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68415b349f
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: e89c041338 ("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>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.