xref: /linux/fs/fuse/file.c (revision 85cdaca6970028bf6f544c355c90035586836ddf)

// SPDX-License-Identifier: GPL-2.0
/*
  FUSE: Filesystem in Userspace
  Copyright (C) 2001-2008  Miklos Szeredi <miklos@szeredi.hu>
*/

#include "fuse_i.h"
#include "dev.h"

#include <linux/pagemap.h>
#include <linux/slab.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/sched/signal.h>
#include <linux/module.h>
#include <linux/swap.h>
#include <linux/falloc.h>
#include <linux/uio.h>
#include <linux/fs.h>
#include <linux/filelock.h>
#include <linux/splice.h>
#include <linux/task_io_accounting_ops.h>
#include <linux/iomap.h>

static int fuse_send_open(struct fuse_mount *fm, u64 nodeid,
			  unsigned int open_flags, int opcode,
			  struct fuse_open_out *outargp)
{
	struct fuse_open_in inarg;
	FUSE_ARGS(args);

	memset(&inarg, 0, sizeof(inarg));
	inarg.flags = open_flags & ~(O_CREAT | O_EXCL | O_NOCTTY);
	if (!fm->fc->atomic_o_trunc)
		inarg.flags &= ~O_TRUNC;

	if (fm->fc->handle_killpriv_v2 &&
	    (inarg.flags & O_TRUNC) && !capable(CAP_FSETID)) {
		inarg.open_flags |= FUSE_OPEN_KILL_SUIDGID;
	}

	args.opcode = opcode;
	args.nodeid = nodeid;
	args.in_numargs = 1;
	args.in_args[0].size = sizeof(inarg);
	args.in_args[0].value = &inarg;
	args.out_numargs = 1;
	args.out_args[0].size = sizeof(*outargp);
	args.out_args[0].value = outargp;

	return fuse_simple_request(fm, &args);
}

struct fuse_file *fuse_file_alloc(struct fuse_mount *fm, bool release)
{
	struct fuse_file *ff;

	ff = kzalloc_obj(struct fuse_file, GFP_KERNEL_ACCOUNT);
	if (unlikely(!ff))
		return NULL;

	ff->fm = fm;
	if (release) {
		ff->args = kzalloc_obj(*ff->args, GFP_KERNEL_ACCOUNT);
		if (!ff->args) {
			kfree(ff);
			return NULL;
		}
	}

	INIT_LIST_HEAD(&ff->write_entry);
	refcount_set(&ff->count, 1);
	RB_CLEAR_NODE(&ff->polled_node);
	init_waitqueue_head(&ff->poll_wait);

	ff->kh = atomic64_inc_return(&fm->fc->khctr);

	return ff;
}

void fuse_file_free(struct fuse_file *ff)
{
	kfree(ff->args);
	kfree(ff);
}

static struct fuse_file *fuse_file_get(struct fuse_file *ff)
{
	refcount_inc(&ff->count);
	return ff;
}

static void fuse_release_end(struct fuse_args *args, int error)
{
	struct fuse_release_args *ra = container_of(args, typeof(*ra), args);

	iput(ra->inode);
	kfree(ra);
}

static void fuse_file_put(struct fuse_file *ff, bool sync)
{
	if (refcount_dec_and_test(&ff->count)) {
		struct fuse_release_args *ra = &ff->args->release_args;
		struct fuse_args *args = (ra ? &ra->args : NULL);

		if (ra && ra->inode)
			fuse_file_io_release(ff, ra->inode);

		if (!args) {
			/* Do nothing when server does not implement 'opendir' */
		} else if (args->opcode == FUSE_RELEASE && ff->fm->fc->no_open) {
			fuse_release_end(args, 0);
		} else if (sync) {
			fuse_simple_request(ff->fm, args);
			fuse_release_end(args, 0);
		} else {
			/*
			 * DAX inodes may need to issue a number of synchronous
			 * request for clearing the mappings.
			 */
			if (ra && ra->inode && FUSE_IS_DAX(ra->inode))
				args->may_block = true;
			args->end = fuse_release_end;
			if (fuse_simple_background(ff->fm, args,
						   GFP_KERNEL | __GFP_NOFAIL))
				fuse_release_end(args, -ENOTCONN);
		}
		kfree(ff);
	}
}

struct fuse_file *fuse_file_open(struct fuse_mount *fm, u64 nodeid,
				 unsigned int open_flags, bool isdir)
{
	struct fuse_conn *fc = fm->fc;
	struct fuse_file *ff;
	int opcode = isdir ? FUSE_OPENDIR : FUSE_OPEN;
	bool open = isdir ? !fc->no_opendir : !fc->no_open;
	bool release = !isdir || open;

	/*
	 * ff->args->release_args still needs to be allocated (so we can hold an
	 * inode reference while there are pending inflight file operations when
	 * ->release() is called, see fuse_prepare_release()) even if
	 * fc->no_open is set else it becomes possible for reclaim to deadlock
	 * if while servicing the readahead request the server triggers reclaim
	 * and reclaim evicts the inode of the file being read ahead.
	 */
	ff = fuse_file_alloc(fm, release);
	if (!ff)
		return ERR_PTR(-ENOMEM);

	ff->fh = 0;
	/* Default for no-open */
	ff->open_flags = FOPEN_KEEP_CACHE | (isdir ? FOPEN_CACHE_DIR : 0);
	if (open) {
		/* Store outarg for fuse_finish_open() */
		struct fuse_open_out *outargp = &ff->args->open_outarg;
		int err;

		err = fuse_send_open(fm, nodeid, open_flags, opcode, outargp);
		if (!err) {
			ff->fh = outargp->fh;
			ff->open_flags = outargp->open_flags;
		} else if (err != -ENOSYS) {
			fuse_file_free(ff);
			return ERR_PTR(err);
		} else {
			if (isdir) {
				/* No release needed */
				kfree(ff->args);
				ff->args = NULL;
				fc->no_opendir = 1;
			} else {
				fc->no_open = 1;
			}
		}
	}

	if (isdir)
		ff->open_flags &= ~FOPEN_DIRECT_IO;

	ff->nodeid = nodeid;

	return ff;
}

int fuse_do_open(struct fuse_mount *fm, u64 nodeid, struct file *file,
		 bool isdir)
{
	struct fuse_file *ff = fuse_file_open(fm, nodeid, file->f_flags, isdir);

	if (!IS_ERR(ff))
		file->private_data = ff;

	return PTR_ERR_OR_ZERO(ff);
}
EXPORT_SYMBOL_GPL(fuse_do_open);

static void fuse_link_write_file(struct file *file)
{
	struct inode *inode = file_inode(file);
	struct fuse_inode *fi = get_fuse_inode(inode);
	struct fuse_file *ff = file->private_data;
	/*
	 * file may be written through mmap, so chain it onto the
	 * inodes's write_file list
	 */
	spin_lock(&fi->lock);
	if (list_empty(&ff->write_entry))
		list_add(&ff->write_entry, &fi->write_files);
	spin_unlock(&fi->lock);
}

int fuse_finish_open(struct inode *inode, struct file *file)
{
	struct fuse_file *ff = file->private_data;
	struct fuse_conn *fc = get_fuse_conn(inode);
	int err;

	err = fuse_file_io_open(file, inode);
	if (err)
		return err;

	if (ff->open_flags & FOPEN_STREAM)
		stream_open(inode, file);
	else if (ff->open_flags & FOPEN_NONSEEKABLE)
		nonseekable_open(inode, file);

	if ((file->f_mode & FMODE_WRITE) && fc->writeback_cache)
		fuse_link_write_file(file);

	return 0;
}

static void fuse_truncate_update_attr(struct inode *inode, struct file *file)
{
	struct fuse_conn *fc = get_fuse_conn(inode);
	struct fuse_inode *fi = get_fuse_inode(inode);

	spin_lock(&fi->lock);
	fi->attr_version = atomic64_inc_return(&fc->attr_version);
	i_size_write(inode, 0);
	spin_unlock(&fi->lock);
	file_update_time(file);
	fuse_invalidate_attr_mask(inode, FUSE_STATX_MODSIZE);
}

static int fuse_open(struct inode *inode, struct file *file)
{
	struct fuse_mount *fm = get_fuse_mount(inode);
	struct fuse_inode *fi = get_fuse_inode(inode);
	struct fuse_conn *fc = fm->fc;
	struct fuse_file *ff;
	int err;
	bool is_truncate = (file->f_flags & O_TRUNC) && fc->atomic_o_trunc;
	bool is_wb_truncate = is_truncate && fc->writeback_cache;
	bool dax_truncate = is_truncate && FUSE_IS_DAX(inode);

	if (fuse_is_bad(inode))
		return -EIO;

	err = generic_file_open(inode, file);
	if (err)
		return err;

	if (is_wb_truncate || dax_truncate)
		inode_lock(inode);

	if (dax_truncate) {
		filemap_invalidate_lock(inode->i_mapping);
		err = fuse_dax_break_layouts(inode, 0, -1);
		if (err)
			goto out_inode_unlock;
	}

	if (is_wb_truncate || dax_truncate)
		fuse_set_nowrite(inode);

	err = fuse_do_open(fm, get_node_id(inode), file, false);
	if (!err) {
		ff = file->private_data;
		err = fuse_finish_open(inode, file);
		if (err)
			fuse_sync_release(fi, ff, file->f_flags);
		else if (is_truncate)
			fuse_truncate_update_attr(inode, file);
	}

	if (is_wb_truncate || dax_truncate)
		fuse_release_nowrite(inode);
	if (!err) {
		if (is_truncate)
			truncate_pagecache(inode, 0);
		else if (!(ff->open_flags & FOPEN_KEEP_CACHE))
			invalidate_inode_pages2(inode->i_mapping);
	}
	if (dax_truncate)
		filemap_invalidate_unlock(inode->i_mapping);
out_inode_unlock:
	if (is_wb_truncate || dax_truncate)
		inode_unlock(inode);

	return err;
}

static void fuse_prepare_release(struct fuse_inode *fi, struct fuse_file *ff,
				 unsigned int flags, int opcode, bool sync)
{
	struct fuse_conn *fc = ff->fm->fc;
	struct fuse_release_args *ra = &ff->args->release_args;

	if (fuse_file_passthrough(ff))
		fuse_passthrough_release(ff, fuse_inode_backing(fi));

	/* Inode is NULL on error path of fuse_create_open() */
	if (likely(fi)) {
		spin_lock(&fi->lock);
		list_del(&ff->write_entry);
		spin_unlock(&fi->lock);
	}
	spin_lock(&fc->lock);
	if (!RB_EMPTY_NODE(&ff->polled_node))
		rb_erase(&ff->polled_node, &fc->polled_files);
	spin_unlock(&fc->lock);

	wake_up_interruptible_all(&ff->poll_wait);

	if (!ra)
		return;

	/* ff->args was used for open outarg */
	memset(ff->args, 0, sizeof(*ff->args));
	ra->inarg.fh = ff->fh;
	ra->inarg.flags = flags;
	ra->args.in_numargs = 1;
	ra->args.in_args[0].size = sizeof(struct fuse_release_in);
	ra->args.in_args[0].value = &ra->inarg;
	ra->args.opcode = opcode;
	ra->args.nodeid = ff->nodeid;
	ra->args.force = true;
	ra->args.nocreds = true;

	/*
	 * Hold inode until release is finished.
	 * From fuse_sync_release() the refcount is 1 and everything's
	 * synchronous, so we are fine with not doing igrab() here.
	 */
	ra->inode = sync ? NULL : igrab(&fi->inode);
}

void fuse_file_release(struct inode *inode, struct fuse_file *ff,
		       unsigned int open_flags, fl_owner_t id, bool isdir)
{
	struct fuse_inode *fi = get_fuse_inode(inode);
	struct fuse_release_args *ra = &ff->args->release_args;
	int opcode = isdir ? FUSE_RELEASEDIR : FUSE_RELEASE;

	fuse_prepare_release(fi, ff, open_flags, opcode, false);

	if (ra && ff->flock) {
		ra->inarg.release_flags |= FUSE_RELEASE_FLOCK_UNLOCK;
		ra->inarg.lock_owner = fuse_lock_owner_id(ff->fm->fc, id);
	}

