btrfs: Add function to distinguish between data and btree inode

This will be used in future patches that remove the optional
extent_io_ops callbacks.
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/btrfs_inode.h

@@ -253,6 +253,11 @@ static inline bool btrfs_is_free_space_inode(struct btrfs_inode *inode)
 	return false;
 }
 
+static inline bool is_data_inode(struct inode *inode)
+{
+	return btrfs_ino(BTRFS_I(inode)) != BTRFS_BTREE_INODE_OBJECTID;
+}
+
 static inline void btrfs_mod_outstanding_extents(struct btrfs_inode *inode,
 						 int mod)
 {