nilfs2: add /sys/fs/nilfs2/<device>/mounted_snapshots group

This patch adds creation of /sys/fs/nilfs2/<device>/mounted_snapshots
group.

The mounted_snapshots group contains group for every
mounted snapshot.
Signed-off-by: Vyacheslav Dubeyko <Vyacheslav.Dubeyko@hgst.com>
Cc: Vyacheslav Dubeyko <slava@dubeyko.com>
Cc: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Cc: Michael L. Semon <mlsemon35@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/ABI/testing/sysfs-fs-nilfs2

@@ -241,3 +241,10 @@ Contact:	"Vyacheslav Dubeyko" <slava@dubeyko.com>
 Description:
 		Describe attributes of /sys/fs/nilfs2/<device>/checkpoints
 		group.
+
+What:		/sys/fs/nilfs2/<device>/mounted_snapshots/README
+Date:		April 2014
+Contact:	"Vyacheslav Dubeyko" <slava@dubeyko.com>
+Description:
+		Describe content of /sys/fs/nilfs2/<device>/mounted_snapshots
+		group.

fs/nilfs2/sysfs.c

@@ -111,6 +111,32 @@ void nilfs_sysfs_delete_##name##_group(struct the_nilfs *nilfs) \
 	kobject_del(&nilfs->ns_##parent_name##_subgroups->sg_##name##_kobj); \
 }
 
+/************************************************************************
+ *                    NILFS mounted snapshots attrs                     *
+ ************************************************************************/
+
+static const char mounted_snapshots_readme_str[] =
+	"The mounted_snapshots group contains group for\n"
+	"every mounted snapshot.\n";
+
+static ssize_t
+nilfs_mounted_snapshots_README_show(struct nilfs_mounted_snapshots_attr *attr,
+				    struct the_nilfs *nilfs, char *buf)
+{
+	return snprintf(buf, PAGE_SIZE, mounted_snapshots_readme_str);
+}
+
+NILFS_MOUNTED_SNAPSHOTS_RO_ATTR(README);
+
+static struct attribute *nilfs_mounted_snapshots_attrs[] = {
+	NILFS_MOUNTED_SNAPSHOTS_ATTR_LIST(README),
+	NULL,
+};
+
+NILFS_DEV_INT_GROUP_OPS(mounted_snapshots, dev);
+NILFS_DEV_INT_GROUP_TYPE(mounted_snapshots, dev);
+NILFS_DEV_INT_GROUP_FNS(mounted_snapshots, dev);
+
 /************************************************************************
  *                      NILFS checkpoints attrs                         *
  ************************************************************************/
@@ -866,10 +892,14 @@ int nilfs_sysfs_create_device_group(struct super_block *sb)
 	if (err)
 		goto free_dev_subgroups;
 
-	err = nilfs_sysfs_create_checkpoints_group(nilfs);
+	err = nilfs_sysfs_create_mounted_snapshots_group(nilfs);
 	if (err)
 		goto cleanup_dev_kobject;
 
+	err = nilfs_sysfs_create_checkpoints_group(nilfs);
+	if (err)
+		goto delete_mounted_snapshots_group;
+
 	err = nilfs_sysfs_create_segments_group(nilfs);
 	if (err)
 		goto delete_checkpoints_group;
@@ -893,6 +923,9 @@ int nilfs_sysfs_create_device_group(struct super_block *sb)
 delete_checkpoints_group:
 	nilfs_sysfs_delete_checkpoints_group(nilfs);
 
+delete_mounted_snapshots_group:
+	nilfs_sysfs_delete_mounted_snapshots_group(nilfs);
+
 cleanup_dev_kobject:
 	kobject_del(&nilfs->ns_dev_kobj);
 
@@ -905,6 +938,7 @@ int nilfs_sysfs_create_device_group(struct super_block *sb)
 
 void nilfs_sysfs_delete_device_group(struct the_nilfs *nilfs)
 {
+	nilfs_sysfs_delete_mounted_snapshots_group(nilfs);
 	nilfs_sysfs_delete_checkpoints_group(nilfs);
 	nilfs_sysfs_delete_segments_group(nilfs);
 	nilfs_sysfs_delete_superblock_group(nilfs);

fs/nilfs2/sysfs.h

@@ -30,6 +30,8 @@
  * @sg_superblock_kobj_unregister: completion state
  * @sg_segctor_kobj: /sys/fs/<nilfs>/<device>/segctor
  * @sg_segctor_kobj_unregister: completion state
+ * @sg_mounted_snapshots_kobj: /sys/fs/<nilfs>/<device>/mounted_snapshots
+ * @sg_mounted_snapshots_kobj_unregister: completion state
  * @sg_checkpoints_kobj: /sys/fs/<nilfs>/<device>/checkpoints
  * @sg_checkpoints_kobj_unregister: completion state
  * @sg_segments_kobj: /sys/fs/<nilfs>/<device>/segments
@@ -44,6 +46,10 @@ struct nilfs_sysfs_dev_subgroups {
 	struct kobject sg_segctor_kobj;
 	struct completion sg_segctor_kobj_unregister;
 
+	/* /sys/fs/<nilfs>/<device>/mounted_snapshots */
+	struct kobject sg_mounted_snapshots_kobj;
+	struct completion sg_mounted_snapshots_kobj_unregister;
+
 	/* /sys/fs/<nilfs>/<device>/checkpoints */
 	struct kobject sg_checkpoints_kobj;
 	struct completion sg_checkpoints_kobj_unregister;
@@ -75,6 +81,7 @@ struct nilfs_##name##_attr { \
 
 NILFS_DEV_ATTR_STRUCT(dev);
 NILFS_DEV_ATTR_STRUCT(segments);
+NILFS_DEV_ATTR_STRUCT(mounted_snapshots);
 NILFS_DEV_ATTR_STRUCT(checkpoints);
 NILFS_DEV_ATTR_STRUCT(superblock);
 NILFS_DEV_ATTR_STRUCT(segctor);
@@ -111,6 +118,9 @@ NILFS_DEV_ATTR_STRUCT(segctor);
 #define NILFS_SEGMENTS_RW_ATTR(name) \
 	NILFS_RW_ATTR(segs_info, name)
 
+#define NILFS_MOUNTED_SNAPSHOTS_RO_ATTR(name) \
+	NILFS_RO_ATTR(mounted_snapshots, name)
+
 #define NILFS_CHECKPOINTS_RO_ATTR(name) \
 	NILFS_RO_ATTR(checkpoints, name)
 #define NILFS_CHECKPOINTS_RW_ATTR(name) \
@@ -134,6 +144,8 @@ NILFS_DEV_ATTR_STRUCT(segctor);
 	(&nilfs_dev_attr_##name.attr)
 #define NILFS_SEGMENTS_ATTR_LIST(name) \
 	(&nilfs_segments_attr_##name.attr)
+#define NILFS_MOUNTED_SNAPSHOTS_ATTR_LIST(name) \
+	(&nilfs_mounted_snapshots_attr_##name.attr)
 #define NILFS_CHECKPOINTS_ATTR_LIST(name) \
 	(&nilfs_checkpoints_attr_##name.attr)
 #define NILFS_SUPERBLOCK_ATTR_LIST(name) \