Re: [PATCH v2 6/9] xfs: implement the GETFSMAP ioctl

[Brian Foster <bfoster@redhat.com>]

On Wed, Mar 01, 2017 at 06:29:15PM -0800, Darrick J. Wong wrote:
> Introduce a new ioctl that uses the reverse mapping btree to return
> information about the physical layout of the filesystem.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---

Reviewed-by: Brian Foster <bfoster@redhat.com>

> v2: improve comments and refactor common code
> v3: move the rmap comparator to libxfs and more refactoring
> ---
>  fs/xfs/Makefile          |    1 
>  fs/xfs/libxfs/xfs_fs.h   |   13 +
>  fs/xfs/libxfs/xfs_rmap.c |   28 ++
>  fs/xfs/libxfs/xfs_rmap.h |    2 
>  fs/xfs/xfs_fsmap.c       |  772 ++++++++++++++++++++++++++++++++++++++++++++++
>  fs/xfs/xfs_fsmap.h       |   53 +++
>  fs/xfs/xfs_ioctl.c       |   84 +++++
>  fs/xfs/xfs_ioctl32.c     |    2 
>  fs/xfs/xfs_trace.c       |    1 
>  fs/xfs/xfs_trace.h       |   84 +++++
>  fs/xfs/xfs_trans.c       |   22 +
>  fs/xfs/xfs_trans.h       |    2 
>  12 files changed, 1064 insertions(+)
>  create mode 100644 fs/xfs/xfs_fsmap.c
>  create mode 100644 fs/xfs/xfs_fsmap.h
> 
> diff --git a/fs/xfs/Makefile b/fs/xfs/Makefile
> index c7515d4..0e7ee30 100644
> --- a/fs/xfs/Makefile
> +++ b/fs/xfs/Makefile
> @@ -80,6 +80,7 @@ xfs-y				+= xfs_aops.o \
>  				   xfs_extent_busy.o \
>  				   xfs_file.o \
>  				   xfs_filestream.o \
> +				   xfs_fsmap.o \
>  				   xfs_fsops.o \
>  				   xfs_globals.o \
>  				   xfs_icache.o \
> diff --git a/fs/xfs/libxfs/xfs_fs.h b/fs/xfs/libxfs/xfs_fs.h
> index b72dc82..095bdf0 100644
> --- a/fs/xfs/libxfs/xfs_fs.h
> +++ b/fs/xfs/libxfs/xfs_fs.h
> @@ -92,6 +92,18 @@ struct getbmapx {
>  #define BMV_OF_LAST		0x4	/* segment is the last in the file */
>  #define BMV_OF_SHARED		0x8	/* segment shared with another file */
>  
> +/*	fmr_owner special values for FS_IOC_GETFSMAP */
> +#define XFS_FMR_OWN_FREE	FMR_OWN_FREE      /* free space */
> +#define XFS_FMR_OWN_UNKNOWN	FMR_OWN_UNKNOWN   /* unknown owner */
> +#define XFS_FMR_OWN_FS		FMR_OWNER('X', 1) /* static fs metadata */
> +#define XFS_FMR_OWN_LOG		FMR_OWNER('X', 2) /* journalling log */
> +#define XFS_FMR_OWN_AG		FMR_OWNER('X', 3) /* per-AG metadata */
> +#define XFS_FMR_OWN_INOBT	FMR_OWNER('X', 4) /* inode btree blocks */
> +#define XFS_FMR_OWN_INODES	FMR_OWNER('X', 5) /* inodes */
> +#define XFS_FMR_OWN_REFC	FMR_OWNER('X', 6) /* refcount tree */
> +#define XFS_FMR_OWN_COW		FMR_OWNER('X', 7) /* cow staging */
> +#define XFS_FMR_OWN_DEFECTIVE	FMR_OWNER('X', 8) /* bad blocks */
> +
>  /*
>   * Structure for XFS_IOC_FSSETDM.
