f2fs: introduce a new per-sb directory in sysfs

Add a new directory 'stat' in path of /sys/fs/f2fs/<devname>/, later
we can add new readonly stat sysfs file into this directory, it will
make <devname> directory less mess.
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/f2fs.h

@@ -1545,9 +1545,12 @@ struct f2fs_sb_info {
 	unsigned int node_io_flag;
 
 	/* For sysfs suppport */
-	struct kobject s_kobj;
+	struct kobject s_kobj;			/* /sys/fs/f2fs/<devname> */
 	struct completion s_kobj_unregister;
 
+	struct kobject s_stat_kobj;		/* /sys/fs/f2fs/<devname>/stat */
+	struct completion s_stat_kobj_unregister;
+
 	/* For shrinker support */
 	struct list_head s_list;
 	int s_ndevs;				/* number of devices */

fs/f2fs/sysfs.c

@@ -702,6 +702,11 @@ static struct attribute *f2fs_feat_attrs[] = {
 };
 ATTRIBUTE_GROUPS(f2fs_feat);
 
+static struct attribute *f2fs_stat_attrs[] = {
+	NULL,
+};
+ATTRIBUTE_GROUPS(f2fs_stat);
+
 static const struct sysfs_ops f2fs_attr_ops = {
 	.show	= f2fs_attr_show,
 	.store	= f2fs_attr_store,
@@ -730,6 +735,44 @@ static struct kobject f2fs_feat = {
 	.kset	= &f2fs_kset,
 };
 
+static ssize_t f2fs_stat_attr_show(struct kobject *kobj,
+				struct attribute *attr, char *buf)
+{
+	struct f2fs_sb_info *sbi = container_of(kobj, struct f2fs_sb_info,
+								s_stat_kobj);
+	struct f2fs_attr *a = container_of(attr, struct f2fs_attr, attr);
+
+	return a->show ? a->show(a, sbi, buf) : 0;
+}
+
+static ssize_t f2fs_stat_attr_store(struct kobject *kobj, struct attribute *attr,
+						const char *buf, size_t len)
+{
+	struct f2fs_sb_info *sbi = container_of(kobj, struct f2fs_sb_info,
+								s_stat_kobj);
+	struct f2fs_attr *a = container_of(attr, struct f2fs_attr, attr);
+
+	return a->store ? a->store(a, sbi, buf, len) : 0;
+}
+
+static void f2fs_stat_kobj_release(struct kobject *kobj)
+{
+	struct f2fs_sb_info *sbi = container_of(kobj, struct f2fs_sb_info,
+								s_stat_kobj);
+	complete(&sbi->s_stat_kobj_unregister);
+}
+
+static const struct sysfs_ops f2fs_stat_attr_ops = {
+	.show	= f2fs_stat_attr_show,
+	.store	= f2fs_stat_attr_store,
+};
+
+static struct kobj_type f2fs_stat_ktype = {
+	.default_groups = f2fs_stat_groups,
+	.sysfs_ops	= &f2fs_stat_attr_ops,
+	.release	= f2fs_stat_kobj_release,
+};
+
 static int __maybe_unused segment_info_seq_show(struct seq_file *seq,
 						void *offset)
 {
@@ -936,11 +979,15 @@ int f2fs_register_sysfs(struct f2fs_sb_info *sbi)
 	init_completion(&sbi->s_kobj_unregister);
 	err = kobject_init_and_add(&sbi->s_kobj, &f2fs_sb_ktype, NULL,
 				"%s", sb->s_id);
-	if (err) {
-		kobject_put(&sbi->s_kobj);
-		wait_for_completion(&sbi->s_kobj_unregister);
-		return err;
-	}
+	if (err)
+		goto put_sb_kobj;
+
+	sbi->s_stat_kobj.kset = &f2fs_kset;
+	init_completion(&sbi->s_stat_kobj_unregister);
+	err = kobject_init_and_add(&sbi->s_stat_kobj, &f2fs_stat_ktype,
+						&sbi->s_kobj, "stat");
+	if (err)
+		goto put_stat_kobj;
 
 	if (f2fs_proc_root)
 		sbi->s_proc = proc_mkdir(sb->s_id, f2fs_proc_root);
@@ -956,6 +1003,13 @@ int f2fs_register_sysfs(struct f2fs_sb_info *sbi)
 				victim_bits_seq_show, sb);
 	}
 	return 0;
+put_stat_kobj:
+	kobject_put(&sbi->s_stat_kobj);
+	wait_for_completion(&sbi->s_stat_kobj_unregister);
+put_sb_kobj:
+	kobject_put(&sbi->s_kobj);
+	wait_for_completion(&sbi->s_kobj_unregister);
+	return err;
 }
 
 void f2fs_unregister_sysfs(struct f2fs_sb_info *sbi)
@@ -967,6 +1021,11 @@ void f2fs_unregister_sysfs(struct f2fs_sb_info *sbi)
 		remove_proc_entry("victim_bits", sbi->s_proc);
 		remove_proc_entry(sbi->sb->s_id, f2fs_proc_root);
 	}
+
+	kobject_del(&sbi->s_stat_kobj);
+	kobject_put(&sbi->s_stat_kobj);
+	wait_for_completion(&sbi->s_stat_kobj_unregister);
+
 	kobject_del(&sbi->s_kobj);
 	kobject_put(&sbi->s_kobj);
 	wait_for_completion(&sbi->s_kobj_unregister);