	/*
	 * Normally this will send the RELEASE request, however if
	 * some asynchronous READ or WRITE requests are outstanding,
	 * the sending will be delayed.
	 *
	 * Make the release synchronous if this is a fuseblk mount,
	 * synchronous RELEASE is allowed (and desirable) in this case
	 * because the server can be trusted not to screw up.
	 *
	 * Always use the asynchronous file put because the current thread
	 * might be the fuse server.  This can happen if a process starts some
	 * aio and closes the fd before the aio completes.  Since aio takes its
	 * own ref to the file, the IO completion has to drop the ref, which is
	 * how the fuse server can end up closing its clients' files.
	 *
	 * Exception is virtio-fs, which is not affected by the above (server is
	 * on host, cannot close open files in guest).  Virtio-fs needs sync
	 * release, because the num_waiting mechanism to wait for all requests
	 * before commencing with fs shutdown doesn't work if submounts are
	 * used.
	 */
	fuse_file_put(ff, ff->fm->fc->auto_submounts);
}

void fuse_release_common(struct file *file, bool isdir)
{
	fuse_file_release(file_inode(file), file->private_data, file->f_flags,
			  (fl_owner_t) file, isdir);
}

static int fuse_release(struct inode *inode, struct file *file)
{
	struct fuse_conn *fc = get_fuse_conn(inode);

	/*
	 * Dirty pages might remain despite write_inode_now() call from
	 * fuse_flush() due to writes racing with the close.
	 */
	if (fc->writeback_cache)
		write_inode_now(inode, 1);

	fuse_release_common(file, false);

	/* return value is ignored by VFS */
	return 0;
}

void fuse_sync_release(struct fuse_inode *fi, struct fuse_file *ff,
		       unsigned int flags)
{
	WARN_ON(refcount_read(&ff->count) > 1);
	fuse_prepare_release(fi, ff, flags, FUSE_RELEASE, true);
	fuse_file_put(ff, true);
}
EXPORT_SYMBOL_GPL(fuse_sync_release);

/*
 * Scramble the ID space with XTEA, so that the value of the files_struct
 * pointer is not exposed to userspace.
 */
u64 fuse_lock_owner_id(struct fuse_conn *fc, fl_owner_t id)
{
	u32 *k = fc->scramble_key;
	u64 v = (unsigned long) id;
	u32 v0 = v;
	u32 v1 = v >> 32;
	u32 sum = 0;
	int i;

	for (i = 0; i < 32; i++) {
		v0 += ((v1 << 4 ^ v1 >> 5) + v1) ^ (sum + k[sum & 3]);
		sum += 0x9E3779B9;
		v1 += ((v0 << 4 ^ v0 >> 5) + v0) ^ (sum + k[sum>>11 & 3]);
	}

	return (u64) v0 + ((u64) v1 << 32);
}

struct fuse_writepage_args {
	struct fuse_io_args ia;
	struct list_head queue_entry;
	struct inode *inode;
	struct fuse_sync_bucket *bucket;
};

/*
 * Wait for all pending writepages on the inode to finish.
 *
 * This is currently done by blocking further writes with FUSE_NOWRITE
 * and waiting for all sent writes to complete.
 *
 * This must be called under i_mutex, otherwise the FUSE_NOWRITE usage
 * could conflict with truncation.
 */
static void fuse_sync_writes(struct inode *inode)
{
	fuse_set_nowrite(inode);
	fuse_release_nowrite(inode);
}

static int fuse_flush(struct file *file, fl_owner_t id)
{
	struct inode *inode = file_inode(file);
	struct fuse_mount *fm = get_fuse_mount(inode);
	struct fuse_file *ff = file->private_data;
	struct fuse_flush_in inarg;
	FUSE_ARGS(args);
	int err;

	if (fuse_is_bad(inode))
		return -EIO;

	if (ff->open_flags & FOPEN_NOFLUSH && !fm->fc->writeback_cache)
		return 0;

	err = write_inode_now(inode, 1);
	if (err)
		return err;

	err = filemap_check_errors(file->f_mapping);
	if (err)
		return err;

	err = 0;
	if (fm->fc->no_flush)
		goto inval_attr_out;

	memset(&inarg, 0, sizeof(inarg));
	inarg.fh = ff->fh;
	inarg.lock_owner = fuse_lock_owner_id(fm->fc, id);
	args.opcode = FUSE_FLUSH;
	args.nodeid = get_node_id(inode);
	args.in_numargs = 1;
	args.in_args[0].size = sizeof(inarg);
	args.in_args[0].value = &inarg;
	args.force = true;

	err = fuse_simple_request(fm, &args);
	if (err == -ENOSYS) {
		fm->fc->no_flush = 1;
		err = 0;
	}

inval_attr_out:
	/*
	 * In memory i_blocks is not maintained by fuse, if writeback cache is
	 * enabled, i_blocks from cached attr may not be accurate.
	 */
	if (!err && fm->fc->writeback_cache)
		fuse_invalidate_attr_mask(inode, STATX_BLOCKS);
	return err;
}

int fuse_fsync_common(struct file *file, loff_t start, loff_t end,
		      int datasync, int opcode)
{
	struct inode *inode = file->f_mapping->host;
	struct fuse_mount *fm = get_fuse_mount(inode);
	struct fuse_file *ff = file->private_data;
	FUSE_ARGS(args);
	struct fuse_fsync_in inarg;

	memset(&inarg, 0, sizeof(inarg));
	inarg.fh = ff->fh;
	inarg.fsync_flags = datasync ? FUSE_FSYNC_FDATASYNC : 0;
	args.opcode = opcode;
	args.nodeid = get_node_id(inode);
	args.in_numargs = 1;
	args.in_args[0].size = sizeof(inarg);
	args.in_args[0].value = &inarg;
	return fuse_simple_request(fm, &args);
}

static int fuse_fsync(struct file *file, loff_t start, loff_t end,
		      int datasync)
{
	struct inode *inode = file->f_mapping->host;
	struct fuse_conn *fc = get_fuse_conn(inode);
	int err;

	if (fuse_is_bad(inode))
		return -EIO;

	inode_lock(inode);

	/*
	 * Start writeback against all dirty pages of the inode, then
	 * wait for all outstanding writes, before sending the FSYNC
	 * request.
	 */
	err = file_write_and_wait_range(file, start, end);
	if (err)
		goto out;

	fuse_sync_writes(inode);

	/*
	 * Due to implementation of fuse writeback
	 * file_write_and_wait_range() does not catch errors.
	 * We have to do this directly after fuse_sync_writes()
	 */
	err = file_check_and_advance_wb_err(file);
	if (err)
		goto out;

	err = sync_inode_metadata(inode, 1);
	if (err)
		goto out;

	if (fc->no_fsync)
		goto out;

	err = fuse_fsync_common(file, start, end, datasync, FUSE_FSYNC);
	if (err == -ENOSYS) {
		fc->no_fsync = 1;
		err = 0;
	}
out:
	inode_unlock(inode);

	return err;
}

void fuse_read_args_fill(struct fuse_io_args *ia, struct file *file, loff_t pos,
			 size_t count, int opcode)
{
	struct fuse_file *ff = file->private_data;
	struct fuse_args *args = &ia->ap.args;

	ia->read.in.fh = ff->fh;
	ia->read.in.offset = pos;
	ia->read.in.size = count;
	ia->read.in.flags = file->f_flags;
	args->opcode = opcode;
	args->nodeid = ff->nodeid;
	args->in_numargs = 1;
	args->in_args[0].size = sizeof(ia->read.in);
	args->in_args[0].value = &ia->read.in;
	args->out_argvar = true;
	args->out_numargs = 1;
	args->out_args[0].size = count;
}

static void fuse_release_user_pages(struct fuse_args_pages *ap, ssize_t nres,
				    bool should_dirty)
{
	unsigned int i;

	for (i = 0; i < ap->num_folios; i++) {
		if (should_dirty)
			folio_mark_dirty_lock(ap->folios[i]);
		if (ap->args.is_pinned)
			unpin_folio(ap->folios[i]);
	}

	if (nres > 0 && ap->args.invalidate_vmap)
		invalidate_kernel_vmap_range(ap->args.vmap_base, nres);
}

static void fuse_io_release(struct kref *kref)
{
	kfree(container_of(kref, struct fuse_io_priv, refcnt));
}

static ssize_t fuse_get_res_by_io(struct fuse_io_priv *io)
{
	if (io->err)
		return io->err;

	if (io->bytes >= 0 && io->write)
		return -EIO;

	return io->bytes < 0 ? io->size : io->bytes;
}

static void fuse_aio_invalidate_worker(struct work_struct *work)
{
	struct fuse_io_priv *io = container_of(work, struct fuse_io_priv, work);
	struct address_space *mapping = io->iocb->ki_filp->f_mapping;
	ssize_t res = fuse_get_res_by_io(io);
	pgoff_t start = io->offset >> PAGE_SHIFT;
	pgoff_t end = (io->offset + res - 1) >> PAGE_SHIFT;

	invalidate_inode_pages2_range(mapping, start, end);
	io->iocb->ki_complete(io->iocb, res);
	kref_put(&io->refcnt, fuse_io_release);
}

/*
 * In case of short read, the caller sets 'pos' to the position of
 * actual end of fuse request in IO request. Otherwise, if bytes_requested
 * == bytes_transferred or rw == WRITE, the caller sets 'pos' to -1.
 *
 * An example:
 * User requested DIO read of 64K. It was split into two 32K fuse requests,
 * both submitted asynchronously. The first of them was ACKed by userspace as
 * fully completed (req->out.args[0].size == 32K) resulting in pos == -1. The
 * second request was ACKed as short, e.g. only 1K was read, resulting in
 * pos == 33K.
 *
 * Thus, when all fuse requests are completed, the minimal non-negative 'pos'
 * will be equal to the length of the longest contiguous fragment of
 * transferred data starting from the beginning of IO request.
 */
static void fuse_aio_complete(struct fuse_io_priv *io, int err, ssize_t pos)
{
	int left;

	spin_lock(&io->lock);
	if (err)
		io->err = io->err ? : err;
	else if (pos >= 0 && (io->bytes < 0 || pos < io->bytes))
		io->bytes = pos;

	left = --io->reqs;
	if (!left && io->blocking)
		complete(io->done);
	spin_unlock(&io->lock);

	if (!left && !io->blocking) {
		struct inode *inode = file_inode(io->iocb->ki_filp);
		struct address_space *mapping = io->iocb->ki_filp->f_mapping;
		ssize_t res = fuse_get_res_by_io(io);

		if (res >= 0) {
			struct fuse_conn *fc = get_fuse_conn(inode);
			struct fuse_inode *fi = get_fuse_inode(inode);

			spin_lock(&fi->lock);
			fi->attr_version = atomic64_inc_return(&fc->attr_version);
			spin_unlock(&fi->lock);
		}

		if (io->write && res > 0 && mapping->nrpages) {
			/*
			 * As in generic_file_direct_write(), invalidate after the
			 * write, to invalidate read-ahead cache that may have competed
			 * with the write.
			 */
			INIT_WORK(&io->work, fuse_aio_invalidate_worker);
			queue_work(inode->i_sb->s_dio_done_wq, &io->work);
			return;
		}

		io->iocb->ki_complete(io->iocb, res);
	}

	kref_put(&io->refcnt, fuse_io_release);
}

static struct fuse_io_args *fuse_io_alloc(struct fuse_io_priv *io,
						 unsigned int nfolios)
{
	struct fuse_io_args *ia;

	ia = kzalloc_obj(*ia);
	if (ia) {
		ia->io = io;
		ia->ap.folios = fuse_folios_alloc(nfolios, GFP_KERNEL,
						  &ia->ap.descs);
		if (!ia->ap.folios) {
			kfree(ia);
			ia = NULL;
		}
	}
	return ia;
}

static void fuse_io_free(struct fuse_io_args *ia)
{
	kfree(ia->ap.folios);
	kfree(ia);
}

static void fuse_aio_complete_req(struct fuse_args *args, int err)
{
	struct fuse_io_args *ia = container_of(args, typeof(*ia), ap.args);
	struct fuse_io_priv *io = ia->io;
	ssize_t pos = -1;
	size_t nres;

	if (err) {
		/* Nothing */
	} else if (io->write) {
		if (ia->write.out.size > ia->write.in.size) {
			err = -EIO;
		} else {
			nres = ia->write.out.size;
			if (ia->write.in.size != ia->write.out.size)
				pos = ia->write.in.offset - io->offset +
				      ia->write.out.size;
		}
	} else {
		u32 outsize = args->out_args[0].size;

		nres = outsize;
		if (ia->read.in.size != outsize)
			pos = ia->read.in.offset - io->offset + outsize;
	}

	fuse_release_user_pages(&ia->ap, err ?: nres, io->should_dirty);

	fuse_aio_complete(io, err, pos);
	fuse_io_free(ia);
}

static ssize_t fuse_async_req_send(struct fuse_mount *fm,
				   struct fuse_io_args *ia, size_t num_bytes)
{
	ssize_t err;
	struct fuse_io_priv *io = ia->io;

