).  In this case the IO has
 * been started and the page is already unlocked.
 *
 * This returns 0 if all went well (page still locked)
 * This returns < 0 if there were errors (page still locked)
 */
static noinline_for_stack int writepage_delalloc(struct btrfs_inode *inode,
		struct page *page, struct writeback_control *wbc)
{
	const u64 page_end = page_offset(page) + PAGE_SIZE - 1;
	u64 delalloc_start = page_offset(page);
	u64 delalloc_to_write = 0;
	/* How many pages are started by btrfs_run_delalloc_range() */
	unsigned long nr_written = 0;
	int ret;
	int page_started = 0;

	while (delalloc_start < page_end) {
		u64 delalloc_end = page_end;
		bool found;

		found = find_lock_delalloc_range(&inode->vfs_inode, page,
					       &delalloc_start,
					       &delalloc_end);
		if (!found) {
			delalloc_start = delalloc_end + 1;
			continue;
		}
		ret = btrfs_run_delalloc_range(inode, page, delalloc_start,
				delalloc_end, &page_started, &nr_written, wbc);
		if (ret) {
			btrfs_page_set_error(inode->root->fs_info, page,
					     page_offset(page), PAGE_SIZE);
			return ret;
		}
		/*
		 * delalloc_end is already one less than the total length, so
		 * we don't subtract one from PAGE_SIZE
		 */
		delalloc_to_write += (delalloc_end - delalloc_start +
				      PAGE_SIZE) >> PAGE_SHIFT;
		delalloc_start = delalloc_end + 1;
	}
	if (wbc->nr_to_write < delalloc_to_write) {
		int thresh = 8192;

		if (delalloc_to_write < thresh * 2)
			thresh = delalloc_to_write;
		wbc->nr_to_write = min_t(u64, delalloc_to_write,
					 thresh);
	}

	/* Did btrfs_run_dealloc_range() already unlock and start the IO? */
	if (page_started) {
		/*
		 * We've unlocked the page, so we can't update the mapping's
		 * writeback index, just update nr_to_write.
		 */
		wbc->nr_to_write -= nr_written;
		return 1;
	}

	return 0;
}

/*
 * Find the first byte we need to write.
 *
 * For subpage, one page can contain several sectors, and
 * __extent_writepage_io() will just grab all extent maps in the page
 * range and try to submit all non-inline/non-compressed extents.
 *
 * This is a big problem for subpage, we shouldn't re-submit already written
 * data at all.
 * This function will lookup subpage dirty bit to find which range we really
 * need to submit.
 *
 * Return the next dirty range in [@start, @end).
 * If no dirty range is found, @start will be page_offset(page) + PAGE_SIZE.
 */
static void find_next_dirty_byte(struct btrfs_fs_info *fs_info,
				 struct page *page, u64 *start, u64 *end)
{
	struct btrfs_subpage *subpage = (struct btrfs_subpage *)page->private;
	struct btrfs_subpage_info *spi = fs_info->subpage_info;
	u64 orig_start = *start;
	/* Declare as unsigned long so we can use bitmap ops */
	unsigned long flags;
	int range_start_bit;
	int range_end_bit;

	/*
	 * For regular sector size == page size case, since one page only
	 * contains one sector, we return the page offset directly.
	 */
	if (!btrfs_is_subpage(fs_info, page)) {
		*start = page_offset(page);
		*end = page_offset(page) + PAGE_SIZE;
		return;
	}

	range_start_bit = spi->dirty_offset +
			  (offset_in_page(orig_start) >> fs_info->sectorsize_bits);

	/* We should have the page locked, but just in case */
	spin_lock_irqsave(&subpage->lock, flags);
	bitmap_next_set_region(subpage->bitmaps, &range_start_bit, &range_end_bit,
			       spi->dirty_offset + spi->bitmap_nr_bits);
	spin_unlock_irqrestore(&subpage->lock, flags);

	range_start_bit -= spi->dirty_offset;
	range_end_bit -= spi->dirty_offset;

	*start = page_offset(page) + range_start_bit * fs_info->sectorsize;
	*end = page_offset(page) + range_end_bit * fs_info->sectorsize;
}

/*
 * helper for __extent_writepage.  This calls the writepage start hooks,
 * and does the loop to map the page into extents and bios.
 *
 * We return 1 if the IO is started and the page is unlocked,
 * 0 if all went well (page still locked)
 * < 0 if there were errors (page still locked)
 */
static noinline_for_stack int __extent_writepage_io(struct btrfs_inode *inode,
				 struct page *page,
				 struct writeback_control *wbc,
				 struct btrfs_bio_ctrl *bio_ctrl,
				 loff_t i_size,
				 int *nr_ret)
{
	struct btrfs_fs_info *fs_info = inode->root->fs_info;
	u64 cur = page_offset(page);
	u64 end = cur + PAGE_SIZE - 1;
	u64 extent_offset;
	u64 block_start;
	struct extent_map *em;
	int saved_ret = 0;
	int ret = 0;
	int nr = 0;
	enum req_op op = REQ_OP_WRITE;
	const blk_opf_t write_flags = wbc_to_write_flags(wbc);
	bool has_error = false;
	bool compressed;

	ret = btrfs_writepage_cow_fixup(page);
	if (ret) {
		/* Fixup worker will requeue */
		redirty_page_for_writepage(wbc, page);
		unlock_page(page);
		return 1;
	}

	/*
	 * we don't want to touch the inode after unlocking the page,
	 * so we update the mapping writeback index now
	 */
	wbc->nr_to_write--;

	bio_ctrl->end_io_func = end_bio_extent_writepage;
	while (cur <= end) {
		u64 disk_bytenr;
		u64 em_end;
		u64 dirty_range_start = cur;
		u64 dirty_range_end;
		u32 iosize;

		if (cur >= i_size) {
			btrfs_writepage_endio_finish_ordered(inode, page, cur,
							     end, true);
			/*
			 * This range is beyond i_size, thus we don't need to
			 * bother writing back.
			 * But we still need to clear the dirty subpage bit, or
			 * the next time the page gets dirtied, we will try to
			 * writeback the sectors with subpage dirty bits,
			 * causing writeback without ordered extent.
			 */
			btrfs_page_clear_dirty(fs_info, page, cur, end + 1 - cur);
			break;
		}

		find_next_dirty_byte(fs_info, page, &dirty_range_start,
				     &dirty_range_end);
		if (cur < dirty_range_start) {
			cur = dirty_range_start;
			continue;
		}

		em = btrfs_get_extent(inode, NULL, 0, cur, end - cur + 1);
		if (IS_ERR(em)) {
			btrfs_page_set_error(fs_info, page, cur, end - cur + 1);
			ret = PTR_ERR_OR_ZERO(em);
			has_error = true;
			if (!saved_ret)
				saved_ret = ret;
			break;
		}

		extent_offset = cur - em->start;
		em_end = extent_map_end(em);
		ASSERT(cur <= em_end);
		ASSERT(cur < end);
		ASSERT(IS_ALIGNED(em->start, fs_info->sectorsize));
		ASSERT(IS_ALIGNED(em->len, fs_info->sectorsize));
		block_start = em->block_start;
		compressed = test_bit(EXTENT_FLAG_COMPRESSED, &em->flags);
		disk_bytenr = em->block_start + extent_offset;

		/*
		 * Note that em_end from extent_map_end() and dirty_range_end from
		 * find_next_dirty_byte() are all exclusive
		 */
		iosize = min(min(em_end, end + 1), dirty_range_end) - cur;
		free_extent_map(em);
		em = NULL;

		/*
		 * compressed and inline extents are written through other
		 * paths in the FS
		 */
		if (compressed || block_start == EXTENT_MAP_HOLE ||
		    block_start == EXTENT_MAP_INLINE) {
			if (compressed)
				nr++;
			else
				btrfs_writepage_endio_finish_ordered(inode,
						page, cur, cur + iosize - 1, true);
			btrfs_page_clear_dirty(fs_info, page, cur, iosize);
			cur += iosize;
			continue;
		}

		btrfs_set_range_writeback(inode, cur, cur + iosize - 1);
		if (!PageWriteback(page)) {
			btrfs_err(inode->root->fs_info,
				   "page %lu not writeback, cur %llu end %llu",
			       page->index, cur, end);
		}

		/*
		 * Although the PageDirty bit is cleared before entering this
		 * function, subpage dirty bit is not cleared.
		 * So clear subpage dirty bit here so next time we won't submit
		 * page for range already written to disk.
		 */
		btrfs_page_clear_dirty(fs_info, page, cur, iosize);

		ret = submit_extent_page(op | write_flags, wbc,
					 bio_ctrl, disk_bytenr,
					 page, iosize,
					 cur - page_offset(page),
					 0, false);
		if (ret) {
			has_error = true;
			if (!saved_ret)
				saved_ret = ret;

			btrfs_page_set_error(fs_info, page, cur, iosize);
			if (PageWriteback(page))
				btrfs_page_clear_writeback(fs_info, page, cur,
							   iosize);
		}

		cur += iosize;
		nr++;
	}
	/*
	 * If we finish without problem, we should not only clear page dirty,
	 * but also empty subpage dirty bits
	 */
	if (!has_error)
		btrfs_page_assert_not_dirty(fs_info, page);
	else
		ret = saved_ret;
	*nr_ret = nr;
	return ret;
}

/*
 * the writepage semantics are similar to regular writepage.  extent
 * records are inserted to lock ranges in the tree, and as dirty areas
 * are found, they are marked writeback.  Then the lock bits are removed
 * and the end_io handler clears the writeback ranges
 *
 * Return 0 if everything goes well.
 * Return <0 for error.
 */
static int __extent_writepage(struct page *page, struct writeback_control *wbc,
			      struct btrfs_bio_ctrl *bio_ctrl)
{
	struct folio *folio = page_folio(page);
	struct inode *inode = page->mapping->host;
	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
	const u64 page_start = page_offset(page);
	const u64 page_end = page_start + PAGE_SIZE - 1;
	int ret;
	int nr = 0;
	size_t pg_offset;
	loff_t i_size = i_size_read(inode);
	unsigned long end_index = i_size >> PAGE_SHIFT;

	trace___extent_writepage(page, inode, wbc);

	WARN_ON(!PageLocked(page));

	btrfs_page_clear_error(btrfs_sb(inode->i_sb), page,
			       page_offset(page), PAGE_SIZE);

	pg_offset = offset_in_page(i_size);
	if (page->index > end_index ||
	   (page->index == end_index && !pg_offset)) {
		folio_invalidate(folio, 0, folio_size(folio));
		folio_unlock(folio);
		return 0;
	}

	if (page->index == end_index)
		memzero_page(page, pg_offset, PAGE_SIZE - pg_offset);

	ret = set_page_extent_mapped(page);
	if (ret < 0) {
		SetPageError(page);
		goto done;
	}

	if (!bio_ctrl->extent_locked) {
		ret = writepage_delalloc(BTRFS_I(inode), page, wbc);
		if (ret == 1)
			return 0;
		if (ret)
			goto done;
	}

	ret = __extent_writepage_io(BTRFS_I(inode), page, wbc, bio_ctrl, i_size,
				    &nr);
	if (ret == 1)
		return 0;

done:
	if (nr == 0) {
		/* make sure the mapping tag for page dirty gets cleared */
		set_page_writeback(page);
		end_page_writeback(page);
	}
	/*
	 * Here we used to have a check for PageError() and then set @ret and
	 * call end_extent_writepage().
	 *
	 * But in fact setting @ret here will cause different error paths
	 * between subpage and regular sectorsize.
	 *
	 * For regular page size, we never submit current page, but only add
	 * current page to current bio.
	 * The bio submission can only happen in next page.
	 * Thus if we hit the PageError() branch, @ret is already set to
	 * non-zero value and will not get updated for regular sectorsize.
	 *
	 * But for subpage case, it's possible we submit part of current page,
	 * thus can get PageError() set by submitted bio of the same page,
	 * while our @ret is still 0.
	 *
	 * So here we unify the behavior and don't set @ret.
	 * Error can still be properly passed to higher layer as page will
	 * be set error, here we just don't handle the IO failure.
	 *
	 * NOTE: This is just a hotfix for subpage.
	 * The root fix will be properly ending ordered extent when we hit
	 * an error during writeback.
	 *
	 * But that needs a bigger refactoring, as we not only need to grab the
	 * submitted OE, but also need to know exactly at which bytenr we hit
	 * the error.
	 * Currently the full page based __extent_writepage_io() is not
	 * capable of that.
	 */
	if (PageError(page))
		end_extent_writepage(page, ret, page_start, page_end);
	if (bio_ctrl->extent_locked) {
		/*
		 * If bio_ctrl->extent_locked, it's from extent_write_locked_range(),
		 * the page can either be locked by lock_page() or
		 * process_one_page().
		 * Let btrfs_page_unlock_writer() handle both cases.
		 */
		ASSERT(wbc);
		btrfs_page_unlock_writer(fs_info, page, wbc->range_start,
					 wbc->range_end + 1 - wbc->range_start);
	} else {
		unlock_page(page);
	}
	ASSERT(ret <= 0);
	return ret;
}

void wait_on_extent_buffer_writeback(struct extent_buffer *eb)
{
	wait_on_bit_io(&eb->bflags, EXTENT_BUFFER_WRITEBACK,
		       TASK_UNINTERRUPTIBLE);
}

static void end_extent_buffer_writeback(struct extent_buffer *eb)
{
	clear_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags);
	smp_mb__after_atomic();
	wake_up_bit(&eb->bflags, EXTENT_BUFFER_WRITEBACK);
}

/*
 * Lock extent buffer status and pages for writeback.
 *
 * May try to flush write bio if we can't get the lock.
 *
 * Return  0 if the extent buffer doesn't need to be submitted.
 *           (E.g. the extent buffer is not dirty)
 * Return >0 is the extent buffer is submitted to bio.
 * Return <0 if something went wrong, no page is locked.
 */
static noinline_for_stack int lock_extent_buffer_for_io(struct extent_buffer *eb,
			  struct btrfs_bio_ctrl *bio_ctrl)
{
	struct btrfs_fs_info *fs_info = eb->fs_info;
	int i, num_pages;
	int flush = 0;
	int ret = 0;

	if (!btrfs_try_tree_write_lock(eb)) {
		submit_write_bio(bio_ctrl, 0);
		flush = 1;
		btrfs_tree_lock(eb);
	}

	if (test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags)) {
		btrfs_tree_unlock(eb);
		if (!bio_ctrl->sync_io)
			return 0;
		if (!flush) {
			submit_write_bio(bio_ctrl, 0);
			flush = 1;
		}
		while (1) {
			wait_on_extent_buffer_writeback(eb);
			btrfs_tree_lock(eb);
			if (!test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags))
				break;
			btrfs_tree_unlock(eb);
		}
	}

	/*
	 * We need to do this to prevent races in people who check if the eb is
	 * under IO since we can end up having no IO bits set for a short period
	 * of time.
	 */
	spin_lock(&eb->refs_lock);
	if (test_and_clear_bit(EXTENT_BUFFER_DIRTY, &eb->bflags)) {
		set_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags);
		spin_unlock(&eb->refs_lock);
		btrfs_set_header_flag(eb, BTRFS_HEADER_FLAG_WRITTEN);
		percpu_counter_add_batch(&fs_info->dirty_metadata_bytes,
					 -eb->len,
					 fs_info->dirty_metadata_batch);
		ret = 1;
	} else {
		spin_unlock(&eb->refs_lock);
	}

	btrfs_tree_unlock(eb);

