btrfs: use a runtime flag to indicate an inode is a free space inode

We always check the root of an inode as well as it's inode number to
determine if it's a free space inode.  This is problematic as the helper
is in a header file where it doesn't have the fs_info definition.  To
avoid this and make the check a little cleaner simply add a flag to the
runtime_flags to indicate that the inode is a free space inode, set that
when we create the inode, and then change the helper to check for this
flag.
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/btrfs_inode.h

@@ -65,6 +65,8 @@ enum {
 	 * on the same file.
 	 */
 	BTRFS_INODE_VERITY_IN_PROGRESS,
+	/* Set when this inode is a free space inode. */
+	BTRFS_INODE_FREE_SPACE_INODE,
 };
 
 /* in memory btrfs inode */
@@ -301,13 +303,7 @@ static inline void btrfs_i_size_write(struct btrfs_inode *inode, u64 size)
 
 static inline bool btrfs_is_free_space_inode(struct btrfs_inode *inode)
 {
-	struct btrfs_root *root = inode->root;
-
-	if (root == root->fs_info->tree_root &&
-	    btrfs_ino(inode) != BTRFS_BTREE_INODE_OBJECTID)
-		return true;
-
-	return false;
+	return test_bit(BTRFS_INODE_FREE_SPACE_INODE, &inode->runtime_flags);
 }
 
 static inline bool is_data_inode(struct inode *inode)

fs/btrfs/inode.c

@@ -5707,6 +5707,11 @@ static int btrfs_init_locked_inode(struct inode *inode, void *p)
 	BTRFS_I(inode)->location.offset = 0;
 	BTRFS_I(inode)->root = btrfs_grab_root(args->root);
 	BUG_ON(args->root && !BTRFS_I(inode)->root);
+
+	if (args->root && args->root == args->root->fs_info->tree_root &&
+	    args->ino != BTRFS_BTREE_INODE_OBJECTID)
+		set_bit(BTRFS_INODE_FREE_SPACE_INODE,
+			&BTRFS_I(inode)->runtime_flags);
 	return 0;
 }