	spin_lock(&io->lock);
	kref_get(&io->refcnt);
	io->size += num_bytes;
	io->reqs++;
	spin_unlock(&io->lock);

	ia->ap.args.end = fuse_aio_complete_req;
	ia->ap.args.may_block = io->should_dirty;
	err = fuse_simple_background(fm, &ia->ap.args, GFP_KERNEL);
	if (err)
		fuse_aio_complete_req(&ia->ap.args, err);

	return num_bytes;
}

static ssize_t fuse_send_read(struct fuse_io_args *ia, loff_t pos, size_t count,
			      fl_owner_t owner)
{
	struct file *file = ia->io->iocb->ki_filp;
	struct fuse_file *ff = file->private_data;
	struct fuse_mount *fm = ff->fm;

	fuse_read_args_fill(ia, file, pos, count, FUSE_READ);
	if (owner != NULL) {
		ia->read.in.read_flags |= FUSE_READ_LOCKOWNER;
		ia->read.in.lock_owner = fuse_lock_owner_id(fm->fc, owner);
	}

	if (ia->io->async)
		return fuse_async_req_send(fm, ia, count);

	return fuse_simple_request(fm, &ia->ap.args);
}

static void fuse_read_update_size(struct inode *inode, loff_t size,
				  u64 attr_ver)
{
	struct fuse_conn *fc = get_fuse_conn(inode);
	struct fuse_inode *fi = get_fuse_inode(inode);

	spin_lock(&fi->lock);
	if (attr_ver >= fi->attr_version && size < inode->i_size &&
	    !test_bit(FUSE_I_SIZE_UNSTABLE, &fi->state)) {
		fi->attr_version = atomic64_inc_return(&fc->attr_version);
		i_size_write(inode, size);
	}
	spin_unlock(&fi->lock);
}

static void fuse_short_read(struct inode *inode, u64 attr_ver, size_t num_read,
			    struct fuse_args_pages *ap)
{
	struct fuse_conn *fc = get_fuse_conn(inode);

	/*
	 * If writeback_cache is enabled, a short read means there's a hole in
	 * the file.  Some data after the hole is in page cache, but has not
	 * reached the client fs yet.  So the hole is not present there.
	 */
	if (!fc->writeback_cache) {
		loff_t pos = folio_pos(ap->folios[0]) + num_read;
		fuse_read_update_size(inode, pos, attr_ver);
	}
}

static int fuse_do_readfolio(struct file *file, struct folio *folio,
			     size_t off, size_t len)
{
	struct inode *inode = folio->mapping->host;
	struct fuse_mount *fm = get_fuse_mount(inode);
	loff_t pos = folio_pos(folio) + off;
	struct fuse_folio_desc desc = {
		.offset = off,
		.length = len,
	};
	struct fuse_io_args ia = {
		.ap.args.page_zeroing = true,
		.ap.args.out_pages = true,
		.ap.num_folios = 1,
		.ap.folios = &folio,
		.ap.descs = &desc,
	};
	ssize_t res;
	u64 attr_ver;

	attr_ver = fuse_get_attr_version(fm->fc);

	/* Don't overflow end offset */
	if (pos + (desc.length - 1) == LLONG_MAX)
		desc.length--;

	fuse_read_args_fill(&ia, file, pos, desc.length, FUSE_READ);
	res = fuse_simple_request(fm, &ia.ap.args);
	if (res < 0)
		return res;
	/*
	 * Short read means EOF.  If file size is larger, truncate it
	 */
	if (res < desc.length)
		fuse_short_read(inode, attr_ver, res, &ia.ap);

	return 0;
}

static int fuse_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
			    unsigned int flags, struct iomap *iomap,
			    struct iomap *srcmap)
{
	iomap->type = IOMAP_MAPPED;
	iomap->length = length;
	iomap->offset = offset;
	return 0;
}

static DEFINE_IOMAP_ITER_NEXT(fuse_iomap_next, fuse_iomap_begin);

static const struct iomap_ops fuse_iomap_ops = {
	.iomap_next	= fuse_iomap_next,
};

struct fuse_fill_read_data {
	struct file *file;

	/* Fields below are used if sending the read request asynchronously */
	struct fuse_conn *fc;
	struct fuse_io_args *ia;
	unsigned int nr_bytes;
};

/* forward declarations */
static bool fuse_folios_need_send(struct fuse_conn *fc, loff_t pos,
				  unsigned len, struct fuse_args_pages *ap,
				  unsigned cur_bytes, bool write);
static void fuse_send_readpages(struct fuse_io_args *ia, struct file *file,
				unsigned int count, bool async);

static int fuse_handle_readahead(struct folio *folio,
				 struct readahead_control *rac,
				 struct fuse_fill_read_data *data, loff_t pos,
				 size_t len)
{
	struct fuse_io_args *ia = data->ia;
	size_t off = offset_in_folio(folio, pos);
	struct fuse_conn *fc = data->fc;
	struct fuse_args_pages *ap;
	unsigned int nr_pages;

	if (ia && fuse_folios_need_send(fc, pos, len, &ia->ap, data->nr_bytes,
					false)) {
		fuse_send_readpages(ia, data->file, data->nr_bytes,
				    fc->async_read);
		data->nr_bytes = 0;
		data->ia = NULL;
		ia = NULL;
	}
	if (!ia) {
		if (fuse_chan_num_background(fc->chan) >= fc->congestion_threshold &&
		    rac->ra->async_size >= readahead_count(rac))
			/*
			 * Congested and only async pages left, so skip the
			 * rest.
			 */
			return -EAGAIN;

		nr_pages = min(fc->max_pages, readahead_count(rac));
		data->ia = fuse_io_alloc(NULL, nr_pages);
		if (!data->ia)
			return -ENOMEM;
		ia = data->ia;
	}
	folio_get(folio);
	ap = &ia->ap;
	ap->folios[ap->num_folios] = folio;
	ap->descs[ap->num_folios].offset = off;
	ap->descs[ap->num_folios].length = len;
	data->nr_bytes += len;
	ap->num_folios++;

	return 0;
}

static int fuse_iomap_read_folio_range_async(const struct iomap_iter *iter,
					     struct iomap_read_folio_ctx *ctx,
					     size_t len)
{
	struct fuse_fill_read_data *data = ctx->read_ctx;
	struct folio *folio = ctx->cur_folio;
	loff_t pos =  iter->pos;
	size_t off = offset_in_folio(folio, pos);
	struct file *file = data->file;
	int ret;

	if (ctx->rac) {
		ret = fuse_handle_readahead(folio, ctx->rac, data, pos, len);
	} else {
		/*
		 *  for non-readahead read requests, do reads synchronously
		 *  since it's not guaranteed that the server can handle
		 *  out-of-order reads
		 */
		ret = fuse_do_readfolio(file, folio, off, len);
		if (!ret)
			iomap_finish_folio_read(folio, off, len, ret);
	}
	return ret;
}

static const struct iomap_read_ops fuse_iomap_read_ops = {
	.read_folio_range = fuse_iomap_read_folio_range_async,
};

static int fuse_read_folio(struct file *file, struct folio *folio)
{
	struct inode *inode = folio->mapping->host;
	struct fuse_fill_read_data data = {
		.file = file,
	};
	struct iomap_read_folio_ctx ctx = {
		.cur_folio = folio,
		.ops = &fuse_iomap_read_ops,
		.read_ctx = &data,

	};

	if (fuse_is_bad(inode)) {
		folio_unlock(folio);
		return -EIO;
	}

	iomap_read_folio(&fuse_iomap_ops, &ctx, NULL);
	fuse_invalidate_atime(inode);
	return 0;
}

static int fuse_iomap_read_folio_range(const struct iomap_iter *iter,
				       struct folio *folio, loff_t pos,
				       size_t len)
{
	struct file *file = iter->private;
	size_t off = offset_in_folio(folio, pos);

	return fuse_do_readfolio(file, folio, off, len);
}

static void fuse_readpages_end(struct fuse_args *args, int err)
{
	int i;
	struct fuse_io_args *ia = container_of(args, typeof(*ia), ap.args);
	struct fuse_args_pages *ap = &ia->ap;
	size_t count = ia->read.in.size;
	size_t num_read = args->out_args[0].size;
	struct address_space *mapping;
	struct inode *inode;

	WARN_ON_ONCE(!ap->num_folios);
	mapping = ap->folios[0]->mapping;
	inode = mapping->host;

	/*
	 * Short read means EOF. If file size is larger, truncate it
	 */
	if (!err && num_read < count)
		fuse_short_read(inode, ia->read.attr_ver, num_read, ap);

	fuse_invalidate_atime(inode);

	for (i = 0; i < ap->num_folios; i++) {
		iomap_finish_folio_read(ap->folios[i], ap->descs[i].offset,
					ap->descs[i].length, err);
		folio_put(ap->folios[i]);
	}
	if (ia->ff)
		fuse_file_put(ia->ff, false);

	fuse_io_free(ia);
}

static void fuse_send_readpages(struct fuse_io_args *ia, struct file *file,
				unsigned int count, bool async)
{
	struct fuse_file *ff = file->private_data;
	struct fuse_mount *fm = ff->fm;
	struct fuse_args_pages *ap = &ia->ap;
	loff_t pos = folio_pos(ap->folios[0]);
	ssize_t res;
	int err;

	ap->args.out_pages = true;
	ap->args.page_zeroing = true;
	ap->args.page_replace = true;

	/* Don't overflow end offset */
	if (pos + (count - 1) == LLONG_MAX) {
		count--;
		ap->descs[ap->num_folios - 1].length--;
	}
	WARN_ON((loff_t) (pos + count) < 0);

	fuse_read_args_fill(ia, file, pos, count, FUSE_READ);
	ia->read.attr_ver = fuse_get_attr_version(fm->fc);
	if (async) {
		ia->ff = fuse_file_get(ff);
		ap->args.end = fuse_readpages_end;
		err = fuse_simple_background(fm, &ap->args, GFP_KERNEL);
		if (!err)
			return;
	} else {
		res = fuse_simple_request(fm, &ap->args);
		err = res < 0 ? res : 0;
	}
	fuse_readpages_end(&ap->args, err);
}

static void fuse_readahead(struct readahead_control *rac)
{
	struct inode *inode = rac->mapping->host;
	struct fuse_conn *fc = get_fuse_conn(inode);
	struct fuse_fill_read_data data = {
		.file = rac->file,
		.fc = fc,
	};
	struct iomap_read_folio_ctx ctx = {
		.ops = &fuse_iomap_read_ops,
		.rac = rac,
		.read_ctx = &data
	};

	if (fuse_is_bad(inode))
		return;

	iomap_readahead(&fuse_iomap_ops, &ctx, NULL);
	if (data.ia)
		fuse_send_readpages(data.ia, data.file, data.nr_bytes,
				    fc->async_read);
}

static ssize_t fuse_cache_read_iter(struct kiocb *iocb, struct iov_iter *to)
{
	struct inode *inode = iocb->ki_filp->f_mapping->host;
	struct fuse_conn *fc = get_fuse_conn(inode);

