[PATCH 5/9] xfs: Fix the owner setting issue for rmap query in xfs fsmap

Darrick J. Wong
2024-08-23T00:00:05Z

From: Zizhi Wo <wozizhi@huawei.com>

I notice a rmap query bug in xfs_io fsmap:
[root@fedora ~]# xfs_io -c 'fsmap -vvvv' /mnt
EXT: DEV BLOCK-RANGE OWNER FILE-OFFSET AG AG-OFFSET TOTAL
0: 253:16 [0..7]: static fs metadata 0 (0..7) 8
1: 253:16 [8..23]: per-AG metadata 0 (8..23) 16
2: 253:16 [24..39]: inode btree 0 (24..39) 16
3: 253:16 [40..47]: per-AG metadata 0 (40..47) 8
4: 253:16 [48..55]: refcount btree 0 (48..55) 8
5: 253:16 [56..103]: per-AG metadata 0 (56..103) 48
6: 253:16 [104..127]: free space 0 (104..127) 24
......

Bug:
[root@fedora ~]# xfs_io -c 'fsmap -vvvv -d 0 3' /mnt
[root@fedora ~]#
Normally, we should be able to get one record, but we got nothing.

The root cause of this problem lies in the incorrect setting of rm_owner in
the rmap query. In the case of the initial query where the owner is not
set, __xfs_getfsmap_datadev() first sets info->high.rm_owner to ULLONG_MAX.
This is done to prevent any omissions when comparing rmap items. However,
if the current ag is detected to be the last one, the function sets info's
high_irec based on the provided key. If high->rm_owner is not specified, it
should continue to be set to ULLONG_MAX; otherwise, there will be issues
with interval omissions. For example, consider "start" and "end" within the
same block. If high->rm_owner == 0, it will be smaller than the founded
record in rmapbt, resulting in a query with no records. The main call stack
is as follows:

xfs_ioc_getfsmap
xfs_getfsmap
xfs_getfsmap_datadev_rmapbt
__xfs_getfsmap_datadev
info->high.rm_owner = ULLONG_MAX
if (pag->pag_agno == end_ag)
xfs_fsmap_owner_to_rmap
// set info->high.rm_owner = 0 because fmr_owner == -1ULL
dest->rm_owner = 0
// get nothing
xfs_getfsmap_datadev_rmapbt_query

The problem can be resolved by simply modify the xfs_fsmap_owner_to_rmap
function internal logic to achieve.

After applying this patch, the above problem have been solved:
[root@fedora ~]# xfs_io -c 'fsmap -vvvv -d 0 3' /mnt
EXT: DEV BLOCK-RANGE OWNER FILE-OFFSET AG AG-OFFSET TOTAL
0: 253:16 [0..7]: static fs metadata 0 (0..7) 8

Fixes: e89c041338ed ("xfs: implement the GETFSMAP ioctl")
Signed-off-by: Zizhi Wo <wozizhi@huawei.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
---
fs/xfs/xfs_fsmap.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/xfs/xfs_fsmap.c b/fs/xfs/xfs_fsmap.c
index 85dbb46452ca0..3a30b36779db5 100644
--- a/fs/xfs/xfs_fsmap.c
+++ b/fs/xfs/xfs_fsmap.c
@@ -71,7 +71,7 @@ xfs_fsmap_owner_to_rmap(
switch (src->fmr_owner) {
case 0: /* "lowest owner id possible" */
case -1ULL: /* "highest owner id possible" */
- dest->rm_owner = 0;
+ dest->rm_owner = src->fmr_owner;
break;
case XFS_FMR_OWN_FREE:
dest->rm_owner = XFS_RMAP_OWN_NULL;