[PATCH 1/2] fs/super: Add a flag to mark super block defunc

[Daniil Lunev <dlunev@chromium.org>]

File system can mark a block "defunc" in order to prevent matching
against it in a new mount.

Signed-off-by: Daniil Lunev <dlunev@chromium.org>
---

 fs/super.c         | 4 ++--
 include/linux/fs.h | 1 +
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/super.c b/fs/super.c
index f1d4a193602d6..fc5b3efe0cd01 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -1216,7 +1216,7 @@ static int set_bdev_super_fc(struct super_block *s, struct fs_context *fc)
 
 static int test_bdev_super_fc(struct super_block *s, struct fs_context *fc)
 {
-	return s->s_bdev == fc->sget_key;
+	return !s->s_defunc && s->s_bdev == fc->sget_key;
 }
 
 /**
@@ -1307,7 +1307,7 @@ EXPORT_SYMBOL(get_tree_bdev);
 
 static int test_bdev_super(struct super_block *s, void *data)
 {
-	return (void *)s->s_bdev == data;
+	return !s->s_defunc && (void *)s->s_bdev == data;
 }
 
 struct dentry *mount_bdev(struct file_system_type *fs_type,
diff --git a/include/linux/fs.h b/include/linux/fs.h
index bbde95387a23a..76feb3fe9bb9e 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1448,6 +1448,7 @@ struct super_block {
 	struct rw_semaphore	s_umount;
 	int			s_count;
 	atomic_t		s_active;
+	bool			s_defunc;
 #ifdef CONFIG_SECURITY
 	void                    *s_security;
 #endif
-- 
2.31.0