	/*
	 * In auto invalidate mode, always update attributes on read.
	 * Otherwise, only update if we attempt to read past EOF (to ensure
	 * i_size is up to date).
	 */
	if (fc->auto_inval_data ||
	    (iocb->ki_pos + iov_iter_count(to) > i_size_read(inode))) {
		int err;
		err = fuse_update_attributes(inode, iocb->ki_filp, STATX_SIZE);
		if (err)
			return err;
	}

	return generic_file_read_iter(iocb, to);
}

static void fuse_write_args_fill(struct fuse_io_args *ia, struct fuse_file *ff,
				 loff_t pos, size_t count)
{
	struct fuse_args *args = &ia->ap.args;

	ia->write.in.fh = ff->fh;
	ia->write.in.offset = pos;
	ia->write.in.size = count;
	args->opcode = FUSE_WRITE;
	args->nodeid = ff->nodeid;
	args->in_numargs = 2;
	if (ff->fm->fc->minor < 9)
		args->in_args[0].size = FUSE_COMPAT_WRITE_IN_SIZE;
	else
		args->in_args[0].size = sizeof(ia->write.in);
	args->in_args[0].value = &ia->write.in;
	args->in_args[1].size = count;
	args->out_numargs = 1;
	args->out_args[0].size = sizeof(ia->write.out);
	args->out_args[0].value = &ia->write.out;
}

static unsigned int fuse_write_flags(struct kiocb *iocb)
{
	unsigned int flags = iocb->ki_filp->f_flags;

	if (iocb_is_dsync(iocb))
		flags |= O_DSYNC;
	if (iocb->ki_flags & IOCB_SYNC)
		flags |= O_SYNC;

	return flags;
}

static ssize_t fuse_send_write(struct fuse_io_args *ia, loff_t pos,
			       size_t count, fl_owner_t owner)
{
	struct kiocb *iocb = ia->io->iocb;
	struct file *file = iocb->ki_filp;
	struct fuse_file *ff = file->private_data;
	struct fuse_mount *fm = ff->fm;
	struct fuse_write_in *inarg = &ia->write.in;
	ssize_t err;

	fuse_write_args_fill(ia, ff, pos, count);
	inarg->flags = fuse_write_flags(iocb);
	if (owner != NULL) {
		inarg->write_flags |= FUSE_WRITE_LOCKOWNER;
		inarg->lock_owner = fuse_lock_owner_id(fm->fc, owner);
	}

	if (ia->io->async)
		return fuse_async_req_send(fm, ia, count);

	err = fuse_simple_request(fm, &ia->ap.args);
	if (!err && ia->write.out.size > count)
		err = -EIO;

	return err ?: ia->write.out.size;
}

bool fuse_write_update_attr(struct inode *inode, loff_t pos, ssize_t written)
{
	struct fuse_conn *fc = get_fuse_conn(inode);
	struct fuse_inode *fi = get_fuse_inode(inode);
	bool ret = false;

	spin_lock(&fi->lock);
	fi->attr_version = atomic64_inc_return(&fc->attr_version);
	if (written > 0 && pos > inode->i_size) {
		i_size_write(inode, pos);
		ret = true;
	}
	spin_unlock(&fi->lock);

	fuse_invalidate_attr_mask(inode, FUSE_STATX_MODSIZE);

	return ret;
}

static ssize_t fuse_send_write_pages(struct fuse_io_args *ia,
				     struct kiocb *iocb, struct inode *inode,
				     loff_t pos, size_t count)
{
	struct fuse_args_pages *ap = &ia->ap;
	struct file *file = iocb->ki_filp;
	struct fuse_file *ff = file->private_data;
	struct fuse_mount *fm = ff->fm;
	unsigned int i;
	int err;

	for (i = 0; i < ap->num_folios; i++)
		folio_wait_writeback(ap->folios[i]);

	fuse_write_args_fill(ia, ff, pos, count);
	ia->write.in.flags = fuse_write_flags(iocb);
	if (fm->fc->handle_killpriv_v2 && !capable(CAP_FSETID))
		ia->write.in.write_flags |= FUSE_WRITE_KILL_SUIDGID;

	err = fuse_simple_request(fm, &ap->args);
	if (!err && ia->write.out.size > count)
		err = -EIO;

	for (i = 0; i < ap->num_folios; i++) {
		struct folio *folio = ap->folios[i];

		if (ia->write.folio_locked && (i == ap->num_folios - 1))
			folio_unlock(folio);
		folio_put(folio);
	}

	return err;
}

static ssize_t fuse_fill_write_pages(struct fuse_io_args *ia,
				     struct address_space *mapping,
				     struct iov_iter *ii, loff_t pos,
				     unsigned int max_folios)
{
	struct fuse_args_pages *ap = &ia->ap;
	struct fuse_conn *fc = get_fuse_conn(mapping->host);
	size_t count = 0;
	unsigned int num;
	int err = 0;

	num = min(iov_iter_count(ii), fc->max_write);

	ap->args.in_pages = true;

	while (num && ap->num_folios < max_folios) {
		size_t tmp;
		struct folio *folio;
		pgoff_t index = pos >> PAGE_SHIFT;
		unsigned int bytes;
		unsigned int folio_offset;

 again:
		folio = __filemap_get_folio(mapping, index, FGP_WRITEBEGIN,
					    mapping_gfp_mask(mapping));
		if (IS_ERR(folio)) {
			err = PTR_ERR(folio);
			break;
		}

		if (mapping_writably_mapped(mapping))
			flush_dcache_folio(folio);

		folio_offset = offset_in_folio(folio, pos);
		bytes = min(folio_size(folio) - folio_offset, num);

		tmp = copy_folio_from_iter_atomic(folio, folio_offset, bytes, ii);
		flush_dcache_folio(folio);

		if (!tmp) {
			folio_unlock(folio);
			folio_put(folio);

			/*
			 * Ensure forward progress by faulting in
			 * while not holding the folio lock:
			 */
			if (fault_in_iov_iter_readable(ii, bytes)) {
				err = -EFAULT;
				break;
			}

			goto again;
		}

		ap->folios[ap->num_folios] = folio;
		ap->descs[ap->num_folios].offset = folio_offset;
		ap->descs[ap->num_folios].length = tmp;
		ap->num_folios++;

		count += tmp;
		pos += tmp;
		num -= tmp;

		/* If we copied full folio, mark it uptodate */
		if (tmp == folio_size(folio))
			iomap_folio_mark_uptodate(folio);

		if (folio_test_uptodate(folio)) {
			folio_unlock(folio);
		} else {
			ia->write.folio_locked = true;
			break;
		}
		if (!fc->big_writes)
			break;
		if (folio_offset + tmp != folio_size(folio))
			break;
	}

	return count > 0 ? count : err;
}

static inline unsigned int fuse_wr_pages(loff_t pos, size_t len,
				     unsigned int max_pages)
{
	unsigned int pages = ((pos + len - 1) >> PAGE_SHIFT) -
			     (pos >> PAGE_SHIFT) + 1;

	return min(pages, max_pages);
}

static ssize_t fuse_perform_write(struct kiocb *iocb, struct iov_iter *ii)
{
	struct address_space *mapping = iocb->ki_filp->f_mapping;
	struct inode *inode = mapping->host;
	struct fuse_conn *fc = get_fuse_conn(inode);
	struct fuse_inode *fi = get_fuse_inode(inode);
	loff_t pos = iocb->ki_pos;
	int err = 0;
	ssize_t res = 0;

	if (inode->i_size < pos + iov_iter_count(ii))
		set_bit(FUSE_I_SIZE_UNSTABLE, &fi->state);

	do {
		ssize_t count;
		struct fuse_io_args ia = {};
		struct fuse_args_pages *ap = &ia.ap;
		unsigned int nr_pages = fuse_wr_pages(pos, iov_iter_count(ii),
						      fc->max_pages);

		ap->folios = fuse_folios_alloc(nr_pages, GFP_KERNEL, &ap->descs);
		if (!ap->folios) {
			err = -ENOMEM;
			break;
		}

		count = fuse_fill_write_pages(&ia, mapping, ii, pos, nr_pages);
		if (count <= 0) {
			err = count;
		} else {
			err = fuse_send_write_pages(&ia, iocb, inode,
						    pos, count);
			if (!err) {
				size_t num_written = ia.write.out.size;

				res += num_written;
				pos += num_written;

				/* break out of the loop on short write */
				if (num_written != count)
					err = -EIO;
			}
		}
		kfree(ap->folios);
	} while (!err && iov_iter_count(ii));

	fuse_write_update_attr(inode, pos, res);
	clear_bit(FUSE_I_SIZE_UNSTABLE, &fi->state);

	if (!res)
		return err;
	iocb->ki_pos += res;
	return res;
}

static bool fuse_io_past_eof(struct kiocb *iocb, struct iov_iter *iter)
{
	struct inode *inode = file_inode(iocb->ki_filp);

	return iocb->ki_pos + iov_iter_count(iter) > i_size_read(inode);
}

/*
 * @return true if an exclusive lock for direct IO writes is needed
 */
static bool fuse_dio_wr_exclusive_lock(struct kiocb *iocb, struct iov_iter *from)
{
	struct file *file = iocb->ki_filp;
	struct fuse_file *ff = file->private_data;
	struct inode *inode = file_inode(iocb->ki_filp);
	struct fuse_inode *fi = get_fuse_inode(inode);

	/* Server side has to advise that it supports parallel dio writes. */
	if (!(ff->open_flags & FOPEN_PARALLEL_DIRECT_WRITES))
		return true;

	/*
	 * Append will need to know the eventual EOF - always needs an
	 * exclusive lock.
	 */
	if (iocb->ki_flags & IOCB_APPEND)
		return true;

	/* shared locks are not allowed with parallel page cache IO */
	if (test_bit(FUSE_I_CACHE_IO_MODE, &fi->state))
		return true;

	/* Parallel dio beyond EOF is not supported, at least for now. */
	if (fuse_io_past_eof(iocb, from))
		return true;

	return false;
}

static void fuse_dio_lock(struct kiocb *iocb, struct iov_iter *from,
			  bool *exclusive)
{
	struct inode *inode = file_inode(iocb->ki_filp);
	struct fuse_inode *fi = get_fuse_inode(inode);

	*exclusive = fuse_dio_wr_exclusive_lock(iocb, from);
	if (*exclusive) {
		inode_lock(inode);
	} else {
		inode_lock_shared(inode);
		/*
		 * New parallal dio allowed only if inode is not in caching
		 * mode and denies new opens in caching mode. This check
		 * should be performed only after taking shared inode lock.
		 * Previous past eof check was without inode lock and might
		 * have raced, so check it again.
		 */
		if (fuse_io_past_eof(iocb, from) ||
		    fuse_inode_uncached_io_start(fi, NULL) != 0) {
			inode_unlock_shared(inode);
			inode_lock(inode);
			*exclusive = true;
		}
	}
}

static void fuse_dio_unlock(struct kiocb *iocb, bool exclusive)
{
	struct inode *inode = file_inode(iocb->ki_filp);
	struct fuse_inode *fi = get_fuse_inode(inode);

	if (exclusive) {
		inode_unlock(inode);
	} else {
		/* Allow opens in caching mode after last parallel dio end */
		fuse_inode_uncached_io_end(fi);
		inode_unlock_shared(inode);
	}
}

static const struct iomap_write_ops fuse_iomap_write_ops = {
	.read_folio_range = fuse_iomap_read_folio_range,
};

static ssize_t fuse_cache_write_iter(struct kiocb *iocb, struct iov_iter *from)
{
	struct file *file = iocb->ki_filp;
	struct mnt_idmap *idmap = file_mnt_idmap(file);
	struct address_space *mapping = file->f_mapping;
	ssize_t written = 0;
	struct inode *inode = mapping->host;
	ssize_t err, count;
	struct fuse_conn *fc = get_fuse_conn(inode);
	bool writeback = false;

	if (fc->writeback_cache) {
		/* Update size (EOF optimization) and mode (SUID clearing) */
		err = fuse_update_attributes(mapping->host, file,
					     STATX_SIZE | STATX_MODE);
		if (err)
			return err;

		if (!fc->handle_killpriv_v2 ||
		    !setattr_should_drop_suidgid(idmap, file_inode(file)))
			writeback = true;
	}

	inode_lock(inode);

	err = count = generic_write_checks(iocb, from);
	if (err <= 0)
		goto out;

	task_io_account_write(count);

	err = kiocb_modified(iocb);
	if (err)
		goto out;

	if (iocb->ki_flags & IOCB_DIRECT) {
		written = generic_file_direct_write(iocb, from);
		if (written < 0 || !iov_iter_count(from))
			goto out;
		written = direct_write_fallback(iocb, from, written,
				fuse_perform_write(iocb, from));
	} else if (writeback) {
		/*
		 * Use iomap so that we can do granular uptodate reads
		 * and granular dirty tracking for large folios.
		 */
		written = iomap_file_buffered_write(iocb, from,
						    &fuse_iomap_ops,
						    &fuse_iomap_write_ops,
						    file);
	} else {
		written = fuse_perform_write(iocb, from);
	}
out:
	inode_unlock(inode);
	if (written > 0)
		written = generic_write_sync(iocb, written);

	return written ? written : err;
}

static inline unsigned long fuse_get_user_addr(const struct iov_iter *ii)
{
	return (unsigned long)iter_iov(ii)->iov_base + ii->iov_offset;
}

static inline size_t fuse_get_frag_size(const struct iov_iter *ii,
					size_t max_size)
{
	return min(iov_iter_single_seg_count(ii), max_size);
}

static int fuse_get_user_pages(struct fuse_args_pages *ap, struct iov_iter *ii,
			       size_t *nbytesp, int write,
			       unsigned int max_pages,
			       bool use_pages_for_kvec_io)
{
	bool flush_or_invalidate = false;
	unsigned int nr_pages = 0;
	size_t nbytes = 0;  /* # bytes already packed in req */
	ssize_t ret = 0;