	/*
	 * Either we don't need to submit any tree block, or we're submitting
	 * subpage eb.
	 * Subpage metadata doesn't use page locking at all, so we can skip
	 * the page locking.
	 */
	if (!ret || fs_info->nodesize < PAGE_SIZE)
		return ret;

	num_pages = num_extent_pages(eb);
	for (i = 0; i < num_pages; i++) {
		struct page *p = eb->pages[i];

		if (!trylock_page(p)) {
			if (!flush) {
				submit_write_bio(bio_ctrl, 0);
				flush = 1;
			}
			lock_page(p);
		}
	}

	return ret;
}

static void set_btree_ioerr(struct page *page, struct extent_buffer *eb)
{
	struct btrfs_fs_info *fs_info = eb->fs_info;

	btrfs_page_set_error(fs_info, page, eb->start, eb->len);
	if (test_and_set_bit(EXTENT_BUFFER_WRITE_ERR, &eb->bflags))
		return;

	/*
	 * A read may stumble upon this buffer later, make sure that it gets an
	 * error and knows there was an error.
	 */
	clear_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);

	/*
	 * We need to set the mapping with the io error as well because a write
	 * error will flip the file system readonly, and then syncfs() will
	 * return a 0 because we are readonly if we don't modify the err seq for
	 * the superblock.
	 */
	mapping_set_error(page->mapping, -EIO);

	/*
	 * If writeback for a btree extent that doesn't belong to a log tree
	 * failed, increment the counter transaction->eb_write_errors.
	 * We do this because while the transaction is running and before it's
	 * committing (when we call filemap_fdata[write|wait]_range against
	 * the btree inode), we might have
	 * btree_inode->i_mapping->a_ops->writepages() called by the VM - if it
	 * returns an error or an error happens during writeback, when we're
	 * committing the transaction we wouldn't know about it, since the pages
	 * can be no longer dirty nor marked anymore for writeback (if a
	 * subsequent modification to the extent buffer didn't happen before the
	 * transaction commit), which makes filemap_fdata[write|wait]_range not
	 * able to find the pages tagged with SetPageError at transaction
	 * commit time. So if this happens we must abort the transaction,
	 * otherwise we commit a super block with btree roots that point to
	 * btree nodes/leafs whose content on disk is invalid - either garbage
	 * or the content of some node/leaf from a past generation that got
	 * cowed or deleted and is no longer valid.
	 *
	 * Note: setting AS_EIO/AS_ENOSPC in the btree inode's i_mapping would
	 * not be enough - we need to distinguish between log tree extents vs
	 * non-log tree extents, and the next filemap_fdatawait_range() call
	 * will catch and clear such errors in the mapping - and that call might
	 * be from a log sync and not from a transaction commit. Also, checking
	 * for the eb flag EXTENT_BUFFER_WRITE_ERR at transaction commit time is
	 * not done and would not be reliable - the eb might have been released
	 * from memory and reading it back again means that flag would not be
	 * set (since it's a runtime flag, not persisted on disk).
	 *
	 * Using the flags below in the btree inode also makes us achieve the
	 * goal of AS_EIO/AS_ENOSPC when writepages() returns success, started
	 * writeback for all dirty pages and before filemap_fdatawait_range()
	 * is called, the writeback for all dirty pages had already finished
	 * with errors - because we were not using AS_EIO/AS_ENOSPC,
	 * filemap_fdatawait_range() would return success, as it could not know
	 * that writeback errors happened (the pages were no longer tagged for
	 * writeback).
	 */
	switch (eb->log_index) {
	case -1:
		set_bit(BTRFS_FS_BTREE_ERR, &fs_info->flags);
		break;
	case 0:
		set_bit(BTRFS_FS_LOG1_ERR, &fs_info->flags);
		break;
	case 1:
		set_bit(BTRFS_FS_LOG2_ERR, &fs_info->flags);
		break;
	default:
		BUG(); /* unexpected, logic error */
	}
}

/*
 * The endio specific version which won't touch any unsafe spinlock in endio
 * context.
 */
static struct extent_buffer *find_extent_buffer_nolock(
		struct btrfs_fs_info *fs_info, u64 start)
{
	struct extent_buffer *eb;

	rcu_read_lock();
	eb = radix_tree_lookup(&fs_info->buffer_radix,
			       start >> fs_info->sectorsize_bits);
	if (eb && atomic_inc_not_zero(&eb->refs)) {
		rcu_read_unlock();
		return eb;
	}
	rcu_read_unlock();
	return NULL;
}

/*
 * The endio function for subpage extent buffer write.
 *
 * Unlike end_bio_extent_buffer_writepage(), we only call end_page_writeback()
 * after all extent buffers in the page has finished their writeback.
 */
static void end_bio_subpage_eb_writepage(struct btrfs_bio *bbio)
{
	struct bio *bio = &bbio->bio;
	struct btrfs_fs_info *fs_info;
	struct bio_vec *bvec;
	struct bvec_iter_all iter_all;

	fs_info = btrfs_sb(bio_first_page_all(bio)->mapping->host->i_sb);
	ASSERT(fs_info->nodesize < PAGE_SIZE);

	ASSERT(!bio_flagged(bio, BIO_CLONED));
	bio_for_each_segment_all(bvec, bio, iter_all) {
		struct page *page = bvec->bv_page;
		u64 bvec_start = page_offset(page) + bvec->bv_offset;
		u64 bvec_end = bvec_start + bvec->bv_len - 1;
		u64 cur_bytenr = bvec_start;

		ASSERT(IS_ALIGNED(bvec->bv_len, fs_info->nodesize));

		/* Iterate through all extent buffers in the range */
		while (cur_bytenr <= bvec_end) {
			struct extent_buffer *eb;
			int done;

			/*
			 * Here we can't use find_extent_buffer(), as it may
			 * try to lock eb->refs_lock, which is not safe in endio
			 * context.
			 */
			eb = find_extent_buffer_nolock(fs_info, cur_bytenr);
			ASSERT(eb);

			cur_bytenr = eb->start + eb->len;

			ASSERT(test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags));
			done = atomic_dec_and_test(&eb->io_pages);
			ASSERT(done);

			if (bio->bi_status ||
			    test_bit(EXTENT_BUFFER_WRITE_ERR, &eb->bflags)) {
				ClearPageUptodate(page);
				set_btree_ioerr(page, eb);
			}

			btrfs_subpage_clear_writeback(fs_info, page, eb->start,
						      eb->len);
			end_extent_buffer_writeback(eb);
			/*
			 * free_extent_buffer() will grab spinlock which is not
			 * safe in endio context. Thus here we manually dec
			 * the ref.
			 */
			atomic_dec(&eb->refs);
		}
	}
	bio_put(bio);
}

static void end_bio_extent_buffer_writepage(struct btrfs_bio *bbio)
{
	struct bio *bio = &bbio->bio;
	struct bio_vec *bvec;
	struct extent_buffer *eb;
	int done;
	struct bvec_iter_all iter_all;

	ASSERT(!bio_flagged(bio, BIO_CLONED));
	bio_for_each_segment_all(bvec, bio, iter_all) {
		struct page *page = bvec->bv_page;

		eb = (struct extent_buffer *)page->private;
		BUG_ON(!eb);
		done = atomic_dec_and_test(&eb->io_pages);

		if (bio->bi_status ||
		    test_bit(EXTENT_BUFFER_WRITE_ERR, &eb->bflags)) {
			ClearPageUptodate(page);
			set_btree_ioerr(page, eb);
		}

		end_page_writeback(page);

		if (!done)
			continue;

		end_extent_buffer_writeback(eb);
	}

	bio_put(bio);
}

static void prepare_eb_write(struct extent_buffer *eb)
{
	u32 nritems;
	unsigned long start;
	unsigned long end;

	clear_bit(EXTENT_BUFFER_WRITE_ERR, &eb->bflags);
	atomic_set(&eb->io_pages, num_extent_pages(eb));

	/* Set btree blocks beyond nritems with 0 to avoid stale content */
	nritems = btrfs_header_nritems(eb);
	if (btrfs_header_level(eb) > 0) {
		end = btrfs_node_key_ptr_offset(eb, nritems);
		memzero_extent_buffer(eb, end, eb->len - end);
	} else {
		/*
		 * Leaf:
		 * header 0 1 2 .. N ... data_N .. data_2 data_1 data_0
		 */
		start = btrfs_item_nr_offset(eb, nritems);
		end = btrfs_item_nr_offset(eb, 0);
		if (nritems == 0)
			end += BTRFS_LEAF_DATA_SIZE(eb->fs_info);
		else
			end += btrfs_item_offset(eb, nritems - 1);
		memzero_extent_buffer(eb, start, end - start);
	}
}

/*
 * Unlike the work in write_one_eb(), we rely completely on extent locking.
 * Page locking is only utilized at minimum to keep the VMM code happy.
 */
static int write_one_subpage_eb(struct extent_buffer *eb,
				struct writeback_control *wbc,
				struct btrfs_bio_ctrl *bio_ctrl)
{
	struct btrfs_fs_info *fs_info = eb->fs_info;
	struct page *page = eb->pages[0];
	blk_opf_t write_flags = wbc_to_write_flags(wbc);
	bool no_dirty_ebs = false;
	int ret;

	prepare_eb_write(eb);

	/* clear_page_dirty_for_io() in subpage helper needs page locked */
	lock_page(page);
	btrfs_subpage_set_writeback(fs_info, page, eb->start, eb->len);

	/* Check if this is the last dirty bit to update nr_written */
	no_dirty_ebs = btrfs_subpage_clear_and_test_dirty(fs_info, page,
							  eb->start, eb->len);
	if (no_dirty_ebs)
		clear_page_dirty_for_io(page);

	bio_ctrl->end_io_func = end_bio_subpage_eb_writepage;

	ret = submit_extent_page(REQ_OP_WRITE | write_flags, wbc,
			bio_ctrl, eb->start, page, eb->len,
			eb->start - page_offset(page), 0, false);
	if (ret) {
		btrfs_subpage_clear_writeback(fs_info, page, eb->start, eb->len);
		set_btree_ioerr(page, eb);
		unlock_page(page);

		if (atomic_dec_and_test(&eb->io_pages))
			end_extent_buffer_writeback(eb);
		return -EIO;
	}
	unlock_page(page);
	/*
	 * Submission finished without problem, if no range of the page is
	 * dirty anymore, we have submitted a page.  Update nr_written in wbc.
	 */
	if (no_dirty_ebs)
		wbc->nr_to_write--;
	return ret;
}

static noinline_for_stack int write_one_eb(struct extent_buffer *eb,
			struct writeback_control *wbc,
			struct btrfs_bio_ctrl *bio_ctrl)
{
	u64 disk_bytenr = eb->start;
	int i, num_pages;
	blk_opf_t write_flags = wbc_to_write_flags(wbc);
	int ret = 0;

	prepare_eb_write(eb);

	bio_ctrl->end_io_func = end_bio_extent_buffer_writepage;

	num_pages = num_extent_pages(eb);
	for (i = 0; i < num_pages; i++) {
		struct page *p = eb->pages[i];

		clear_page_dirty_for_io(p);
		set_page_writeback(p);
		ret = submit_extent_page(REQ_OP_WRITE | write_flags, wbc,
					 bio_ctrl, disk_bytenr, p,
					 PAGE_SIZE, 0, 0, false);
		if (ret) {
			set_btree_ioerr(p, eb);
			if (PageWriteback(p))
				end_page_writeback(p);
			if (atomic_sub_and_test(num_pages - i, &eb->io_pages))
				end_extent_buffer_writeback(eb);
			ret = -EIO;
			break;
		}
		disk_bytenr += PAGE_SIZE;
		wbc->nr_to_write--;
		unlock_page(p);
	}

	if (unlikely(ret)) {
		for (; i < num_pages; i++) {
			struct page *p = eb->pages[i];
			clear_page_dirty_for_io(p);
			unlock_page(p);
		}
	}

	return ret;
}

/*
 * Submit one subpage btree page.
 *
 * The main difference to submit_eb_page() is:
 * - Page locking
 *   For subpage, we don't rely on page locking at all.
 *
 * - Flush write bio
 *   We only flush bio if we may be unable to fit current extent buffers into
 *   current bio.
 *
 * Return >=0 for the number of submitted extent buffers.
 * Return <0 for fatal error.
 */
static int submit_eb_subpage(struct page *page,
			     struct writeback_control *wbc,
			     struct btrfs_bio_ctrl *bio_ctrl)
{
	struct btrfs_fs_info *fs_info = btrfs_sb(page->mapping->host->i_sb);
	int submitted = 0;
	u64 page_start = page_offset(page);
	int bit_start = 0;
	int sectors_per_node = fs_info->nodesize >> fs_info->sectorsize_bits;
	int ret;

	/* Lock and write each dirty extent buffers in the range */
	while (bit_start < fs_info->subpage_info->bitmap_nr_bits) {
		struct btrfs_subpage *subpage = (struct btrfs_subpage *)page->private;
		struct extent_buffer *eb;
		unsigned long flags;
		u64 start;

		/*
		 * Take private lock to ensure the subpage won't be detached
		 * in the meantime.
		 */
		spin_lock(&page->mapping->private_lock);
		if (!PagePrivate(page)) {
			spin_unlock(&page->mapping->private_lock);
			break;
		}
		spin_lock_irqsave(&subpage->lock, flags);
		if (!test_bit(bit_start + fs_info->subpage_info->dirty_offset,
			      subpage->bitmaps)) {
			spin_unlock_irqrestore(&subpage->lock, flags);
			spin_unlock(&page->mapping->private_lock);
			bit_start++;
			continue;
		}

		start = page_start + bit_start * fs_info->sectorsize;
		bit_start += sectors_per_node;

		/*
		 * Here we just want to grab the eb without touching extra
		 * spin locks, so call find_extent_buffer_nolock().
		 */
		eb = find_extent_buffer_nolock(fs_info, start);
		spin_unlock_irqrestore(&subpage->lock, flags);
		spin_unlock(&page->mapping->private_lock);

		/*
		 * The eb has already reached 0 refs thus find_extent_buffer()
		 * doesn't return it. We don't need to write back such eb
		 * anyway.
		 */
		if (!eb)
			continue;

		ret = lock_extent_buffer_for_io(eb, bio_ctrl);
		if (ret == 0) {
			free_extent_buffer(eb);
			continue;
		}
		if (ret < 0) {
			free_extent_buffer(eb);
			goto cleanup;
		}
		ret = write_one_subpage_eb(eb, wbc, bio_ctrl);
		free_extent_buffer(eb);
		if (ret < 0)
			goto cleanup;
		submitted++;
	}
	return submitted;

cleanup:
	/* We hit error, end bio for the submitted extent buffers */
	submit_write_bio(bio_ctrl, ret);
	return ret;
}

/*
 * Submit all page(s) of one extent buffer.
 *
 * @page:	the page of one extent buffer
 * @eb_context:	to determine if we need to submit this page, if current page
 *		belongs to this eb, we don't need to submit
 *
 * The caller should pass each page in their bytenr order, and here we use
 * @eb_context to determine if we have submitted pages of one extent buffer.
 *
 * If we have, we just skip until we hit a new page that doesn't belong to
 * current @eb_context.
 *
 * If not, we submit all the page(s) of the extent buffer.
 *
 * Return >0 if we have submitted the extent buffer successfully.
 * Return 0 if we don't need to submit the page, as it's already submitted by
 * previous call.
 * Return <0 for fatal error.
 */
static int submit_eb_page(struct page *page, struct writeback_control *wbc,
			  struct btrfs_bio_ctrl *bio_ctrl,
			  struct extent_buffer **eb_context)
{
	struct address_space *mapping = page->mapping;
	struct btrfs_block_group *cache = NULL;
	struct extent_buffer *eb;
	int ret;

	if (!PagePrivate(page))
		return 0;

	if (btrfs_sb(page->mapping->host->i_sb)->nodesize < PAGE_SIZE)
		return submit_eb_subpage(page, wbc, bio_ctrl);

	spin_lock(&mapping->private_lock);
	if (!PagePrivate(page)) {
		spin_unlock(&mapping->private_lock);
		return 0;
	}

	eb = (struct extent_buffer *)page->private;