>   * For use by backup and restore programs to set the XFS on-disk inode
> @@ -502,6 +514,7 @@ typedef struct xfs_swapext
>  #define XFS_IOC_GETBMAPX	_IOWR('X', 56, struct getbmap)
>  #define XFS_IOC_ZERO_RANGE	_IOW ('X', 57, struct xfs_flock64)
>  #define XFS_IOC_FREE_EOFBLOCKS	_IOR ('X', 58, struct xfs_fs_eofblocks)
> +/*	XFS_IOC_GETFSMAP ------ hoisted 59         */
>  
>  /*
>   * ioctl commands that replace IRIX syssgi()'s
> diff --git a/fs/xfs/libxfs/xfs_rmap.c b/fs/xfs/libxfs/xfs_rmap.c
> index 3840556..06cfb93 100644
> --- a/fs/xfs/libxfs/xfs_rmap.c
> +++ b/fs/xfs/libxfs/xfs_rmap.c
> @@ -2305,3 +2305,31 @@ xfs_rmap_free_extent(
>  	return __xfs_rmap_add(mp, dfops, XFS_RMAP_FREE, owner,
>  			XFS_DATA_FORK, &bmap);
>  }
> +
> +/* Compare rmap records.  Returns -1 if a < b, 1 if a > b, and 0 if equal. */
> +int
> +xfs_rmap_compare(
> +	const struct xfs_rmap_irec	*a,
> +	const struct xfs_rmap_irec	*b)
> +{
> +	__u64				oa;
> +	__u64				ob;
> +
> +	oa = xfs_rmap_irec_offset_pack(a);
> +	ob = xfs_rmap_irec_offset_pack(b);
> +
> +	if (a->rm_startblock < b->rm_startblock)
> +		return -1;
> +	else if (a->rm_startblock > b->rm_startblock)
> +		return 1;
> +	else if (a->rm_owner < b->rm_owner)
> +		return -1;
> +	else if (a->rm_owner > b->rm_owner)
> +		return 1;
> +	else if (oa < ob)
> +		return -1;
> +	else if (oa > ob)
> +		return 1;
> +	else
> +		return 0;
> +}
> diff --git a/fs/xfs/libxfs/xfs_rmap.h b/fs/xfs/libxfs/xfs_rmap.h
> index faf2c1a..98f908f 100644
> --- a/fs/xfs/libxfs/xfs_rmap.h
> +++ b/fs/xfs/libxfs/xfs_rmap.h
> @@ -214,5 +214,7 @@ int xfs_rmap_find_left_neighbor(struct xfs_btree_cur *cur, xfs_agblock_t bno,
>  int xfs_rmap_lookup_le_range(struct xfs_btree_cur *cur, xfs_agblock_t bno,
>  		uint64_t owner, uint64_t offset, unsigned int flags,
>  		struct xfs_rmap_irec *irec, int	*stat);
> +int xfs_rmap_compare(const struct xfs_rmap_irec *a,
> +		const struct xfs_rmap_irec *b);
>  
>  #endif	/* __XFS_RMAP_H__ */
> diff --git a/fs/xfs/xfs_fsmap.c b/fs/xfs/xfs_fsmap.c
> new file mode 100644
> index 0000000..2fd05a0
> --- /dev/null
> +++ b/fs/xfs/xfs_fsmap.c
> @@ -0,0 +1,772 @@
> +/*
> + * Copyright (C) 2017 Oracle.  All Rights Reserved.
> + *
> + * Author: Darrick J. Wong <darrick.wong@oracle.com>
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License
> + * as published by the Free Software Foundation; either version 2
> + * of the License, or (at your option) any later version.
> + *
> + * This program is distributed in the hope that it would be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program; if not, write the Free Software Foundation,
> + * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301, USA.
> + */
> +#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_sb.h"
> +#include "xfs_mount.h"
> +#include "xfs_defer.h"
> +#include "xfs_inode.h"
> +#include "xfs_trans.h"
> +#include "xfs_error.h"
> +#include "xfs_btree.h"
> +#include "xfs_rmap_btree.h"
> +#include "xfs_trace.h"
> +#include "xfs_log.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"
> +
> +/* Convert an xfs_fsmap to an fsmap. */
> +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. */
> +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,
> +	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 = 0;
> +		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_rmap(
> +	struct xfs_fsmap	*dest,
> +	struct xfs_rmap_irec	*src)
> +{
> +	dest->fmr_flags = 0;
> +	if (!XFS_RMAP_NON_INODE_OWNER(src->rm_owner)) {
> +		dest->fmr_owner = src->rm_owner;
> +		return 0;
> +	}
> +	dest->fmr_flags |= FMR_OF_SPECIAL_OWNER;
> +
> +	switch (src->rm_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;
> +	default:
> +		return -EFSCORRUPTED;
> +	}
> +	return 0;
> +}
> +
> +/* getfsmap query state */
> +struct xfs_getfsmap_info {
> +	struct xfs_fsmap_head	*head;
> +	xfs_fsmap_format_t	formatter;	/* formatting fn */
> +	void			*format_arg;	/* format buffer */
> +	struct xfs_buf		*agf_bp;	/* AGF, for refcount queries */
> +	xfs_daddr_t		next_daddr;	/* next daddr we expect */
> +	u64			missing_owner;	/* owner of holes */
> +	u32			dev;		/* device id */
> +	xfs_agnumber_t		agno;		/* AG number, if applicable */
> +	struct xfs_rmap_irec	low;		/* low rmap key */
> +	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,
> +				      struct xfs_fsmap *keys,
> +				      struct xfs_getfsmap_info *info);
> +};
> +
> +/* 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,
> +	struct xfs_rmap_irec		*rec,
> +	bool				*stat)
> +{
> +	struct xfs_mount		*mp = tp->t_mountp;
> +	struct xfs_btree_cur		*cur;
> +	xfs_agblock_t			fbno;
> +	xfs_extlen_t			flen;
> +	int				error;
> +
> +	*stat = false;
> +	if (!xfs_sb_version_hasreflink(&mp->m_sb))
> +		return 0;
> +	/* rt files will have agno set to NULLAGNUMBER */
> +	if (info->agno == NULLAGNUMBER)
> +		return 0;
> +
> +	/* Are there any shared blocks here? */
> +	flen = 0;
> +	cur = xfs_refcountbt_init_cursor(mp, tp, info->agf_bp,
> +			info->agno, NULL);
> +
> +	error = xfs_refcount_find_shared(cur, rec->rm_startblock,
> +			rec->rm_blockcount, &fbno, &flen, false);
> +
> +	xfs_btree_del_cursor(cur, error ? XFS_BTREE_ERROR : XFS_BTREE_NOERROR);
> +	if (error)
> +		return error;
> +
> +	*stat = flen > 0;
> +	return 0;
> +}
> +
> +/*
> + * Format a reverse mapping for getfsmap, having translated rm_startblock
> + * into the appropriate daddr units.
