btrfs: sysfs: make UUID/debug have its own kobject

Btrfs only allowed attributes to be exposed in debug/. Let's let other
groups be created by making debug its own kobject.

This also makes the per-fs debug options separate from the global
features mount attributes. This seems to be needed as
sysfs_create_files() requires const struct attribute * while
sysfs_create_group() can take struct attribute *. This seems nicer as
per file system, you'll probably use to_fs_info().
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Dennis Zhou <dennis@kernel.org>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/ctree.h

@@ -927,6 +927,10 @@ struct btrfs_fs_info {
 	spinlock_t ref_verify_lock;
 	struct rb_root block_tree;
 #endif
+
+#ifdef CONFIG_BTRFS_DEBUG
+	struct kobject *debug_kobj;
+#endif
 };
 
 static inline struct btrfs_fs_info *btrfs_sb(struct super_block *sb)

fs/btrfs/sysfs.c

@@ -344,6 +344,10 @@ static const struct attribute_group btrfs_static_feature_attr_group = {
  * /sys/fs/btrfs/debug - applies to module or all filesystems
  * /sys/fs/btrfs/UUID  - applies only to the given filesystem
  */
+static const struct attribute *btrfs_debug_mount_attrs[] = {
+	NULL,
+};
+
 static struct attribute *btrfs_debug_feature_attrs[] = {
 	NULL
 };
@@ -772,8 +776,11 @@ void btrfs_sysfs_remove_mounted(struct btrfs_fs_info *fs_info)
 		kobject_put(fs_info->space_info_kobj);
 	}
 #ifdef CONFIG_BTRFS_DEBUG
-	sysfs_remove_group(&fs_info->fs_devices->fsid_kobj,
-			   &btrfs_debug_feature_attr_group);
+	if (fs_info->debug_kobj) {
+		sysfs_remove_files(fs_info->debug_kobj, btrfs_debug_mount_attrs);
+		kobject_del(fs_info->debug_kobj);
+		kobject_put(fs_info->debug_kobj);
+	}
 #endif
 	addrm_unknown_feature_attrs(fs_info, false);
 	sysfs_remove_group(&fs_info->fs_devices->fsid_kobj, &btrfs_feature_attr_group);
@@ -1111,8 +1118,13 @@ int btrfs_sysfs_add_mounted(struct btrfs_fs_info *fs_info)
 		goto failure;
 
 #ifdef CONFIG_BTRFS_DEBUG
-	error = sysfs_create_group(fsid_kobj,
-				   &btrfs_debug_feature_attr_group);
+	fs_info->debug_kobj = kobject_create_and_add("debug", fsid_kobj);
+	if (!fs_info->debug_kobj) {
+		error = -ENOMEM;
+		goto failure;
+	}
+
+	error = sysfs_create_files(fs_info->debug_kobj, btrfs_debug_mount_attrs);
 	if (error)
 		goto failure;
 #endif