[PATCH 5/8] fs: introduce struct super_operations::destroy_super() callback

[Qi Zheng]

From: Kirill Tkhai <tkhai@xxxxx>

The patch introduces a new callback, which will be called
asynchronous from delayed work.

This will allows to make ::nr_cached_objects() safe
to be called on destroying superblock in next patches,
and to split unregister_shrinker() into two primitives.

Signed-off-by: Kirill Tkhai <tkhai@xxxxx>
Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
---
 fs/super.c         | 3 +++
 include/linux/fs.h | 1 +
 2 files changed, 4 insertions(+)

diff --git a/fs/super.c b/fs/super.c
index 2ce54561e82e..4e9d08224f86 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -170,6 +170,9 @@ static void destroy_super_work(struct work_struct *work)
 	list_lru_destroy(&s->s_dentry_lru);
 	list_lru_destroy(&s->s_inode_lru);
 
+	if (s->s_op->destroy_super)
+		s->s_op->destroy_super(s);
+
 	for (i = 0; i < SB_FREEZE_LEVELS; i++)
 		percpu_free_rwsem(&s->s_writers.rw_sem[i]);
 	kfree(s);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 0b54ac1d331b..30b46d0facfc 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1910,6 +1910,7 @@ struct super_operations {
 	int (*drop_inode) (struct inode *);
 	void (*evict_inode) (struct inode *);
 	void (*put_super) (struct super_block *);
+	void (*destroy_super) (struct super_block *);
 	int (*sync_fs)(struct super_block *sb, int wait);
 	int (*freeze_super) (struct super_block *);
 	int (*freeze_fs) (struct super_block *);
-- 
2.30.2