Btrfs: fix a bug of per-file nocow

Users report a bug, the reproducer is:
$ mkfs.btrfs /dev/loop0
$ mount /dev/loop0 /mnt/btrfs/
$ mkdir /mnt/btrfs/dir
$ chattr +C /mnt/btrfs/dir/
$ dd if=/dev/zero of=/mnt/btrfs/dir/foo bs=4K count=10;
$ lsattr /mnt/btrfs/dir/foo
---------------C- /mnt/btrfs/dir/foo
$ filefrag /mnt/btrfs/dir/foo
/mnt/btrfs/dir/foo: 1 extent found    ---> an extent
$ dd if=/dev/zero of=/mnt/btrfs/dir/foo bs=4K count=1 seek=5 conv=notrunc,nocreat; sync
$ filefrag /mnt/btrfs/dir/foo
/mnt/btrfs/dir/foo: 3 extents found   ---> with nocow, btrfs breaks the extent into three parts

The new created file should not only inherit the NODATACOW flag, but also
honor NODATASUM flag, because we must do COW on a file extent with checksum.

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>

2 files changed, 5 insertions, 3 deletions

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index e95b1f90a1f6..67ed24ae86bb 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -4818,8 +4818,7 @@ static struct inode *btrfs_new_inode(struct btrfs_trans_handle *trans,
         if (S_ISREG(mode)) {
                 if (btrfs_test_opt(root, NODATASUM))
                         BTRFS_I(inode)->flags |= BTRFS_INODE_NODATASUM;
-                if (btrfs_test_opt(root, NODATACOW) ||
-                    (BTRFS_I(dir)->flags & BTRFS_INODE_NODATACOW))
+                if (btrfs_test_opt(root, NODATACOW))
                         BTRFS_I(inode)->flags |= BTRFS_INODE_NODATACOW;
         }
 
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index d4608ab72b79..7624212ae926 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -141,8 +141,11 @@ void btrfs_inherit_iflags(struct inode *inode, struct inode *dir)
                 BTRFS_I(inode)->flags |= BTRFS_INODE_COMPRESS;
         }
 
-        if (flags & BTRFS_INODE_NODATACOW)
+        if (flags & BTRFS_INODE_NODATACOW) {
                 BTRFS_I(inode)->flags |= BTRFS_INODE_NODATACOW;
+                if (S_ISREG(inode->i_mode))
+                        BTRFS_I(inode)->flags |= BTRFS_INODE_NODATASUM;
+        }
 
         btrfs_update_iflags(inode);
 }