zonefs: Export open zone resource information through sysfs

To allow applications to easily check the current usage status of the
open zone resources of the mounted device, export through sysfs the
counter of write open sequential files s_wro_seq_files field of
struct zonefs_sb_info. The attribute is named nr_wro_seq_files and is
read only.

The maximum number of write open sequential files (zones) indicated by
the s_max_wro_seq_files field of struct zonefs_sb_info is also exported
as the read only attribute max_wro_seq_files.

Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Hans Holmberg <hans.holmberg@wdc.com>

1 files changed, 125 insertions, 0 deletions

diff --git a/fs/zonefs/sysfs.c b/fs/zonefs/sysfs.c
new file mode 100644
index 000000000000..eaeaf983ed87
--- /dev/null
+++ b/fs/zonefs/sysfs.c
@@ -0,0 +1,125 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Simple file system for zoned block devices exposing zones as files.
+ *
+ * Copyright (C) 2022 Western Digital Corporation or its affiliates.
+ */
+#include <linux/fs.h>
+#include <linux/seq_file.h>
+#include <linux/blkdev.h>
+
+#include "zonefs.h"
+
+struct zonefs_sysfs_attr {
+	struct attribute attr;
+	ssize_t (*show)(struct zonefs_sb_info *sbi, char *buf);
+};
+
+static inline struct zonefs_sysfs_attr *to_attr(struct attribute *attr)
+{
+	return container_of(attr, struct zonefs_sysfs_attr, attr);
+}
+
+#define ZONEFS_SYSFS_ATTR_RO(name) \
+static struct zonefs_sysfs_attr zonefs_sysfs_attr_##name = __ATTR_RO(name)
+
+#define ATTR_LIST(name) &zonefs_sysfs_attr_##name.attr
+
+static ssize_t zonefs_sysfs_attr_show(struct kobject *kobj,
+				      struct attribute *attr, char *buf)
+{
+	struct zonefs_sb_info *sbi =
+		container_of(kobj, struct zonefs_sb_info, s_kobj);
+	struct zonefs_sysfs_attr *zonefs_attr =
+		container_of(attr, struct zonefs_sysfs_attr, attr);
+
+	if (!zonefs_attr->show)
+		return 0;
+
+	return zonefs_attr->show(sbi, buf);
+}
+
+static ssize_t max_wro_seq_files_show(struct zonefs_sb_info *sbi, char *buf)
+{
+	return sysfs_emit(buf, "%u\n", sbi->s_max_wro_seq_files);
+}
+ZONEFS_SYSFS_ATTR_RO(max_wro_seq_files);
+
+static ssize_t nr_wro_seq_files_show(struct zonefs_sb_info *sbi, char *buf)
+{
+	return sysfs_emit(buf, "%d\n", atomic_read(&sbi->s_wro_seq_files));
+}
+ZONEFS_SYSFS_ATTR_RO(nr_wro_seq_files);
+
+static struct attribute *zonefs_sysfs_attrs[] = {
+	ATTR_LIST(max_wro_seq_files),
+	ATTR_LIST(nr_wro_seq_files),
+	NULL,
+};
+ATTRIBUTE_GROUPS(zonefs_sysfs);
+
+static void zonefs_sysfs_sb_release(struct kobject *kobj)
+{
+	struct zonefs_sb_info *sbi =
+		container_of(kobj, struct zonefs_sb_info, s_kobj);
+
+	complete(&sbi->s_kobj_unregister);
+}
+
+static const struct sysfs_ops zonefs_sysfs_attr_ops = {
+	.show	= zonefs_sysfs_attr_show,
+};
+
+static struct kobj_type zonefs_sb_ktype = {
+	.default_groups = zonefs_sysfs_groups,
+	.sysfs_ops	= &zonefs_sysfs_attr_ops,
+	.release	= zonefs_sysfs_sb_release,
+};
+
+static struct kobject *zonefs_sysfs_root;
+
+int zonefs_sysfs_register(struct super_block *sb)
+{
+	struct zonefs_sb_info *sbi = ZONEFS_SB(sb);
+	int ret;
+
+	init_completion(&sbi->s_kobj_unregister);
+	ret = kobject_init_and_add(&sbi->s_kobj, &zonefs_sb_ktype,
+				   zonefs_sysfs_root, "%s", sb->s_id);
+	if (ret) {
+		kobject_put(&sbi->s_kobj);
+		wait_for_completion(&sbi->s_kobj_unregister);
+		return ret;
+	}
+
+	sbi->s_sysfs_registered = true;
+
+	return 0;
+}
+
+void zonefs_sysfs_unregister(struct super_block *sb)
+{
+	struct zonefs_sb_info *sbi = ZONEFS_SB(sb);
+
+	if (!sbi || !sbi->s_sysfs_registered)
+		return;
+
+	kobject_del(&sbi->s_kobj);
+	kobject_put(&sbi->s_kobj);
+	wait_for_completion(&sbi->s_kobj_unregister);
+}
+
+int __init zonefs_sysfs_init(void)
+{
+	zonefs_sysfs_root = kobject_create_and_add("zonefs", fs_kobj);
+	if (!zonefs_sysfs_root)
+		return -ENOMEM;
+
+	return 0;
+}
+
+void zonefs_sysfs_exit(void)
+{
+	kobject_put(zonefs_sysfs_root);
+	zonefs_sysfs_root = NULL;
+}