	/* Special case for kernel I/O: can copy directly into the buffer.
	 * However if the implementation of fuse_conn requires pages instead of
	 * pointer (e.g., virtio-fs), use iov_iter_extract_pages() instead.
	 */
	if (iov_iter_is_kvec(ii)) {
		void *user_addr = (void *)fuse_get_user_addr(ii);

		if (!use_pages_for_kvec_io) {
			size_t frag_size = fuse_get_frag_size(ii, *nbytesp);

			if (write)
				ap->args.in_args[1].value = user_addr;
			else
				ap->args.out_args[0].value = user_addr;

			iov_iter_advance(ii, frag_size);
			*nbytesp = frag_size;
			return 0;
		}

		if (is_vmalloc_addr(user_addr)) {
			ap->args.vmap_base = user_addr;
			flush_or_invalidate = true;
		}
	}

	/*
	 * Until there is support for iov_iter_extract_folios(), we have to
	 * manually extract pages using iov_iter_extract_pages() and then
	 * copy that to a folios array.
	 */
	struct page **pages = kcalloc(max_pages, sizeof(struct page *),
				      GFP_KERNEL);
	if (!pages) {
		ret = -ENOMEM;
		goto out;
	}

	while (nbytes < *nbytesp && nr_pages < max_pages) {
		unsigned nfolios, i;
		size_t start;

		ret = iov_iter_extract_pages(ii, &pages,
					     *nbytesp - nbytes,
					     max_pages - nr_pages,
					     0, &start);
		if (ret < 0)
			break;

		nbytes += ret;

		nfolios = DIV_ROUND_UP(ret + start, PAGE_SIZE);

		for (i = 0; i < nfolios; i++) {
			struct folio *folio = page_folio(pages[i]);
			unsigned int offset = start +
				(folio_page_idx(folio, pages[i]) << PAGE_SHIFT);
			unsigned int len = umin(ret, PAGE_SIZE - start);

			ap->descs[ap->num_folios].offset = offset;
			ap->descs[ap->num_folios].length = len;
			ap->folios[ap->num_folios] = folio;
			start = 0;
			ret -= len;
			ap->num_folios++;
		}

		nr_pages += nfolios;
	}
	kfree(pages);

	if (write && flush_or_invalidate)
		flush_kernel_vmap_range(ap->args.vmap_base, nbytes);

	ap->args.invalidate_vmap = !write && flush_or_invalidate;
	ap->args.is_pinned = iov_iter_extract_will_pin(ii);
	ap->args.user_pages = true;
	if (write)
		ap->args.in_pages = true;
	else
		ap->args.out_pages = true;

out:
	*nbytesp = nbytes;

	return ret < 0 ? ret : 0;
}

ssize_t fuse_direct_io(struct fuse_io_priv *io, struct iov_iter *iter,
		       loff_t *ppos, int flags)
{
	int write = flags & FUSE_DIO_WRITE;
	int cuse = flags & FUSE_DIO_CUSE;
	struct file *file = io->iocb->ki_filp;
	struct address_space *mapping = file->f_mapping;
	struct inode *inode = mapping->host;
	struct fuse_file *ff = file->private_data;
	struct fuse_conn *fc = ff->fm->fc;
	size_t nmax = write ? fc->max_write : fc->max_read;
	loff_t pos = *ppos;
	size_t count = iov_iter_count(iter);
	pgoff_t idx_from = pos >> PAGE_SHIFT;
	pgoff_t idx_to = (pos + count - 1) >> PAGE_SHIFT;
	ssize_t res = 0;
	int err = 0;
	struct fuse_io_args *ia;
	unsigned int max_pages;
	bool fopen_direct_io = ff->open_flags & FOPEN_DIRECT_IO;

	max_pages = iov_iter_npages(iter, fc->max_pages);
	ia = fuse_io_alloc(io, max_pages);
	if (!ia)
		return -ENOMEM;

	if (fopen_direct_io) {
		res = filemap_write_and_wait_range(mapping, pos, pos + count - 1);
		if (res) {
			fuse_io_free(ia);
			return res;
		}
	}
	if (!cuse && filemap_range_has_writeback(mapping, pos, (pos + count - 1))) {
		if (!write)
			inode_lock(inode);
		fuse_sync_writes(inode);
		if (!write)
			inode_unlock(inode);
	}

	if (fopen_direct_io && write) {
		res = invalidate_inode_pages2_range(mapping, idx_from, idx_to);
		if (res) {
			fuse_io_free(ia);
			return res;
		}
	}

	io->should_dirty = !write && user_backed_iter(iter);
	while (count) {
		ssize_t nres;
		fl_owner_t owner = current->files;
		size_t nbytes = min(count, nmax);

		err = fuse_get_user_pages(&ia->ap, iter, &nbytes, write,
					  max_pages, fc->use_pages_for_kvec_io);
		if (err && !nbytes)
			break;

		if (write) {
			if (!capable(CAP_FSETID))
				ia->write.in.write_flags |= FUSE_WRITE_KILL_SUIDGID;

			nres = fuse_send_write(ia, pos, nbytes, owner);
		} else {
			nres = fuse_send_read(ia, pos, nbytes, owner);
		}

		if (!io->async || nres < 0) {
			fuse_release_user_pages(&ia->ap, nres, io->should_dirty);
			fuse_io_free(ia);
		}
		ia = NULL;
		if (nres < 0) {
			iov_iter_revert(iter, nbytes);
			err = nres;
			break;
		}
		WARN_ON(nres > nbytes);

		count -= nres;
		res += nres;
		pos += nres;
		if (nres != nbytes) {
			iov_iter_revert(iter, nbytes - nres);
			break;
		}
		if (count) {
			max_pages = iov_iter_npages(iter, fc->max_pages);
			ia = fuse_io_alloc(io, max_pages);
			if (!ia)
				break;
		}
	}
	if (ia)
		fuse_io_free(ia);
	if (res > 0)
		*ppos = pos;

	return res > 0 ? res : err;
}
EXPORT_SYMBOL_GPL(fuse_direct_io);

static ssize_t __fuse_direct_read(struct fuse_io_priv *io,
				  struct iov_iter *iter,
				  loff_t *ppos)
{
	ssize_t res;
	struct inode *inode = file_inode(io->iocb->ki_filp);

	res = fuse_direct_io(io, iter, ppos, 0);

	fuse_invalidate_atime(inode);

	return res;
}

static ssize_t fuse_direct_IO(struct kiocb *iocb, struct iov_iter *iter);

static ssize_t fuse_direct_read_iter(struct kiocb *iocb, struct iov_iter *to)
{
	ssize_t res;

	if (!is_sync_kiocb(iocb)) {
		res = fuse_direct_IO(iocb, to);
	} else {
		struct fuse_io_priv io = FUSE_IO_PRIV_SYNC(iocb);

		res = __fuse_direct_read(&io, to, &iocb->ki_pos);
	}

	return res;
}

static ssize_t fuse_direct_write_iter(struct kiocb *iocb, struct iov_iter *from)
{
	struct inode *inode = file_inode(iocb->ki_filp);
	struct address_space *mapping = inode->i_mapping;
	loff_t pos = iocb->ki_pos;
	ssize_t res;
	bool exclusive;

	fuse_dio_lock(iocb, from, &exclusive);
	res = generic_write_checks(iocb, from);
	if (res > 0) {
		task_io_account_write(res);
		if (!is_sync_kiocb(iocb)) {
			res = fuse_direct_IO(iocb, from);
		} else {
			struct fuse_io_priv io = FUSE_IO_PRIV_SYNC(iocb);

			res = fuse_direct_io(&io, from, &iocb->ki_pos,
					     FUSE_DIO_WRITE);
			fuse_write_update_attr(inode, iocb->ki_pos, res);
		}
		if (res > 0 && mapping->nrpages) {
			/*
			 * As in generic_file_direct_write(), invalidate after
			 * write, to invalidate read-ahead cache that may have
			 * with the write.
			 */
			invalidate_inode_pages2_range(mapping,
				pos >> PAGE_SHIFT,
				(pos + res - 1) >> PAGE_SHIFT);
		}
	}
	fuse_dio_unlock(iocb, exclusive);

	return res;
}

static ssize_t fuse_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
{
	struct file *file = iocb->ki_filp;
	struct fuse_file *ff = file->private_data;
	struct inode *inode = file_inode(file);

	if (fuse_is_bad(inode))
		return -EIO;

	if (FUSE_IS_DAX(inode))
		return fuse_dax_read_iter(iocb, to);

	/* FOPEN_DIRECT_IO overrides FOPEN_PASSTHROUGH */
	if (ff->open_flags & FOPEN_DIRECT_IO)
		return fuse_direct_read_iter(iocb, to);
	else if (fuse_file_passthrough(ff))
		return fuse_passthrough_read_iter(iocb, to);
	else
		return fuse_cache_read_iter(iocb, to);
}

static ssize_t fuse_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
{
	struct file *file = iocb->ki_filp;
	struct fuse_file *ff = file->private_data;
	struct inode *inode = file_inode(file);

	if (fuse_is_bad(inode))
		return -EIO;

	if (FUSE_IS_DAX(inode))
		return fuse_dax_write_iter(iocb, from);

	/* FOPEN_DIRECT_IO overrides FOPEN_PASSTHROUGH */
	if (ff->open_flags & FOPEN_DIRECT_IO)
		return fuse_direct_write_iter(iocb, from);
	else if (fuse_file_passthrough(ff))
		return fuse_passthrough_write_iter(iocb, from);
	else
		return fuse_cache_write_iter(iocb, from);
}

static ssize_t fuse_splice_read(struct file *in, loff_t *ppos,
				struct pipe_inode_info *pipe, size_t len,
				unsigned int flags)
{
	struct fuse_file *ff = in->private_data;

	/* FOPEN_DIRECT_IO overrides FOPEN_PASSTHROUGH */
	if (fuse_file_passthrough(ff) && !(ff->open_flags & FOPEN_DIRECT_IO))
		return fuse_passthrough_splice_read(in, ppos, pipe, len, flags);
	else
		return filemap_splice_read(in, ppos, pipe, len, flags);
}

static ssize_t fuse_splice_write(struct pipe_inode_info *pipe, struct file *out,
				 loff_t *ppos, size_t len, unsigned int flags)
{
	struct fuse_file *ff = out->private_data;

	/* FOPEN_DIRECT_IO overrides FOPEN_PASSTHROUGH */
	if (fuse_file_passthrough(ff) && !(ff->open_flags & FOPEN_DIRECT_IO))
		return fuse_passthrough_splice_write(pipe, out, ppos, len, flags);
	else
		return iter_file_splice_write(pipe, out, ppos, len, flags);
}

static void fuse_writepage_free(struct fuse_writepage_args *wpa)
{
	struct fuse_args_pages *ap = &wpa->ia.ap;

	if (wpa->bucket)
		fuse_sync_bucket_dec(wpa->bucket);

	fuse_file_put(wpa->ia.ff, false);

	kfree(ap->folios);
	kfree(wpa);
}

static void fuse_writepage_finish(struct fuse_writepage_args *wpa)
{
	struct fuse_args_pages *ap = &wpa->ia.ap;
	struct inode *inode = wpa->inode;
	struct fuse_inode *fi = get_fuse_inode(inode);
	int i;

	for (i = 0; i < ap->num_folios; i++)
		/*
		 * Benchmarks showed that ending writeback within the
		 * scope of the fi->lock alleviates xarray lock
		 * contention and noticeably improves performance.
		 */
		iomap_finish_folio_write(inode, ap->folios[i],
					 ap->descs[i].length);

	wake_up(&fi->page_waitq);
}

/* Called under fi->lock, may release and reacquire it */
static void fuse_send_writepage(struct fuse_mount *fm,
				struct fuse_writepage_args *wpa, loff_t size)
__releases(fi->lock)
__acquires(fi->lock)
{
	struct fuse_inode *fi = get_fuse_inode(wpa->inode);
	struct fuse_args_pages *ap = &wpa->ia.ap;
	struct fuse_write_in *inarg = &wpa->ia.write.in;
	struct fuse_args *args = &ap->args;
	__u64 data_size = 0;
	int err, i;

	for (i = 0; i < ap->num_folios; i++)
		data_size += ap->descs[i].length;

	fi->writectr++;
	if (inarg->offset + data_size <= size) {
		inarg->size = data_size;
	} else if (inarg->offset < size) {
		inarg->size = size - inarg->offset;
	} else {
		/* Got truncated off completely */
		goto out_free;
	}

	args->in_args[1].size = inarg->size;
	args->force = true;
	args->nocreds = true;

	err = fuse_simple_background(fm, args, GFP_ATOMIC);
	if (err == -ENOMEM) {
		spin_unlock(&fi->lock);
		err = fuse_simple_background(fm, args, GFP_NOFS | __GFP_NOFAIL);
		spin_lock(&fi->lock);
	}

