From 2ed1d2a0a5bf09ab741f5c3d6d10021c0702be08 Mon Sep 17 00:00:00 2001
From: David Howells <dhowells@redhat.com>
Date: Fri, 5 Jul 2019 11:10:10 +0100
Subject: [PATCH 1/3] fsinfo: Introduce a non-repeating system-unique
 superblock ID

Introduce an (effectively) non-repeating system-unique superblock ID that
can be used to determine that two objects are in the same superblock
without needing to worry about the ID changing in the meantime (as is
possible with device IDs).

The counter could also be used to tag other features, such as mount
objects.

Signed-off-by: David Howells <dhowells@redhat.com>
---
 fs/internal.h      | 1 +
 fs/super.c         | 2 ++
 include/linux/fs.h | 3 +++
 3 files changed, 6 insertions(+)

diff --git a/fs/internal.h b/fs/internal.h
index a7cd0f64faa4a..1b7460f055a3b 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -112,6 +112,7 @@ extern struct file *alloc_empty_file_noaccount(int, const struct cred *);
 /*
  * super.c
  */
+extern atomic64_t vfs_unique_counter;
 extern int reconfigure_super(struct fs_context *);
 extern bool trylock_super(struct super_block *sb);
 extern struct super_block *user_get_super(dev_t);
diff --git a/fs/super.c b/fs/super.c
index 98bb0629ee108..31fadb7189d27 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -44,6 +44,7 @@ static int thaw_super_locked(struct super_block *sb);
 
 static LIST_HEAD(super_blocks);
 static DEFINE_SPINLOCK(sb_lock);
+atomic64_t vfs_unique_counter; /* Unique identifier counter */
 
 static char *sb_writers_name[SB_FREEZE_LEVELS] = {
 	"sb_writers",
@@ -273,6 +274,7 @@ static struct super_block *alloc_super(struct file_system_type *type, int flags,
 		goto fail;
 	if (list_lru_init_memcg(&s->s_inode_lru, &s->s_shrink))
 		goto fail;
+	s->s_unique_id = atomic64_inc_return(&vfs_unique_counter);
 	return s;
 
 fail:
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 8bde32cf97115..e1325dec4fa86 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1547,6 +1547,9 @@ struct super_block {
 
 	spinlock_t		s_inode_wblist_lock;
 	struct list_head	s_inodes_wb;	/* writeback inodes */
+
+	/* Superblock information */
+	u64			s_unique_id;
 } __randomize_layout;
 
 /* Helper functions so that in most cases filesystems will
-- 
2.25.1