Btrfs: introduce grab/put functions for the root of the fs/file tree

[firefly-linux-kernel-4.4.55.git] / fs / btrfs / disk-io.h

diff --git a/fs/btrfs/disk-io.h b/fs/btrfs/disk-io.h
index 534d583e609db9cbb4686461057d27412750d45f..b71acd6e1e5b1941e75ed4c5c056d47268cdc407 100644 (file)
--- a/fs/btrfs/disk-io.h
+++ b/fs/btrfs/disk-io.h
@@ -76,6 +76,27 @@ void btrfs_btree_balance_dirty_nodelay(struct btrfs_root *root);
 void btrfs_drop_and_free_fs_root(struct btrfs_fs_info *fs_info,
                                 struct btrfs_root *root);
 void btrfs_free_fs_root(struct btrfs_root *root);
+
+/*
+ * This function is used to grab the root, and avoid it is freed when we
+ * access it. But it doesn't ensure that the tree is not dropped.
+ *
+ * If you want to ensure the whole tree is safe, you should use
+ *     fs_info->subvol_srcu
+ */
+static inline struct btrfs_root *btrfs_grab_fs_root(struct btrfs_root *root)
+{
+       if (atomic_inc_not_zero(&root->refs))
+               return root;
+       return NULL;
+}
+
+static inline void btrfs_put_fs_root(struct btrfs_root *root)
+{
+       if (atomic_dec_and_test(&root->refs))
+               kfree(root);
+}
+
 void btrfs_mark_buffer_dirty(struct extent_buffer *buf);
 int btrfs_buffer_uptodate(struct extent_buffer *buf, u64 parent_transid,
                          int atomic);