> + */
> +STATIC int
> +xfs_getfsmap_helper(
> +	struct xfs_trans		*tp,
> +	struct xfs_getfsmap_info	*info,
> +	struct xfs_rmap_irec		*rec,
> +	xfs_daddr_t			rec_daddr)
> +{
> +	struct xfs_fsmap		fmr;
> +	struct xfs_mount		*mp = tp->t_mountp;
> +	bool				shared;
> +	int				error;
> +
> +	if (fatal_signal_pending(current))
> +		return -EINTR;
> +
> +	/*
> +	 * Filter out records that start before our startpoint, if the
> +	 * caller requested that.
> +	 */
> +	if (xfs_rmap_compare(rec, &info->low) < 0) {
> +		rec_daddr += XFS_FSB_TO_BB(mp, rec->rm_blockcount);
> +		if (info->next_daddr < rec_daddr)
> +			info->next_daddr = rec_daddr;
> +		return XFS_BTREE_QUERY_RANGE_CONTINUE;
> +	}
> +
> +	/* Are we just counting mappings? */
> +	if (info->head->fmh_count == 0) {
> +		if (rec_daddr > info->next_daddr)
> +			info->head->fmh_entries++;
> +
> +		if (info->last)
> +			return XFS_BTREE_QUERY_RANGE_CONTINUE;
> +
> +		info->head->fmh_entries++;
> +
> +		rec_daddr += XFS_FSB_TO_BB(mp, rec->rm_blockcount);
> +		if (info->next_daddr < rec_daddr)
> +			info->next_daddr = rec_daddr;
> +		return XFS_BTREE_QUERY_RANGE_CONTINUE;
> +	}
> +
> +	/*
> +	 * 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 (rec_daddr > info->next_daddr) {
> +		if (info->head->fmh_entries >= info->head->fmh_count)
> +			return XFS_BTREE_QUERY_RANGE_ABORT;
> +
> +		fmr.fmr_device = info->dev;
> +		fmr.fmr_physical = info->next_daddr;
> +		fmr.fmr_owner = info->missing_owner;
> +		fmr.fmr_offset = 0;
> +		fmr.fmr_length = rec_daddr - info->next_daddr;
> +		fmr.fmr_flags = FMR_OF_SPECIAL_OWNER;
> +		error = info->formatter(&fmr, info->format_arg);
> +		if (error)
> +			return error;
> +		info->head->fmh_entries++;
> +	}
> +
> +	if (info->last)
> +		goto out;
> +
> +	/* Fill out the extent we found */
> +	if (info->head->fmh_entries >= info->head->fmh_count)
> +		return XFS_BTREE_QUERY_RANGE_ABORT;
> +
> +	trace_xfs_fsmap_mapping(mp, info->dev, info->agno, rec);
> +
> +	fmr.fmr_device = info->dev;
> +	fmr.fmr_physical = rec_daddr;
> +	error = xfs_fsmap_owner_from_rmap(&fmr, rec);
> +	if (error)
> +		return error;
> +	fmr.fmr_offset = XFS_FSB_TO_BB(mp, rec->rm_offset);
> +	fmr.fmr_length = XFS_FSB_TO_BB(mp, rec->rm_blockcount);
> +	if (rec->rm_flags & XFS_RMAP_UNWRITTEN)
> +		fmr.fmr_flags |= FMR_OF_PREALLOC;
> +	if (rec->rm_flags & XFS_RMAP_ATTR_FORK)
> +		fmr.fmr_flags |= FMR_OF_ATTR_FORK;
> +	if (rec->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, rec, &shared);
> +		if (error)
> +			return error;
> +		if (shared)
> +			fmr.fmr_flags |= FMR_OF_SHARED;
> +	}
> +	error = info->formatter(&fmr, info->format_arg);
> +	if (error)
> +		return error;
> +	info->head->fmh_entries++;
> +
> +out:
> +	rec_daddr += XFS_FSB_TO_BB(mp, rec->rm_blockcount);
> +	if (info->next_daddr < rec_daddr)
> +		info->next_daddr = rec_daddr;
> +	return XFS_BTREE_QUERY_RANGE_CONTINUE;
> +}
> +
> +/* Transform a rmapbt irec into a fsmap */
> +STATIC int
> +xfs_getfsmap_datadev_helper(
> +	struct xfs_btree_cur		*cur,
> +	struct xfs_rmap_irec		*rec,
> +	void				*priv)
> +{
> +	struct xfs_mount		*mp = cur->bc_mp;
> +	struct xfs_getfsmap_info	*info = priv;
> +	xfs_fsblock_t			fsb;
> +	xfs_daddr_t			rec_daddr;
> +
> +	fsb = XFS_AGB_TO_FSB(mp, cur->bc_private.a.agno, rec->rm_startblock);
> +	rec_daddr = XFS_FSB_TO_DADDR(mp, fsb);
> +
> +	return xfs_getfsmap_helper(cur->bc_tp, info, rec, rec_daddr);
> +}
> +
> +/* Transform a absolute-startblock rmap (rtdev, logdev) into a fsmap */
> +STATIC int
> +xfs_getfsmap_rtdev_helper(
> +	struct xfs_btree_cur		*cur,
