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 (file)
--- a/fs/xfs/xfs_aops.c
+++ b/fs/xfs/xfs_aops.c
@@ -1508,6 +1508,17 @@ xfs_vm_bmap(
 
        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 (file)
--- 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;
 }