xfs: report shared extent mappings to userspace correctly

Report shared extents through the iomap interface so that FIEMAP flags
shared blocks accurately.  Have xfs_vm_bmap return zero for reflinked
files because the bmap-based swap code requires static block mappings,
which is incompatible with copy on write.

NOTE: Existing userspace bmap users such as lilo will have the same
problem with reflink files.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

1 files changed, 11 insertions, 1 deletions

diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index ad6939df9680..765849ed9b70 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -961,6 +961,7 @@ xfs_file_iomap_begin(
 	struct xfs_mount	*mp = ip->i_mount;
 	struct xfs_bmbt_irec	imap;
 	xfs_fileoff_t		offset_fsb, end_fsb;
+	bool			shared, trimmed;
 	int			nimaps = 1, error = 0;
 	unsigned		lockmode;
 
@@ -989,7 +990,14 @@ xfs_file_iomap_begin(
 	end_fsb = XFS_B_TO_FSB(mp, offset + length);
 
 	error = xfs_bmapi_read(ip, offset_fsb, end_fsb - offset_fsb, &imap,
-			       &nimaps, XFS_BMAPI_ENTIRE);
+			       &nimaps, 0);
+	if (error) {
+		xfs_iunlock(ip, lockmode);
+		return error;
+	}
+
+	/* Trim the mapping to the nearest shared extent boundary. */
+	error = xfs_reflink_trim_around_shared(ip, &imap, &shared, &trimmed);
 	if (error) {
 		xfs_iunlock(ip, lockmode);
 		return error;
@@ -1028,6 +1036,8 @@ xfs_file_iomap_begin(
 	}
 
 	xfs_bmbt_to_iomap(ip, iomap, &imap);
+	if (shared)
+		iomap->flags |= IOMAP_F_SHARED;
 	return 0;
 }