xfs: fix overlapping extents returned for pNFS LAYOUTGET

xfs: fix overlapping extents returned for pNFS LAYOUTGET

xfs_fs_map_blocks() currently passes XFS_BMAPI_ENTIRE to xfs_bmapi_read(),
which causes the bmap code to expand the mapping to cover the entire
extent rather than the requested range.

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.

Problem discovered with xfstest generic/075 test using NFSv4.2 mount
with SCSI layout.

Fix this by replacing the XFS_BMAPI_ENTIRE flag with '0' so that
xfs_bmapi_read() returns only the mapping for the requested range.

Fixes: cc6c40e09d7b1 ("NFSD/blocklayout: Support multiple extents per LAYOUTGET").
Signed-off-by: Dai Ngo <dai.ngo@oracle.com>
Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Carlos Maiolino <cem@kernel.org>