On Mon, Aug 12, 2024 at 09:15:04AM +0800, Zizhi Wo wrote:
> 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 == 0
> dest->rm_owner = 0
> // get nothing
> xfs_getfsmap_datadev_rmapbt_query
>
> The problem can be resolved by setting the rm_owner of high to ULLONG_MAX
> again under certain conditions.
>
> 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@xxxxxxxxxx>
> ---
> fs/xfs/xfs_fsmap.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/fs/xfs/xfs_fsmap.c b/fs/xfs/xfs_fsmap.c
> index 85dbb46452ca..d346acff7725 100644
> --- a/fs/xfs/xfs_fsmap.c
> +++ b/fs/xfs/xfs_fsmap.c
> @@ -655,6 +655,13 @@ __xfs_getfsmap_datadev(
> error = xfs_fsmap_owner_to_rmap(&info->high, &keys[1]);
> if (error)
> break;
> + /*
> + * Set the owner of high_key to the maximum again to
> + * prevent missing intervals during the query.
> + */
> + if (info->high.rm_owner == 0 &&
> + info->missing_owner == XFS_FMR_OWN_FREE)
> + info->high.rm_owner = ULLONG_MAX;
Shouldn't this be in xfs_fsmap_owner_to_rmap?
And, looking at that function, isn't this the solution:
switch (src->fmr_owner) {
case 0: /* "lowest owner id possible" */
case -1ULL: /* "highest owner id possible" */
dest->rm_owner = src->fmr_owner;
break;
instead of this special-casing outside the setter function?
--D
> xfs_getfsmap_set_irec_flags(&info->high, &keys[1]);
> }
>
> --
> 2.39.2
>
>