	/*
	 * Shouldn't happen and normally this would be a BUG_ON but no point
	 * crashing the machine for something we can survive anyway.
	 */
	if (WARN_ON(!eb)) {
		spin_unlock(&mapping->private_lock);
		return 0;
	}

	if (eb == *eb_context) {
		spin_unlock(&mapping->private_lock);
		return 0;
	}
	ret = atomic_inc_not_zero(&eb->refs);
	spin_unlock(&mapping->private_lock);
	if (!ret)
		return 0;

	if (!btrfs_check_meta_write_pointer(eb->fs_info, eb, &cache)) {
		/*
		 * If for_sync, this hole will be filled with
		 * trasnsaction commit.
		 */
		if (wbc->sync_mode == WB_SYNC_ALL && !wbc->for_sync)
			ret = -EAGAIN;
		else
			ret = 0;
		free_extent_buffer(eb);
		return ret;
	}

	*eb_context = eb;

	ret = lock_extent_buffer_for_io(eb, bio_ctrl);
	if (ret <= 0) {
		btrfs_revert_meta_write_pointer(cache, eb);
		if (cache)
			btrfs_put_block_group(cache);
		free_extent_buffer(eb);
		return ret;
	}
	if (cache) {
		/*
		 * Implies write in zoned mode. Mark the last eb in a block group.
		 */
		btrfs_schedule_zone_finish_bg(cache, eb);
		btrfs_put_block_group(cache);
	}
	ret = write_one_eb(eb, wbc, bio_ctrl);
	free_extent_buffer(eb);
	if (ret < 0)
		return ret;
	return 1;
}

int btree_write_cache_pages(struct address_space *mapping,
				   struct writeback_control *wbc)
{
	struct extent_buffer *eb_context = NULL;
	struct btrfs_bio_ctrl bio_ctrl = {
		.extent_locked = 0,
		.sync_io = (wbc->sync_mode == WB_SYNC_ALL),
	};
	struct btrfs_fs_info *fs_info = BTRFS_I(mapping->host)->root->fs_info;
	int ret = 0;
	int done = 0;
	int nr_to_write_done = 0;
	struct pagevec pvec;
	int nr_pages;
	pgoff_t index;
	pgoff_t end;		/* Inclusive */
	int scanned = 0;
	xa_mark_t tag;

	pagevec_init(&pvec);
	if (wbc->range_cyclic) {
		index = mapping->writeback_index; /* Start from prev offset */
		end = -1;
		/*
		 * Start from the beginning does not need to cycle over the
		 * range, mark it as scanned.
		 */
		scanned = (index == 0);
	} else {
		index = wbc->range_start >> PAGE_SHIFT;
		end = wbc->range_end >> PAGE_SHIFT;
		scanned = 1;
	}
	if (wbc->sync_mode == WB_SYNC_ALL)
		tag = PAGECACHE_TAG_TOWRITE;
	else
		tag = PAGECACHE_TAG_DIRTY;
	btrfs_zoned_meta_io_lock(fs_info);
retry:
	if (wbc->sync_mode == WB_SYNC_ALL)
		tag_pages_for_writeback(mapping, index, end);
	while (!done && !nr_to_write_done && (index <= end) &&
	       (nr_pages = pagevec_lookup_range_tag(&pvec, mapping, &index, end,
			tag))) {
		unsigned i;

		for (i = 0; i < nr_pages; i++) {
			struct page *page = pvec.pages[i];

			ret = submit_eb_page(page, wbc, &bio_ctrl, &eb_context);
			if (ret == 0)
				continue;
			if (ret < 0) {
				done = 1;
				break;
			}

			/*
			 * the filesystem may choose to bump up nr_to_write.
			 * We have to make sure to honor the new nr_to_write
			 * at any time
			 */
			nr_to_write_done = wbc->nr_to_write <= 0;
		}
		pagevec_release(&pvec);
		cond_resched();
	}
	if (!scanned && !done) {
		/*
		 * We hit the last page and there is more work to be done: wrap
		 * back to the start of the file
		 */
		scanned = 1;
		index = 0;
		goto retry;
	}
	/*
	 * If something went wrong, don't allow any metadata write bio to be
	 * submitted.
	 *
	 * This would prevent use-after-free if we had dirty pages not
	 * cleaned up, which can still happen by fuzzed images.
	 *
	 * - Bad extent tree
	 *   Allowing existing tree block to be allocated for other trees.
	 *
	 * - Log tree operations
	 *   Exiting tree blocks get allocated to log tree, bumps its
	 *   generation, then get cleaned in tree re-balance.
	 *   Such tree block will not be written back, since it's clean,
	 *   thus no WRITTEN flag set.
	 *   And after log writes back, this tree block is not traced by
	 *   any dirty extent_io_tree.
	 *
	 * - Offending tree block gets re-dirtied from its original owner
	 *   Since it has bumped generation, no WRITTEN flag, it can be
	 *   reused without COWing. This tree block will not be traced
	 *   by btrfs_transaction::dirty_pages.
	 *
	 *   Now such dirty tree block will not be cleaned by any dirty
	 *   extent io tree. Thus we don't want to submit such wild eb
	 *   if the fs already has error.
	 *
	 * We can get ret > 0 from submit_extent_page() indicating how many ebs
	 * were submitted. Reset it to 0 to avoid false alerts for the caller.
	 */
	if (ret > 0)
		ret = 0;
	if (!ret && BTRFS_FS_ERROR(fs_info))
		ret = -EROFS;
	submit_write_bio(&bio_ctrl, ret);

	btrfs_zoned_meta_io_unlock(fs_info);
	return ret;
}

/*
 * Walk the list of dirty pages of the given address space and write all of them.
 *
 * @mapping:   address space structure to write
 * @wbc:       subtract the number of written pages from *@wbc->nr_to_write
 * @bio_ctrl:  holds context for the write, namely the bio
 *
 * If a page is already under I/O, write_cache_pages() skips it, even
 * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
 * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
 * and msync() need to guarantee that all the data which was dirty at the time
 * the call was made get new I/O started against them.  If wbc->sync_mode is
 * WB_SYNC_ALL then we were called for data integrity and we must wait for
 * existing IO to complete.
 */
static int extent_write_cache_pages(struct address_space *mapping,
			     struct writeback_control *wbc,
			     struct btrfs_bio_ctrl *bio_ctrl)
{
	struct inode *inode = mapping->host;
	int ret = 0;
	int done = 0;
	int nr_to_write_done = 0;
	struct pagevec pvec;
	int nr_pages;
	pgoff_t index;
	pgoff_t end;		/* Inclusive */
	pgoff_t done_index;
	int range_whole = 0;
	int scanned = 0;
	xa_mark_t tag;

	/*
	 * We have to hold onto the inode so that ordered extents can do their
	 * work when the IO finishes.  The alternative to this is failing to add
	 * an ordered extent if the igrab() fails there and that is a huge pain
	 * to deal with, so instead just hold onto the inode throughout the
	 * writepages operation.  If it fails here we are freeing up the inode
	 * anyway and we'd rather not waste our time writing out stuff that is
	 * going to be truncated anyway.
	 */
	if (!igrab(inode))
		return 0;

	pagevec_init(&pvec);
	if (wbc->range_cyclic) {
		index = mapping->writeback_index; /* Start from prev offset */
		end = -1;
		/*
		 * Start from the beginning does not need to cycle over the
		 * range, mark it as scanned.
		 */
		scanned = (index == 0);
	} else {
		index = wbc->range_start >> PAGE_SHIFT;
		end = wbc->range_end >> PAGE_SHIFT;
		if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
			range_whole = 1;
		scanned = 1;
	}

	/*
	 * We do the tagged writepage as long as the snapshot flush bit is set
	 * and we are the first one who do the filemap_flush() on this inode.
	 *
	 * The nr_to_write == LONG_MAX is needed to make sure other flushers do
	 * not race in and drop the bit.
	 */
	if (range_whole && wbc->nr_to_write == LONG_MAX &&
	    test_and_clear_bit(BTRFS_INODE_SNAPSHOT_FLUSH,
			       &BTRFS_I(inode)->runtime_flags))
		wbc->tagged_writepages = 1;

	if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
		tag = PAGECACHE_TAG_TOWRITE;
	else
		tag = PAGECACHE_TAG_DIRTY;
retry:
	if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
		tag_pages_for_writeback(mapping, index, end);
	done_index = index;
	while (!done && !nr_to_write_done && (index <= end) &&
			(nr_pages = pagevec_lookup_range_tag(&pvec, mapping,
						&index, end, tag))) {
		unsigned i;

		for (i = 0; i < nr_pages; i++) {
			struct page *page = pvec.pages[i];

			done_index = page->index + 1;
			/*
			 * At this point we hold neither the i_pages lock nor
			 * the page lock: the page may be truncated or
			 * invalidated (changing page->mapping to NULL),
			 * or even swizzled back from swapper_space to
			 * tmpfs file mapping
			 */
			if (!trylock_page(page)) {
				submit_write_bio(bio_ctrl, 0);
				lock_page(page);
			}

			if (unlikely(page->mapping != mapping)) {
				unlock_page(page);
				continue;
			}

			if (wbc->sync_mode != WB_SYNC_NONE) {
				if (PageWriteback(page))
					submit_write_bio(bio_ctrl, 0);
				wait_on_page_writeback(page);
			}

			if (PageWriteback(page) ||
			    !clear_page_dirty_for_io(page)) {
				unlock_page(page);
				continue;
			}

			ret = __extent_writepage(page, wbc, bio_ctrl);
			if (ret < 0) {
				done = 1;
				break;
			}

			/*
			 * the filesystem may choose to bump up nr_to_write.
			 * We have to make sure to honor the new nr_to_write
			 * at any time
			 */
			nr_to_write_done = wbc->nr_to_write <= 0;
		}
		pagevec_release(&pvec);
		cond_resched();
	}
	if (!scanned && !done) {
		/*
		 * We hit the last page and there is more work to be done: wrap
		 * back to the start of the file
		 */
		scanned = 1;
		index = 0;

		/*
		 * If we're looping we could run into a page that is locked by a
		 * writer and that writer could be waiting on writeback for a
		 * page in our current bio, and thus deadlock, so flush the
		 * write bio here.
		 */
		submit_write_bio(bio_ctrl, 0);
		goto retry;
	}

	if (wbc->range_cyclic || (wbc->nr_to_write > 0 && range_whole))
		mapping->writeback_index = done_index;

	btrfs_add_delayed_iput(BTRFS_I(inode));
	return ret;
}

/*
 * Submit the pages in the range to bio for call sites which delalloc range has
 * already been ran (aka, ordered extent inserted) and all pages are still
 * locked.
 */
int extent_write_locked_range(struct inode *inode, u64 start, u64 end)
{
	bool found_error = false;
	int first_error = 0;
	int ret = 0;
	struct address_space *mapping = inode->i_mapping;
	struct page *page;
	u64 cur = start;
	unsigned long nr_pages;
	const u32 sectorsize = btrfs_sb(inode->i_sb)->sectorsize;
	struct btrfs_bio_ctrl bio_ctrl = {
		.extent_locked = 1,
		.sync_io = 1,
	};
	struct writeback_control wbc_writepages = {
		.sync_mode	= WB_SYNC_ALL,
		.range_start	= start,
		.range_end	= end + 1,
		/* We're called from an async helper function */
		.punt_to_cgroup	= 1,
		.no_cgroup_owner = 1,
	};

	ASSERT(IS_ALIGNED(start, sectorsize) && IS_ALIGNED(end + 1, sectorsize));
	nr_pages = (round_up(end, PAGE_SIZE) - round_down(start, PAGE_SIZE)) >>
		   PAGE_SHIFT;
	wbc_writepages.nr_to_write = nr_pages * 2;

	wbc_attach_fdatawrite_inode(&wbc_writepages, inode);
	while (cur <= end) {
		u64 cur_end = min(round_down(cur, PAGE_SIZE) + PAGE_SIZE - 1, end);

		page = find_get_page(mapping, cur >> PAGE_SHIFT);
		/*
		 * All pages in the range are locked since
		 * btrfs_run_delalloc_range(), thus there is no way to clear
		 * the page dirty flag.
		 */
		ASSERT(PageLocked(page));
		ASSERT(PageDirty(page));
		clear_page_dirty_for_io(page);
		ret = __extent_writepage(page, &wbc_writepages, &bio_ctrl);
		ASSERT(ret <= 0);
		if (ret < 0) {
			found_error = true;
			first_error = ret;
		}
		put_page(page);
		cur = cur_end + 1;
	}

	submit_write_bio(&bio_ctrl, found_error ? ret : 0);

	wbc_detach_inode(&wbc_writepages);
	if (found_error)
		return first_error;
	return ret;
}

int extent_writepages(struct address_space *mapping,
		      struct writeback_control *wbc)
{
	struct inode *inode = mapping->host;
	int ret = 0;
	struct btrfs_bio_ctrl bio_ctrl = {
		.extent_locked = 0,
		.sync_io = (wbc->sync_mode == WB_SYNC_ALL),
	};

	/*
	 * Allow only a single thread to do the reloc work in zoned mode to
	 * protect the write pointer updates.
	 */
	btrfs_zoned_data_reloc_lock(BTRFS_I(inode));
	ret = extent_write_cache_pages(mapping, wbc, &bio_ctrl);
	submit_write_bio(&bio_ctrl, ret);
	btrfs_zoned_data_reloc_unlock(BTRFS_I(inode));
	return ret;
}

void extent_readahead(struct readahead_control *rac)
{
	struct btrfs_bio_ctrl bio_ctrl = { 0 };
	struct page *pagepool[16];
	struct extent_map *em_cached = NULL;
	u64 prev_em_start = (u64)-1;
	int nr;

	while ((nr = readahead_page_batch(rac, pagepool))) {
		u64 contig_start = readahead_pos(rac);
		u64 contig_end = contig_start + readahead_batch_length(rac) - 1;

		contiguous_readpages(pagepool, nr, contig_start, contig_end,
				&em_cached, &bio_ctrl, &prev_em_start);
	}

	if (em_cached)
		free_extent_map(em_cached);
	submit_one_bio(&bio_ctrl);
}

/*
 * basic invalidate_folio code, this waits on any locked or writeback
 * ranges corresponding to the folio, and then deletes any extent state
 * records from the tree
 */
int extent_invalidate_folio(struct extent_io_tree *tree,
			  struct folio *folio, size_t offset)
{
	struct extent_state *cached_state = NULL;
	u64 start = folio_pos(folio);
	u64 end = start + folio_size(folio) - 1;
	size_t blocksize = folio->mapping->host->i_sb->s_blocksize;

	/* This function is only called for the btree inode */
	ASSERT(tree->owner == IO_TREE_BTREE_INODE_IO);

	start += ALIGN(offset, blocksize);
	if (start > end)
		return 0;

	lock_extent(tree, start, end, &cached_state);
	folio_wait_writeback(folio);

	/*
	 * Currently for btree io tree, only EXTENT_LOCKED is utilized,
	 * so here we only need to unlock the extent range to free any
	 * existing extent state.
	 */
	unlock_extent(tree, start, end, &cached_state);
	return 0;
}

/*
 * a helper for release_folio, this tests for areas of the page that
 * are locked or under IO and drops the related state bits if it is safe
 * to drop the page.
 */
static int try_release_extent_state(struct extent_io_tree *tree,
				    struct page *page, gfp_t mask)
{
	u64 start = page_offset(page);
	u64 end = start + PAGE_SIZE - 1;
	int ret = 1;

	if (test_range_bit(tree, start, end, EXTENT_LOCKED, 0, NULL)) {
		ret = 0;
	} else {
		u32 clear_bits = ~(EXTENT_LOCKED | EXTENT_NODATASUM |
				   EXTENT_DELALLOC_NEW | EXTENT_CTLBITS);

