From: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
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@xxxxxxxxxx>
Reviewed-by: Brian Foster <bfoster@xxxxxxxxxx>
---
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 | 756 ++++++++++++++++++++++++++++++++++++++++++++++
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, 1048 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..24b3e53
--- /dev/null
+++ b/fs/xfs/xfs_fsmap.c
@@ -0,0 +1,756 @@
+/*
+ * Copyright (C) 2017 Oracle. All Rights Reserved.
+ *
+ * Author: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
+ *
+ * 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);
+}
+
+/* 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@xxxxxxxxxx>
+ *
+ * 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 2fd7fdf..39aac0a 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/cred.h>
@@ -1608,6 +1611,84 @@ 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 = {0};
+ 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)
@@ -1788,6 +1869,9 @@ 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 383ac22..4f96dc9 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),
@@ -3267,6 +3269,88 @@ 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 1646f65..2a9292d 100644
--- a/fs/xfs/xfs_trans.h
+++ b/fs/xfs/xfs_trans.h
@@ -158,6 +158,8 @@ 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,
