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From:   Daeho Jeong <daeho43@gmail.com>
To:     linux-kernel@vger.kernel.org,
        linux-f2fs-devel@lists.sourceforge.net, kernel-team@android.com
Cc:     Daeho Jeong <daehojeong@google.com>
Subject: [PATCH v3] f2fs: add symbolic link to kobject in sysfs
Date:   Fri,  3 Jul 2020 15:54:20 +0900
Message-Id: <20200703065420.3544269-1-daeho43@gmail.com>
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From: Daeho Jeong <daehojeong@google.com>

Added a symbolic link to directory of sysfs. It will
create a symbolic link such as "mount_0" and "mount_1" to
each f2fs mount in the order of mounting filesystem. But
once one mount point was umounted, that sequential number
@x in "mount_@x" could be reused by later newly mounted
point. It will provide easy access to sysfs node even if
not knowing the specific device node name like sda19 and
dm-3.

Signed-off-by: Daeho Jeong <daehojeong@google.com>
---
 Documentation/filesystems/f2fs.rst | 13 ++++++++++++-
 fs/f2fs/f2fs.h                     |  4 ++++
 fs/f2fs/sysfs.c                    | 31 ++++++++++++++++++++++++++----
 3 files changed, 43 insertions(+), 5 deletions(-)

diff --git a/Documentation/filesystems/f2fs.rst b/Documentation/filesystems/f2fs.rst
index 535021c46260..916956d433b2 100644
--- a/Documentation/filesystems/f2fs.rst
+++ b/Documentation/filesystems/f2fs.rst
@@ -279,7 +279,18 @@ Sysfs Entries
 
 Information about mounted f2fs file systems can be found in
 /sys/fs/f2fs.  Each mounted filesystem will have a directory in
-/sys/fs/f2fs based on its device name (i.e., /sys/fs/f2fs/sda).
+/sys/fs/f2fs based on its device name (i.e., /sys/fs/f2fs/sda),
+or mount_#x (#x is the number representing the order of mounting).
+But once one mount point was umounted, that sequential number @x
+in "mount_@x" could be reused by later newly mounted point.
+
+Here is an example of this.
+
+mount dev0 mount0 (mount_0 -> dev0)
+mount dev1 mount1 (mount_1 -> dev1)
+umount mount0
+mount dev2 (mount_0 -> dev2)
+
 The files in each per-device directory are shown in table below.
 
 Files in /sys/fs/f2fs/<devname>
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 4b28fd42fdbc..7d6c5f8ce16b 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -1419,6 +1419,8 @@ struct decompress_io_ctx {
 #define MAX_COMPRESS_LOG_SIZE		8
 #define MAX_COMPRESS_WINDOW_SIZE	((PAGE_SIZE) << MAX_COMPRESS_LOG_SIZE)
 
+#define MOUNT_NAME_SIZE			20
+
 struct f2fs_sb_info {
 	struct super_block *sb;			/* pointer to VFS super block */
 	struct proc_dir_entry *s_proc;		/* proc entry */
@@ -1599,6 +1601,8 @@ struct f2fs_sb_info {
 	/* For sysfs suppport */
 	struct kobject s_kobj;
 	struct completion s_kobj_unregister;
+	int s_mount_id;
+	char s_mount_name[MOUNT_NAME_SIZE];
 
 	/* For shrinker support */
 	struct list_head s_list;
diff --git a/fs/f2fs/sysfs.c b/fs/f2fs/sysfs.c
index 2a140657fc4d..703d9f460d03 100644
--- a/fs/f2fs/sysfs.c
+++ b/fs/f2fs/sysfs.c
@@ -18,6 +18,7 @@
 #include <trace/events/f2fs.h>
 
 static struct proc_dir_entry *f2fs_proc_root;
+static struct ida f2fs_mount_ida;
 
 /* Sysfs support for f2fs */
 enum {
@@ -908,6 +909,9 @@ int __init f2fs_init_sysfs(void)
 	} else {
 		f2fs_proc_root = proc_mkdir("fs/f2fs", NULL);
 	}
+
+	ida_init(&f2fs_mount_ida);
+
 	return ret;
 }
 
@@ -917,6 +921,7 @@ void f2fs_exit_sysfs(void)
 	kset_unregister(&f2fs_kset);
 	remove_proc_entry("fs/f2fs", NULL);
 	f2fs_proc_root = NULL;
+	ida_destroy(&f2fs_mount_ida);
 }
 
 int f2fs_register_sysfs(struct f2fs_sb_info *sbi)
@@ -928,12 +933,22 @@ 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 err1;
+
+	sbi->s_mount_id = ida_simple_get(&f2fs_mount_ida, 0, 0, GFP_KERNEL);
+	if (sbi->s_mount_id < 0) {
+		err = sbi->s_mount_id;
+		goto err1;
 	}
 
+	snprintf(sbi->s_mount_name, MOUNT_NAME_SIZE, "mount_%d",
+			sbi->s_mount_id);
+	err = sysfs_create_link(&f2fs_kset.kobj, &sbi->s_kobj,
+			sbi->s_mount_name);
+	if (err)
+		goto err2;
+
 	if (f2fs_proc_root)
 		sbi->s_proc = proc_mkdir(sb->s_id, f2fs_proc_root);
 
@@ -948,6 +963,12 @@ int f2fs_register_sysfs(struct f2fs_sb_info *sbi)
 				victim_bits_seq_show, sb);
 	}
 	return 0;
+err2:
+	ida_simple_remove(&f2fs_mount_ida, sbi->s_mount_id);
+err1:
+	kobject_put(&sbi->s_kobj);
+	wait_for_completion(&sbi->s_kobj_unregister);
+	return err;
 }
 
 void f2fs_unregister_sysfs(struct f2fs_sb_info *sbi)
@@ -959,6 +980,8 @@ 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);
 	}
+	sysfs_remove_link(&f2fs_kset.kobj, sbi->s_mount_name);
+	ida_simple_remove(&f2fs_mount_ida, sbi->s_mount_id);
 	kobject_del(&sbi->s_kobj);
 	kobject_put(&sbi->s_kobj);
 }
-- 
2.27.0.383.g050319c2ae-goog