xref: /linux/fs/xfs/xfs_fsmap.c (revision 096384deed6b873e62ac854b624f5be94f8f7357)

// SPDX-License-Identifier: GPL-2.0+
/*
 * Copyright (C) 2017 Oracle.  All Rights Reserved.
 * Author: Darrick J. Wong <darrick.wong@oracle.com>
 */
#include "xfs.h"
#include "xfs_fs.h"
#include "xfs_shared.h"
#include "xfs_format.h"
#include "xfs_log_format.h"
#include "xfs_trans_resv.h"
#include "xfs_mount.h"
#include "xfs_inode.h"
#include "xfs_trans.h"
#include "xfs_btree.h"
#include "xfs_rmap_btree.h"
#include "xfs_trace.h"
#include "xfs_rmap.h"
#include "xfs_alloc.h"
#include "xfs_bit.h"
#include <linux/fsmap.h>
#include "xfs_fsmap.h"
#include "xfs_refcount.h"
#include "xfs_refcount_btree.h"
#include "xfs_alloc_btree.h"
#include "xfs_rtbitmap.h"
#include "xfs_ag.h"
#include "xfs_rtgroup.h"
#include "xfs_rtrmap_btree.h"
#include "xfs_rtrefcount_btree.h"

/* Convert an xfs_fsmap to an fsmap. */
static void
xfs_fsmap_from_internal(
	struct fsmap		*dest,
	struct xfs_fsmap	*src)
{
	dest->fmr_device = src->fmr_device;
	dest->fmr_flags = src->fmr_flags;
	dest->fmr_physical = BBTOB(src->fmr_physical);
	dest->fmr_owner = src->fmr_owner;
	dest->fmr_offset = BBTOB(src->fmr_offset);
	dest->fmr_length = BBTOB(src->fmr_length);
	dest->fmr_reserved[0] = 0;
	dest->fmr_reserved[1] = 0;
	dest->fmr_reserved[2] = 0;
}

/* Convert an fsmap to an xfs_fsmap. */
static void
xfs_fsmap_to_internal(
	struct xfs_fsmap	*dest,
	struct fsmap		*src)
{
	dest->fmr_device = src->fmr_device;
	dest->fmr_flags = src->fmr_flags;
	dest->fmr_physical = BTOBBT(src->fmr_physical);
	dest->fmr_owner = src->fmr_owner;
	dest->fmr_offset = BTOBBT(src->fmr_offset);
	dest->fmr_length = BTOBBT(src->fmr_length);
}

/* Convert an fsmap owner into an rmapbt owner. */
static int
xfs_fsmap_owner_to_rmap(
	struct xfs_rmap_irec	*dest,
	const struct xfs_fsmap	*src)
{
	if (!(src->fmr_flags & FMR_OF_SPECIAL_OWNER)) {
		dest->rm_owner = src->fmr_owner;
		return 0;
	}

	switch (src->fmr_owner) {
	case 0:			/* "lowest owner id possible" */
	case -1ULL:		/* "highest owner id possible" */
		dest->rm_owner = src->fmr_owner;
		break;
	case XFS_FMR_OWN_FREE:
		dest->rm_owner = XFS_RMAP_OWN_NULL;
		break;
	case XFS_FMR_OWN_UNKNOWN:
		dest->rm_owner = XFS_RMAP_OWN_UNKNOWN;
		break;
	case XFS_FMR_OWN_FS:
		dest->rm_owner = XFS_RMAP_OWN_FS;
		break;
	case XFS_FMR_OWN_LOG:
		dest->rm_owner = XFS_RMAP_OWN_LOG;
		break;
	case XFS_FMR_OWN_AG:
		dest->rm_owner = XFS_RMAP_OWN_AG;
		break;
	case XFS_FMR_OWN_INOBT:
		dest->rm_owner = XFS_RMAP_OWN_INOBT;
		break;
	case XFS_FMR_OWN_INODES:
		dest->rm_owner = XFS_RMAP_OWN_INODES;
		break;
	case XFS_FMR_OWN_REFC:
		dest->rm_owner = XFS_RMAP_OWN_REFC;
		break;
	case XFS_FMR_OWN_COW:
		dest->rm_owner = XFS_RMAP_OWN_COW;
		break;
	case XFS_FMR_OWN_DEFECTIVE:	/* not implemented */
		/* fall through */
	default:
		return -EINVAL;
	}
	return 0;
}

/* Convert an rmapbt owner into an fsmap owner. */
static int
xfs_fsmap_owner_from_frec(
	struct xfs_fsmap		*dest,
	const struct xfs_fsmap_irec	*frec)
{
	dest->fmr_flags = 0;
	if (!XFS_RMAP_NON_INODE_OWNER(frec->owner)) {
		dest->fmr_owner = frec->owner;
		return 0;
	}
	dest->fmr_flags |= FMR_OF_SPECIAL_OWNER;

	switch (frec->owner) {
	case XFS_RMAP_OWN_FS:
		dest->fmr_owner = XFS_FMR_OWN_FS;
		break;
	case XFS_RMAP_OWN_LOG:
		dest->fmr_owner = XFS_FMR_OWN_LOG;
		break;
	case XFS_RMAP_OWN_AG:
		dest->fmr_owner = XFS_FMR_OWN_AG;
		break;
	case XFS_RMAP_OWN_INOBT:
		dest->fmr_owner = XFS_FMR_OWN_INOBT;
		break;
	case XFS_RMAP_OWN_INODES:
		dest->fmr_owner = XFS_FMR_OWN_INODES;
		break;
	case XFS_RMAP_OWN_REFC:
		dest->fmr_owner = XFS_FMR_OWN_REFC;
		break;
	case XFS_RMAP_OWN_COW:
		dest->fmr_owner = XFS_FMR_OWN_COW;
		break;
	case XFS_RMAP_OWN_NULL:	/* "free" */
		dest->fmr_owner = XFS_FMR_OWN_FREE;
		break;
	default:
		ASSERT(0);
		return -EFSCORRUPTED;
	}
	return 0;
}

/* getfsmap query state */
struct xfs_getfsmap_info {
	struct xfs_fsmap_head	*head;
	struct fsmap		*fsmap_recs;	/* mapping records */
	struct xfs_buf		*agf_bp;	/* AGF, for refcount queries */
	struct xfs_group	*group;		/* group info, if applicable */
	xfs_daddr_t		next_daddr;	/* next daddr we expect */
	/* daddr of low fsmap key when we're using the rtbitmap */
	xfs_daddr_t		low_daddr;
	/* daddr of high fsmap key, or the last daddr on the device */
	xfs_daddr_t		end_daddr;
	u64			missing_owner;	/* owner of holes */
	u32			dev;		/* device id */
	/*
	 * Low rmap key for the query.  If low.rm_blockcount is nonzero, this
	 * is the second (or later) call to retrieve the recordset in pieces.
	 * xfs_getfsmap_rec_before_start will compare all records retrieved
	 * by the rmapbt query to filter out any records that start before
	 * the last record.
	 */
	struct xfs_rmap_irec	low;
	struct xfs_rmap_irec	high;		/* high rmap key */
	bool			last;		/* last extent? */
};