> +	struct xfs_rmap_irec		*rec,
> +	void				*priv)
> +{
> +	struct xfs_mount		*mp = cur->bc_mp;
> +	struct xfs_getfsmap_info	*info = priv;
> +	xfs_daddr_t			rec_daddr;
> +
> +	rec_daddr = XFS_FSB_TO_BB(mp, rec->rm_startblock);
> +
> +	return xfs_getfsmap_helper(cur->bc_tp, info, rec, rec_daddr);
> +}
> +
> +/* Set rmap flags based on the getfsmap flags */
> +static void
> +xfs_getfsmap_set_irec_flags(
> +	struct xfs_rmap_irec	*irec,
> +	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;
> +}
> +
> +/* Execute a getfsmap query against the log device. */
> +STATIC int
> +xfs_getfsmap_logdev(
> +	struct xfs_trans		*tp,
> +	struct xfs_fsmap		*keys,
> +	struct xfs_getfsmap_info	*info)
> +{
> +	struct xfs_mount		*mp = tp->t_mountp;
> +	struct xfs_rmap_irec		rmap;
> +	int				error;
> +
> +	/* Set up search keys */
> +	info->low.rm_startblock = XFS_BB_TO_FSBT(mp, keys[0].fmr_physical);
> +	info->low.rm_offset = XFS_BB_TO_FSBT(mp, keys[0].fmr_offset);
> +	error = xfs_fsmap_owner_to_rmap(&info->low, keys);
> +	if (error)
> +		return error;
> +	info->low.rm_blockcount = 0;
> +	xfs_getfsmap_set_irec_flags(&info->low, &keys[0]);
> +
> +	error = xfs_fsmap_owner_to_rmap(&info->high, keys + 1);
> +	if (error)
> +		return error;
> +	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;
> +	info->missing_owner = XFS_FMR_OWN_FREE;
> +
> +	trace_xfs_fsmap_low_key(mp, info->dev, info->agno, &info->low);
> +	trace_xfs_fsmap_high_key(mp, info->dev, info->agno, &info->high);
> +
> +	if (keys[0].fmr_physical > 0)
> +		return 0;
> +
> +	/* Fabricate an rmap entry for the external log device. */
> +	rmap.rm_startblock = 0;
> +	rmap.rm_blockcount = mp->m_sb.sb_logblocks;
> +	rmap.rm_owner = XFS_RMAP_OWN_LOG;
> +	rmap.rm_offset = 0;
> +	rmap.rm_flags = 0;
> +
> +	return xfs_getfsmap_helper(tp, info, &rmap, 0);
> +}
> +
> +/* Execute a getfsmap query against the regular data device. */
> +STATIC int
> +__xfs_getfsmap_datadev(
> +	struct xfs_trans		*tp,
> +	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_btree_cur		*bt_cur = NULL;
> +	xfs_fsblock_t			start_fsb;
> +	xfs_fsblock_t			end_fsb;
> +	xfs_agnumber_t			start_ag;
> +	xfs_agnumber_t			end_ag;
> +	xfs_daddr_t			eofs;
> +	int				error = 0;
> +
> +	eofs = XFS_FSB_TO_BB(mp, mp->m_sb.sb_dblocks);
> +	if (keys[0].fmr_physical >= eofs)
> +		return 0;
> +	if (keys[1].fmr_physical >= eofs)
> +		keys[1].fmr_physical = eofs - 1;
> +	start_fsb = XFS_DADDR_TO_FSB(mp, keys[0].fmr_physical);
> +	end_fsb = XFS_DADDR_TO_FSB(mp, 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_startblock = XFS_FSB_TO_AGBNO(mp, start_fsb);
> +	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 = 0;
> +	xfs_getfsmap_set_irec_flags(&info->low, &keys[0]);
> +
> +	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);
> +
> +	/* Query each AG */
> +	for (info->agno = start_ag; info->agno <= end_ag; info->agno++) {
> +		/*
> +		 * Set the AG high key from the fsmap high key if this
> +		 * is the last AG that we're querying.
> +		 */
> +		if (info->agno == 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)
> +				goto err;
> +			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(mp, tp, info->agno, 0,
> +				&info->agf_bp);
> +		if (error)
> +			goto err;
> +
> +		trace_xfs_fsmap_low_key(mp, info->dev, info->agno, &info->low);
> +		trace_xfs_fsmap_high_key(mp, info->dev, info->agno,
> +				&info->high);
> +
> +		error = query_fn(tp, info, &bt_cur, priv);
> +		if (error)
> +			goto err;
> +
> +		/*
> +		 * Set the AG low key to the start of the AG prior to
> +		 * moving on to the next AG.
