[PATCH RFC 07/10] fs: Introduce struct super_operations::destroy_super() callback.

[Kirill Tkhai]

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 <ktk...@virtuozzo.com>
---
 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 9222cfc196bf..c60f092538c7 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 842fde0f0981..33dfaed0a01a 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1880,6 +1880,7 @@ 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 *);