As btrfs(5) specified:
Note
If nodatacow or nodatasum are enabled, compression is disabled.
If NODATASUM or NODATACOW set, we should not compress the extent.
Normally NODATACOW is detected properly in run_delalloc_range() so
compression won't happen for NODATACOW.
However for NODATASUM we don't have any check, and it can cause
compressed extent without csum pretty easily, just by:
mkfs.btrfs -f $dev
mount $dev $mnt -o nodatasum
touch $mnt/foobar
mount -o remount,datasum,compress $mnt
xfs_io -f -c "pwrite 0 128K" $mnt/foobar
And in fact, we have bug report about corrupted compressed extent
without proper data checksum so even RAID1 can't recover the corruption.
(https://bugzilla.kernel.org/show_bug.cgi?id=199707)
Running compression without proper checksum could cause more damage when
corruption happens, so there is no need to allow compression for
NODATACSUM.
Reported-by: James Harvey <jamespharve...@gmail.com>
Signed-off-by: Qu Wenruo <w...@suse.com>
---
fs/btrfs/inode.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index a2aabdb85226..4e0c7f18fa3a 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -398,6 +398,14 @@ static inline int inode_need_compress(struct inode *inode,
u64 start, u64 end)
{
struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
+ /*
+ * Btrfs doesn't support compression without csum or CoW.
+ * This should have the highest priority.
+ */
+ if (BTRFS_I(inode)->flags & BTRFS_INODE_NODATACOW ||
+ BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM)
+ return 0;
+
/* force compress */
if (btrfs_test_opt(fs_info, FORCE_COMPRESS))
return 1;
--
2.22.0
