From: Christoph Hellwig <hch@xxxxxx>
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@xxxxxx>
[darrick.wong@xxxxxxxxxx: add a more descriptive changelog]
Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
---
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 a85bc62..f564d02 100644
--- a/fs/xfs/xfs_aops.c
+++ b/fs/xfs/xfs_aops.c
@@ -1553,6 +1553,17 @@ 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);
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