/* Associate a device with a getfsmap handler. */
struct xfs_getfsmap_dev {
	u32			dev;
	int			(*fn)(struct xfs_trans *tp,
				      const struct xfs_fsmap *keys,
				      struct xfs_getfsmap_info *info);
	sector_t		nr_sectors;
};

/* Compare two getfsmap device handlers. */
static int
xfs_getfsmap_dev_compare(
	const void			*p1,
	const void			*p2)
{
	const struct xfs_getfsmap_dev	*d1 = p1;
	const struct xfs_getfsmap_dev	*d2 = p2;

	return d1->dev - d2->dev;
}

/* Decide if this mapping is shared. */
STATIC int
xfs_getfsmap_is_shared(
	struct xfs_trans		*tp,
	struct xfs_getfsmap_info	*info,
	const struct xfs_fsmap_irec	*frec,
	bool				*stat)
{
	struct xfs_mount		*mp = tp->t_mountp;
	struct xfs_btree_cur		*cur;
	xfs_agblock_t			fbno;
	xfs_extlen_t			flen = 0;
	int				error;

	*stat = false;
	if (!xfs_has_reflink(mp) || !info->group)
		return 0;

	if (info->group->xg_type == XG_TYPE_RTG)
		cur = xfs_rtrefcountbt_init_cursor(tp, to_rtg(info->group));
	else
		cur = xfs_refcountbt_init_cursor(mp, tp, info->agf_bp,
				to_perag(info->group));

	/* Are there any shared blocks here? */
	error = xfs_refcount_find_shared(cur, frec->rec_key,
			XFS_BB_TO_FSBT(mp, frec->len_daddr), &fbno, &flen,
			false);

	xfs_btree_del_cursor(cur, error);
	if (error)
		return error;

	*stat = flen > 0;
	return 0;
}

static inline void
xfs_getfsmap_format(
	struct xfs_mount		*mp,
	struct xfs_fsmap		*xfm,
	struct xfs_getfsmap_info	*info)
{
	struct fsmap			*rec;

	trace_xfs_getfsmap_mapping(mp, xfm);

	rec = &info->fsmap_recs[info->head->fmh_entries++];
	xfs_fsmap_from_internal(rec, xfm);
}

static inline bool
xfs_getfsmap_frec_before_start(
	struct xfs_getfsmap_info	*info,
	const struct xfs_fsmap_irec	*frec)
{
	if (info->low_daddr != XFS_BUF_DADDR_NULL)
		return frec->start_daddr < info->low_daddr;
	if (info->low.rm_blockcount) {
		struct xfs_rmap_irec	rec = {
			.rm_startblock	= frec->rec_key,
			.rm_owner	= frec->owner,
			.rm_flags	= frec->rm_flags,
		};

		return xfs_rmap_compare(&rec, &info->low) < 0;
	}

	return false;
}

/*
 * Format a reverse mapping for getfsmap, having translated rm_startblock
 * into the appropriate daddr units.  Pass in a nonzero @len_daddr if the
 * length could be larger than rm_blockcount in struct xfs_rmap_irec.
 */
STATIC int
xfs_getfsmap_helper(
	struct xfs_trans		*tp,
	struct xfs_getfsmap_info	*info,
	const struct xfs_fsmap_irec	*frec)
{
	struct xfs_fsmap		fmr;
	struct xfs_mount		*mp = tp->t_mountp;
	bool				shared;
	int				error = 0;

	if (fatal_signal_pending(current))
		return -EINTR;

	/*
	 * Filter out records that start before our startpoint, if the
	 * caller requested that.
	 */
	if (xfs_getfsmap_frec_before_start(info, frec))
		goto out;

	/* Are we just counting mappings? */
	if (info->head->fmh_count == 0) {
		if (info->head->fmh_entries == UINT_MAX)
			return -ECANCELED;

		if (frec->start_daddr > info->next_daddr)
			info->head->fmh_entries++;

		if (info->last)
			return 0;

		info->head->fmh_entries++;
		goto out;
	}

	/*
	 * If the record starts past the last physical block we saw,
	 * then we've found a gap.  Report the gap as being owned by
	 * whatever the caller specified is the missing owner.
	 */
	if (frec->start_daddr > info->next_daddr) {
		if (info->head->fmh_entries >= info->head->fmh_count)
			return -ECANCELED;

		fmr.fmr_device = info->dev;
		fmr.fmr_physical = info->next_daddr;
		fmr.fmr_owner = info->missing_owner;
		fmr.fmr_offset = 0;
		fmr.fmr_length = frec->start_daddr - info->next_daddr;
		fmr.fmr_flags = FMR_OF_SPECIAL_OWNER;
		xfs_getfsmap_format(mp, &fmr, info);
	}

	if (info->last)
		goto out;

	/* Fill out the extent we found */
	if (info->head->fmh_entries >= info->head->fmh_count)
		return -ECANCELED;

	trace_xfs_fsmap_mapping(mp, info->dev,
			info->group ? info->group->xg_gno : NULLAGNUMBER,
			frec);

	fmr.fmr_device = info->dev;
	fmr.fmr_physical = frec->start_daddr;
	error = xfs_fsmap_owner_from_frec(&fmr, frec);
	if (error)
		return error;
	fmr.fmr_offset = XFS_FSB_TO_BB(mp, frec->offset);
	fmr.fmr_length = frec->len_daddr;
	if (frec->rm_flags & XFS_RMAP_UNWRITTEN)
		fmr.fmr_flags |= FMR_OF_PREALLOC;
	if (frec->rm_flags & XFS_RMAP_ATTR_FORK)
		fmr.fmr_flags |= FMR_OF_ATTR_FORK;
	if (frec->rm_flags & XFS_RMAP_BMBT_BLOCK)
		fmr.fmr_flags |= FMR_OF_EXTENT_MAP;
	if (fmr.fmr_flags == 0) {
		error = xfs_getfsmap_is_shared(tp, info, frec, &shared);
		if (error)
			return error;
		if (shared)
			fmr.fmr_flags |= FMR_OF_SHARED;
	}

	xfs_getfsmap_format(mp, &fmr, info);
out:
	info->next_daddr = max(info->next_daddr,
			       frec->start_daddr + frec->len_daddr);
	return 0;
}

static inline int
xfs_getfsmap_group_helper(
	struct xfs_getfsmap_info	*info,
	struct xfs_trans		*tp,
	struct xfs_group		*xg,
	xfs_agblock_t			startblock,
	xfs_extlen_t			blockcount,
	struct xfs_fsmap_irec		*frec)
{
	/*
	 * For an info->last query, we're looking for a gap between the last
	 * mapping emitted and the high key specified by userspace.  If the
	 * user's query spans less than 1 fsblock, then info->high and
	 * info->low will have the same rm_startblock, which causes rec_daddr
	 * and next_daddr to be the same.  Therefore, use the end_daddr that
	 * we calculated from userspace's high key to synthesize the record.
	 * Note that if the btree query found a mapping, there won't be a gap.
	 */
	if (info->last)
		frec->start_daddr = info->end_daddr + 1;
	else
		frec->start_daddr = xfs_gbno_to_daddr(xg, startblock);

	frec->len_daddr = XFS_FSB_TO_BB(xg->xg_mount, blockcount);
	return xfs_getfsmap_helper(tp, info, frec);
}

