btrfs: sysfs: add UUID/debug/discard directory

Setup base sysfs directory for discard stats + tunables.
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

@@ -930,6 +930,7 @@ struct btrfs_fs_info {
 
 #ifdef CONFIG_BTRFS_DEBUG
 	struct kobject *debug_kobj;
+	struct kobject *discard_debug_kobj;
 #endif
 };
 

fs/btrfs/sysfs.c

@@ -338,6 +338,13 @@ static const struct attribute_group btrfs_static_feature_attr_group = {
 
 #ifdef CONFIG_BTRFS_DEBUG
 
+/*
+ * Discard statistics and tunables
+ */
+static const struct attribute *discard_debug_attrs[] = {
+	NULL,
+};
+
 /*
  * Runtime debugging exported via sysfs
  *
@@ -776,6 +783,12 @@ void btrfs_sysfs_remove_mounted(struct btrfs_fs_info *fs_info)
 		kobject_put(fs_info->space_info_kobj);
 	}
 #ifdef CONFIG_BTRFS_DEBUG
+	if (fs_info->discard_debug_kobj) {
+		sysfs_remove_files(fs_info->discard_debug_kobj,
+				   discard_debug_attrs);
+		kobject_del(fs_info->discard_debug_kobj);
+		kobject_put(fs_info->discard_debug_kobj);
+	}
 	if (fs_info->debug_kobj) {
 		sysfs_remove_files(fs_info->debug_kobj, btrfs_debug_mount_attrs);
 		kobject_del(fs_info->debug_kobj);
@@ -1127,6 +1140,19 @@ int btrfs_sysfs_add_mounted(struct btrfs_fs_info *fs_info)
 	error = sysfs_create_files(fs_info->debug_kobj, btrfs_debug_mount_attrs);
 	if (error)
 		goto failure;
+
+	/* Discard directory */
+	fs_info->discard_debug_kobj = kobject_create_and_add("discard",
+						     fs_info->debug_kobj);
+	if (!fs_info->discard_debug_kobj) {
+		error = -ENOMEM;
+		goto failure;
+	}
+
+	error = sysfs_create_files(fs_info->discard_debug_kobj,
+				   discard_debug_attrs);
+	if (error)
+		goto failure;
 #endif
 
 	error = addrm_unknown_feature_attrs(fs_info, true);