[PATCH 110/119] xfs: fail ->bmap for reflink inodes

Darrick J. Wong
2016-06-17T01:29:53Z

From: Christoph Hellwig <hch@lst.de>

Have xfs_vm_bmap return zero for reflinked files. This hack prevents
using a file with shared blocks as a swap file, because we don't want
to deal with CoW when we're (probably) low on memory.

Signed-off-by: Christoph Hellwig <hch@lst.de>
[darrick.wong@oracle.com: add a more descriptive changelog]
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
fs/xfs/xfs_aops.c | 11 +++++++++++
1 file changed, 11 insertions(+)

diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
index 31205fa..83fd028 100644
--- a/fs/xfs/xfs_aops.c
+++ b/fs/xfs/xfs_aops.c
@@ -1827,6 +1827,17 @@ 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);