> +		 */
> +		if (info->agno == start_ag) {
> +			info->low.rm_startblock = 0;
> +			info->low.rm_owner = 0;
> +			info->low.rm_offset = 0;
> +			info->low.rm_flags = 0;
> +		}
> +	}
> +
> +	/* Report any gap at the end of the AG */
> +	info->last = true;
> +	error = query_fn(tp, info, &bt_cur, priv);
> +	if (error)
> +		goto err;
> +
> +err:
> +	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;
> +	}
> +
> +	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_datadev_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,
> +			info->agno);
> +	return xfs_rmap_query_range(*curpp, &info->low, &info->high,
> +			xfs_getfsmap_datadev_helper, info);
> +}
> +
> +/* Execute a getfsmap query against the regular data device rmapbt. */
> +STATIC int
> +xfs_getfsmap_datadev_rmapbt(
> +	struct xfs_trans		*tp,
> +	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);
> +}
> +
> +/* Do we recognize the device? */
> +STATIC bool
> +xfs_getfsmap_is_valid_device(
> +	struct xfs_mount	*mp,
> +	struct xfs_fsmap	*fm)
> +{
> +	if (fm->fmr_device == 0 || fm->fmr_device == UINT_MAX ||
> +	    fm->fmr_device == new_encode_dev(mp->m_ddev_targp->bt_dev))
> +		return true;
> +	if (mp->m_logdev_targp &&
> +	    fm->fmr_device == new_encode_dev(mp->m_logdev_targp->bt_dev))
> +		return true;
> +	return false;
> +}
> +
> +/* 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_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;
> +}
> +
> +#define XFS_GETFSMAP_DEVS	2
> +/*
> + * Get filesystem's extents as described in head, and format for
> + * output.  Calls formatter to fill the user's buffer until all
> + * extents are mapped, until the passed-in head->fmh_count slots have
> + * been filled, or until the formatter short-circuits the loop, if it
> + * is tracking filled-in extents on its own.
> + *
> + * 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.
> + */
> +int
> +xfs_getfsmap(
> +	struct xfs_mount		*mp,
> +	struct xfs_fsmap_head		*head,
> +	xfs_fsmap_format_t		formatter,
> +	void				*arg)
> +{
> +	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 = {0};
> +	int				i;
> +	int				error = 0;
> +
> +	if (!xfs_sb_version_hasrmapbt(&mp->m_sb))
> +		return -EOPNOTSUPP;
> +	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;
> +
> +	head->fmh_entries = 0;
> +
> +	/* Set up our device handlers. */
> +	memset(handlers, 0, sizeof(handlers));
> +	handlers[0].dev = new_encode_dev(mp->m_ddev_targp->bt_dev);
> +	handlers[0].fn = xfs_getfsmap_datadev_rmapbt;
> +	if (mp->m_logdev_targp != mp->m_ddev_targp) {
> +		handlers[1].dev = new_encode_dev(mp->m_logdev_targp->bt_dev);
> +		handlers[1].fn = xfs_getfsmap_logdev;
> +	}
> +
> +	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, bump the file offset to
> +	 * continue the search appropriately.  For all other low key
> +	 * mapping types (attr blocks, metadata), bump the physical
> +	 * offset as there can be no other mapping for the same physical
> +	 * block range.
> +	 */
> +	dkeys[0] = head->fmh_keys[0];
> +	if (dkeys[0].fmr_flags & (FMR_OF_SPECIAL_OWNER | FMR_OF_EXTENT_MAP)) {
> +		dkeys[0].fmr_physical += dkeys[0].fmr_length;
> +		dkeys[0].fmr_owner = 0;
> +		if (dkeys[0].fmr_offset)
> +			return -EINVAL;
> +	} else
> +		dkeys[0].fmr_offset += dkeys[0].fmr_length;
> +	dkeys[0].fmr_length = 0;
> +	memset(&dkeys[1], 0xFF, sizeof(struct xfs_fsmap));
> +
> +	if (!xfs_getfsmap_check_keys(dkeys, &head->fmh_keys[1]))
> +		return -EINVAL;
> +
> +	info.next_daddr = head->fmh_keys[0].fmr_physical +
> +			  head->fmh_keys[0].fmr_length;
> +	info.formatter = formatter;
> +	info.format_arg = arg;
> +	info.head = head;
> +
> +	/* 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.  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[1].fmr_device)
> +			dkeys[1] = head->fmh_keys[1];
> +		if (handlers[i].dev > head->fmh_keys[0].fmr_device)
> +			memset(&dkeys[0], 0, sizeof(struct xfs_fsmap));
> +
> +		error = xfs_trans_alloc_empty(mp, &tp);
> +		if (error)
> +			break;
> +
> +		info.dev = handlers[i].dev;
> +		info.last = false;
> +		info.agno = NULLAGNUMBER;
> +		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);
> +	head->fmh_oflags = FMH_OF_DEV_T;
> +	return error;
> +}
> diff --git a/fs/xfs/xfs_fsmap.h b/fs/xfs/xfs_fsmap.h
> new file mode 100644
> index 0000000..0b9bf82
> --- /dev/null
> +++ b/fs/xfs/xfs_fsmap.h
> @@ -0,0 +1,53 @@
> +/*
> + * Copyright (C) 2017 Oracle.  All Rights Reserved.
