Re: [PATCH V4 1/2] xfs: Fix the owner setting issue for rmap query in xfs fsmap

["Darrick J. Wong" <djwong@kernel.org>]

On Mon, Aug 19, 2024 at 08:53:19AM +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 == -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>

Looks good,
Reviewed-by: Darrick J. Wong <djwong@kernel.org>

--D

> ---
>  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 85dbb46452ca..3a30b36779db 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;
> -- 
> 2.39.2
> 
>