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>

diff --git a/fs/btrfs/ordered-data.c b/fs/btrfs/ordered-data.c
index b5745bb..e7317c8 100644
--- a/fs/btrfs/ordered-data.c
+++ b/fs/btrfs/ordered-data.c
@@ -165,8 +165,7 @@
  * inserted.
  */
 int btrfs_add_ordered_extent(struct inode *inode, u64 file_offset,
-			     u64 start, u64 len, u64 disk_len, int nocow,
-			     int compressed)
+			     u64 start, u64 len, u64 disk_len, int type)
 {
 	struct btrfs_ordered_inode_tree *tree;
 	struct rb_node *node;
@@ -183,10 +182,8 @@
 	entry->len = len;
 	entry->disk_len = disk_len;
 	entry->inode = inode;
-	if (nocow)
-		set_bit(BTRFS_ORDERED_NOCOW, &entry->flags);
-	if (compressed)
-		set_bit(BTRFS_ORDERED_COMPRESSED, &entry->flags);
+	if (type == BTRFS_ORDERED_NOCOW || type == BTRFS_ORDERED_COMPRESSED)
+		set_bit(type, &entry->flags);
 
 	/* one ref for the tree */
 	atomic_set(&entry->refs, 1);