/* Transform a rmapbt irec into a fsmap */
STATIC int
xfs_getfsmap_rmapbt_helper(
	struct xfs_btree_cur		*cur,
	const struct xfs_rmap_irec	*rec,
	void				*priv)
{
	struct xfs_fsmap_irec		frec = {
		.owner			= rec->rm_owner,
		.offset			= rec->rm_offset,
		.rm_flags		= rec->rm_flags,
		.rec_key		= rec->rm_startblock,
	};
	struct xfs_getfsmap_info	*info = priv;

	return xfs_getfsmap_group_helper(info, cur->bc_tp, cur->bc_group,
			rec->rm_startblock, rec->rm_blockcount, &frec);
}

/* Transform a bnobt irec into a fsmap */
STATIC int
xfs_getfsmap_datadev_bnobt_helper(
	struct xfs_btree_cur		*cur,
	const struct xfs_alloc_rec_incore *rec,
	void				*priv)
{
	struct xfs_fsmap_irec		frec = {
		.owner			= XFS_RMAP_OWN_NULL, /* "free" */
		.rec_key		= rec->ar_startblock,
	};
	struct xfs_getfsmap_info	*info = priv;

	return xfs_getfsmap_group_helper(info, cur->bc_tp, cur->bc_group,
			rec->ar_startblock, rec->ar_blockcount, &frec);
}

/* Set rmap flags based on the getfsmap flags */
static void
xfs_getfsmap_set_irec_flags(
	struct xfs_rmap_irec	*irec,
	const struct xfs_fsmap	*fmr)
{
	irec->rm_flags = 0;
	if (fmr->fmr_flags & FMR_OF_ATTR_FORK)
		irec->rm_flags |= XFS_RMAP_ATTR_FORK;
	if (fmr->fmr_flags & FMR_OF_EXTENT_MAP)
		irec->rm_flags |= XFS_RMAP_BMBT_BLOCK;
	if (fmr->fmr_flags & FMR_OF_PREALLOC)
		irec->rm_flags |= XFS_RMAP_UNWRITTEN;
}

static inline bool
rmap_not_shareable(struct xfs_mount *mp, const struct xfs_rmap_irec *r)
{
	if (!xfs_has_reflink(mp))
		return true;
	if (XFS_RMAP_NON_INODE_OWNER(r->rm_owner))
		return true;
	if (r->rm_flags & (XFS_RMAP_ATTR_FORK | XFS_RMAP_BMBT_BLOCK |
			   XFS_RMAP_UNWRITTEN))
		return true;
	return false;
}

/* Execute a getfsmap query against the regular data device. */
STATIC int
__xfs_getfsmap_datadev(
	struct xfs_trans		*tp,
	const struct xfs_fsmap		*keys,
	struct xfs_getfsmap_info	*info,
	int				(*query_fn)(struct xfs_trans *,
						    struct xfs_getfsmap_info *,
						    struct xfs_btree_cur **,
						    void *),
	void				*priv)
{
	struct xfs_mount		*mp = tp->t_mountp;
	struct xfs_perag		*pag = NULL;
	struct xfs_btree_cur		*bt_cur = NULL;
	xfs_fsblock_t			start_fsb;
	xfs_fsblock_t			end_fsb;
	xfs_agnumber_t			start_ag, end_ag;
	uint64_t			eofs;
	int				error = 0;

	eofs = XFS_FSB_TO_BB(mp, mp->m_sb.sb_dblocks);
	if (keys[0].fmr_physical >= eofs)
		return 0;
	start_fsb = XFS_DADDR_TO_FSB(mp, keys[0].fmr_physical);
	end_fsb = XFS_DADDR_TO_FSB(mp, min(eofs - 1, keys[1].fmr_physical));

	/*
	 * Convert the fsmap low/high keys to AG based keys.  Initialize
	 * low to the fsmap low key and max out the high key to the end
	 * of the AG.
	 */
	info->low.rm_offset = XFS_BB_TO_FSBT(mp, keys[0].fmr_offset);
	error = xfs_fsmap_owner_to_rmap(&info->low, &keys[0]);
	if (error)
		return error;
	info->low.rm_blockcount = XFS_BB_TO_FSBT(mp, keys[0].fmr_length);
	xfs_getfsmap_set_irec_flags(&info->low, &keys[0]);

	/* Adjust the low key if we are continuing from where we left off. */
	if (info->low.rm_blockcount == 0) {
		/* No previous record from which to continue */
	} else if (rmap_not_shareable(mp, &info->low)) {
		/* Last record seen was an unshareable extent */
		info->low.rm_owner = 0;
		info->low.rm_offset = 0;

		start_fsb += info->low.rm_blockcount;
		if (XFS_FSB_TO_DADDR(mp, start_fsb) >= eofs)
			return 0;
	} else {
		/* Last record seen was a shareable file data extent */
		info->low.rm_offset += info->low.rm_blockcount;
	}
	info->low.rm_startblock = XFS_FSB_TO_AGBNO(mp, start_fsb);

	info->high.rm_startblock = -1U;
	info->high.rm_owner = ULLONG_MAX;
	info->high.rm_offset = ULLONG_MAX;
	info->high.rm_blockcount = 0;
	info->high.rm_flags = XFS_RMAP_KEY_FLAGS | XFS_RMAP_REC_FLAGS;

	start_ag = XFS_FSB_TO_AGNO(mp, start_fsb);
	end_ag = XFS_FSB_TO_AGNO(mp, end_fsb);

	while ((pag = xfs_perag_next_range(mp, pag, start_ag, end_ag))) {
		/*
		 * Set the AG high key from the fsmap high key if this
		 * is the last AG that we're querying.
		 */
		info->group = pag_group(pag);
		if (pag_agno(pag) == end_ag) {
			info->high.rm_startblock = XFS_FSB_TO_AGBNO(mp,
					end_fsb);
			info->high.rm_offset = XFS_BB_TO_FSBT(mp,
					keys[1].fmr_offset);
			error = xfs_fsmap_owner_to_rmap(&info->high, &keys[1]);
			if (error)
				break;
			xfs_getfsmap_set_irec_flags(&info->high, &keys[1]);
		}

		if (bt_cur) {
			xfs_btree_del_cursor(bt_cur, XFS_BTREE_NOERROR);
			bt_cur = NULL;
			xfs_trans_brelse(tp, info->agf_bp);
			info->agf_bp = NULL;
		}

		error = xfs_alloc_read_agf(pag, tp, 0, &info->agf_bp);
		if (error)
			break;

		trace_xfs_fsmap_low_group_key(mp, info->dev, pag_agno(pag),
				&info->low);
		trace_xfs_fsmap_high_group_key(mp, info->dev, pag_agno(pag),
				&info->high);

		error = query_fn(tp, info, &bt_cur, priv);
		if (error)
			break;

