Re: [PATCH V3 1/2] xfs: Fix the owner setting issue for rmap query in xfs fsmap

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

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@huawei.com>
> ---
>  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
> 
>