	/* Fails on broken connection only */
	if (unlikely(err))
		goto out_free;

	return;

 out_free:
	fi->writectr--;
	fuse_writepage_finish(wpa);
	spin_unlock(&fi->lock);
	fuse_writepage_free(wpa);
	spin_lock(&fi->lock);
}

/*
 * If fi->writectr is positive (no truncate or fsync going on) send
 * all queued writepage requests.
 *
 * Called with fi->lock
 */
void fuse_flush_writepages(struct inode *inode)
__releases(fi->lock)
__acquires(fi->lock)
{
	struct fuse_mount *fm = get_fuse_mount(inode);
	struct fuse_inode *fi = get_fuse_inode(inode);
	loff_t crop = i_size_read(inode);
	struct fuse_writepage_args *wpa;

	while (fi->writectr >= 0 && !list_empty(&fi->queued_writes)) {
		wpa = list_entry(fi->queued_writes.next,
				 struct fuse_writepage_args, queue_entry);
		list_del_init(&wpa->queue_entry);
		fuse_send_writepage(fm, wpa, crop);
	}
}

static void fuse_writepage_end(struct fuse_args *args, int error)
{
	struct fuse_writepage_args *wpa =
		container_of(args, typeof(*wpa), ia.ap.args);
	struct inode *inode = wpa->inode;
	struct fuse_inode *fi = get_fuse_inode(inode);
	struct fuse_conn *fc = get_fuse_conn(inode);

	mapping_set_error(inode->i_mapping, error);
	/*
	 * A writeback finished and this might have updated mtime/ctime on
	 * server making local mtime/ctime stale.  Hence invalidate attrs.
	 * Do this only if writeback_cache is not enabled.  If writeback_cache
	 * is enabled, we trust local ctime/mtime.
	 */
	if (!fc->writeback_cache)
		fuse_invalidate_attr_mask(inode, FUSE_STATX_MODIFY);
	spin_lock(&fi->lock);
	fi->writectr--;
	fuse_writepage_finish(wpa);
	spin_unlock(&fi->lock);
	fuse_writepage_free(wpa);
}

static struct fuse_file *__fuse_write_file_get(struct fuse_inode *fi)
{
	struct fuse_file *ff;

	spin_lock(&fi->lock);
	ff = list_first_entry_or_null(&fi->write_files, struct fuse_file,
				      write_entry);
	if (ff)
		fuse_file_get(ff);
	spin_unlock(&fi->lock);

	return ff;
}

static struct fuse_file *fuse_write_file_get(struct fuse_inode *fi)
{
	struct fuse_file *ff = __fuse_write_file_get(fi);
	WARN_ON(!ff);
	return ff;
}

int fuse_write_inode(struct inode *inode, struct writeback_control *wbc)
{
	struct fuse_inode *fi = get_fuse_inode(inode);
	struct fuse_file *ff;
	int err;

	ff = __fuse_write_file_get(fi);
	err = fuse_flush_times(inode, ff);
	if (ff)
		fuse_file_put(ff, false);

	return err;
}

static struct fuse_writepage_args *fuse_writepage_args_alloc(void)
{
	struct fuse_writepage_args *wpa;
	struct fuse_args_pages *ap;

	wpa = kzalloc_obj(*wpa, GFP_NOFS);
	if (wpa) {
		ap = &wpa->ia.ap;
		ap->num_folios = 0;
		ap->folios = fuse_folios_alloc(1, GFP_NOFS, &ap->descs);
		if (!ap->folios) {
			kfree(wpa);
			wpa = NULL;
		}
	}
	return wpa;

}

static void fuse_writepage_add_to_bucket(struct fuse_conn *fc,
					 struct fuse_writepage_args *wpa)
{
	if (!fc->sync_fs)
		return;

	rcu_read_lock();
	/* Prevent resurrection of dead bucket in unlikely race with syncfs */
	do {
		wpa->bucket = rcu_dereference(fc->curr_bucket);
	} while (unlikely(!atomic_inc_not_zero(&wpa->bucket->count)));
	rcu_read_unlock();
}

static void fuse_writepage_args_page_fill(struct fuse_writepage_args *wpa, struct folio *folio,
					  uint32_t folio_index, loff_t offset, unsigned len)
{
	struct fuse_args_pages *ap = &wpa->ia.ap;

	ap->folios[folio_index] = folio;
	ap->descs[folio_index].offset = offset;
	ap->descs[folio_index].length = len;
}

static struct fuse_writepage_args *fuse_writepage_args_setup(struct folio *folio,
							     size_t offset,
							     struct fuse_file *ff)
{
	struct inode *inode = folio->mapping->host;
	struct fuse_conn *fc = get_fuse_conn(inode);
	struct fuse_writepage_args *wpa;
	struct fuse_args_pages *ap;

	wpa = fuse_writepage_args_alloc();
	if (!wpa)
		return NULL;

	fuse_writepage_add_to_bucket(fc, wpa);
	fuse_write_args_fill(&wpa->ia, ff, folio_pos(folio) + offset, 0);
	wpa->ia.write.in.write_flags |= FUSE_WRITE_CACHE;
	wpa->inode = inode;
	wpa->ia.ff = ff;

	ap = &wpa->ia.ap;
	ap->args.in_pages = true;
	ap->args.end = fuse_writepage_end;

	return wpa;
}

struct fuse_fill_wb_data {
	struct fuse_writepage_args *wpa;
	struct fuse_file *ff;
	unsigned int max_folios;
	/*
	 * nr_bytes won't overflow since fuse_folios_need_send() caps
	 * wb requests to never exceed fc->max_pages (which has an upper bound
	 * of U16_MAX).
	 */
	unsigned int nr_bytes;
};

static bool fuse_pages_realloc(struct fuse_fill_wb_data *data,
			       unsigned int max_pages)
{
	struct fuse_args_pages *ap = &data->wpa->ia.ap;
	struct folio **folios;
	struct fuse_folio_desc *descs;
	unsigned int nfolios = min_t(unsigned int,
				     max_t(unsigned int, data->max_folios * 2,
					   FUSE_DEFAULT_MAX_PAGES_PER_REQ),
				    max_pages);
	WARN_ON(nfolios <= data->max_folios);

	folios = fuse_folios_alloc(nfolios, GFP_NOFS, &descs);
	if (!folios)
		return false;

	memcpy(folios, ap->folios, sizeof(struct folio *) * ap->num_folios);
	memcpy(descs, ap->descs, sizeof(struct fuse_folio_desc) * ap->num_folios);
	kfree(ap->folios);
	ap->folios = folios;
	ap->descs = descs;
	data->max_folios = nfolios;

	return true;
}

static void fuse_writepages_send(struct inode *inode,
				 struct fuse_fill_wb_data *data)
{
	struct fuse_writepage_args *wpa = data->wpa;
	struct fuse_inode *fi = get_fuse_inode(inode);

	spin_lock(&fi->lock);
	list_add_tail(&wpa->queue_entry, &fi->queued_writes);
	fuse_flush_writepages(inode);
	spin_unlock(&fi->lock);
}

static bool fuse_folios_need_send(struct fuse_conn *fc, loff_t pos,
				  unsigned len, struct fuse_args_pages *ap,
				  unsigned cur_bytes, bool write)
{
	struct folio *prev_folio;
	struct fuse_folio_desc prev_desc;
	unsigned bytes = cur_bytes + len;
	loff_t prev_pos;
	size_t max_bytes = write ? fc->max_write : fc->max_read;

	WARN_ON(!ap->num_folios);

	/* Reached max pages or max folio slots */
	if (ap->num_folios >= fc->max_pages)
		return true;

	if (DIV_ROUND_UP(bytes, PAGE_SIZE) > fc->max_pages)
		return true;

	if (bytes > max_bytes)
		return true;

	/* Discontinuity */
	prev_folio = ap->folios[ap->num_folios - 1];
	prev_desc = ap->descs[ap->num_folios - 1];
	prev_pos = folio_pos(prev_folio) + prev_desc.offset + prev_desc.length;
	if (prev_pos != pos)
		return true;

	return false;
}

static ssize_t fuse_iomap_writeback_range(struct iomap_writepage_ctx *wpc,
					  struct folio *folio, u64 pos,
					  unsigned len, u64 end_pos)
{
	struct fuse_fill_wb_data *data = wpc->wb_ctx;
	struct fuse_writepage_args *wpa = data->wpa;
	struct fuse_args_pages *ap = &wpa->ia.ap;
	struct inode *inode = wpc->inode;
	struct fuse_inode *fi = get_fuse_inode(inode);
	struct fuse_conn *fc = get_fuse_conn(inode);
	loff_t offset = offset_in_folio(folio, pos);

	WARN_ON_ONCE(!data);

	if (!data->ff) {
		data->ff = fuse_write_file_get(fi);
		if (!data->ff)
			return -EIO;
	}

	if (wpa) {
		bool send = fuse_folios_need_send(fc, pos, len, ap,
						  data->nr_bytes, true);

		if (!send) {
			/*
			 * Need to grow the pages array?  If so, did the
			 * expansion fail?
			 */
			send = (ap->num_folios == data->max_folios) &&
				!fuse_pages_realloc(data, fc->max_pages);
		}

		if (send) {
			fuse_writepages_send(inode, data);
			data->wpa = NULL;
			data->nr_bytes = 0;
		}
	}

	if (data->wpa == NULL) {
		wpa = fuse_writepage_args_setup(folio, offset, data->ff);
		if (!wpa)
			return -ENOMEM;
		fuse_file_get(wpa->ia.ff);
		data->max_folios = 1;
		ap = &wpa->ia.ap;
	}

	fuse_writepage_args_page_fill(wpa, folio, ap->num_folios,
				      offset, len);
	data->nr_bytes += len;

	ap->num_folios++;
	if (!data->wpa)
		data->wpa = wpa;

	return len;
}

static int fuse_iomap_writeback_submit(struct iomap_writepage_ctx *wpc,
				       int error)
{
	struct fuse_fill_wb_data *data = wpc->wb_ctx;

	WARN_ON_ONCE(!data);

	if (data->wpa) {
		WARN_ON(!data->wpa->ia.ap.num_folios);
		fuse_writepages_send(wpc->inode, data);
	}

	if (data->ff)
		fuse_file_put(data->ff, false);

	return error;
}

static const struct iomap_writeback_ops fuse_writeback_ops = {
	.writeback_range	= fuse_iomap_writeback_range,
	.writeback_submit	= fuse_iomap_writeback_submit,
};

static int fuse_writepages(struct address_space *mapping,
			   struct writeback_control *wbc)
{
	struct inode *inode = mapping->host;
	struct fuse_conn *fc = get_fuse_conn(inode);
	struct fuse_fill_wb_data data = {};
	struct iomap_writepage_ctx wpc = {
		.inode = inode,
		.iomap.type = IOMAP_MAPPED,
		.wbc = wbc,
		.ops = &fuse_writeback_ops,
		.wb_ctx	= &data,
	};

	if (fuse_is_bad(inode))
		return -EIO;

	if (wbc->sync_mode == WB_SYNC_NONE &&
	    fuse_chan_num_background(fc->chan) >= fc->congestion_threshold)
		return 0;

	return iomap_writepages(&wpc);
}

static int fuse_launder_folio(struct folio *folio)
{
	int err = 0;
	struct fuse_fill_wb_data data = {};
	struct iomap_writepage_ctx wpc = {
		.inode = folio->mapping->host,
		.iomap.type = IOMAP_MAPPED,
		.ops = &fuse_writeback_ops,
		.wb_ctx	= &data,
	};

	if (folio_clear_dirty_for_io(folio)) {
		err = iomap_writeback_folio(&wpc, folio);
		err = fuse_iomap_writeback_submit(&wpc, err);
		if (!err)
			folio_wait_writeback(folio);
	}
	return err;
}

/*
 * Write back dirty data/metadata now (there may not be any suitable
 * open files later for data)
 */
static void fuse_vma_close(struct vm_area_struct *vma)
{
	int err;

	err = write_inode_now(vma->vm_file->f_mapping->host, 1);
	mapping_set_error(vma->vm_file->f_mapping, err);
}