		/*
		 * Set the AG low key to the start of the AG prior to
		 * moving on to the next AG.
		 */
		if (pag_agno(pag) == start_ag)
			memset(&info->low, 0, sizeof(info->low));

		/*
		 * If this is the last AG, report any gap at the end of it
		 * before we drop the reference to the perag when the loop
		 * terminates.
		 */
		if (pag_agno(pag) == end_ag) {
			info->last = true;
			error = query_fn(tp, info, &bt_cur, priv);
			if (error)
				break;
		}
		info->group = NULL;
	}

	if (bt_cur)
		xfs_btree_del_cursor(bt_cur, error < 0 ? XFS_BTREE_ERROR :
							 XFS_BTREE_NOERROR);
	if (info->agf_bp) {
		xfs_trans_brelse(tp, info->agf_bp);
		info->agf_bp = NULL;
	}
	if (info->group) {
		xfs_perag_rele(pag);
		info->group = NULL;
	} else if (pag) {
		/* loop termination case */
		xfs_perag_rele(pag);
	}

	return error;
}

/* Actually query the rmap btree. */
STATIC int
xfs_getfsmap_datadev_rmapbt_query(
	struct xfs_trans		*tp,
	struct xfs_getfsmap_info	*info,
	struct xfs_btree_cur		**curpp,
	void				*priv)
{
	/* Report any gap at the end of the last AG. */
	if (info->last)
		return xfs_getfsmap_rmapbt_helper(*curpp, &info->high, info);

	/* Allocate cursor for this AG and query_range it. */
	*curpp = xfs_rmapbt_init_cursor(tp->t_mountp, tp, info->agf_bp,
			to_perag(info->group));
	return xfs_rmap_query_range(*curpp, &info->low, &info->high,
			xfs_getfsmap_rmapbt_helper, info);
}

/* Execute a getfsmap query against the regular data device rmapbt. */
STATIC int
xfs_getfsmap_datadev_rmapbt(
	struct xfs_trans		*tp,
	const struct xfs_fsmap		*keys,
	struct xfs_getfsmap_info	*info)
{
	info->missing_owner = XFS_FMR_OWN_FREE;
	return __xfs_getfsmap_datadev(tp, keys, info,
			xfs_getfsmap_datadev_rmapbt_query, NULL);
}

/* Actually query the bno btree. */
STATIC int
xfs_getfsmap_datadev_bnobt_query(
	struct xfs_trans		*tp,
	struct xfs_getfsmap_info	*info,
	struct xfs_btree_cur		**curpp,
	void				*priv)
{
	struct xfs_alloc_rec_incore	*key = priv;

	/* Report any gap at the end of the last AG. */
	if (info->last)
		return xfs_getfsmap_datadev_bnobt_helper(*curpp, &key[1], info);

	/* Allocate cursor for this AG and query_range it. */
	*curpp = xfs_bnobt_init_cursor(tp->t_mountp, tp, info->agf_bp,
			to_perag(info->group));
	key->ar_startblock = info->low.rm_startblock;
	key[1].ar_startblock = info->high.rm_startblock;
	return xfs_alloc_query_range(*curpp, key, &key[1],
			xfs_getfsmap_datadev_bnobt_helper, info);
}

/* Execute a getfsmap query against the regular data device's bnobt. */
STATIC int
xfs_getfsmap_datadev_bnobt(
	struct xfs_trans		*tp,
	const struct xfs_fsmap		*keys,
	struct xfs_getfsmap_info	*info)
{
	struct xfs_alloc_rec_incore	akeys[2];

	memset(akeys, 0, sizeof(akeys));
	info->missing_owner = XFS_FMR_OWN_UNKNOWN;
	return __xfs_getfsmap_datadev(tp, keys, info,
			xfs_getfsmap_datadev_bnobt_query, &akeys[0]);
}

/* Execute a getfsmap query against the log device. */
STATIC int
xfs_getfsmap_logdev(
	struct xfs_trans		*tp,
	const struct xfs_fsmap		*keys,
	struct xfs_getfsmap_info	*info)
{
	struct xfs_fsmap_irec		frec = {
		.start_daddr		= 0,
		.rec_key		= 0,
		.owner			= XFS_RMAP_OWN_LOG,
	};
	struct xfs_mount		*mp = tp->t_mountp;
	xfs_fsblock_t			start_fsb, end_fsb;
	uint64_t			eofs;

	eofs = XFS_FSB_TO_BB(mp, mp->m_sb.sb_logblocks);
	if (keys[0].fmr_physical >= eofs)
		return 0;
	start_fsb = XFS_BB_TO_FSBT(mp,
				keys[0].fmr_physical + keys[0].fmr_length);
	end_fsb = XFS_BB_TO_FSB(mp, min(eofs - 1, keys[1].fmr_physical));

	/* Adjust the low key if we are continuing from where we left off. */
	if (keys[0].fmr_length > 0)
		info->low_daddr = XFS_FSB_TO_BB(mp, start_fsb);

	trace_xfs_fsmap_low_linear_key(mp, info->dev, start_fsb);
	trace_xfs_fsmap_high_linear_key(mp, info->dev, end_fsb);

	if (start_fsb > 0)
		return 0;

	/* Fabricate an rmap entry for the external log device. */
	frec.len_daddr = XFS_FSB_TO_BB(mp, mp->m_sb.sb_logblocks);
	return xfs_getfsmap_helper(tp, info, &frec);
}

#ifdef CONFIG_XFS_RT
/* Transform a rtbitmap "record" into a fsmap */
STATIC int
xfs_getfsmap_rtdev_rtbitmap_helper(
	struct xfs_rtgroup		*rtg,
	struct xfs_trans		*tp,
	const struct xfs_rtalloc_rec	*rec,
	void				*priv)
{
	struct xfs_fsmap_irec		frec = {
		.owner			= XFS_RMAP_OWN_NULL, /* "free" */
	};
	struct xfs_mount		*mp = rtg_mount(rtg);
	struct xfs_getfsmap_info	*info = priv;
	xfs_rtblock_t			start_rtb =
				xfs_rtx_to_rtb(rtg, rec->ar_startext);
	uint64_t			rtbcount =
				xfs_rtbxlen_to_blen(mp, rec->ar_extcount);