> + *
> + * Author: Darrick J. Wong <darrick.wong@oracle.com>
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License
> + * as published by the Free Software Foundation; either version 2
> + * of the License, or (at your option) any later version.
> + *
> + * This program is distributed in the hope that it would be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program; if not, write the Free Software Foundation,
> + * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301, USA.
> + */
> +#ifndef __XFS_FSMAP_H__
> +#define __XFS_FSMAP_H__
> +
> +struct fsmap;
> +
> +/* internal fsmap representation */
> +struct xfs_fsmap {
> +	dev_t		fmr_device;	/* device id */
> +	uint32_t	fmr_flags;	/* mapping flags */
> +	uint64_t	fmr_physical;	/* device offset of segment */
> +	uint64_t	fmr_owner;	/* owner id */
> +	xfs_fileoff_t	fmr_offset;	/* file offset of segment */
> +	xfs_filblks_t	fmr_length;	/* length of segment, blocks */
> +};
> +
> +struct xfs_fsmap_head {
> +	uint32_t	fmh_iflags;	/* control flags */
> +	uint32_t	fmh_oflags;	/* output flags */
> +	unsigned int	fmh_count;	/* # of entries in array incl. input */
> +	unsigned int	fmh_entries;	/* # of entries filled in (output). */
> +
> +	struct xfs_fsmap fmh_keys[2];	/* low and high keys */
> +};
> +
> +void xfs_fsmap_from_internal(struct fsmap *dest, struct xfs_fsmap *src);
> +void xfs_fsmap_to_internal(struct xfs_fsmap *dest, struct fsmap *src);
> +
> +/* fsmap to userspace formatter - copy to user & advance pointer */
> +typedef int (*xfs_fsmap_format_t)(struct xfs_fsmap *, void *);
> +
> +int xfs_getfsmap(struct xfs_mount *mp, struct xfs_fsmap_head *head,
> +		xfs_fsmap_format_t formatter, void *arg);
> +
> +#endif /* __XFS_FSMAP_H__ */
> diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
> index c67cfb4..52f635a 100644
> --- a/fs/xfs/xfs_ioctl.c
> +++ b/fs/xfs/xfs_ioctl.c
> @@ -41,6 +41,9 @@
>  #include "xfs_trans.h"
>  #include "xfs_pnfs.h"
>  #include "xfs_acl.h"
> +#include "xfs_btree.h"
> +#include <linux/fsmap.h>
> +#include "xfs_fsmap.h"
>  
>  #include <linux/capability.h>
>  #include <linux/dcache.h>
> @@ -1607,6 +1610,84 @@ xfs_ioc_getbmapx(
>  	return 0;
>  }
>  
> +struct getfsmap_info {
> +	struct xfs_mount	*mp;
> +	struct fsmap __user	*data;
> +	__u32			last_flags;
> +};
> +
> +STATIC int
> +xfs_getfsmap_format(struct xfs_fsmap *xfm, void *priv)
> +{
> +	struct getfsmap_info	*info = priv;
> +	struct fsmap		fm;
> +
> +	trace_xfs_getfsmap_mapping(info->mp, xfm);
> +
> +	info->last_flags = xfm->fmr_flags;
> +	xfs_fsmap_from_internal(&fm, xfm);
> +	if (copy_to_user(info->data, &fm, sizeof(struct fsmap)))
> +		return -EFAULT;
> +
> +	info->data++;
> +	return 0;
> +}
> +
> +STATIC int
> +xfs_ioc_getfsmap(
> +	struct xfs_inode	*ip,
> +	void			__user *arg)
> +{
> +	struct getfsmap_info	info;
> +	struct xfs_fsmap_head	xhead = {0};
> +	struct fsmap_head	head;
> +	bool			aborted = 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;
> +
> +	xhead.fmh_iflags = head.fmh_iflags;
> +	xhead.fmh_count = head.fmh_count;
> +	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]);
> +
> +	info.mp = ip->i_mount;
> +	info.data = ((__force struct fsmap_head *)arg)->fmh_recs;
> +	error = xfs_getfsmap(ip->i_mount, &xhead, xfs_getfsmap_format, &info);
> +	if (error == XFS_BTREE_QUERY_RANGE_ABORT) {
> +		error = 0;
> +		aborted = true;
> +	} else if (error)
> +		return error;
> +
> +	/* If we didn't abort, set the "last" flag in the last fmx */
> +	if (!aborted && xhead.fmh_entries) {
> +		info.data--;
> +		info.last_flags |= FMR_OF_LAST;