/*
 * Wait for writeback against this page to complete before allowing it
 * to be marked dirty again, and hence written back again, possibly
 * before the previous writepage completed.
 *
 * Block here, instead of in ->writepage(), so that the userspace fs
 * can only block processes actually operating on the filesystem.
 *
 * Otherwise unprivileged userspace fs would be able to block
 * unrelated:
 *
 * - page migration
 * - sync(2)
 * - try_to_free_pages() with order > PAGE_ALLOC_COSTLY_ORDER
 */
static vm_fault_t fuse_page_mkwrite(struct vm_fault *vmf)
{
	struct folio *folio = page_folio(vmf->page);
	struct inode *inode = file_inode(vmf->vma->vm_file);

	file_update_time(vmf->vma->vm_file);
	folio_lock(folio);
	if (folio->mapping != inode->i_mapping) {
		folio_unlock(folio);
		return VM_FAULT_NOPAGE;
	}

	folio_wait_writeback(folio);
	return VM_FAULT_LOCKED;
}

static const struct vm_operations_struct fuse_file_vm_ops = {
	.close		= fuse_vma_close,
	.fault		= filemap_fault,
	.map_pages	= filemap_map_pages,
	.page_mkwrite	= fuse_page_mkwrite,
};

static int fuse_file_mmap(struct file *file, struct vm_area_struct *vma)
{
	struct fuse_file *ff = file->private_data;
	struct fuse_conn *fc = ff->fm->fc;
	struct inode *inode = file_inode(file);
	int rc;

	/* DAX mmap is superior to direct_io mmap */
	if (FUSE_IS_DAX(inode))
		return fuse_dax_mmap(file, vma);

	/*
	 * If inode is in passthrough io mode, because it has some file open
	 * in passthrough mode, either mmap to backing file or fail mmap,
	 * because mixing cached mmap and passthrough io mode is not allowed.
	 */
	if (fuse_file_passthrough(ff))
		return fuse_passthrough_mmap(file, vma);
	else if (fuse_inode_backing(get_fuse_inode(inode)))
		return -ENODEV;

	/*
	 * FOPEN_DIRECT_IO handling is special compared to O_DIRECT,
	 * as does not allow MAP_SHARED mmap without FUSE_DIRECT_IO_ALLOW_MMAP.
	 */
	if (ff->open_flags & FOPEN_DIRECT_IO) {
		/*
		 * Can't provide the coherency needed for MAP_SHARED
		 * if FUSE_DIRECT_IO_ALLOW_MMAP isn't set.
		 */
		if ((vma->vm_flags & VM_MAYSHARE) && !fc->direct_io_allow_mmap)
			return -ENODEV;

		invalidate_inode_pages2(file->f_mapping);

		if (!(vma->vm_flags & VM_MAYSHARE)) {
			/* MAP_PRIVATE */
			return generic_file_mmap(file, vma);
		}

		/*
		 * First mmap of direct_io file enters caching inode io mode.
		 * Also waits for parallel dio writers to go into serial mode
		 * (exclusive instead of shared lock).
		 * After first mmap, the inode stays in caching io mode until
		 * the direct_io file release.
		 */
		rc = fuse_file_cached_io_open(inode, ff);
		if (rc)
			return rc;
	}

	if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_MAYWRITE))
		fuse_link_write_file(file);

	file_accessed(file);
	vma->vm_ops = &fuse_file_vm_ops;
	return 0;
}

static int convert_fuse_file_lock(struct fuse_conn *fc,
				  const struct fuse_file_lock *ffl,
				  struct file_lock *fl)
{
	switch (ffl->type) {
	case F_UNLCK:
		break;

	case F_RDLCK:
	case F_WRLCK:
		if (ffl->start > OFFSET_MAX || ffl->end > OFFSET_MAX ||
		    ffl->end < ffl->start)
			return -EIO;

		fl->fl_start = ffl->start;
		fl->fl_end = ffl->end;

		/*
		 * Convert pid into init's pid namespace.  The locks API will
		 * translate it into the caller's pid namespace.
		 */
		rcu_read_lock();
		fl->c.flc_pid = pid_nr_ns(find_pid_ns(ffl->pid, fc->pid_ns), &init_pid_ns);
		rcu_read_unlock();
		break;

	default:
		return -EIO;
	}
	fl->c.flc_type = ffl->type;
	return 0;
}

static void fuse_lk_fill(struct fuse_args *args, struct file *file,
			 const struct file_lock *fl, int opcode, pid_t pid,
			 int flock, struct fuse_lk_in *inarg)
{
	struct inode *inode = file_inode(file);
	struct fuse_conn *fc = get_fuse_conn(inode);
	struct fuse_file *ff = file->private_data;

	memset(inarg, 0, sizeof(*inarg));
	inarg->fh = ff->fh;
	inarg->owner = fuse_lock_owner_id(fc, fl->c.flc_owner);
	inarg->lk.start = fl->fl_start;
	inarg->lk.end = fl->fl_end;
	inarg->lk.type = fl->c.flc_type;
	inarg->lk.pid = pid;
	if (flock)
		inarg->lk_flags |= FUSE_LK_FLOCK;
	args->opcode = opcode;
	args->nodeid = get_node_id(inode);
	args->in_numargs = 1;
	args->in_args[0].size = sizeof(*inarg);
	args->in_args[0].value = inarg;
}

static int fuse_getlk(struct file *file, struct file_lock *fl)
{
	struct inode *inode = file_inode(file);
	struct fuse_mount *fm = get_fuse_mount(inode);
	FUSE_ARGS(args);
	struct fuse_lk_in inarg;
	struct fuse_lk_out outarg;
	int err;

	fuse_lk_fill(&args, file, fl, FUSE_GETLK, 0, 0, &inarg);
	args.out_numargs = 1;
	args.out_args[0].size = sizeof(outarg);
	args.out_args[0].value = &outarg;
	err = fuse_simple_request(fm, &args);
	if (!err)
		err = convert_fuse_file_lock(fm->fc, &outarg.lk, fl);

	return err;
}

static int fuse_setlk(struct file *file, struct file_lock *fl, int flock)
{
	struct inode *inode = file_inode(file);
	struct fuse_mount *fm = get_fuse_mount(inode);
	FUSE_ARGS(args);
	struct fuse_lk_in inarg;
	int opcode = (fl->c.flc_flags & FL_SLEEP) ? FUSE_SETLKW : FUSE_SETLK;
	struct pid *pid = fl->c.flc_type != F_UNLCK ? task_tgid(current) : NULL;
	pid_t pid_nr = pid_nr_ns(pid, fm->fc->pid_ns);
	int err;

	if (fl->fl_lmops && fl->fl_lmops->lm_grant) {
		/* NLM needs asynchronous locks, which we don't support yet */
		return -ENOLCK;
	}

	fuse_lk_fill(&args, file, fl, opcode, pid_nr, flock, &inarg);
	err = fuse_simple_request(fm, &args);

	/* locking is restartable */
	if (err == -EINTR)
		err = -ERESTARTSYS;

	return err;
}

static int fuse_file_lock(struct file *file, int cmd, struct file_lock *fl)
{
	struct inode *inode = file_inode(file);
	struct fuse_conn *fc = get_fuse_conn(inode);
	int err;

	if (cmd == F_CANCELLK) {
		err = 0;
	} else if (cmd == F_GETLK) {
		if (fc->no_lock) {
			posix_test_lock(file, fl);
			err = 0;
		} else
			err = fuse_getlk(file, fl);
	} else {
		if (fc->no_lock)
			err = posix_lock_file(file, fl, NULL);
		else
			err = fuse_setlk(file, fl, 0);
	}
	return err;
}

static int fuse_file_flock(struct file *file, int cmd, struct file_lock *fl)
{
	struct inode *inode = file_inode(file);
	struct fuse_conn *fc = get_fuse_conn(inode);
	int err;

	if (fc->no_flock) {
		err = locks_lock_file_wait(file, fl);
	} else {
		struct fuse_file *ff = file->private_data;

		/* emulate flock with POSIX locks */
		err = fuse_setlk(file, fl, 1);
		if (!err)
			ff->flock = true;
	}

	return err;
}

static sector_t fuse_bmap(struct address_space *mapping, sector_t block)
{
	struct inode *inode = mapping->host;
	struct fuse_mount *fm = get_fuse_mount(inode);
	FUSE_ARGS(args);
	struct fuse_bmap_in inarg;
	struct fuse_bmap_out outarg;
	int err;

	if (!inode->i_sb->s_bdev || fm->fc->no_bmap)
		return 0;

	memset(&inarg, 0, sizeof(inarg));
	inarg.block = block;
	inarg.blocksize = inode->i_sb->s_blocksize;
	args.opcode = FUSE_BMAP;
	args.nodeid = get_node_id(inode);
	args.in_numargs = 1;
	args.in_args[0].size = sizeof(inarg);
	args.in_args[0].value = &inarg;
	args.out_numargs = 1;
	args.out_args[0].size = sizeof(outarg);
	args.out_args[0].value = &outarg;
	err = fuse_simple_request(fm, &args);
	if (err == -ENOSYS)
		fm->fc->no_bmap = 1;

	return err ? 0 : outarg.block;
}

static loff_t fuse_lseek(struct file *file, loff_t offset, int whence)
{
	struct inode *inode = file->f_mapping->host;
	struct fuse_mount *fm = get_fuse_mount(inode);
	struct fuse_file *ff = file->private_data;
	FUSE_ARGS(args);
	struct fuse_lseek_in inarg = {
		.fh = ff->fh,
		.offset = offset,
		.whence = whence
	};
	struct fuse_lseek_out outarg;
	int err;

	if (fm->fc->no_lseek)
		goto fallback;

	args.opcode = FUSE_LSEEK;
	args.nodeid = ff->nodeid;
	args.in_numargs = 1;
	args.in_args[0].size = sizeof(inarg);
	args.in_args[0].value = &inarg;
	args.out_numargs = 1;
	args.out_args[0].size = sizeof(outarg);
	args.out_args[0].value = &outarg;
	err = fuse_simple_request(fm, &args);
	if (err) {
		if (err == -ENOSYS) {
			fm->fc->no_lseek = 1;
			goto fallback;
		}
		return err;
	}

	return vfs_setpos(file, outarg.offset, inode->i_sb->s_maxbytes);

fallback:
	err = fuse_update_attributes(inode, file, STATX_SIZE);
	if (!err)
		return generic_file_llseek(file, offset, whence);
	else
		return err;
}

static loff_t fuse_file_llseek(struct file *file, loff_t offset, int whence)
{
	loff_t retval;
	struct inode *inode = file_inode(file);

	switch (whence) {
	case SEEK_SET:
	case SEEK_CUR:
		 /* No i_mutex protection necessary for SEEK_CUR and SEEK_SET */
		retval = generic_file_llseek(file, offset, whence);
		break;
	case SEEK_END:
		inode_lock(inode);
		retval = fuse_update_attributes(inode, file, STATX_SIZE);
		if (!retval)
			retval = generic_file_llseek(file, offset, whence);
		inode_unlock(inode);
		break;
	case SEEK_HOLE:
	case SEEK_DATA:
		inode_lock(inode);
		retval = fuse_lseek(file, offset, whence);
		inode_unlock(inode);
		break;
	default:
		retval = -EINVAL;
	}

	return retval;
}

static void fuse_do_truncate(struct file *file)
{
	struct inode *inode = file->f_mapping->host;
	struct iattr attr;

	attr.ia_valid = ATTR_SIZE;
	attr.ia_size = i_size_read(inode);

	attr.ia_file = file;
	attr.ia_valid |= ATTR_FILE;

	fuse_do_setattr(file_mnt_idmap(file), file_dentry(file), &attr, file);
}

static inline loff_t fuse_round_up(struct fuse_conn *fc, loff_t off)
{
	return round_up(off, fc->max_pages << PAGE_SHIFT);
}

static ssize_t
fuse_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
{
	DECLARE_COMPLETION_ONSTACK(wait);
	ssize_t ret = 0;
	struct file *file = iocb->ki_filp;
	struct fuse_file *ff = file->private_data;
	loff_t pos = 0;
	struct inode *inode;
	loff_t i_size;
	size_t count = iov_iter_count(iter), shortened = 0;
	loff_t offset = iocb->ki_pos;
	struct fuse_io_priv *io;
	bool async = ff->fm->fc->async_dio;

	pos = offset;
	inode = file->f_mapping->host;
	i_size = i_size_read(inode);

	if ((iov_iter_rw(iter) == READ) && (offset >= i_size))
		return 0;

	if ((iov_iter_rw(iter) == WRITE) && async && !inode->i_sb->s_dio_done_wq) {
		ret = sb_init_dio_done_wq(inode->i_sb);
		if (ret < 0)
			return ret;
	}

	io = kmalloc_obj(struct fuse_io_priv);
	if (!io)
		return -ENOMEM;
	spin_lock_init(&io->lock);
	kref_init(&io->refcnt);
	io->reqs = 1;
	io->bytes = -1;
	io->size = 0;
	io->offset = offset;
	io->write = (iov_iter_rw(iter) == WRITE);
	io->err = 0;
	/*
	 * By default, we want to optimize all I/Os with async request
	 * submission to the client filesystem if supported.
	 */
	io->async = async;
	io->iocb = iocb;
	io->blocking = is_sync_kiocb(iocb);