	/*
	 * For an info->last query, we're looking for a gap between the last
	 * mapping emitted and the high key specified by userspace.  If the
	 * user's query spans less than 1 fsblock, then info->high and
	 * info->low will have the same rm_startblock, which causes rec_daddr
	 * and next_daddr to be the same.  Therefore, use the end_daddr that
	 * we calculated from userspace's high key to synthesize the record.
	 * Note that if the btree query found a mapping, there won't be a gap.
	 */
	if (info->last)
		frec.start_daddr = info->end_daddr + 1;
	else
		frec.start_daddr = xfs_rtb_to_daddr(mp, start_rtb);

	frec.len_daddr = XFS_FSB_TO_BB(mp, rtbcount);
	return xfs_getfsmap_helper(tp, info, &frec);
}

/* Execute a getfsmap query against the realtime device rtbitmap. */
STATIC int
xfs_getfsmap_rtdev_rtbitmap(
	struct xfs_trans		*tp,
	const struct xfs_fsmap		*keys,
	struct xfs_getfsmap_info	*info)
{
	struct xfs_mount		*mp = tp->t_mountp;
	xfs_rtblock_t			start_rtbno, end_rtbno;
	xfs_rtxnum_t			start_rtx, end_rtx;
	xfs_rgnumber_t			start_rgno, end_rgno;
	struct xfs_rtgroup		*rtg = NULL;
	uint64_t			eofs;
	int				error;

	eofs = XFS_FSB_TO_BB(mp, mp->m_sb.sb_rblocks);
	if (keys[0].fmr_physical >= eofs)
		return 0;

	info->missing_owner = XFS_FMR_OWN_UNKNOWN;

	/* Adjust the low key if we are continuing from where we left off. */
	start_rtbno = xfs_daddr_to_rtb(mp,
			keys[0].fmr_physical + keys[0].fmr_length);
	if (keys[0].fmr_length > 0) {
		info->low_daddr = xfs_rtb_to_daddr(mp, start_rtbno);
		if (info->low_daddr >= eofs)
			return 0;
	}
	start_rtx = xfs_rtb_to_rtx(mp, start_rtbno);
	start_rgno = xfs_rtb_to_rgno(mp, start_rtbno);

	end_rtbno = xfs_daddr_to_rtb(mp, min(eofs - 1, keys[1].fmr_physical));
	end_rgno = xfs_rtb_to_rgno(mp, end_rtbno);

	trace_xfs_fsmap_low_linear_key(mp, info->dev, start_rtbno);
	trace_xfs_fsmap_high_linear_key(mp, info->dev, end_rtbno);

	end_rtx = -1ULL;

	while ((rtg = xfs_rtgroup_next_range(mp, rtg, start_rgno, end_rgno))) {
		if (rtg_rgno(rtg) == end_rgno)
			end_rtx = xfs_rtb_to_rtx(mp,
					end_rtbno + mp->m_sb.sb_rextsize - 1);

		info->group = rtg_group(rtg);
		xfs_rtgroup_lock(rtg, XFS_RTGLOCK_BITMAP_SHARED);
		error = xfs_rtalloc_query_range(rtg, tp, start_rtx, end_rtx,
				xfs_getfsmap_rtdev_rtbitmap_helper, info);
		if (error)
			break;

		/*
		 * Report any gaps at the end of the rtbitmap by simulating a
		 * zero-length free extent starting at the rtx after the end
		 * of the query range.
		 */
		if (rtg_rgno(rtg) == end_rgno) {
			struct xfs_rtalloc_rec	ahigh = {
				.ar_startext	= min(end_rtx + 1,
						      rtg->rtg_extents),
			};

			info->last = true;
			error = xfs_getfsmap_rtdev_rtbitmap_helper(rtg, tp,
					&ahigh, info);
			if (error)
				break;
		}

		xfs_rtgroup_unlock(rtg, XFS_RTGLOCK_BITMAP_SHARED);
		info->group = NULL;
		start_rtx = 0;
	}

	/* loop termination case */
	if (rtg) {
		if (info->group) {
			xfs_rtgroup_unlock(rtg, XFS_RTGLOCK_BITMAP_SHARED);
			info->group = NULL;
		}
		xfs_rtgroup_rele(rtg);
	}

	return error;
}

/* Transform a realtime rmapbt record into a fsmap */
STATIC int
xfs_getfsmap_rtdev_rmapbt_helper(
	struct xfs_btree_cur		*cur,
	const struct xfs_rmap_irec	*rec,
	void				*priv)
{
	struct xfs_fsmap_irec		frec = {
		.owner			= rec->rm_owner,
		.offset			= rec->rm_offset,
		.rm_flags		= rec->rm_flags,
		.rec_key		= rec->rm_startblock,
	};
	struct xfs_getfsmap_info	*info = priv;

	return xfs_getfsmap_group_helper(info, cur->bc_tp, cur->bc_group,
			rec->rm_startblock, rec->rm_blockcount, &frec);
}

/* Actually query the rtrmap btree. */
STATIC int
xfs_getfsmap_rtdev_rmapbt_query(
	struct xfs_trans		*tp,
	struct xfs_getfsmap_info	*info,
	struct xfs_btree_cur		**curpp)
{
	struct xfs_rtgroup		*rtg = to_rtg(info->group);

	/* Query the rtrmapbt */
	xfs_rtgroup_lock(rtg, XFS_RTGLOCK_RMAP | XFS_RTGLOCK_REFCOUNT);
	*curpp = xfs_rtrmapbt_init_cursor(tp, rtg);
	return xfs_rmap_query_range(*curpp, &info->low, &info->high,
			xfs_getfsmap_rtdev_rmapbt_helper, info);
}

/* Execute a getfsmap query against the realtime device rmapbt. */
STATIC int
xfs_getfsmap_rtdev_rmapbt(
	struct xfs_trans		*tp,
	const struct xfs_fsmap		*keys,
	struct xfs_getfsmap_info	*info)
{
	struct xfs_fsmap		key0 = *keys; /* struct copy */
	struct xfs_mount		*mp = tp->t_mountp;
	struct xfs_rtgroup		*rtg = NULL;
	struct xfs_btree_cur		*bt_cur = NULL;
	xfs_daddr_t			rtstart_daddr;
	xfs_rtblock_t			start_rtb;
	xfs_rtblock_t			end_rtb;
	xfs_rgnumber_t			start_rg, end_rg;
	uint64_t			eofs;
	int				error = 0;

	eofs = XFS_FSB_TO_BB(mp, mp->m_sb.sb_rtstart + mp->m_sb.sb_rblocks);
	if (key0.fmr_physical >= eofs)
		return 0;