> +		if (copy_to_user(&info.data->fmr_flags, &info.last_flags,
> +				sizeof(info.last_flags)))
> +			return -EFAULT;
> +	}
> +
> +	/* copy back header */
> +	head.fmh_entries = xhead.fmh_entries;
> +	head.fmh_oflags = xhead.fmh_oflags;
> +	if (copy_to_user(arg, &head, sizeof(struct fsmap_head)))
> +		return -EFAULT;
> +
> +	return 0;
> +}
> +
>  int
>  xfs_ioc_swapext(
>  	xfs_swapext_t	*sxp)
> @@ -1787,6 +1868,9 @@ xfs_file_ioctl(
>  	case XFS_IOC_GETBMAPX:
>  		return xfs_ioc_getbmapx(ip, arg);
>  
> +	case FS_IOC_GETFSMAP:
> +		return xfs_ioc_getfsmap(ip, arg);
> +
>  	case XFS_IOC_FD_TO_HANDLE:
>  	case XFS_IOC_PATH_TO_HANDLE:
>  	case XFS_IOC_PATH_TO_FSHANDLE: {
> diff --git a/fs/xfs/xfs_ioctl32.c b/fs/xfs/xfs_ioctl32.c
> index 7c49938..fa0bc4d 100644
> --- a/fs/xfs/xfs_ioctl32.c
> +++ b/fs/xfs/xfs_ioctl32.c
> @@ -20,6 +20,7 @@
>  #include <linux/mount.h>
>  #include <linux/slab.h>
>  #include <linux/uaccess.h>
> +#include <linux/fsmap.h>
>  #include "xfs.h"
>  #include "xfs_fs.h"
>  #include "xfs_format.h"
> @@ -554,6 +555,7 @@ xfs_file_compat_ioctl(
>  	case XFS_IOC_GOINGDOWN:
>  	case XFS_IOC_ERROR_INJECTION:
>  	case XFS_IOC_ERROR_CLEARALL:
> +	case FS_IOC_GETFSMAP:
>  		return xfs_file_ioctl(filp, cmd, p);
>  #ifndef BROKEN_X86_ALIGNMENT
>  	/* These are handled fine if no alignment issues */
> diff --git a/fs/xfs/xfs_trace.c b/fs/xfs/xfs_trace.c
> index 7f17ae6..5d95fe3 100644
> --- a/fs/xfs/xfs_trace.c
> +++ b/fs/xfs/xfs_trace.c
> @@ -47,6 +47,7 @@
>  #include "xfs_inode_item.h"
>  #include "xfs_bmap_btree.h"
>  #include "xfs_filestream.h"
> +#include "xfs_fsmap.h"
>  
>  /*
>   * We include this last to have the helpers above available for the trace
> diff --git a/fs/xfs/xfs_trace.h b/fs/xfs/xfs_trace.h
> index d3d11905..ef666e6 100644
> --- a/fs/xfs/xfs_trace.h
> +++ b/fs/xfs/xfs_trace.h
> @@ -40,6 +40,8 @@ struct xfs_inode_log_format;
>  struct xfs_bmbt_irec;
>  struct xfs_btree_cur;
>  struct xfs_refcount_irec;
> +struct xfs_fsmap;
> +struct xfs_rmap_irec;
>  
>  DECLARE_EVENT_CLASS(xfs_attr_list_class,
>  	TP_PROTO(struct xfs_attr_list_context *ctx),
> @@ -3270,6 +3272,88 @@ DEFINE_INODE_IREC_EVENT(xfs_swap_extent_rmap_remap);
>  DEFINE_INODE_IREC_EVENT(xfs_swap_extent_rmap_remap_piece);
>  DEFINE_INODE_ERROR_EVENT(xfs_swap_extent_rmap_error);
>  
> +/* fsmap traces */
> +DECLARE_EVENT_CLASS(xfs_fsmap_class,
> +	TP_PROTO(struct xfs_mount *mp, u32 keydev, xfs_agnumber_t agno,
> +		 struct xfs_rmap_irec *rmap),
> +	TP_ARGS(mp, keydev, agno, rmap),
> +	TP_STRUCT__entry(
> +		__field(dev_t, dev)
> +		__field(dev_t, keydev)
> +		__field(xfs_agnumber_t, agno)
> +		__field(xfs_fsblock_t, bno)
> +		__field(xfs_filblks_t, len)
> +		__field(__uint64_t, owner)
> +		__field(__uint64_t, offset)
> +		__field(unsigned int, flags)
> +	),
> +	TP_fast_assign(
> +		__entry->dev = mp->m_super->s_dev;
> +		__entry->keydev = new_decode_dev(keydev);
> +		__entry->agno = agno;
> +		__entry->bno = rmap->rm_startblock;
> +		__entry->len = rmap->rm_blockcount;
> +		__entry->owner = rmap->rm_owner;
> +		__entry->offset = rmap->rm_offset;
> +		__entry->flags = rmap->rm_flags;
> +	),
> +	TP_printk("dev %d:%d keydev %d:%d agno %u bno %llu len %llu owner %lld offset %llu flags 0x%x\n",
> +		  MAJOR(__entry->dev), MINOR(__entry->dev),
> +		  MAJOR(__entry->keydev), MINOR(__entry->keydev),
> +		  __entry->agno,
> +		  __entry->bno,
> +		  __entry->len,
> +		  __entry->owner,
> +		  __entry->offset,
> +		  __entry->flags)
> +)
> +#define DEFINE_FSMAP_EVENT(name) \
> +DEFINE_EVENT(xfs_fsmap_class, name, \