		/*
		 * At this point we can safely clear everything except the
		 * locked bit, the nodatasum bit and the delalloc new bit.
		 * The delalloc new bit will be cleared by ordered extent
		 * completion.
		 */
		ret = __clear_extent_bit(tree, start, end, clear_bits, NULL,
					 mask, NULL);

		/* if clear_extent_bit failed for enomem reasons,
		 * we can't allow the release to continue.
		 */
		if (ret < 0)
			ret = 0;
		else
			ret = 1;
	}
	return ret;
}

/*
 * a helper for release_folio.  As long as there are no locked extents
 * in the range corresponding to the page, both state records and extent
 * map records are removed
 */
int try_release_extent_mapping(struct page *page, gfp_t mask)
{
	struct extent_map *em;
	u64 start = page_offset(page);
	u64 end = start + PAGE_SIZE - 1;
	struct btrfs_inode *btrfs_inode = BTRFS_I(page->mapping->host);
	struct extent_io_tree *tree = &btrfs_inode->io_tree;
	struct extent_map_tree *map = &btrfs_inode->extent_tree;

	if (gfpflags_allow_blocking(mask) &&
	    page->mapping->host->i_size > SZ_16M) {
		u64 len;
		while (start <= end) {
			struct btrfs_fs_info *fs_info;
			u64 cur_gen;

			len = end - start + 1;
			write_lock(&map->lock);
			em = lookup_extent_mapping(map, start, len);
			if (!em) {
				write_unlock(&map->lock);
				break;
			}
			if (test_bit(EXTENT_FLAG_PINNED, &em->flags) ||
			    em->start != start) {
				write_unlock(&map->lock);
				free_extent_map(em);
				break;
			}
			if (test_range_bit(tree, em->start,
					   extent_map_end(em) - 1,
					   EXTENT_LOCKED, 0, NULL))
				goto next;
			/*
			 * If it's not in the list of modified extents, used
			 * by a fast fsync, we can remove it. If it's being
			 * logged we can safely remove it since fsync took an
			 * extra reference on the em.
			 */
			if (list_empty(&em->list) ||
			    test_bit(EXTENT_FLAG_LOGGING, &em->flags))
				goto remove_em;
			/*
			 * If it's in the list of modified extents, remove it
			 * only if its generation is older then the current one,
			 * in which case we don't need it for a fast fsync.
			 * Otherwise don't remove it, we could be racing with an
			 * ongoing fast fsync that could miss the new extent.
			 */
			fs_info = btrfs_inode->root->fs_info;
			spin_lock(&fs_info->trans_lock);
			cur_gen = fs_info->generation;
			spin_unlock(&fs_info->trans_lock);
			if (em->generation >= cur_gen)
				goto next;
remove_em:
			/*
			 * We only remove extent maps that are not in the list of
			 * modified extents or that are in the list but with a
			 * generation lower then the current generation, so there
			 * is no need to set the full fsync flag on the inode (it
			 * hurts the fsync performance for workloads with a data
			 * size that exceeds or is close to the system's memory).
			 */
			remove_extent_mapping(map, em);
			/* once for the rb tree */
			free_extent_map(em);
next:
			start = extent_map_end(em);
			write_unlock(&map->lock);

			/* once for us */
			free_extent_map(em);

			cond_resched(); /* Allow large-extent preemption. */
		}
	}
	return try_release_extent_state(tree, page, mask);
}

/*
 * To cache previous fiemap extent
 *
 * Will be used for merging fiemap extent
 */
struct fiemap_cache {
	u64 offset;
	u64 phys;
	u64 len;
	u32 flags;
	bool cached;
};

/*
 * Helper to submit fiemap extent.
 *
 * Will try to merge current fiemap extent specified by @offset, @phys,
 * @len and @flags with cached one.
 * And only when we fails to merge, cached one will be submitted as
 * fiemap extent.
 *
 * Return value is the same as fiemap_fill_next_extent().
 */
static int emit_fiemap_extent(struct fiemap_extent_info *fieinfo,
				struct fiemap_cache *cache,
				u64 offset, u64 phys, u64 len, u32 flags)
{
	int ret = 0;

	/* Set at the end of extent_fiemap(). */
	ASSERT((flags & FIEMAP_EXTENT_LAST) == 0);

	if (!cache->cached)
		goto assign;

	/*
	 * Sanity check, extent_fiemap() should have ensured that new
	 * fiemap extent won't overlap with cached one.
	 * Not recoverable.
	 *
	 * NOTE: Physical address can overlap, due to compression
	 */
	if (cache->offset + cache->len > offset) {
		WARN_ON(1);
		return -EINVAL;
	}

	/*
	 * Only merges fiemap extents if
	 * 1) Their logical addresses are continuous
	 *
	 * 2) Their physical addresses are continuous
	 *    So truly compressed (physical size smaller than logical size)
	 *    extents won't get merged with each other
	 *
	 * 3) Share same flags
	 */
	if (cache->offset + cache->len  == offset &&
	    cache->phys + cache->len == phys  &&
	    cache->flags == flags) {
		cache->len += len;
		return 0;
	}

	/* Not mergeable, need to submit cached one */
	ret = fiemap_fill_next_extent(fieinfo, cache->offset, cache->phys,
				      cache->len, cache->flags);
	cache->cached = false;
	if (ret)
		return ret;
assign:
	cache->cached = true;
	cache->offset = offset;
	cache->phys = phys;
	cache->len = len;
	cache->flags = flags;

	return 0;
}

/*
 * Emit last fiemap cache
 *
 * The last fiemap cache may still be cached in the following case:
 * 0		      4k		    8k
 * |<- Fiemap range ->|
 * |<------------  First extent ----------->|
 *
 * In this case, the first extent range will be cached but not emitted.
 * So we must emit it before ending extent_fiemap().
 */
static int emit_last_fiemap_cache(struct fiemap_extent_info *fieinfo,
				  struct fiemap_cache *cache)
{
	int ret;

	if (!cache->cached)
		return 0;

	ret = fiemap_fill_next_extent(fieinfo, cache->offset, cache->phys,
				      cache->len, cache->flags);
	cache->cached = false;
	if (ret > 0)
		ret = 0;
	return ret;
}

static int fiemap_next_leaf_item(struct btrfs_inode *inode, struct btrfs_path *path)
{
	struct extent_buffer *clone;
	struct btrfs_key key;
	int slot;
	int ret;

	path->slots[0]++;
	if (path->slots[0] < btrfs_header_nritems(path->nodes[0]))
		return 0;

	ret = btrfs_next_leaf(inode->root, path);
	if (ret != 0)
		return ret;

	/*
	 * Don't bother with cloning if there are no more file extent items for
	 * our inode.
	 */
	btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
	if (key.objectid != btrfs_ino(inode) || key.type != BTRFS_EXTENT_DATA_KEY)
		return 1;

	/* See the comment at fiemap_search_slot() about why we clone. */
	clone = btrfs_clone_extent_buffer(path->nodes[0]);
	if (!clone)
		return -ENOMEM;

	slot = path->slots[0];
	btrfs_release_path(path);
	path->nodes[0] = clone;
	path->slots[0] = slot;

	return 0;
}

/*
 * Search for the first file extent item that starts at a given file offset or
 * the one that starts immediately before that offset.
 * Returns: 0 on success, < 0 on error, 1 if not found.
 */
static int fiemap_search_slot(struct btrfs_inode *inode, struct btrfs_path *path,
			      u64 file_offset)
{
	const u64 ino = btrfs_ino(inode);
	struct btrfs_root *root = inode->root;
	struct extent_buffer *clone;
	struct btrfs_key key;
	int slot;
	int ret;

	key.objectid = ino;
	key.type = BTRFS_EXTENT_DATA_KEY;
	key.offset = file_offset;

	ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
	if (ret < 0)
		return ret;

	if (ret > 0 && path->slots[0] > 0) {
		btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0] - 1);
		if (key.objectid == ino && key.type == BTRFS_EXTENT_DATA_KEY)
			path->slots[0]--;
	}

	if (path->slots[0] >= btrfs_header_nritems(path->nodes[0])) {
		ret = btrfs_next_leaf(root, path);
		if (ret != 0)
			return ret;

		btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
		if (key.objectid != ino || key.type != BTRFS_EXTENT_DATA_KEY)
			return 1;
	}

	/*
	 * We clone the leaf and use it during fiemap. This is because while
	 * using the leaf we do expensive things like checking if an extent is
	 * shared, which can take a long time. In order to prevent blocking
	 * other tasks for too long, we use a clone of the leaf. We have locked
	 * the file range in the inode's io tree, so we know none of our file
	 * extent items can change. This way we avoid blocking other tasks that
	 * want to insert items for other inodes in the same leaf or b+tree
	 * rebalance operations (triggered for example when someone is trying
	 * to push items into this leaf when trying to insert an item in a
	 * neighbour leaf).
	 * We also need the private clone because holding a read lock on an
	 * extent buffer of the subvolume's b+tree will make lockdep unhappy
	 * when we call fiemap_fill_next_extent(), because that may cause a page
	 * fault when filling the user space buffer with fiemap data.
	 */
	clone = btrfs_clone_extent_buffer(path->nodes[0]);
	if (!clone)
		return -ENOMEM;

	slot = path->slots[0];
	btrfs_release_path(path);
	path->nodes[0] = clone;
	path->slots[0] = slot;

	return 0;
}

/*
 * Process a range which is a hole or a prealloc extent in the inode's subvolume
 * btree. If @disk_bytenr is 0, we are dealing with a hole, otherwise a prealloc
 * extent. The end offset (@end) is inclusive.
 */
static int fiemap_process_hole(struct btrfs_inode *inode,
			       struct fiemap_extent_info *fieinfo,
			       struct fiemap_cache *cache,
			       struct extent_state **delalloc_cached_state,
			       struct btrfs_backref_share_check_ctx *backref_ctx,
			       u64 disk_bytenr, u64 extent_offset,
			       u64 extent_gen,
			       u64 start, u64 end)
{
	const u64 i_size = i_size_read(&inode->vfs_inode);
	u64 cur_offset = start;
	u64 last_delalloc_end = 0;
	u32 prealloc_flags = FIEMAP_EXTENT_UNWRITTEN;
	bool checked_extent_shared = false;
	int ret;

	/*
	 * There can be no delalloc past i_size, so don't waste time looking for
	 * it beyond i_size.
	 */
	while (cur_offset < end && cur_offset < i_size) {
		u64 delalloc_start;
		u64 delalloc_end;
		u64 prealloc_start;
		u64 prealloc_len = 0;
		bool delalloc;

		delalloc = btrfs_find_delalloc_in_range(inode, cur_offset, end,
							delalloc_cached_state,
							&delalloc_start,
							&delalloc_end);
		if (!delalloc)
			break;

		/*
		 * If this is a prealloc extent we have to report every section
		 * of it that has no delalloc.
		 */
		if (disk_bytenr != 0) {
			if (last_delalloc_end == 0) {
				prealloc_start = start;
				prealloc_len = delalloc_start - start;
			} else {
				prealloc_start = last_delalloc_end + 1;
				prealloc_len = delalloc_start - prealloc_start;
			}
		}

		if (prealloc_len > 0) {
			if (!checked_extent_shared && fieinfo->fi_extents_max) {
				ret = btrfs_is_data_extent_shared(inode,
								  disk_bytenr,
								  extent_gen,
								  backref_ctx);
				if (ret < 0)
					return ret;
				else if (ret > 0)
					prealloc_flags |= FIEMAP_EXTENT_SHARED;

				checked_extent_shared = true;
			}
			ret = emit_fiemap_extent(fieinfo, cache, prealloc_start,
						 disk_bytenr + extent_offset,
						 prealloc_len, prealloc_flags);
			if (ret)
				return ret;
			extent_offset += prealloc_len;
		}

		ret = emit_fiemap_extent(fieinfo, cache, delalloc_start, 0,
					 delalloc_end + 1 - delalloc_start,
					 FIEMAP_EXTENT_DELALLOC |
					 FIEMAP_EXTENT_UNKNOWN);
		if (ret)
			return ret;

		last_delalloc_end = delalloc_end;
		cur_offset = delalloc_end + 1;
		extent_offset += cur_offset - delalloc_start;
		cond_resched();
	}

	/*
	 * Either we found no delalloc for the whole prealloc extent or we have
	 * a prealloc extent that spans i_size or starts at or after i_size.
	 */
	if (disk_bytenr != 0 && last_delalloc_end < end) {
		u64 prealloc_start;
		u64 prealloc_len;

		if (last_delalloc_end == 0) {
			prealloc_start = start;
			prealloc_len = end + 1 - start;
		} else {
			prealloc_start = last_delalloc_end + 1;
			prealloc_len = end + 1 - prealloc_start;
		}

		if (!checked_extent_shared && fieinfo->fi_extents_max) {
			ret = btrfs_is_data_extent_shared(inode,
							  disk_bytenr,
							  extent_gen,
							  backref_ctx);
			if (ret < 0)
				return ret;
			else if (ret > 0)
				prealloc_flags |= FIEMAP_EXTENT_SHARED;
		}
		ret = emit_fiemap_extent(fieinfo, cache, prealloc_start,
					 disk_bytenr + extent_offset,
					 prealloc_len, prealloc_flags);
		if (ret)
			return ret;
	}

	return 0;
}

static int fiemap_find_last_extent_offset(struct btrfs_inode *inode,
					  struct btrfs_path *path,
					  u64 *last_extent_end_ret)
{
	const u64 ino = btrfs_ino(inode);
	struct btrfs_root *root = inode->root;
	struct extent_buffer *leaf;
	struct btrfs_file_extent_item *ei;
	struct btrfs_key key;
	u64 disk_bytenr;
	int ret;

	/*
	 * Lookup the last file extent. We're not using i_size here because
	 * there might be preallocation past i_size.
	 */
	ret = btrfs_lookup_file_extent(NULL, root, path, ino, (u64)-1, 0);
	/* There can't be a file extent item at offset (u64)-1 */
	ASSERT(ret != 0);
	if (ret < 0)
		return ret;

	/*
	 * For a non-existing key, btrfs_search_slot() always leaves us at a
	 * slot > 0, except if the btree is empty, which is impossible because
	 * at least it has the inode item for this inode and all the items for
	 * the root inode 256.
	 */
	ASSERT(path->slots[0] > 0);
	path->slots[0]--;
	leaf = path->nodes[0];
	btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
	if (key.objectid != ino || key.type != BTRFS_EXTENT_DATA_KEY) {
		/* No file extent items in the subvolume tree. */
		*last_extent_end_ret = 0;
		return 0;
	}

	/*
	 * For an inline extent, the disk_bytenr is where inline data starts at,
	 * so first check if we have an inline extent item before checking if we
	 * have an implicit hole (disk_bytenr == 0).
	 */
	ei = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_file_extent_item);
	if (btrfs_file_extent_type(leaf, ei) == BTRFS_FILE_EXTENT_INLINE) {
		*last_extent_end_ret = btrfs_file_extent_end(path);
		return 0;
	}

	/*
	 * Find the last file extent item that is not a hole (when NO_HOLES is
	 * not enabled). This should take at most 2 iterations in the worst
	 * case: we have one hole file extent item at slot 0 of a leaf and
	 * another hole file extent item as the last item in the previous leaf.
	 * This is because we merge file extent items that represent holes.
	 */
	disk_bytenr = btrfs_file_extent_disk_bytenr(leaf, ei);
	while (disk_bytenr == 0) {
		ret = btrfs_previous_item(root, path, ino, BTRFS_EXTENT_DATA_KEY);
		if (ret < 0) {
			return ret;
		} else if (ret > 0) {
			/* No file extent items that are not holes. */
			*last_extent_end_ret = 0;
			return 0;
		}
		leaf = path->nodes[0];
		ei = btrfs_item_ptr(leaf, path->slots[0],
				    struct btrfs_file_extent_item);
		disk_bytenr = btrfs_file_extent_disk_bytenr(leaf, ei);
	}