	/*
	 * On zoned filesystems with an internal rt volume, the volume comes
	 * immediately after the end of the data volume.  However, the
	 * xfs_rtblock_t address space is relative to the start of the data
	 * device, which means that the first @rtstart fsblocks do not actually
	 * point anywhere.  If a fsmap query comes in with the low key starting
	 * below @rtstart, report it as "owned by filesystem".
	 */
	rtstart_daddr = XFS_FSB_TO_BB(mp, mp->m_sb.sb_rtstart);
	if (xfs_has_zoned(mp) && key0.fmr_physical < rtstart_daddr) {
		struct xfs_fsmap_irec		frec = {
			.owner			= XFS_RMAP_OWN_FS,
			.len_daddr		= rtstart_daddr,
		};

		/*
		 * Adjust the start of the query range if we're picking up from
		 * a previous round, and only emit the record if we haven't
		 * already gone past.
		 */
		key0.fmr_physical += key0.fmr_length;
		if (key0.fmr_physical < rtstart_daddr) {
			error = xfs_getfsmap_helper(tp, info, &frec);
			if (error)
				return error;

			key0.fmr_physical = rtstart_daddr;
		}

		/* Zero the other fields to avoid further adjustments. */
		key0.fmr_owner = 0;
		key0.fmr_offset = 0;
		key0.fmr_length = 0;
	}

	start_rtb = xfs_daddr_to_rtb(mp, key0.fmr_physical);
	end_rtb = xfs_daddr_to_rtb(mp, min(eofs - 1, keys[1].fmr_physical));
	info->missing_owner = XFS_FMR_OWN_FREE;

	/*
	 * Convert the fsmap low/high keys to rtgroup based keys.  Initialize
	 * low to the fsmap low key and max out the high key to the end
	 * of the rtgroup.
	 */
	info->low.rm_offset = XFS_BB_TO_FSBT(mp, key0.fmr_offset);
	error = xfs_fsmap_owner_to_rmap(&info->low, &key0);
	if (error)
		return error;
	info->low.rm_blockcount = XFS_BB_TO_FSBT(mp, key0.fmr_length);
	xfs_getfsmap_set_irec_flags(&info->low, &key0);

	/* Adjust the low key if we are continuing from where we left off. */
	if (info->low.rm_blockcount == 0) {
		/* No previous record from which to continue */
	} else if (rmap_not_shareable(mp, &info->low)) {
		/* Last record seen was an unshareable extent */
		info->low.rm_owner = 0;
		info->low.rm_offset = 0;

		start_rtb += info->low.rm_blockcount;
		if (xfs_rtb_to_daddr(mp, start_rtb) >= eofs)
			return 0;
	} else {
		/* Last record seen was a shareable file data extent */
		info->low.rm_offset += info->low.rm_blockcount;
	}
	info->low.rm_startblock = xfs_rtb_to_rgbno(mp, start_rtb);

	info->high.rm_startblock = -1U;
	info->high.rm_owner = ULLONG_MAX;
	info->high.rm_offset = ULLONG_MAX;
	info->high.rm_blockcount = 0;
	info->high.rm_flags = XFS_RMAP_KEY_FLAGS | XFS_RMAP_REC_FLAGS;

	start_rg = xfs_rtb_to_rgno(mp, start_rtb);
	end_rg = xfs_rtb_to_rgno(mp, end_rtb);

	while ((rtg = xfs_rtgroup_next_range(mp, rtg, start_rg, end_rg))) {
		/*
		 * Set the rtgroup high key from the fsmap high key if this
		 * is the last rtgroup that we're querying.
		 */
		info->group = rtg_group(rtg);
		if (rtg_rgno(rtg) == end_rg) {
			info->high.rm_startblock =
				xfs_rtb_to_rgbno(mp, end_rtb);
			info->high.rm_offset =
				XFS_BB_TO_FSBT(mp, keys[1].fmr_offset);
			error = xfs_fsmap_owner_to_rmap(&info->high, &keys[1]);
			if (error)
				break;
			xfs_getfsmap_set_irec_flags(&info->high, &keys[1]);
		}

		if (bt_cur) {
			xfs_rtgroup_unlock(to_rtg(bt_cur->bc_group),
					XFS_RTGLOCK_RMAP |
					XFS_RTGLOCK_REFCOUNT);
			xfs_btree_del_cursor(bt_cur, XFS_BTREE_NOERROR);
			bt_cur = NULL;
		}

		trace_xfs_fsmap_low_group_key(mp, info->dev, rtg_rgno(rtg),
				&info->low);
		trace_xfs_fsmap_high_group_key(mp, info->dev, rtg_rgno(rtg),
				&info->high);

		error = xfs_getfsmap_rtdev_rmapbt_query(tp, info, &bt_cur);
		if (error)
			break;

		/*
		 * Set the rtgroup low key to the start of the rtgroup prior to
		 * moving on to the next rtgroup.
		 */
		if (rtg_rgno(rtg) == start_rg)
			memset(&info->low, 0, sizeof(info->low));

		/*
		 * If this is the last rtgroup, report any gap at the end of it
		 * before we drop the reference to the perag when the loop
		 * terminates.
		 */
		if (rtg_rgno(rtg) == end_rg) {
			info->last = true;
			error = xfs_getfsmap_rtdev_rmapbt_helper(bt_cur,
					&info->high, info);
			if (error)
				break;
		}
		info->group = NULL;
	}

	if (bt_cur) {
		xfs_rtgroup_unlock(to_rtg(bt_cur->bc_group),
				XFS_RTGLOCK_RMAP | XFS_RTGLOCK_REFCOUNT);
		xfs_btree_del_cursor(bt_cur, error < 0 ? XFS_BTREE_ERROR :
							 XFS_BTREE_NOERROR);
	}

	/* loop termination case */
	if (rtg) {
		info->group = NULL;
		xfs_rtgroup_rele(rtg);
	}

	return error;
}
#endif /* CONFIG_XFS_RT */

static uint32_t
xfs_getfsmap_device(
	struct xfs_mount	*mp,
	enum xfs_device		dev)
{
	if (mp->m_sb.sb_rtstart)
		return dev;

	switch (dev) {
	case XFS_DEV_DATA:
		return new_encode_dev(mp->m_ddev_targp->bt_dev);
	case XFS_DEV_LOG:
		return new_encode_dev(mp->m_logdev_targp->bt_dev);
	case XFS_DEV_RT:
		if (!mp->m_rtdev_targp)
			break;
		return new_encode_dev(mp->m_rtdev_targp->bt_dev);
	}

	return -1;
}

/* Do we recognize the device? */
STATIC bool
xfs_getfsmap_is_valid_device(
	struct xfs_mount	*mp,
	struct xfs_fsmap	*fm)
{
	return fm->fmr_device == 0 ||
		fm->fmr_device == UINT_MAX ||
		fm->fmr_device == xfs_getfsmap_device(mp, XFS_DEV_DATA) ||
		fm->fmr_device == xfs_getfsmap_device(mp, XFS_DEV_LOG) ||
		(mp->m_rtdev_targp &&
		 fm->fmr_device == xfs_getfsmap_device(mp, XFS_DEV_RT));
}

