Btrfs: update nodatacow code v2

This patch simplifies the nodatacow checker. If all references
were created after the latest snapshot, then we can avoid COW
safely. This patch also updates run_delalloc_nocow to do more
fine-grained checking.

Signed-off-by: Yan Zheng <zheng.yan@oracle.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index fd3c8b5676c1..7f915d478399 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -112,6 +112,7 @@ static noinline int create_subvol(struct btrfs_root *root,
         btrfs_set_root_level(&root_item, 0);
         btrfs_set_root_refs(&root_item, 1);
         btrfs_set_root_used(&root_item, 0);
+        btrfs_set_root_last_snapshot(&root_item, 0);
 
         memset(&root_item.drop_progress, 0, sizeof(root_item.drop_progress));
         root_item.drop_level = 0;