> +	TP_PROTO(struct xfs_mount *mp, u32 keydev, xfs_agnumber_t agno, \
> +		 struct xfs_rmap_irec *rmap), \
> +	TP_ARGS(mp, keydev, agno, rmap))
> +DEFINE_FSMAP_EVENT(xfs_fsmap_low_key);
> +DEFINE_FSMAP_EVENT(xfs_fsmap_high_key);
> +DEFINE_FSMAP_EVENT(xfs_fsmap_mapping);
> +
> +DECLARE_EVENT_CLASS(xfs_getfsmap_class,
> +	TP_PROTO(struct xfs_mount *mp, struct xfs_fsmap *fsmap),
> +	TP_ARGS(mp, fsmap),
> +	TP_STRUCT__entry(
> +		__field(dev_t, dev)
> +		__field(dev_t, keydev)
> +		__field(xfs_daddr_t, block)
> +		__field(xfs_daddr_t, len)
> +		__field(__uint64_t, owner)
> +		__field(__uint64_t, offset)
> +		__field(__uint64_t, flags)
> +	),
> +	TP_fast_assign(
> +		__entry->dev = mp->m_super->s_dev;
> +		__entry->keydev = new_decode_dev(fsmap->fmr_device);
> +		__entry->block = fsmap->fmr_physical;
> +		__entry->len = fsmap->fmr_length;
> +		__entry->owner = fsmap->fmr_owner;
> +		__entry->offset = fsmap->fmr_offset;
> +		__entry->flags = fsmap->fmr_flags;
> +	),
> +	TP_printk("dev %d:%d keydev %d:%d block %llu len %llu owner %lld offset %llu flags 0x%llx\n",
> +		  MAJOR(__entry->dev), MINOR(__entry->dev),
> +		  MAJOR(__entry->keydev), MINOR(__entry->keydev),
> +		  __entry->block,
> +		  __entry->len,
> +		  __entry->owner,
> +		  __entry->offset,
> +		  __entry->flags)
> +)
> +#define DEFINE_GETFSMAP_EVENT(name) \
> +DEFINE_EVENT(xfs_getfsmap_class, name, \
> +	TP_PROTO(struct xfs_mount *mp, struct xfs_fsmap *fsmap), \
> +	TP_ARGS(mp, fsmap))
> +DEFINE_GETFSMAP_EVENT(xfs_getfsmap_low_key);
> +DEFINE_GETFSMAP_EVENT(xfs_getfsmap_high_key);
> +DEFINE_GETFSMAP_EVENT(xfs_getfsmap_mapping);
> +
>  #endif /* _TRACE_XFS_H */
>  
>  #undef TRACE_INCLUDE_PATH
> diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
> index 70f42ea..a280e12 100644
> --- a/fs/xfs/xfs_trans.c
> +++ b/fs/xfs/xfs_trans.c
> @@ -263,6 +263,28 @@ xfs_trans_alloc(
>  }
>  
>  /*
> + * Create an empty transaction with no reservation.  This is a defensive
> + * mechanism for routines that query metadata without actually modifying
> + * them -- if the metadata being queried is somehow cross-linked (think a
> + * btree block pointer that points higher in the tree), we risk deadlock.
> + * However, blocks grabbed as part of a transaction can be re-grabbed.
> + * The verifiers will notice the corrupt block and the operation will fail
> + * back to userspace without deadlocking.
> + *
> + * Note the zero-length reservation; this transaction MUST be cancelled
> + * without any dirty data.
> + */
> +int
> +xfs_trans_alloc_empty(
> +	struct xfs_mount		*mp,
> +	struct xfs_trans		**tpp)
> +{
> +	struct xfs_trans_res		resv = {0};
> +
> +	return xfs_trans_alloc(mp, &resv, 0, 0, XFS_TRANS_NO_WRITECOUNT, tpp);
> +}
> +
> +/*
>   * Record the indicated change to the given field for application
>   * to the file system's superblock when the transaction commits.
>   * For now, just store the change in the transaction structure.
> diff --git a/fs/xfs/xfs_trans.h b/fs/xfs/xfs_trans.h
> index 61b7fbd..98024cb 100644
> --- a/fs/xfs/xfs_trans.h
> +++ b/fs/xfs/xfs_trans.h
> @@ -159,6 +159,8 @@ typedef struct xfs_trans {
>  int		xfs_trans_alloc(struct xfs_mount *mp, struct xfs_trans_res *resp,
>  			uint blocks, uint rtextents, uint flags,
>  			struct xfs_trans **tpp);
> +int		xfs_trans_alloc_empty(struct xfs_mount *mp,
> +			struct xfs_trans **tpp);
>  void		xfs_trans_mod_sb(xfs_trans_t *, uint, int64_t);
>  
>  struct xfs_buf	*xfs_trans_get_buf_map(struct xfs_trans *tp,
> --
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