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>
diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
index f6f5bbc..2f4a15e 100644
--- a/fs/xfs/xfs_aops.c
+++ b/fs/xfs/xfs_aops.c
@@ -1508,6 +1508,17 @@
trace_xfs_vm_bmap(XFS_I(inode));
xfs_ilock(ip, XFS_IOLOCK_SHARED);
+
+ /*
+ * The swap code (ab-)uses ->bmap to get a block mapping and then
+ * bypasseѕ the file system for actual I/O. We really can't allow
+ * that on reflinks inodes, so we have to skip out here. And yes,
+ * 0 is the magic code for a bmap error..
+ */
+ if (xfs_is_reflink_inode(ip)) {
+ xfs_iunlock(ip, XFS_IOLOCK_SHARED);
+ return 0;
+ }
filemap_write_and_wait(mapping);
xfs_iunlock(ip, XFS_IOLOCK_SHARED);
return generic_block_bmap(mapping, block, xfs_get_blocks);
diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index ad6939d..765849e 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -961,6 +961,7 @@
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 @@
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_bmbt_to_iomap(ip, iomap, &imap);
+ if (shared)
+ iomap->flags |= IOMAP_F_SHARED;
return 0;
}