	*last_extent_end_ret = btrfs_file_extent_end(path);
	return 0;
}

int extent_fiemap(struct btrfs_inode *inode, struct fiemap_extent_info *fieinfo,
		  u64 start, u64 len)
{
	const u64 ino = btrfs_ino(inode);
	struct extent_state *cached_state = NULL;
	struct extent_state *delalloc_cached_state = NULL;
	struct btrfs_path *path;
	struct fiemap_cache cache = { 0 };
	struct btrfs_backref_share_check_ctx *backref_ctx;
	u64 last_extent_end;
	u64 prev_extent_end;
	u64 lockstart;
	u64 lockend;
	bool stopped = false;
	int ret;

	backref_ctx = btrfs_alloc_backref_share_check_ctx();
	path = btrfs_alloc_path();
	if (!backref_ctx || !path) {
		ret = -ENOMEM;
		goto out;
	}

	lockstart = round_down(start, inode->root->fs_info->sectorsize);
	lockend = round_up(start + len, inode->root->fs_info->sectorsize);
	prev_extent_end = lockstart;

	btrfs_inode_lock(inode, BTRFS_ILOCK_SHARED);
	lock_extent(&inode->io_tree, lockstart, lockend, &cached_state);

	ret = fiemap_find_last_extent_offset(inode, path, &last_extent_end);
	if (ret < 0)
		goto out_unlock;
	btrfs_release_path(path);

	path->reada = READA_FORWARD;
	ret = fiemap_search_slot(inode, path, lockstart);
	if (ret < 0) {
		goto out_unlock;
	} else if (ret > 0) {
		/*
		 * No file extent item found, but we may have delalloc between
		 * the current offset and i_size. So check for that.
		 */
		ret = 0;
		goto check_eof_delalloc;
	}

	while (prev_extent_end < lockend) {
		struct extent_buffer *leaf = path->nodes[0];
		struct btrfs_file_extent_item *ei;
		struct btrfs_key key;
		u64 extent_end;
		u64 extent_len;
		u64 extent_offset = 0;
		u64 extent_gen;
		u64 disk_bytenr = 0;
		u64 flags = 0;
		int extent_type;
		u8 compression;

		btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
		if (key.objectid != ino || key.type != BTRFS_EXTENT_DATA_KEY)
			break;

		extent_end = btrfs_file_extent_end(path);

		/*
		 * The first iteration can leave us at an extent item that ends
		 * before our range's start. Move to the next item.
		 */
		if (extent_end <= lockstart)
			goto next_item;

		backref_ctx->curr_leaf_bytenr = leaf->start;

		/* We have in implicit hole (NO_HOLES feature enabled). */
		if (prev_extent_end < key.offset) {
			const u64 range_end = min(key.offset, lockend) - 1;

			ret = fiemap_process_hole(inode, fieinfo, &cache,
						  &delalloc_cached_state,
						  backref_ctx, 0, 0, 0,
						  prev_extent_end, range_end);
			if (ret < 0) {
				goto out_unlock;
			} else if (ret > 0) {
				/* fiemap_fill_next_extent() told us to stop. */
				stopped = true;
				break;
			}

			/* We've reached the end of the fiemap range, stop. */
			if (key.offset >= lockend) {
				stopped = true;
				break;
			}
		}

		extent_len = extent_end - key.offset;
		ei = btrfs_item_ptr(leaf, path->slots[0],
				    struct btrfs_file_extent_item);
		compression = btrfs_file_extent_compression(leaf, ei);
		extent_type = btrfs_file_extent_type(leaf, ei);
		extent_gen = btrfs_file_extent_generation(leaf, ei);

		if (extent_type != BTRFS_FILE_EXTENT_INLINE) {
			disk_bytenr = btrfs_file_extent_disk_bytenr(leaf, ei);
			if (compression == BTRFS_COMPRESS_NONE)
				extent_offset = btrfs_file_extent_offset(leaf, ei);
		}

		if (compression != BTRFS_COMPRESS_NONE)
			flags |= FIEMAP_EXTENT_ENCODED;

		if (extent_type == BTRFS_FILE_EXTENT_INLINE) {
			flags |= FIEMAP_EXTENT_DATA_INLINE;
			flags |= FIEMAP_EXTENT_NOT_ALIGNED;
			ret = emit_fiemap_extent(fieinfo, &cache, key.offset, 0,
						 extent_len, flags);
		} else if (extent_type == BTRFS_FILE_EXTENT_PREALLOC) {
			ret = fiemap_process_hole(inode, fieinfo, &cache,
						  &delalloc_cached_state,
						  backref_ctx,
						  disk_bytenr, extent_offset,
						  extent_gen, key.offset,
						  extent_end - 1);
		} else if (disk_bytenr == 0) {
			/* We have an explicit hole. */
			ret = fiemap_process_hole(inode, fieinfo, &cache,
						  &delalloc_cached_state,
						  backref_ctx, 0, 0, 0,
						  key.offset, extent_end - 1);
		} else {
			/* We have a regular extent. */
			if (fieinfo->fi_extents_max) {
				ret = btrfs_is_data_extent_shared(inode,
								  disk_bytenr,
								  extent_gen,
								  backref_ctx);
				if (ret < 0)
					goto out_unlock;
				else if (ret > 0)
					flags |= FIEMAP_EXTENT_SHARED;
			}

			ret = emit_fiemap_extent(fieinfo, &cache, key.offset,
						 disk_bytenr + extent_offset,
						 extent_len, flags);
		}

		if (ret < 0) {
			goto out_unlock;
		} else if (ret > 0) {
			/* fiemap_fill_next_extent() told us to stop. */
			stopped = true;
			break;
		}

		prev_extent_end = extent_end;
next_item:
		if (fatal_signal_pending(current)) {
			ret = -EINTR;
			goto out_unlock;
		}

		ret = fiemap_next_leaf_item(inode, path);
		if (ret < 0) {
			goto out_unlock;
		} else if (ret > 0) {
			/* No more file extent items for this inode. */
			break;
		}
		cond_resched();
	}

check_eof_delalloc:
	/*
	 * Release (and free) the path before emitting any final entries to
	 * fiemap_fill_next_extent() to keep lockdep happy. This is because
	 * once we find no more file extent items exist, we may have a
	 * non-cloned leaf, and fiemap_fill_next_extent() can trigger page
	 * faults when copying data to the user space buffer.
	 */
	btrfs_free_path(path);
	path = NULL;

	if (!stopped && prev_extent_end < lockend) {
		ret = fiemap_process_hole(inode, fieinfo, &cache,
					  &delalloc_cached_state, backref_ctx,
					  0, 0, 0, prev_extent_end, lockend - 1);
		if (ret < 0)
			goto out_unlock;
		prev_extent_end = lockend;
	}

	if (cache.cached && cache.offset + cache.len >= last_extent_end) {
		const u64 i_size = i_size_read(&inode->vfs_inode);

		if (prev_extent_end < i_size) {
			u64 delalloc_start;
			u64 delalloc_end;
			bool delalloc;

			delalloc = btrfs_find_delalloc_in_range(inode,
								prev_extent_end,
								i_size - 1,
								&delalloc_cached_state,
								&delalloc_start,
								&delalloc_end);
			if (!delalloc)
				cache.flags |= FIEMAP_EXTENT_LAST;
		} else {
			cache.flags |= FIEMAP_EXTENT_LAST;
		}
	}

	ret = emit_last_fiemap_cache(fieinfo, &cache);

out_unlock:
	unlock_extent(&inode->io_tree, lockstart, lockend, &cached_state);
	btrfs_inode_unlock(inode, BTRFS_ILOCK_SHARED);
out:
	free_extent_state(delalloc_cached_state);
	btrfs_free_backref_share_ctx(backref_ctx);
	btrfs_free_path(path);
	return ret;
}

static void __free_extent_buffer(struct extent_buffer *eb)
{
	kmem_cache_free(extent_buffer_cache, eb);
}

int extent_buffer_under_io(const struct extent_buffer *eb)
{
	return (atomic_read(&eb->io_pages) ||
		test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags) ||
		test_bit(EXTENT_BUFFER_DIRTY, &eb->bflags));
}

static bool page_range_has_eb(struct btrfs_fs_info *fs_info, struct page *page)
{
	struct btrfs_subpage *subpage;

	lockdep_assert_held(&page->mapping->private_lock);

	if (PagePrivate(page)) {
		subpage = (struct btrfs_subpage *)page->private;
		if (atomic_read(&subpage->eb_refs))
			return true;
		/*
		 * Even there is no eb refs here, we may still have
		 * end_page_read() call relying on page::private.
		 */
		if (atomic_read(&subpage->readers))
			return true;
	}
	return false;
}

static void detach_extent_buffer_page(struct extent_buffer *eb, struct page *page)
{
	struct btrfs_fs_info *fs_info = eb->fs_info;
	const bool mapped = !test_bit(EXTENT_BUFFER_UNMAPPED, &eb->bflags);

	/*
	 * For mapped eb, we're going to change the page private, which should
	 * be done under the private_lock.
	 */
	if (mapped)
		spin_lock(&page->mapping->private_lock);

	if (!PagePrivate(page)) {
		if (mapped)
			spin_unlock(&page->mapping->private_lock);
		return;
	}

	if (fs_info->nodesize >= PAGE_SIZE) {
		/*
		 * We do this since we'll remove the pages after we've
		 * removed the eb from the radix tree, so we could race
		 * and have this page now attached to the new eb.  So
		 * only clear page_private if it's still connected to
		 * this eb.
		 */
		if (PagePrivate(page) &&
		    page->private == (unsigned long)eb) {
			BUG_ON(test_bit(EXTENT_BUFFER_DIRTY, &eb->bflags));
			BUG_ON(PageDirty(page));
			BUG_ON(PageWriteback(page));
			/*
			 * We need to make sure we haven't be attached
			 * to a new eb.
			 */
			detach_page_private(page);
		}
		if (mapped)
			spin_unlock(&page->mapping->private_lock);
		return;
	}

	/*
	 * For subpage, we can have dummy eb with page private.  In this case,
	 * we can directly detach the private as such page is only attached to
	 * one dummy eb, no sharing.
	 */
	if (!mapped) {
		btrfs_detach_subpage(fs_info, page);
		return;
	}

	btrfs_page_dec_eb_refs(fs_info, page);

	/*
	 * We can only detach the page private if there are no other ebs in the
	 * page range and no unfinished IO.
	 */
	if (!page_range_has_eb(fs_info, page))
		btrfs_detach_subpage(fs_info, page);

	spin_unlock(&page->mapping->private_lock);
}

/* Release all pages attached to the extent buffer */
static void btrfs_release_extent_buffer_pages(struct extent_buffer *eb)
{
	int i;
	int num_pages;

	ASSERT(!extent_buffer_under_io(eb));

	num_pages = num_extent_pages(eb);
	for (i = 0; i < num_pages; i++) {
		struct page *page = eb->pages[i];

		if (!page)
			continue;

		detach_extent_buffer_page(eb, page);

		/* One for when we allocated the page */
		put_page(page);
	}
}

/*
 * Helper for releasing the extent buffer.
 */
static inline void btrfs_release_extent_buffer(struct extent_buffer *eb)
{
	btrfs_release_extent_buffer_pages(eb);
	btrfs_leak_debug_del_eb(eb);
	__free_extent_buffer(eb);
}

static struct extent_buffer *
__alloc_extent_buffer(struct btrfs_fs_info *fs_info, u64 start,
		      unsigned long len)
{
	struct extent_buffer *eb = NULL;

	eb = kmem_cache_zalloc(extent_buffer_cache, GFP_NOFS|__GFP_NOFAIL);
	eb->start = start;
	eb->len = len;
	eb->fs_info = fs_info;
	init_rwsem(&eb->lock);

	btrfs_leak_debug_add_eb(eb);
	INIT_LIST_HEAD(&eb->release_list);

	spin_lock_init(&eb->refs_lock);
	atomic_set(&eb->refs, 1);
	atomic_set(&eb->io_pages, 0);

	ASSERT(len <= BTRFS_MAX_METADATA_BLOCKSIZE);

	return eb;
}

struct extent_buffer *btrfs_clone_extent_buffer(const struct extent_buffer *src)
{
	int i;
	struct extent_buffer *new;
	int num_pages = num_extent_pages(src);
	int ret;

	new = __alloc_extent_buffer(src->fs_info, src->start, src->len);
	if (new == NULL)
		return NULL;

	/*
	 * Set UNMAPPED before calling btrfs_release_extent_buffer(), as
	 * btrfs_release_extent_buffer() have different behavior for
	 * UNMAPPED subpage extent buffer.
	 */
	set_bit(EXTENT_BUFFER_UNMAPPED, &new->bflags);

	ret = btrfs_alloc_page_array(num_pages, new->pages);
	if (ret) {
		btrfs_release_extent_buffer(new);
		return NULL;
	}

	for (i = 0; i < num_pages; i++) {
		int ret;
		struct page *p = new->pages[i];

		ret = attach_extent_buffer_page(new, p, NULL);
		if (ret < 0) {
			btrfs_release_extent_buffer(new);
			return NULL;
		}
		WARN_ON(PageDirty(p));
		copy_page(page_address(p), page_address(src->pages[i]));
	}
	set_extent_buffer_uptodate(new);

	return new;
}

struct extent_buffer *__alloc_dummy_extent_buffer(struct btrfs_fs_info *fs_info,
						  u64 start, unsigned long len)
{
	struct extent_buffer *eb;
	int num_pages;
	int i;
	int ret;

	eb = __alloc_extent_buffer(fs_info, start, len);
	if (!eb)
		return NULL;

	num_pages = num_extent_pages(eb);
	ret = btrfs_alloc_page_array(num_pages, eb->pages);
	if (ret)
		goto err;

	for (i = 0; i < num_pages; i++) {
		struct page *p = eb->pages[i];

		ret = attach_extent_buffer_page(eb, p, NULL);
		if (ret < 0)
			goto err;
	}

	set_extent_buffer_uptodate(eb);
	btrfs_set_header_nritems(eb, 0);
	set_bit(EXTENT_BUFFER_UNMAPPED, &eb->bflags);

	return eb;
err:
	for (i = 0; i < num_pages; i++) {
		if (eb->pages[i]) {
			detach_extent_buffer_page(eb, eb->pages[i]);
			__free_page(eb->pages[i]);
		}
	}
	__free_extent_buffer(eb);
	return NULL;
}

struct extent_buffer *alloc_dummy_extent_buffer(struct btrfs_fs_info *fs_info,
						u64 start)
{
	return __alloc_dummy_extent_buffer(fs_info, start, fs_info->nodesize);
}

static void check_buffer_tree_ref(struct extent_buffer *eb)
{
	int refs;
	/*
	 * The TREE_REF bit is first set when the extent_buffer is added
	 * to the radix tree. It is also reset, if unset, when a new reference
	 * is created by find_extent_buffer.
	 *
	 * It is only cleared in two cases: freeing the last non-tree
	 * reference to the extent_buffer when its STALE bit is set or
	 * calling release_folio when the tree reference is the only reference.
	 *
	 * In both cases, care is taken to ensure that the extent_buffer's
	 * pages are not under io. However, release_folio can be concurrently
	 * called with creating new references, which is prone to race
	 * conditions between the calls to check_buffer_tree_ref in those
	 * codepaths and clearing TREE_REF in try_release_extent_buffer.
	 *
	 * The actual lifetime of the extent_buffer in the radix tree is
	 * adequately protected by the refcount, but the TREE_REF bit and
	 * its corresponding reference are not. To protect against this
	 * class of races, we call check_buffer_tree_ref from the codepaths
	 * which trigger io after they set eb->io_pages. Note that once io is
	 * initiated, TREE_REF can no longer be cleared, so that is the
	 * moment at which any such race is best fixed.
	 */
	refs = atomic_read(&eb->refs);
	if (refs >= 2 && test_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags))
		return;

	spin_lock(&eb->refs_lock);
	if (!test_and_set_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags))
		atomic_inc(&eb->refs);
	spin_unlock(&eb->refs_lock);
}

static void mark_extent_buffer_accessed(struct extent_buffer *eb,
		struct page *accessed)
{
	int num_pages, i;

	check_buffer_tree_ref(eb);

	num_pages = num_extent_pages(eb);
	for (i = 0; i < num_pages; i++) {
		struct page *p = eb->pages[i];

		if (p != accessed)
			mark_page_accessed(p);
	}
}

struct extent_buffer *find_extent_buffer(struct btrfs_fs_info *fs_info,
					 u64 start)
{
	struct extent_buffer *eb;

	eb = find_extent_buffer_nolock(fs_info, start);
	if (!eb)
		return NULL;
	/*
	 * Lock our eb's refs_lock to avoid races with free_extent_buffer().
	 * When we get our eb it might be flagged with EXTENT_BUFFER_STALE and
	 * another task running free_extent_buffer() might have seen that flag
	 * set, eb->refs == 2, that the buffer isn't under IO (dirty and
	 * writeback flags not set) and it's still in the tree (flag
	 * EXTENT_BUFFER_TREE_REF set), therefore being in the process of
	 * decrementing the extent buffer's reference count twice.  So here we
	 * could race and increment the eb's reference count, clear its stale
	 * flag, mark it as dirty and drop our reference before the other task
	 * finishes executing free_extent_buffer, which would later result in
	 * an attempt to free an extent buffer that is dirty.
	 */
	if (test_bit(EXTENT_BUFFER_STALE, &eb->bflags)) {
		spin_lock(&eb->refs_lock);
		spin_unlock(&eb->refs_lock);
	}
	mark_extent_buffer_accessed(eb, NULL);
	return eb;
}

