Re: [PATCH 1/1] xfs: fix overlapping extents returned for pNFS LAYOUTGET

[Christoph Hellwig <hch@infradead.org>]

On Tue, May 12, 2026 at 10:21:53AM -0700, Dai Ngo wrote:
> A single LAYOUTGET request from the client can cause the server to
> issue multiple calls to xfs_fs_map_blocks() for different offsets
> within the same extent. Because the use of XFS_BMAPI_ENTIRE flag,
> these calls can produce overlapping mappings.
> 
> As a result, the LAYOUTGET reply sent to the NFS client may contain
> overlapping extents. This creates ambiguity in extent selection for a
> given file range, which can lead to incorrect device selection,
> inconsistent handling of datastate, and ultimately data corruption or
> protocol violations on the client side.

Please also add a check to the client that catches this and doesn't
use the layout that has extents outside the requested range.  And maybe
warn about it as well.

> Also drop the check for (!error) since it was checked after call to
> xfs_bmapi_read().
> 
> Fixes: cc6c40e09d7b1 ("NFSD/blocklayout: Support multiple extents per LAYOUTGET").
> Signed-off-by: Dai Ngo <dai.ngo@oracle.com>
> ---
>  fs/xfs/xfs_pnfs.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> - This patch is based on top of the patch:
>   xfs: fix use of uninitialized imap in xfs_fs_map_blocks error path

The error changes should go into that patch, so please resend it with
that fixes.  Maybe as a series together with this patch to keep them
together.

> @@ -172,6 +172,7 @@ xfs_fs_map_blocks(
>  	offset_fsb = XFS_B_TO_FSBT(mp, offset);
>  
>  	lock_flags = xfs_ilock_data_map_shared(ip);
> +	bmapi_flags = 0;	/* return map for requested range only */

Just remove the variable and hard code the 0 in the xfs_bmapi_read call.