	/* optimization for short read */
	if (io->async && !io->write && offset + count > i_size) {
		iov_iter_truncate(iter, fuse_round_up(ff->fm->fc, i_size - offset));
		shortened = count - iov_iter_count(iter);
		count -= shortened;
	}

	/*
	 * We cannot asynchronously extend the size of a file.
	 * In such case the aio will behave exactly like sync io.
	 */
	if ((offset + count > i_size) && io->write)
		io->blocking = true;

	if (io->async && io->blocking) {
		/*
		 * Additional reference to keep io around after
		 * calling fuse_aio_complete()
		 */
		kref_get(&io->refcnt);
		io->done = &wait;
	}

	if (iov_iter_rw(iter) == WRITE) {
		ret = fuse_direct_io(io, iter, &pos, FUSE_DIO_WRITE);
		fuse_invalidate_attr_mask(inode, FUSE_STATX_MODSIZE);
	} else {
		ret = __fuse_direct_read(io, iter, &pos);
	}
	iov_iter_reexpand(iter, iov_iter_count(iter) + shortened);

	if (io->async) {
		bool blocking = io->blocking;

		fuse_aio_complete(io, ret < 0 ? ret : 0, -1);

		/* we have a non-extending, async request, so return */
		if (!blocking)
			return -EIOCBQUEUED;

		wait_for_completion(&wait);
		ret = fuse_get_res_by_io(io);
	}

	kref_put(&io->refcnt, fuse_io_release);

	if (iov_iter_rw(iter) == WRITE) {
		fuse_write_update_attr(inode, pos, ret);
		/* For extending writes we already hold exclusive lock */
		if (ret < 0 && offset + count > i_size)
			fuse_do_truncate(file);
	}

	return ret;
}

static int fuse_writeback_range(struct inode *inode, loff_t start, loff_t end)
{
	int err = filemap_write_and_wait_range(inode->i_mapping, start, LLONG_MAX);

	if (!err)
		fuse_sync_writes(inode);

	return err;
}

static long fuse_file_fallocate(struct file *file, int mode, loff_t offset,
				loff_t length)
{
	struct fuse_file *ff = file->private_data;
	struct inode *inode = file_inode(file);
	struct fuse_inode *fi = get_fuse_inode(inode);
	struct fuse_mount *fm = ff->fm;
	FUSE_ARGS(args);
	struct fuse_fallocate_in inarg = {
		.fh = ff->fh,
		.offset = offset,
		.length = length,
		.mode = mode
	};
	int err;
	bool block_faults = FUSE_IS_DAX(inode) &&
		(!(mode & FALLOC_FL_KEEP_SIZE) ||
		 (mode & (FALLOC_FL_PUNCH_HOLE | FALLOC_FL_ZERO_RANGE)));

	if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE |
		     FALLOC_FL_ZERO_RANGE))
		return -EOPNOTSUPP;

	if (fm->fc->no_fallocate)
		return -EOPNOTSUPP;

	inode_lock(inode);
	if (block_faults) {
		filemap_invalidate_lock(inode->i_mapping);
		err = fuse_dax_break_layouts(inode, 0, -1);
		if (err)
			goto out;
	}

	if (mode & (FALLOC_FL_PUNCH_HOLE | FALLOC_FL_ZERO_RANGE)) {
		loff_t endbyte = offset + length - 1;

		err = fuse_writeback_range(inode, offset, endbyte);
		if (err)
			goto out;
	}

	if (!(mode & FALLOC_FL_KEEP_SIZE) &&
	    offset + length > i_size_read(inode)) {
		err = inode_newsize_ok(inode, offset + length);
		if (err)
			goto out;
	}

	err = file_modified(file);
	if (err)
		goto out;

	if (!(mode & FALLOC_FL_KEEP_SIZE))
		set_bit(FUSE_I_SIZE_UNSTABLE, &fi->state);

	args.opcode = FUSE_FALLOCATE;
	args.nodeid = ff->nodeid;
	args.in_numargs = 1;
	args.in_args[0].size = sizeof(inarg);
	args.in_args[0].value = &inarg;
	err = fuse_simple_request(fm, &args);
	if (err == -ENOSYS) {
		fm->fc->no_fallocate = 1;
		err = -EOPNOTSUPP;
	}
	if (err)
		goto out;

	/* we could have extended the file */
	if (!(mode & FALLOC_FL_KEEP_SIZE)) {
		if (fuse_write_update_attr(inode, offset + length, length))
			file_update_time(file);
	}

	if (mode & (FALLOC_FL_PUNCH_HOLE | FALLOC_FL_ZERO_RANGE))
		truncate_pagecache_range(inode, offset, offset + length - 1);

	fuse_invalidate_attr_mask(inode, FUSE_STATX_MODSIZE);

out:
	if (!(mode & FALLOC_FL_KEEP_SIZE))
		clear_bit(FUSE_I_SIZE_UNSTABLE, &fi->state);

	if (block_faults)
		filemap_invalidate_unlock(inode->i_mapping);

	inode_unlock(inode);

	fuse_flush_time_update(inode);

	return err;
}

static ssize_t __fuse_copy_file_range(struct file *file_in, loff_t pos_in,
				      struct file *file_out, loff_t pos_out,
				      size_t len, unsigned int flags)
{
	struct fuse_file *ff_in = file_in->private_data;
	struct fuse_file *ff_out = file_out->private_data;
	struct inode *inode_in = file_inode(file_in);
	struct inode *inode_out = file_inode(file_out);
	struct fuse_inode *fi_out = get_fuse_inode(inode_out);
	struct fuse_mount *fm = ff_in->fm;
	struct fuse_conn *fc = fm->fc;
	FUSE_ARGS(args);
	struct fuse_copy_file_range_in inarg = {
		.fh_in = ff_in->fh,
		.off_in = pos_in,
		.nodeid_out = ff_out->nodeid,
		.fh_out = ff_out->fh,
		.off_out = pos_out,
		.len = len,
		.flags = flags
	};
	struct fuse_write_out outarg;
	struct fuse_copy_file_range_out outarg_64;
	u64 bytes_copied;
	ssize_t err;
	/* mark unstable when write-back is not used, and file_out gets
	 * extended */
	bool is_unstable = (!fc->writeback_cache) &&
			   ((pos_out + len) > inode_out->i_size);

	if (fc->no_copy_file_range)
		return -EOPNOTSUPP;

	if (file_inode(file_in)->i_sb != file_inode(file_out)->i_sb)
		return -EXDEV;

	inode_lock(inode_in);
	err = fuse_writeback_range(inode_in, pos_in, pos_in + len - 1);
	inode_unlock(inode_in);
	if (err)
		return err;

	inode_lock(inode_out);

	err = file_modified(file_out);
	if (err)
		goto out;

	/*
	 * Write out dirty pages in the destination file before sending the COPY
	 * request to userspace.  After the request is completed, truncate off
	 * pages (including partial ones) from the cache that have been copied,
	 * since these contain stale data at that point.
	 *
	 * This should be mostly correct, but if the COPY writes to partial
	 * pages (at the start or end) and the parts not covered by the COPY are
	 * written through a memory map after calling fuse_writeback_range(),
	 * then these partial page modifications will be lost on truncation.
	 *
	 * It is unlikely that someone would rely on such mixed style
	 * modifications.  Yet this does give less guarantees than if the
	 * copying was performed with write(2).
	 *
	 * To fix this a mapping->invalidate_lock could be used to prevent new
	 * faults while the copy is ongoing.
	 */
	err = fuse_writeback_range(inode_out, pos_out, pos_out + len - 1);
	if (err)
		goto out;

	if (is_unstable)
		set_bit(FUSE_I_SIZE_UNSTABLE, &fi_out->state);

	args.opcode = FUSE_COPY_FILE_RANGE_64;
	args.nodeid = ff_in->nodeid;
	args.in_numargs = 1;
	args.in_args[0].size = sizeof(inarg);
	args.in_args[0].value = &inarg;
	args.out_numargs = 1;
	args.out_args[0].size = sizeof(outarg_64);
	args.out_args[0].value = &outarg_64;
	if (fc->no_copy_file_range_64) {
fallback:
		/* Fall back to old op that can't handle large copy length */
		args.opcode = FUSE_COPY_FILE_RANGE;
		args.out_args[0].size = sizeof(outarg);
		args.out_args[0].value = &outarg;
		inarg.len = len = min_t(size_t, len, UINT_MAX & PAGE_MASK);
	}
	err = fuse_simple_request(fm, &args);
	if (err == -ENOSYS) {
		if (fc->no_copy_file_range_64) {
			fc->no_copy_file_range = 1;
			err = -EOPNOTSUPP;
		} else {
			fc->no_copy_file_range_64 = 1;
			goto fallback;
		}
	}
	if (err)
		goto out;

	bytes_copied = fc->no_copy_file_range_64 ?
		outarg.size : outarg_64.bytes_copied;

	if (bytes_copied > len) {
		err = -EIO;
		goto out;
	}

	truncate_inode_pages_range(inode_out->i_mapping,
				   ALIGN_DOWN(pos_out, PAGE_SIZE),
				   ALIGN(pos_out + bytes_copied, PAGE_SIZE) - 1);

	file_update_time(file_out);
	fuse_write_update_attr(inode_out, pos_out + bytes_copied, bytes_copied);

	err = bytes_copied;
out:
	if (is_unstable)
		clear_bit(FUSE_I_SIZE_UNSTABLE, &fi_out->state);

	inode_unlock(inode_out);
	file_accessed(file_in);

	fuse_flush_time_update(inode_out);

	return err;
}

static ssize_t fuse_copy_file_range(struct file *src_file, loff_t src_off,
				    struct file *dst_file, loff_t dst_off,
				    size_t len, unsigned int flags)
{
	ssize_t ret;

	ret = __fuse_copy_file_range(src_file, src_off, dst_file, dst_off,
				     len, flags);

	if (ret == -EOPNOTSUPP || ret == -EXDEV)
		ret = splice_copy_file_range(src_file, src_off, dst_file,
					     dst_off, len);
	return ret;
}

static const struct file_operations fuse_file_operations = {
	.llseek		= fuse_file_llseek,
	.read_iter	= fuse_file_read_iter,
	.write_iter	= fuse_file_write_iter,
	.mmap		= fuse_file_mmap,
	.open		= fuse_open,
	.flush		= fuse_flush,
	.release	= fuse_release,
	.fsync		= fuse_fsync,
	.lock		= fuse_file_lock,
	.get_unmapped_area = thp_get_unmapped_area,
	.flock		= fuse_file_flock,
	.splice_read	= fuse_splice_read,
	.splice_write	= fuse_splice_write,
	.unlocked_ioctl	= fuse_file_ioctl,
	.compat_ioctl	= fuse_file_compat_ioctl,
	.poll		= fuse_file_poll,
	.fallocate	= fuse_file_fallocate,
	.copy_file_range = fuse_copy_file_range,
	.setlease	= generic_setlease,
};

static const struct address_space_operations fuse_file_aops  = {
	.read_folio	= fuse_read_folio,
	.readahead	= fuse_readahead,
	.writepages	= fuse_writepages,
	.launder_folio	= fuse_launder_folio,
	.dirty_folio	= iomap_dirty_folio,
	.release_folio	= iomap_release_folio,
	.invalidate_folio = iomap_invalidate_folio,
	.is_partially_uptodate = iomap_is_partially_uptodate,
	.migrate_folio	= filemap_migrate_folio,
	.bmap		= fuse_bmap,
	.direct_IO	= fuse_direct_IO,
};

void fuse_init_file_inode(struct inode *inode, unsigned int flags)
{
	struct fuse_inode *fi = get_fuse_inode(inode);
	struct fuse_conn *fc = get_fuse_conn(inode);

	inode->i_fop = &fuse_file_operations;
	inode->i_data.a_ops = &fuse_file_aops;
	if (fc->writeback_cache)
		mapping_set_writeback_may_deadlock_on_reclaim(&inode->i_data);

	INIT_LIST_HEAD(&fi->write_files);
	INIT_LIST_HEAD(&fi->queued_writes);
	fi->writectr = 0;
	fi->iocachectr = 0;
	init_waitqueue_head(&fi->page_waitq);
	init_waitqueue_head(&fi->direct_io_waitq);

	if (IS_ENABLED(CONFIG_FUSE_DAX))
		fuse_dax_inode_init(inode, flags);
}