#ifdef CONFIG_BTRFS_FS_RUN_SANITY_TESTS
struct extent_buffer *alloc_test_extent_buffer(struct btrfs_fs_info *fs_info,
					u64 start)
{
	struct extent_buffer *eb, *exists = NULL;
	int ret;

	eb = find_extent_buffer(fs_info, start);
	if (eb)
		return eb;
	eb = alloc_dummy_extent_buffer(fs_info, start);
	if (!eb)
		return ERR_PTR(-ENOMEM);
	eb->fs_info = fs_info;
again:
	ret = radix_tree_preload(GFP_NOFS);
	if (ret) {
		exists = ERR_PTR(ret);
		goto free_eb;
	}
	spin_lock(&fs_info->buffer_lock);
	ret = radix_tree_insert(&fs_info->buffer_radix,
				start >> fs_info->sectorsize_bits, eb);
	spin_unlock(&fs_info->buffer_lock);
	radix_tree_preload_end();
	if (ret == -EEXIST) {
		exists = find_extent_buffer(fs_info, start);
		if (exists)
			goto free_eb;
		else
			goto again;
	}
	check_buffer_tree_ref(eb);
	set_bit(EXTENT_BUFFER_IN_TREE, &eb->bflags);

	return eb;
free_eb:
	btrfs_release_extent_buffer(eb);
	return exists;
}
#endif

static struct extent_buffer *grab_extent_buffer(
		struct btrfs_fs_info *fs_info, struct page *page)
{
	struct extent_buffer *exists;

	/*
	 * For subpage case, we completely rely on radix tree to ensure we
	 * don't try to insert two ebs for the same bytenr.  So here we always
	 * return NULL and just continue.
	 */
	if (fs_info->nodesize < PAGE_SIZE)
		return NULL;

	/* Page not yet attached to an extent buffer */
	if (!PagePrivate(page))
		return NULL;

	/*
	 * We could have already allocated an eb for this page and attached one
	 * so lets see if we can get a ref on the existing eb, and if we can we
	 * know it's good and we can just return that one, else we know we can
	 * just overwrite page->private.
	 */
	exists = (struct extent_buffer *)page->private;
	if (atomic_inc_not_zero(&exists->refs))
		return exists;

	WARN_ON(PageDirty(page));
	detach_page_private(page);
	return NULL;
}

static int check_eb_alignment(struct btrfs_fs_info *fs_info, u64 start)
{
	if (!IS_ALIGNED(start, fs_info->sectorsize)) {
		btrfs_err(fs_info, "bad tree block start %llu", start);
		return -EINVAL;
	}

	if (fs_info->nodesize < PAGE_SIZE &&
	    offset_in_page(start) + fs_info->nodesize > PAGE_SIZE) {
		btrfs_err(fs_info,
		"tree block crosses page boundary, start %llu nodesize %u",
			  start, fs_info->nodesize);
		return -EINVAL;
	}
	if (fs_info->nodesize >= PAGE_SIZE &&
	    !PAGE_ALIGNED(start)) {
		btrfs_err(fs_info,
		"tree block is not page aligned, start %llu nodesize %u",
			  start, fs_info->nodesize);
		return -EINVAL;
	}
	return 0;
}

struct extent_buffer *alloc_extent_buffer(struct btrfs_fs_info *fs_info,
					  u64 start, u64 owner_root, int level)
{
	unsigned long len = fs_info->nodesize;
	int num_pages;
	int i;
	unsigned long index = start >> PAGE_SHIFT;
	struct extent_buffer *eb;
	struct extent_buffer *exists = NULL;
	struct page *p;
	struct address_space *mapping = fs_info->btree_inode->i_mapping;
	u64 lockdep_owner = owner_root;
	int uptodate = 1;
	int ret;

	if (check_eb_alignment(fs_info, start))
		return ERR_PTR(-EINVAL);

#if BITS_PER_LONG == 32
	if (start >= MAX_LFS_FILESIZE) {
		btrfs_err_rl(fs_info,
		"extent buffer %llu is beyond 32bit page cache limit", start);
		btrfs_err_32bit_limit(fs_info);
		return ERR_PTR(-EOVERFLOW);
	}
	if (start >= BTRFS_32BIT_EARLY_WARN_THRESHOLD)
		btrfs_warn_32bit_limit(fs_info);
#endif

	eb = find_extent_buffer(fs_info, start);
	if (eb)
		return eb;

	eb = __alloc_extent_buffer(fs_info, start, len);
	if (!eb)
		return ERR_PTR(-ENOMEM);

	/*
	 * The reloc trees are just snapshots, so we need them to appear to be
	 * just like any other fs tree WRT lockdep.
	 */
	if (lockdep_owner == BTRFS_TREE_RELOC_OBJECTID)
		lockdep_owner = BTRFS_FS_TREE_OBJECTID;

	btrfs_set_buffer_lockdep_class(lockdep_owner, eb, level);

	num_pages = num_extent_pages(eb);
	for (i = 0; i < num_pages; i++, index++) {
		struct btrfs_subpage *prealloc = NULL;

		p = find_or_create_page(mapping, index, GFP_NOFS|__GFP_NOFAIL);
		if (!p) {
			exists = ERR_PTR(-ENOMEM);
			goto free_eb;
		}

		/*
		 * Preallocate page->private for subpage case, so that we won't
		 * allocate memory with private_lock hold.  The memory will be
		 * freed by attach_extent_buffer_page() or freed manually if
		 * we exit earlier.
		 *
		 * Although we have ensured one subpage eb can only have one
		 * page, but it may change in the future for 16K page size
		 * support, so we still preallocate the memory in the loop.
		 */
		if (fs_info->nodesize < PAGE_SIZE) {
			prealloc = btrfs_alloc_subpage(fs_info, BTRFS_SUBPAGE_METADATA);
			if (IS_ERR(prealloc)) {
				ret = PTR_ERR(prealloc);
				unlock_page(p);
				put_page(p);
				exists = ERR_PTR(ret);
				goto free_eb;
			}
		}

		spin_lock(&mapping->private_lock);
		exists = grab_extent_buffer(fs_info, p);
		if (exists) {
			spin_unlock(&mapping->private_lock);
			unlock_page(p);
			put_page(p);
			mark_extent_buffer_accessed(exists, p);
			btrfs_free_subpage(prealloc);
			goto free_eb;
		}
		/* Should not fail, as we have preallocated the memory */
		ret = attach_extent_buffer_page(eb, p, prealloc);
		ASSERT(!ret);
		/*
		 * To inform we have extra eb under allocation, so that
		 * detach_extent_buffer_page() won't release the page private
		 * when the eb hasn't yet been inserted into radix tree.
		 *
		 * The ref will be decreased when the eb released the page, in
		 * detach_extent_buffer_page().
		 * Thus needs no special handling in error path.
		 */
		btrfs_page_inc_eb_refs(fs_info, p);
		spin_unlock(&mapping->private_lock);

		WARN_ON(btrfs_page_test_dirty(fs_info, p, eb->start, eb->len));
		eb->pages[i] = p;
		if (!PageUptodate(p))
			uptodate = 0;

		/*
		 * We can't unlock the pages just yet since the extent buffer
		 * hasn't been properly inserted in the radix tree, this
		 * opens a race with btree_release_folio which can free a page
		 * while we are still filling in all pages for the buffer and
		 * we could crash.
		 */
	}
	if (uptodate)
		set_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
again:
	ret = radix_tree_preload(GFP_NOFS);
	if (ret) {
		exists = ERR_PTR(ret);
		goto free_eb;
	}

	spin_lock(&fs_info->buffer_lock);
	ret = radix_tree_insert(&fs_info->buffer_radix,
				start >> fs_info->sectorsize_bits, eb);
	spin_unlock(&fs_info->buffer_lock);
	radix_tree_preload_end();
	if (ret == -EEXIST) {
		exists = find_extent_buffer(fs_info, start);
		if (exists)
			goto free_eb;
		else
			goto again;
	}
	/* add one reference for the tree */
	check_buffer_tree_ref(eb);
	set_bit(EXTENT_BUFFER_IN_TREE, &eb->bflags);

	/*
	 * Now it's safe to unlock the pages because any calls to
	 * btree_release_folio will correctly detect that a page belongs to a
	 * live buffer and won't free them prematurely.
	 */
	for (i = 0; i < num_pages; i++)
		unlock_page(eb->pages[i]);
	return eb;

free_eb:
	WARN_ON(!atomic_dec_and_test(&eb->refs));
	for (i = 0; i < num_pages; i++) {
		if (eb->pages[i])
			unlock_page(eb->pages[i]);
	}

	btrfs_release_extent_buffer(eb);
	return exists;
}

static inline void btrfs_release_extent_buffer_rcu(struct rcu_head *head)
{
	struct extent_buffer *eb =
			container_of(head, struct extent_buffer, rcu_head);

	__free_extent_buffer(eb);
}

static int release_extent_buffer(struct extent_buffer *eb)
	__releases(&eb->refs_lock)
{
	lockdep_assert_held(&eb->refs_lock);

	WARN_ON(atomic_read(&eb->refs) == 0);
	if (atomic_dec_and_test(&eb->refs)) {
		if (test_and_clear_bit(EXTENT_BUFFER_IN_TREE, &eb->bflags)) {
			struct btrfs_fs_info *fs_info = eb->fs_info;

			spin_unlock(&eb->refs_lock);

			spin_lock(&fs_info->buffer_lock);
			radix_tree_delete(&fs_info->buffer_radix,
					  eb->start >> fs_info->sectorsize_bits);
			spin_unlock(&fs_info->buffer_lock);
		} else {
			spin_unlock(&eb->refs_lock);
		}

		btrfs_leak_debug_del_eb(eb);
		/* Should be safe to release our pages at this point */
		btrfs_release_extent_buffer_pages(eb);
#ifdef CONFIG_BTRFS_FS_RUN_SANITY_TESTS
		if (unlikely(test_bit(EXTENT_BUFFER_UNMAPPED, &eb->bflags))) {
			__free_extent_buffer(eb);
			return 1;
		}
#endif
		call_rcu(&eb->rcu_head, btrfs_release_extent_buffer_rcu);
		return 1;
	}
	spin_unlock(&eb->refs_lock);

	return 0;
}

void free_extent_buffer(struct extent_buffer *eb)
{
	int refs;
	if (!eb)
		return;

	refs = atomic_read(&eb->refs);
	while (1) {
		if ((!test_bit(EXTENT_BUFFER_UNMAPPED, &eb->bflags) && refs <= 3)
		    || (test_bit(EXTENT_BUFFER_UNMAPPED, &eb->bflags) &&
			refs == 1))
			break;
		if (atomic_try_cmpxchg(&eb->refs, &refs, refs - 1))
			return;
	}

	spin_lock(&eb->refs_lock);
	if (atomic_read(&eb->refs) == 2 &&
	    test_bit(EXTENT_BUFFER_STALE, &eb->bflags) &&
	    !extent_buffer_under_io(eb) &&
	    test_and_clear_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags))
		atomic_dec(&eb->refs);

	/*
	 * I know this is terrible, but it's temporary until we stop tracking
	 * the uptodate bits and such for the extent buffers.
	 */
	release_extent_buffer(eb);
}

void free_extent_buffer_stale(struct extent_buffer *eb)
{
	if (!eb)
		return;

	spin_lock(&eb->refs_lock);
	set_bit(EXTENT_BUFFER_STALE, &eb->bflags);

	if (atomic_read(&eb->refs) == 2 && !extent_buffer_under_io(eb) &&
	    test_and_clear_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags))
		atomic_dec(&eb->refs);
	release_extent_buffer(eb);
}

static void btree_clear_page_dirty(struct page *page)
{
	ASSERT(PageDirty(page));
	ASSERT(PageLocked(page));
	clear_page_dirty_for_io(page);
	xa_lock_irq(&page->mapping->i_pages);
	if (!PageDirty(page))
		__xa_clear_mark(&page->mapping->i_pages,
				page_index(page), PAGECACHE_TAG_DIRTY);
	xa_unlock_irq(&page->mapping->i_pages);
}

static void clear_subpage_extent_buffer_dirty(const struct extent_buffer *eb)
{
	struct btrfs_fs_info *fs_info = eb->fs_info;
	struct page *page = eb->pages[0];
	bool last;

	/* btree_clear_page_dirty() needs page locked */
	lock_page(page);
	last = btrfs_subpage_clear_and_test_dirty(fs_info, page, eb->start,
						  eb->len);
	if (last)
		btree_clear_page_dirty(page);
	unlock_page(page);
	WARN_ON(atomic_read(&eb->refs) == 0);
}

void btrfs_clear_buffer_dirty(struct btrfs_trans_handle *trans,
			      struct extent_buffer *eb)
{
	struct btrfs_fs_info *fs_info = eb->fs_info;
	int i;
	int num_pages;
	struct page *page;

	btrfs_assert_tree_write_locked(eb);

	if (trans && btrfs_header_generation(eb) != trans->transid)
		return;

	if (!test_and_clear_bit(EXTENT_BUFFER_DIRTY, &eb->bflags))
		return;

	percpu_counter_add_batch(&fs_info->dirty_metadata_bytes, -eb->len,
				 fs_info->dirty_metadata_batch);

	if (eb->fs_info->nodesize < PAGE_SIZE)
		return clear_subpage_extent_buffer_dirty(eb);

	num_pages = num_extent_pages(eb);

	for (i = 0; i < num_pages; i++) {
		page = eb->pages[i];
		if (!PageDirty(page))
			continue;
		lock_page(page);
		btree_clear_page_dirty(page);
		ClearPageError(page);
		unlock_page(page);
	}
	WARN_ON(atomic_read(&eb->refs) == 0);
}

bool set_extent_buffer_dirty(struct extent_buffer *eb)
{
	int i;
	int num_pages;
	bool was_dirty;

	check_buffer_tree_ref(eb);

	was_dirty = test_and_set_bit(EXTENT_BUFFER_DIRTY, &eb->bflags);

	num_pages = num_extent_pages(eb);
	WARN_ON(atomic_read(&eb->refs) == 0);
	WARN_ON(!test_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags));

	if (!was_dirty) {
		bool subpage = eb->fs_info->nodesize < PAGE_SIZE;