/* Ensure that the low key is less than the high key. */
STATIC bool
xfs_getfsmap_check_keys(
	struct xfs_fsmap		*low_key,
	struct xfs_fsmap		*high_key)
{
	if (low_key->fmr_flags & (FMR_OF_SPECIAL_OWNER | FMR_OF_EXTENT_MAP)) {
		if (low_key->fmr_offset)
			return false;
	}
	if (high_key->fmr_flags != -1U &&
	    (high_key->fmr_flags & (FMR_OF_SPECIAL_OWNER |
				    FMR_OF_EXTENT_MAP))) {
		if (high_key->fmr_offset && high_key->fmr_offset != -1ULL)
			return false;
	}
	if (high_key->fmr_length && high_key->fmr_length != -1ULL)
		return false;

	if (low_key->fmr_device > high_key->fmr_device)
		return false;
	if (low_key->fmr_device < high_key->fmr_device)
		return true;

	if (low_key->fmr_physical > high_key->fmr_physical)
		return false;
	if (low_key->fmr_physical < high_key->fmr_physical)
		return true;

	if (low_key->fmr_owner > high_key->fmr_owner)
		return false;
	if (low_key->fmr_owner < high_key->fmr_owner)
		return true;

	if (low_key->fmr_offset > high_key->fmr_offset)
		return false;
	if (low_key->fmr_offset < high_key->fmr_offset)
		return true;

	return false;
}

/*
 * There are only two devices if we didn't configure RT devices at build time.
 */
#ifdef CONFIG_XFS_RT
#define XFS_GETFSMAP_DEVS	3
#else
#define XFS_GETFSMAP_DEVS	2
#endif /* CONFIG_XFS_RT */

/*
 * Get filesystem's extents as described in head, and format for output. Fills
 * in the supplied records array until there are no more reverse mappings to
 * return or head.fmh_entries == head.fmh_count.  In the second case, this
 * function returns -ECANCELED to indicate that more records would have been
 * returned.
 *
 * Key to Confusion
 * ----------------
 * There are multiple levels of keys and counters at work here:
 * xfs_fsmap_head.fmh_keys	-- low and high fsmap keys passed in;
 *				   these reflect fs-wide sector addrs.
 * dkeys			-- fmh_keys used to query each device;
 *				   these are fmh_keys but w/ the low key
 *				   bumped up by fmr_length.
 * xfs_getfsmap_info.next_daddr	-- next disk addr we expect to see; this
 *				   is how we detect gaps in the fsmap
				   records and report them.
 * xfs_getfsmap_info.low/high	-- per-AG low/high keys computed from
 *				   dkeys; used to query the metadata.
 */
STATIC int
xfs_getfsmap(
	struct xfs_mount		*mp,
	struct xfs_fsmap_head		*head,
	struct fsmap			*fsmap_recs)
{
	struct xfs_trans		*tp = NULL;
	struct xfs_fsmap		dkeys[2];	/* per-dev keys */
	struct xfs_getfsmap_dev		handlers[XFS_GETFSMAP_DEVS];
	struct xfs_getfsmap_info	info = {
		.fsmap_recs		= fsmap_recs,
		.head			= head,
	};
	bool				use_rmap;
	int				i;
	int				error = 0;

	if (head->fmh_iflags & ~FMH_IF_VALID)
		return -EINVAL;
	if (!xfs_getfsmap_is_valid_device(mp, &head->fmh_keys[0]) ||
	    !xfs_getfsmap_is_valid_device(mp, &head->fmh_keys[1]))
		return -EINVAL;
	if (!xfs_getfsmap_check_keys(&head->fmh_keys[0], &head->fmh_keys[1]))
		return -EINVAL;

	use_rmap = xfs_has_rmapbt(mp) &&
		   has_capability_noaudit(current, CAP_SYS_ADMIN);
	head->fmh_entries = 0;

	/* Set up our device handlers. */
	memset(handlers, 0, sizeof(handlers));
	handlers[0].nr_sectors = XFS_FSB_TO_BB(mp, mp->m_sb.sb_dblocks);
	handlers[0].dev = xfs_getfsmap_device(mp, XFS_DEV_DATA);
	if (use_rmap)
		handlers[0].fn = xfs_getfsmap_datadev_rmapbt;
	else
		handlers[0].fn = xfs_getfsmap_datadev_bnobt;
	if (mp->m_logdev_targp != mp->m_ddev_targp) {
		handlers[1].nr_sectors = XFS_FSB_TO_BB(mp,
						       mp->m_sb.sb_logblocks);
		handlers[1].dev = xfs_getfsmap_device(mp, XFS_DEV_LOG);
		handlers[1].fn = xfs_getfsmap_logdev;
	}
#ifdef CONFIG_XFS_RT
	/*
	 * For zoned file systems there is no rtbitmap, so only support fsmap
	 * if the callers is privileged enough to use the full rmap version.
	 */
	if (mp->m_rtdev_targp && (use_rmap || !xfs_has_zoned(mp))) {
		handlers[2].nr_sectors = XFS_FSB_TO_BB(mp, mp->m_sb.sb_rblocks);
		handlers[2].dev = xfs_getfsmap_device(mp, XFS_DEV_RT);
		if (use_rmap)
			handlers[2].fn = xfs_getfsmap_rtdev_rmapbt;
		else
			handlers[2].fn = xfs_getfsmap_rtdev_rtbitmap;
	}
#endif /* CONFIG_XFS_RT */

	xfs_sort(handlers, XFS_GETFSMAP_DEVS, sizeof(struct xfs_getfsmap_dev),
			xfs_getfsmap_dev_compare);

	/*
	 * To continue where we left off, we allow userspace to use the
	 * last mapping from a previous call as the low key of the next.
	 * This is identified by a non-zero length in the low key. We
	 * have to increment the low key in this scenario to ensure we
	 * don't return the same mapping again, and instead return the
	 * very next mapping.
	 *
	 * If the low key mapping refers to file data, the same physical
	 * blocks could be mapped to several other files/offsets.
	 * According to rmapbt record ordering, the minimal next
	 * possible record for the block range is the next starting
	 * offset in the same inode. Therefore, each fsmap backend bumps
	 * the file offset to continue the search appropriately.  For
	 * all other low key mapping types (attr blocks, metadata), each
	 * fsmap backend bumps the physical offset as there can be no
	 * other mapping for the same physical block range.
	 */
	dkeys[0] = head->fmh_keys[0];
	memset(&dkeys[1], 0xFF, sizeof(struct xfs_fsmap));

	info.next_daddr = head->fmh_keys[0].fmr_physical +
			  head->fmh_keys[0].fmr_length;

