btrfs: kill magical embedded struct superblock

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/btrfs/ctree.h

@@ -1219,7 +1219,7 @@ struct btrfs_root {
 	 * right now this just gets used so that a root has its own devid
 	 * for stat.  It may be used for more later
 	 */
-	struct super_block anon_super;
+	dev_t anon_dev;
 };
 
 struct btrfs_ioctl_defrag_range_args {

fs/btrfs/disk-io.c

@@ -1077,12 +1077,7 @@ static int __setup_root(u32 nodesize, u32 leafsize, u32 sectorsize,
 	init_completion(&root->kobj_unregister);
 	root->defrag_running = 0;
 	root->root_key.objectid = objectid;
-	root->anon_super.s_root = NULL;
-	root->anon_super.s_dev = 0;
-	INIT_LIST_HEAD(&root->anon_super.s_list);
-	INIT_LIST_HEAD(&root->anon_super.s_instances);
-	init_rwsem(&root->anon_super.s_umount);
-
+	root->anon_dev = 0;
 	return 0;
 }
 
@@ -1311,7 +1306,7 @@ again:
 	spin_lock_init(&root->cache_lock);
 	init_waitqueue_head(&root->cache_wait);
 
-	ret = set_anon_super(&root->anon_super, NULL);
+	ret = get_anon_bdev(&root->anon_dev);
 	if (ret)
 		goto fail;
 
@@ -2393,10 +2388,8 @@ static void free_fs_root(struct btrfs_root *root)
 {
 	iput(root->cache_inode);
 	WARN_ON(!RB_EMPTY_ROOT(&root->inode_tree));
-	if (root->anon_super.s_dev) {
-		down_write(&root->anon_super.s_umount);
-		kill_anon_super(&root->anon_super);
-	}
+	if (root->anon_dev)
+		free_anon_bdev(root->anon_dev);
 	free_extent_buffer(root->node);
 	free_extent_buffer(root->commit_root);
 	kfree(root->free_ino_ctl);

fs/btrfs/inode.c

@@ -6900,7 +6900,7 @@ static int btrfs_getattr(struct vfsmount *mnt,
 {
 	struct inode *inode = dentry->d_inode;
 	generic_fillattr(inode, stat);
-	stat->dev = BTRFS_I(inode)->root->anon_super.s_dev;
+	stat->dev = BTRFS_I(inode)->root->anon_dev;
 	stat->blksize = PAGE_CACHE_SIZE;
 	stat->blocks = (inode_get_bytes(inode) +
 			BTRFS_I(inode)->delalloc_bytes) >> 9;

fs/super.c

@@ -693,7 +693,7 @@ static DEFINE_IDA(unnamed_dev_ida);
 static DEFINE_SPINLOCK(unnamed_dev_lock);/* protects the above */
 static int unnamed_dev_start = 0; /* don't bother trying below it */
 
-int set_anon_super(struct super_block *s, void *data)
+int get_anon_bdev(dev_t *p)
 {
 	int dev;
 	int error;
@@ -720,23 +720,37 @@ int set_anon_super(struct super_block *s, void *data)
 		spin_unlock(&unnamed_dev_lock);
 		return -EMFILE;
 	}
-	s->s_dev = MKDEV(0, dev & MINORMASK);
-	s->s_bdi = &noop_backing_dev_info;
+	*p = MKDEV(0, dev & MINORMASK);
 	return 0;
 }
+EXPORT_SYMBOL(get_anon_bdev);
+
+void free_anon_bdev(dev_t dev)
+{
+	int slot = MINOR(dev);
+	spin_lock(&unnamed_dev_lock);
+	ida_remove(&unnamed_dev_ida, slot);
+	if (slot < unnamed_dev_start)
+		unnamed_dev_start = slot;
+	spin_unlock(&unnamed_dev_lock);
+}
+EXPORT_SYMBOL(free_anon_bdev);
+
+int set_anon_super(struct super_block *s, void *data)
+{
+	int error = get_anon_bdev(&s->s_dev);
+	if (!error)
+		s->s_bdi = &noop_backing_dev_info;
+	return error;
+}
 
 EXPORT_SYMBOL(set_anon_super);
 
 void kill_anon_super(struct super_block *sb)
 {
-	int slot = MINOR(sb->s_dev);
-
+	dev_t dev = sb->s_dev;
 	generic_shutdown_super(sb);
-	spin_lock(&unnamed_dev_lock);
-	ida_remove(&unnamed_dev_ida, slot);
-	if (slot < unnamed_dev_start)
-		unnamed_dev_start = slot;
-	spin_unlock(&unnamed_dev_lock);
+	free_anon_bdev(dev);
 }
 
 EXPORT_SYMBOL(kill_anon_super);

include/linux/fs.h

@@ -1835,6 +1835,8 @@ void kill_litter_super(struct super_block *sb);
 void deactivate_super(struct super_block *sb);
 void deactivate_locked_super(struct super_block *sb);
 int set_anon_super(struct super_block *s, void *data);
+int get_anon_bdev(dev_t *);
+void free_anon_bdev(dev_t);
 struct super_block *sget(struct file_system_type *type,
 			int (*test)(struct super_block *,void *),
 			int (*set)(struct super_block *,void *),