		/*
		 * For subpage case, we can have other extent buffers in the
		 * same page, and in clear_subpage_extent_buffer_dirty() we
		 * have to clear page dirty without subpage lock held.
		 * This can cause race where our page gets dirty cleared after
		 * we just set it.
		 *
		 * Thankfully, clear_subpage_extent_buffer_dirty() has locked
		 * its page for other reasons, we can use page lock to prevent
		 * the above race.
		 */
		if (subpage)
			lock_page(eb->pages[0]);
		for (i = 0; i < num_pages; i++)
			btrfs_page_set_dirty(eb->fs_info, eb->pages[i],
					     eb->start, eb->len);
		if (subpage)
			unlock_page(eb->pages[0]);
	}
#ifdef CONFIG_BTRFS_DEBUG
	for (i = 0; i < num_pages; i++)
		ASSERT(PageDirty(eb->pages[i]));
#endif

	return was_dirty;
}

void clear_extent_buffer_uptodate(struct extent_buffer *eb)
{
	struct btrfs_fs_info *fs_info = eb->fs_info;
	struct page *page;
	int num_pages;
	int i;

	clear_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
	num_pages = num_extent_pages(eb);
	for (i = 0; i < num_pages; i++) {
		page = eb->pages[i];
		if (!page)
			continue;

		/*
		 * This is special handling for metadata subpage, as regular
		 * btrfs_is_subpage() can not handle cloned/dummy metadata.
		 */
		if (fs_info->nodesize >= PAGE_SIZE)
			ClearPageUptodate(page);
		else
			btrfs_subpage_clear_uptodate(fs_info, page, eb->start,
						     eb->len);
	}
}

void set_extent_buffer_uptodate(struct extent_buffer *eb)
{
	struct btrfs_fs_info *fs_info = eb->fs_info;
	struct page *page;
	int num_pages;
	int i;

	set_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
	num_pages = num_extent_pages(eb);
	for (i = 0; i < num_pages; i++) {
		page = eb->pages[i];

		/*
		 * This is special handling for metadata subpage, as regular
		 * btrfs_is_subpage() can not handle cloned/dummy metadata.
		 */
		if (fs_info->nodesize >= PAGE_SIZE)
			SetPageUptodate(page);
		else
			btrfs_subpage_set_uptodate(fs_info, page, eb->start,
						   eb->len);
	}
}

static int read_extent_buffer_subpage(struct extent_buffer *eb, int wait,
				      int mirror_num,
				      struct btrfs_tree_parent_check *check)
{
	struct btrfs_fs_info *fs_info = eb->fs_info;
	struct extent_io_tree *io_tree;
	struct page *page = eb->pages[0];
	struct extent_state *cached_state = NULL;
	struct btrfs_bio_ctrl bio_ctrl = {
		.mirror_num = mirror_num,
		.parent_check = check,
	};
	int ret = 0;

	ASSERT(!test_bit(EXTENT_BUFFER_UNMAPPED, &eb->bflags));
	ASSERT(PagePrivate(page));
	ASSERT(check);
	io_tree = &BTRFS_I(fs_info->btree_inode)->io_tree;

	if (wait == WAIT_NONE) {
		if (!try_lock_extent(io_tree, eb->start, eb->start + eb->len - 1,
				     &cached_state))
			return -EAGAIN;
	} else {
		ret = lock_extent(io_tree, eb->start, eb->start + eb->len - 1,
				  &cached_state);
		if (ret < 0)
			return ret;
	}

	ret = 0;
	if (test_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags) ||
	    PageUptodate(page) ||
	    btrfs_subpage_test_uptodate(fs_info, page, eb->start, eb->len)) {
		set_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
		unlock_extent(io_tree, eb->start, eb->start + eb->len - 1,
			      &cached_state);
		return ret;
	}

	clear_bit(EXTENT_BUFFER_READ_ERR, &eb->bflags);
	eb->read_mirror = 0;
	atomic_set(&eb->io_pages, 1);
	check_buffer_tree_ref(eb);
	bio_ctrl.end_io_func = end_bio_extent_readpage;

	btrfs_subpage_clear_error(fs_info, page, eb->start, eb->len);

	btrfs_subpage_start_reader(fs_info, page, eb->start, eb->len);
	ret = submit_extent_page(REQ_OP_READ, NULL, &bio_ctrl,
				 eb->start, page, eb->len,
				 eb->start - page_offset(page), 0, true);
	if (ret) {
		/*
		 * In the endio function, if we hit something wrong we will
		 * increase the io_pages, so here we need to decrease it for
		 * error path.
		 */
		atomic_dec(&eb->io_pages);
	}
	submit_one_bio(&bio_ctrl);
	if (ret || wait != WAIT_COMPLETE) {
		free_extent_state(cached_state);
		return ret;
	}

	wait_extent_bit(io_tree, eb->start, eb->start + eb->len - 1,
			EXTENT_LOCKED, &cached_state);
	if (!test_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags))
		ret = -EIO;
	return ret;
}

int read_extent_buffer_pages(struct extent_buffer *eb, int wait, int mirror_num,
			     struct btrfs_tree_parent_check *check)
{
	int i;
	struct page *page;
	int err;
	int ret = 0;
	int locked_pages = 0;
	int all_uptodate = 1;
	int num_pages;
	unsigned long num_reads = 0;
	struct btrfs_bio_ctrl bio_ctrl = {
		.mirror_num = mirror_num,
		.parent_check = check,
	};

	if (test_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags))
		return 0;

	/*
	 * We could have had EXTENT_BUFFER_UPTODATE cleared by the write
	 * operation, which could potentially still be in flight.  In this case
	 * we simply want to return an error.
	 */
	if (unlikely(test_bit(EXTENT_BUFFER_WRITE_ERR, &eb->bflags)))
		return -EIO;

	if (eb->fs_info->nodesize < PAGE_SIZE)
		return read_extent_buffer_subpage(eb, wait, mirror_num, check);

	num_pages = num_extent_pages(eb);
	for (i = 0; i < num_pages; i++) {
		page = eb->pages[i];
		if (wait == WAIT_NONE) {
			/*
			 * WAIT_NONE is only utilized by readahead. If we can't
			 * acquire the lock atomically it means either the eb
			 * is being read out or under modification.
			 * Either way the eb will be or has been cached,
			 * readahead can exit safely.
			 */
			if (!trylock_page(page))
				goto unlock_exit;
		} else {
			lock_page(page);
		}
		locked_pages++;
	}
	/*
	 * We need to firstly lock all pages to make sure that
	 * the uptodate bit of our pages won't be affected by
	 * clear_extent_buffer_uptodate().
	 */
	for (i = 0; i < num_pages; i++) {
		page = eb->pages[i];
		if (!PageUptodate(page)) {
			num_reads++;
			all_uptodate = 0;
		}
	}

	if (all_uptodate) {
		set_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
		goto unlock_exit;
	}

	clear_bit(EXTENT_BUFFER_READ_ERR, &eb->bflags);
	eb->read_mirror = 0;
	atomic_set(&eb->io_pages, num_reads);
	/*
	 * It is possible for release_folio to clear the TREE_REF bit before we
	 * set io_pages. See check_buffer_tree_ref for a more detailed comment.
	 */
	check_buffer_tree_ref(eb);
	bio_ctrl.end_io_func = end_bio_extent_readpage;
	for (i = 0; i < num_pages; i++) {
		page = eb->pages[i];

		if (!PageUptodate(page)) {
			if (ret) {
				atomic_dec(&eb->io_pages);
				unlock_page(page);
				continue;
			}

			ClearPageError(page);
			err = submit_extent_page(REQ_OP_READ, NULL,
					 &bio_ctrl, page_offset(page), page,
					 PAGE_SIZE, 0, 0, false);
			if (err) {
				/*
				 * We failed to submit the bio so it's the
				 * caller's responsibility to perform cleanup
				 * i.e unlock page/set error bit.
				 */
				ret = err;
				SetPageError(page);
				unlock_page(page);
				atomic_dec(&eb->io_pages);
			}
		} else {
			unlock_page(page);
		}
	}

	submit_one_bio(&bio_ctrl);

	if (ret || wait != WAIT_COMPLETE)
		return ret;

	for (i = 0; i < num_pages; i++) {
		page = eb->pages[i];
		wait_on_page_locked(page);
		if (!PageUptodate(page))
			ret = -EIO;
	}

	return ret;

unlock_exit:
	while (locked_pages > 0) {
		locked_pages--;
		page = eb->pages[locked_pages];
		unlock_page(page);
	}
	return ret;
}

static bool report_eb_range(const struct extent_buffer *eb, unsigned long start,
			    unsigned long len)
{
	btrfs_warn(eb->fs_info,
		"access to eb bytenr %llu len %lu out of range start %lu len %lu",
		eb->start, eb->len, start, len);
	WARN_ON(IS_ENABLED(CONFIG_BTRFS_DEBUG));

	return true;
}

/*
 * Check if the [start, start + len) range is valid before reading/writing
 * the eb.
 * NOTE: @start and @len are offset inside the eb, not logical address.
 *
 * Caller should not touch the dst/src memory if this function returns error.
 */
static inline int check_eb_range(const struct extent_buffer *eb,
				 unsigned long start, unsigned long len)
{
	unsigned long offset;

	/* start, start + len should not go beyond eb->len nor overflow */
	if (unlikely(check_add_overflow(start, len, &offset) || offset > eb->len))
		return report_eb_range(eb, start, len);

	return false;
}

void read_extent_buffer(const struct extent_buffer *eb, void *dstv,
			unsigned long start, unsigned long len)
{
	size_t cur;
	size_t offset;
	struct page *page;
	char *kaddr;
	char *dst = (char *)dstv;
	unsigned long i = get_eb_page_index(start);

	if (check_eb_range(eb, start, len))
		return;

	offset = get_eb_offset_in_page(eb, start);

	while (len > 0) {
		page = eb->pages[i];

		cur = min(len, (PAGE_SIZE - offset));
		kaddr = page_address(page);
		memcpy(dst, kaddr + offset, cur);

		dst += cur;
		len -= cur;
		offset = 0;
		i++;
	}
}

int read_extent_buffer_to_user_nofault(const struct extent_buffer *eb,
				       void __user *dstv,
				       unsigned long start, unsigned long len)
{
	size_t cur;
	size_t offset;
	struct page *page;
	char *kaddr;
	char __user *dst = (char __user *)dstv;
	unsigned long i = get_eb_page_index(start);
	int ret = 0;

	WARN_ON(start > eb->len);
	WARN_ON(start + len > eb->start + eb->len);

	offset = get_eb_offset_in_page(eb, start);

	while (len > 0) {
		page = eb->pages[i];

		cur = min(len, (PAGE_SIZE - offset));
		kaddr = page_address(page);
		if (copy_to_user_nofault(dst, kaddr + offset, cur)) {
			ret = -EFAULT;
			break;
		}

		dst += cur;
		len -= cur;
		offset = 0;
		i++;
	}

	return ret;
}

int memcmp_extent_buffer(const struct extent_buffer *eb, const void *ptrv,
			 unsigned long start, unsigned long len)
{
	size_t cur;
	size_t offset;
	struct page *page;
	char *kaddr;
	char *ptr = (char *)ptrv;
	unsigned long i = get_eb_page_index(start);
	int ret = 0;

	if (check_eb_range(eb, start, len))
		return -EINVAL;

	offset = get_eb_offset_in_page(eb, start);

	while (len > 0) {
		page = eb->pages[i];

		cur = min(len, (PAGE_SIZE - offset));

		kaddr = page_address(page);
		ret = memcmp(ptr, kaddr + offset, cur);
		if (ret)
			break;

		ptr += cur;
		len -= cur;
		offset = 0;
		i++;
	}
	return ret;
}

/*
 * Check that the extent buffer is uptodate.
 *
 * For regular sector size == PAGE_SIZE case, check if @page is uptodate.
 * For subpage case, check if the range covered by the eb has EXTENT_UPTODATE.
 */
static void assert_eb_page_uptodate(const struct extent_buffer *eb,
				    struct page *page)
{
	struct btrfs_fs_info *fs_info = eb->fs_info;

	/*
	 * If we are using the commit root we could potentially clear a page
	 * Uptodate while we're using the extent buffer that we've previously
	 * looked up.  We don't want to complain in this case, as the page was
	 * valid before, we just didn't write it out.  Instead we want to catch
	 * the case where we didn't actually read the block properly, which
	 * would have !PageUptodate && !PageError, as we clear PageError before
	 * reading.
	 */
	if (fs_info->nodesize < PAGE_SIZE) {
		bool uptodate, error;

		uptodate = btrfs_subpage_test_uptodate(fs_info, page,
						       eb->start, eb->len);
		error = btrfs_subpage_test_error(fs_info, page, eb->start, eb->len);
		WARN_ON(!uptodate && !error);
	} else {
		WARN_ON(!PageUptodate(page) && !PageError(page));
	}
}

void write_extent_buffer_chunk_tree_uuid(const struct extent_buffer *eb,
		const void *srcv)
{
	char *kaddr;

	assert_eb_page_uptodate(eb, eb->pages[0]);
	kaddr = page_address(eb->pages[0]) +
		get_eb_offset_in_page(eb, offsetof(struct btrfs_header,
						   chunk_tree_uuid));
	memcpy(kaddr, srcv, BTRFS_FSID_SIZE);
}

void write_extent_buffer_fsid(const struct extent_buffer *eb, const void *srcv)
{
	char *kaddr;

	assert_eb_page_uptodate(eb, eb->pages[0]);
	kaddr = page_address(eb->pages[0]) +
		get_eb_offset_in_page(eb, offsetof(struct btrfs_header, fsid));
	memcpy(kaddr, srcv, BTRFS_FSID_SIZE);
}

void write_extent_buffer(const struct extent_buffer *eb, const void *srcv,
			 unsigned long start, unsigned long len)
{
	size_t cur;
	size_t offset;
	struct page *page;
	char *kaddr;
	char *src = (char *)srcv;
	unsigned long i = get_eb_page_index(start);

	WARN_ON(test_bit(EXTENT_BUFFER_NO_CHECK, &eb->bflags));

	if (check_eb_range(eb, start, len))
		return;

	offset = get_eb_offset_in_page(eb, start);

	while (len > 0) {
		page = eb->pages[i];
		assert_eb_page_uptodate(eb, page);

		cur = min(len, PAGE_SIZE - offset);
		kaddr = page_address(page);
		memcpy(kaddr + offset, src, cur);

		src += cur;
		len -= cur;
		offset = 0;
		i++;
	}
}

void memzero_extent_buffer(const struct extent_buffer *eb, unsigned long start,
		unsigned long len)
{
	size_t cur;
	size_t offset;
	struct page *page;
	char *kaddr;
	unsigned long i = get_eb_page_index(start);

	if (check_eb_range(eb, start, len))
		return;

	offset = get_eb_offset_in_page(eb, start);

	while (len > 0) {
		page = eb->pages[i];
		assert_eb_page_uptodate(eb, page);

		cur = min(len, PAGE_SIZE - offset);
		kaddr = page_address(page);
		memset(kaddr + offset, 0, cur);

		len -= cur;
		offset = 0;
		i++;
	}
}

void copy_extent_buffer_full(const struct extent_buffer *dst,
			     const struct extent_buffer *src)
{
	int i;
	int num_pages;

	ASSERT(dst->len == src->len);

	if (dst->fs_info->nodesize >= PAGE_SIZE) {
		num_pages = num_extent_pages(dst);
		for (i = 0; i < num_pages; i++)
			copy_page(page_address(dst->pages[i]),
				  page_address(src->pages[i]));
	} else {
		size_t src_offset = get_eb_offset_in_page(src, 0);
		size_t dst_offset = get_eb_offset_in_page(dst, 0);