	/* For each device we support... */
	for (i = 0; i < XFS_GETFSMAP_DEVS; i++) {
		/* Is this device within the range the user asked for? */
		if (!handlers[i].fn)
			continue;
		if (head->fmh_keys[0].fmr_device > handlers[i].dev)
			continue;
		if (head->fmh_keys[1].fmr_device < handlers[i].dev)
			break;

		/*
		 * If this device number matches the high key, we have to pass
		 * the high key to the handler to limit the query results, and
		 * set the end_daddr so that we can synthesize records at the
		 * end of the query range or device.
		 */
		if (handlers[i].dev == head->fmh_keys[1].fmr_device) {
			dkeys[1] = head->fmh_keys[1];
			info.end_daddr = min(handlers[i].nr_sectors - 1,
					     dkeys[1].fmr_physical);
		} else {
			info.end_daddr = handlers[i].nr_sectors - 1;
		}

		/*
		 * If the device number exceeds the low key, zero out the low
		 * key so that we get everything from the beginning.
		 */
		if (handlers[i].dev > head->fmh_keys[0].fmr_device)
			memset(&dkeys[0], 0, sizeof(struct xfs_fsmap));

		/*
		 * Grab an empty transaction so that we can use its recursive
		 * buffer locking abilities to detect cycles in the rmapbt
		 * without deadlocking.
		 */
		error = xfs_trans_alloc_empty(mp, &tp);
		if (error)
			break;

		info.dev = handlers[i].dev;
		info.last = false;
		info.group = NULL;
		info.low_daddr = XFS_BUF_DADDR_NULL;
		info.low.rm_blockcount = 0;
		error = handlers[i].fn(tp, dkeys, &info);
		if (error)
			break;
		xfs_trans_cancel(tp);
		tp = NULL;
		info.next_daddr = 0;
	}

	if (tp)
		xfs_trans_cancel(tp);

	/*
	 * For internal RT device we need to report different synthetic devices
	 * for a single physical device, and thus can't report the actual dev_t.
	 */
	if (!mp->m_sb.sb_rtstart)
		head->fmh_oflags = FMH_OF_DEV_T;
	return error;
}

int
xfs_ioc_getfsmap(
	struct xfs_inode	*ip,
	struct fsmap_head	__user *arg)
{
	struct xfs_fsmap_head	xhead = {0};
	struct fsmap_head	head;
	struct fsmap		*recs;
	unsigned int		count;
	__u32			last_flags = 0;
	bool			done = false;
	int			error;

	if (copy_from_user(&head, arg, sizeof(struct fsmap_head)))
		return -EFAULT;
	if (memchr_inv(head.fmh_reserved, 0, sizeof(head.fmh_reserved)) ||
	    memchr_inv(head.fmh_keys[0].fmr_reserved, 0,
		       sizeof(head.fmh_keys[0].fmr_reserved)) ||
	    memchr_inv(head.fmh_keys[1].fmr_reserved, 0,
		       sizeof(head.fmh_keys[1].fmr_reserved)))
		return -EINVAL;

	/*
	 * Use an internal memory buffer so that we don't have to copy fsmap
	 * data to userspace while holding locks.  Start by trying to allocate
	 * up to 128k for the buffer, but fall back to a single page if needed.
	 */
	count = min_t(unsigned int, head.fmh_count,
			131072 / sizeof(struct fsmap));
	recs = kvcalloc(count, sizeof(struct fsmap), GFP_KERNEL);
	if (!recs) {
		count = min_t(unsigned int, head.fmh_count,
				PAGE_SIZE / sizeof(struct fsmap));
		recs = kvcalloc(count, sizeof(struct fsmap), GFP_KERNEL);
		if (!recs)
			return -ENOMEM;
	}

	xhead.fmh_iflags = head.fmh_iflags;
	xfs_fsmap_to_internal(&xhead.fmh_keys[0], &head.fmh_keys[0]);
	xfs_fsmap_to_internal(&xhead.fmh_keys[1], &head.fmh_keys[1]);

	trace_xfs_getfsmap_low_key(ip->i_mount, &xhead.fmh_keys[0]);
	trace_xfs_getfsmap_high_key(ip->i_mount, &xhead.fmh_keys[1]);

	head.fmh_entries = 0;
	do {
		struct fsmap __user	*user_recs;
		struct fsmap		*last_rec;

		user_recs = &arg->fmh_recs[head.fmh_entries];
		xhead.fmh_entries = 0;
		xhead.fmh_count = min_t(unsigned int, count,
					head.fmh_count - head.fmh_entries);

		/* Run query, record how many entries we got. */
		error = xfs_getfsmap(ip->i_mount, &xhead, recs);
		switch (error) {
		case 0:
			/*
			 * There are no more records in the result set.  Copy
			 * whatever we got to userspace and break out.
			 */
			done = true;
			break;
		case -ECANCELED:
			/*
			 * The internal memory buffer is full.  Copy whatever
			 * records we got to userspace and go again if we have
			 * not yet filled the userspace buffer.
			 */
			error = 0;
			break;
		default:
			goto out_free;
		}
		head.fmh_entries += xhead.fmh_entries;
		head.fmh_oflags = xhead.fmh_oflags;

		/*
		 * If the caller wanted a record count or there aren't any
		 * new records to return, we're done.
		 */
		if (head.fmh_count == 0 || xhead.fmh_entries == 0)
			break;

		/* Copy all the records we got out to userspace. */
		if (copy_to_user(user_recs, recs,
				 xhead.fmh_entries * sizeof(struct fsmap))) {
			error = -EFAULT;
			goto out_free;
		}

		/* Remember the last record flags we copied to userspace. */
		last_rec = &recs[xhead.fmh_entries - 1];
		last_flags = last_rec->fmr_flags;

		/* Set up the low key for the next iteration. */
		xfs_fsmap_to_internal(&xhead.fmh_keys[0], last_rec);
		trace_xfs_getfsmap_low_key(ip->i_mount, &xhead.fmh_keys[0]);
	} while (!done && head.fmh_entries < head.fmh_count);

	/*
	 * If there are no more records in the query result set and we're not
	 * in counting mode, mark the last record returned with the LAST flag.
	 */
	if (done && head.fmh_count > 0 && head.fmh_entries > 0) {
		struct fsmap __user	*user_rec;

		last_flags |= FMR_OF_LAST;
		user_rec = &arg->fmh_recs[head.fmh_entries - 1];

		if (copy_to_user(&user_rec->fmr_flags, &last_flags,
					sizeof(last_flags))) {
			error = -EFAULT;
			goto out_free;
		}
	}

	/* copy back header */
	if (copy_to_user(arg, &head, sizeof(struct fsmap_head))) {
		error = -EFAULT;
		goto out_free;
	}

out_free:
	kvfree(recs);
	return error;
}