		ASSERT(src->fs_info->nodesize < PAGE_SIZE);
		memcpy(page_address(dst->pages[0]) + dst_offset,
		       page_address(src->pages[0]) + src_offset,
		       src->len);
	}
}

void copy_extent_buffer(const struct extent_buffer *dst,
			const struct extent_buffer *src,
			unsigned long dst_offset, unsigned long src_offset,
			unsigned long len)
{
	u64 dst_len = dst->len;
	size_t cur;
	size_t offset;
	struct page *page;
	char *kaddr;
	unsigned long i = get_eb_page_index(dst_offset);

	if (check_eb_range(dst, dst_offset, len) ||
	    check_eb_range(src, src_offset, len))
		return;

	WARN_ON(src->len != dst_len);

	offset = get_eb_offset_in_page(dst, dst_offset);

	while (len > 0) {
		page = dst->pages[i];
		assert_eb_page_uptodate(dst, page);

		cur = min(len, (unsigned long)(PAGE_SIZE - offset));

		kaddr = page_address(page);
		read_extent_buffer(src, kaddr + offset, src_offset, cur);

		src_offset += cur;
		len -= cur;
		offset = 0;
		i++;
	}
}

/*
 * eb_bitmap_offset() - calculate the page and offset of the byte containing the
 * given bit number
 * @eb: the extent buffer
 * @start: offset of the bitmap item in the extent buffer
 * @nr: bit number
 * @page_index: return index of the page in the extent buffer that contains the
 * given bit number
 * @page_offset: return offset into the page given by page_index
 *
 * This helper hides the ugliness of finding the byte in an extent buffer which
 * contains a given bit.
 */
static inline void eb_bitmap_offset(const struct extent_buffer *eb,
				    unsigned long start, unsigned long nr,
				    unsigned long *page_index,
				    size_t *page_offset)
{
	size_t byte_offset = BIT_BYTE(nr);
	size_t offset;

	/*
	 * The byte we want is the offset of the extent buffer + the offset of
	 * the bitmap item in the extent buffer + the offset of the byte in the
	 * bitmap item.
	 */
	offset = start + offset_in_page(eb->start) + byte_offset;

	*page_index = offset >> PAGE_SHIFT;
	*page_offset = offset_in_page(offset);
}

/*
 * Determine whether a bit in a bitmap item is set.
 *
 * @eb:     the extent buffer
 * @start:  offset of the bitmap item in the extent buffer
 * @nr:     bit number to test
 */
int extent_buffer_test_bit(const struct extent_buffer *eb, unsigned long start,
			   unsigned long nr)
{
	u8 *kaddr;
	struct page *page;
	unsigned long i;
	size_t offset;

	eb_bitmap_offset(eb, start, nr, &i, &offset);
	page = eb->pages[i];
	assert_eb_page_uptodate(eb, page);
	kaddr = page_address(page);
	return 1U & (kaddr[offset] >> (nr & (BITS_PER_BYTE - 1)));
}

/*
 * Set an area of a bitmap to 1.
 *
 * @eb:     the extent buffer
 * @start:  offset of the bitmap item in the extent buffer
 * @pos:    bit number of the first bit
 * @len:    number of bits to set
 */
void extent_buffer_bitmap_set(const struct extent_buffer *eb, unsigned long start,
			      unsigned long pos, unsigned long len)
{
	u8 *kaddr;
	struct page *page;
	unsigned long i;
	size_t offset;
	const unsigned int size = pos + len;
	int bits_to_set = BITS_PER_BYTE - (pos % BITS_PER_BYTE);
	u8 mask_to_set = BITMAP_FIRST_BYTE_MASK(pos);

	eb_bitmap_offset(eb, start, pos, &i, &offset);
	page = eb->pages[i];
	assert_eb_page_uptodate(eb, page);
	kaddr = page_address(page);

	while (len >= bits_to_set) {
		kaddr[offset] |= mask_to_set;
		len -= bits_to_set;
		bits_to_set = BITS_PER_BYTE;
		mask_to_set = ~0;
		if (++offset >= PAGE_SIZE && len > 0) {
			offset = 0;
			page = eb->pages[++i];
			assert_eb_page_uptodate(eb, page);
			kaddr = page_address(page);
		}
	}
	if (len) {
		mask_to_set &= BITMAP_LAST_BYTE_MASK(size);
		kaddr[offset] |= mask_to_set;
	}
}


/*
 * Clear an area of a bitmap.
 *
 * @eb:     the extent buffer
 * @start:  offset of the bitmap item in the extent buffer
 * @pos:    bit number of the first bit
 * @len:    number of bits to clear
 */
void extent_buffer_bitmap_clear(const struct extent_buffer *eb,
				unsigned long start, unsigned long pos,
				unsigned long len)
{
	u8 *kaddr;
	struct page *page;
	unsigned long i;
	size_t offset;
	const unsigned int size = pos + len;
	int bits_to_clear = BITS_PER_BYTE - (pos % BITS_PER_BYTE);
	u8 mask_to_clear = BITMAP_FIRST_BYTE_MASK(pos);

	eb_bitmap_offset(eb, start, pos, &i, &offset);
	page = eb->pages[i];
	assert_eb_page_uptodate(eb, page);
	kaddr = page_address(page);

	while (len >= bits_to_clear) {
		kaddr[offset] &= ~mask_to_clear;
		len -= bits_to_clear;
		bits_to_clear = BITS_PER_BYTE;
		mask_to_clear = ~0;
		if (++offset >= PAGE_SIZE && len > 0) {
			offset = 0;
			page = eb->pages[++i];
			assert_eb_page_uptodate(eb, page);
			kaddr = page_address(page);
		}
	}
	if (len) {
		mask_to_clear &= BITMAP_LAST_BYTE_MASK(size);
		kaddr[offset] &= ~mask_to_clear;
	}
}

static inline bool areas_overlap(unsigned long src, unsigned long dst, unsigned long len)
{
	unsigned long distance = (src > dst) ? src - dst : dst - src;
	return distance < len;
}

static void copy_pages(struct page *dst_page, struct page *src_page,
		       unsigned long dst_off, unsigned long src_off,
		       unsigned long len)
{
	char *dst_kaddr = page_address(dst_page);
	char *src_kaddr;
	int must_memmove = 0;

	if (dst_page != src_page) {
		src_kaddr = page_address(src_page);
	} else {
		src_kaddr = dst_kaddr;
		if (areas_overlap(src_off, dst_off, len))
			must_memmove = 1;
	}

	if (must_memmove)
		memmove(dst_kaddr + dst_off, src_kaddr + src_off, len);
	else
		memcpy(dst_kaddr + dst_off, src_kaddr + src_off, len);
}

void memcpy_extent_buffer(const struct extent_buffer *dst,
			  unsigned long dst_offset, unsigned long src_offset,
			  unsigned long len)
{
	size_t cur;
	size_t dst_off_in_page;
	size_t src_off_in_page;
	unsigned long dst_i;
	unsigned long src_i;

	if (check_eb_range(dst, dst_offset, len) ||
	    check_eb_range(dst, src_offset, len))
		return;

	while (len > 0) {
		dst_off_in_page = get_eb_offset_in_page(dst, dst_offset);
		src_off_in_page = get_eb_offset_in_page(dst, src_offset);

		dst_i = get_eb_page_index(dst_offset);
		src_i = get_eb_page_index(src_offset);

		cur = min(len, (unsigned long)(PAGE_SIZE -
					       src_off_in_page));
		cur = min_t(unsigned long, cur,
			(unsigned long)(PAGE_SIZE - dst_off_in_page));

		copy_pages(dst->pages[dst_i], dst->pages[src_i],
			   dst_off_in_page, src_off_in_page, cur);

		src_offset += cur;
		dst_offset += cur;
		len -= cur;
	}
}

void memmove_extent_buffer(const struct extent_buffer *dst,
			   unsigned long dst_offset, unsigned long src_offset,
			   unsigned long len)
{
	size_t cur;
	size_t dst_off_in_page;
	size_t src_off_in_page;
	unsigned long dst_end = dst_offset + len - 1;
	unsigned long src_end = src_offset + len - 1;
	unsigned long dst_i;
	unsigned long src_i;

	if (check_eb_range(dst, dst_offset, len) ||
	    check_eb_range(dst, src_offset, len))
		return;
	if (dst_offset < src_offset) {
		memcpy_extent_buffer(dst, dst_offset, src_offset, len);
		return;
	}
	while (len > 0) {
		dst_i = get_eb_page_index(dst_end);
		src_i = get_eb_page_index(src_end);

		dst_off_in_page = get_eb_offset_in_page(dst, dst_end);
		src_off_in_page = get_eb_offset_in_page(dst, src_end);

		cur = min_t(unsigned long, len, src_off_in_page + 1);
		cur = min(cur, dst_off_in_page + 1);
		copy_pages(dst->pages[dst_i], dst->pages[src_i],
			   dst_off_in_page - cur + 1,
			   src_off_in_page - cur + 1, cur);

		dst_end -= cur;
		src_end -= cur;
		len -= cur;
	}
}

#define GANG_LOOKUP_SIZE	16
static struct extent_buffer *get_next_extent_buffer(
		struct btrfs_fs_info *fs_info, struct page *page, u64 bytenr)
{
	struct extent_buffer *gang[GANG_LOOKUP_SIZE];
	struct extent_buffer *found = NULL;
	u64 page_start = page_offset(page);
	u64 cur = page_start;

	ASSERT(in_range(bytenr, page_start, PAGE_SIZE));
	lockdep_assert_held(&fs_info->buffer_lock);

	while (cur < page_start + PAGE_SIZE) {
		int ret;
		int i;

		ret = radix_tree_gang_lookup(&fs_info->buffer_radix,
				(void **)gang, cur >> fs_info->sectorsize_bits,
				min_t(unsigned int, GANG_LOOKUP_SIZE,
				      PAGE_SIZE / fs_info->nodesize));
		if (ret == 0)
			goto out;
		for (i = 0; i < ret; i++) {
			/* Already beyond page end */
			if (gang[i]->start >= page_start + PAGE_SIZE)
				goto out;
			/* Found one */
			if (gang[i]->start >= bytenr) {
				found = gang[i];
				goto out;
			}
		}
		cur = gang[ret - 1]->start + gang[ret - 1]->len;
	}
out:
	return found;
}

static int try_release_subpage_extent_buffer(struct page *page)
{
	struct btrfs_fs_info *fs_info = btrfs_sb(page->mapping->host->i_sb);
	u64 cur = page_offset(page);
	const u64 end = page_offset(page) + PAGE_SIZE;
	int ret;

	while (cur < end) {
		struct extent_buffer *eb = NULL;

		/*
		 * Unlike try_release_extent_buffer() which uses page->private
		 * to grab buffer, for subpage case we rely on radix tree, thus
		 * we need to ensure radix tree consistency.
		 *
		 * We also want an atomic snapshot of the radix tree, thus go
		 * with spinlock rather than RCU.
		 */
		spin_lock(&fs_info->buffer_lock);
		eb = get_next_extent_buffer(fs_info, page, cur);
		if (!eb) {
			/* No more eb in the page range after or at cur */
			spin_unlock(&fs_info->buffer_lock);
			break;
		}
		cur = eb->start + eb->len;

		/*
		 * The same as try_release_extent_buffer(), to ensure the eb
		 * won't disappear out from under us.
		 */
		spin_lock(&eb->refs_lock);
		if (atomic_read(&eb->refs) != 1 || extent_buffer_under_io(eb)) {
			spin_unlock(&eb->refs_lock);
			spin_unlock(&fs_info->buffer_lock);
			break;
		}
		spin_unlock(&fs_info->buffer_lock);

		/*
		 * If tree ref isn't set then we know the ref on this eb is a
		 * real ref, so just return, this eb will likely be freed soon
		 * anyway.
		 */
		if (!test_and_clear_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags)) {
			spin_unlock(&eb->refs_lock);
			break;
		}

		/*
		 * Here we don't care about the return value, we will always
		 * check the page private at the end.  And
		 * release_extent_buffer() will release the refs_lock.
		 */
		release_extent_buffer(eb);
	}
	/*
	 * Finally to check if we have cleared page private, as if we have
	 * released all ebs in the page, the page private should be cleared now.
	 */
	spin_lock(&page->mapping->private_lock);
	if (!PagePrivate(page))
		ret = 1;
	else
		ret = 0;
	spin_unlock(&page->mapping->private_lock);
	return ret;

}

int try_release_extent_buffer(struct page *page)
{
	struct extent_buffer *eb;

	if (btrfs_sb(page->mapping->host->i_sb)->nodesize < PAGE_SIZE)
		return try_release_subpage_extent_buffer(page);

	/*
	 * We need to make sure nobody is changing page->private, as we rely on
	 * page->private as the pointer to extent buffer.
	 */
	spin_lock(&page->mapping->private_lock);
	if (!PagePrivate(page)) {
		spin_unlock(&page->mapping->private_lock);
		return 1;
	}

	eb = (struct extent_buffer *)page->private;
	BUG_ON(!eb);

	/*
	 * This is a little awful but should be ok, we need to make sure that
	 * the eb doesn't disappear out from under us while we're looking at
	 * this page.
	 */
	spin_lock(&eb->refs_lock);
	if (atomic_read(&eb->refs) != 1 || extent_buffer_under_io(eb)) {
		spin_unlock(&eb->refs_lock);
		spin_unlock(&page->mapping->private_lock);
		return 0;
	}
	spin_unlock(&page->mapping->private_lock);

	/*
	 * If tree ref isn't set then we know the ref on this eb is a real ref,
	 * so just return, this page will likely be freed soon anyway.
	 */
	if (!test_and_clear_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags)) {
		spin_unlock(&eb->refs_lock);
		return 0;
	}

	return release_extent_buffer(eb);
}

/*
 * btrfs_readahead_tree_block - attempt to readahead a child block
 * @fs_info:	the fs_info
 * @bytenr:	bytenr to read
 * @owner_root: objectid of the root that owns this eb
 * @gen:	generation for the uptodate check, can be 0
 * @level:	level for the eb
 *
 * Attempt to readahead a tree block at @bytenr.  If @gen is 0 then we do a
 * normal uptodate check of the eb, without checking the generation.  If we have
 * to read the block we will not block on anything.
 */
void btrfs_readahead_tree_block(struct btrfs_fs_info *fs_info,
				u64 bytenr, u64 owner_root, u64 gen, int level)
{
	struct btrfs_tree_parent_check check = {
		.has_first_key = 0,
		.level = level,
		.transid = gen
	};
	struct extent_buffer *eb;
	int ret;

	eb = btrfs_find_create_tree_block(fs_info, bytenr, owner_root, level);
	if (IS_ERR(eb))
		return;

	if (btrfs_buffer_uptodate(eb, gen, 1)) {
		free_extent_buffer(eb);
		return;
	}

	ret = read_extent_buffer_pages(eb, WAIT_NONE, 0, &check);
	if (ret < 0)
		free_extent_buffer_stale(eb);
	else
		free_extent_buffer(eb);
}

/*
 * btrfs_readahead_node_child - readahead a node's child block
 * @node:	parent node we're reading from
 * @slot:	slot in the parent node for the child we want to read
 *
 * A helper for btrfs_readahead_tree_block, we simply read the bytenr pointed at
 * the slot in the node provided.
 */
void btrfs_readahead_node_child(struct extent_buffer *node, int slot)
{
	btrfs_readahead_tree_block(node->fs_info,
				   btrfs_node_blockptr(node, slot),
				   btrfs_header_owner(node),
				   btrfs_node_ptr_generation(node, slot),
				   btrfs_header_level(node) - 1);
}