[PATCH v4 2/4] vfs: keep list of mounts for each superblock

[Miklos Szeredi <miklos@szeredi.hu>]

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From: Miklos Szeredi <mszeredi@suse.cz>

Keep track of vfsmounts belonging to a superblock.  List is protected
by vfsmount_lock.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
---
 fs/namespace.c        |    5 +++++
 fs/super.c            |    7 +++++++
 include/linux/fs.h    |    1 +
 include/linux/mount.h |    1 +
 4 files changed, 14 insertions(+)

Index: linux-2.6/include/linux/fs.h
===================================================================
--- linux-2.6.orig/include/linux/fs.h	2011-01-18 12:35:42.000000000 +0100
+++ linux-2.6/include/linux/fs.h	2011-01-18 12:36:41.000000000 +0100
@@ -1386,6 +1386,7 @@ struct super_block {
 #else
 	struct list_head	s_files;
 #endif
+	struct list_head	s_mounts;	/* list of mounts */
 	/* s_dentry_lru, s_nr_dentry_unused protected by dcache.c lru locks */
 	struct list_head	s_dentry_lru;	/* unused dentry lru */
 	int			s_nr_dentry_unused;	/* # of dentry on lru */
Index: linux-2.6/include/linux/mount.h
===================================================================
--- linux-2.6.orig/include/linux/mount.h	2011-01-18 12:35:42.000000000 +0100
+++ linux-2.6/include/linux/mount.h	2011-01-18 12:36:41.000000000 +0100
@@ -67,6 +67,7 @@ struct vfsmount {
 #endif
 	struct list_head mnt_mounts;	/* list of children, anchored here */
 	struct list_head mnt_child;	/* and going through their mnt_child */
+	struct list_head mnt_instance;	/* mount instance on sb->s_mounts */
 	int mnt_flags;
 	/* 4 bytes hole on 64bits arches without fsnotify */
 #ifdef CONFIG_FSNOTIFY
Index: linux-2.6/fs/namespace.c
===================================================================
--- linux-2.6.orig/fs/namespace.c	2011-01-18 12:35:42.000000000 +0100
+++ linux-2.6/fs/namespace.c	2011-01-18 12:37:27.000000000 +0100
@@ -723,6 +723,10 @@ static struct vfsmount *clone_mnt(struct
 			if (!list_empty(&old->mnt_expire))
 				list_add(&mnt->mnt_expire, &old->mnt_expire);
 		}
+
+		br_write_lock(vfsmount_lock);
+		list_add_tail(&mnt->mnt_instance, &mnt->mnt_sb->s_mounts);
+		br_write_unlock(vfsmount_lock);
 	}
 	return mnt;
 
@@ -783,6 +787,7 @@ static void mntput_no_expire(struct vfsm
 		acct_auto_close_mnt(mnt);
 		goto put_again;
 	}
+	list_del(&mnt->mnt_instance);
 	br_write_unlock(vfsmount_lock);
 	mntfree(mnt);
 }
Index: linux-2.6/fs/super.c
===================================================================
--- linux-2.6.orig/fs/super.c	2011-01-18 12:36:02.000000000 +0100
+++ linux-2.6/fs/super.c	2011-01-18 12:36:41.000000000 +0100
@@ -75,6 +75,7 @@ static struct super_block *alloc_super(s
 		INIT_HLIST_BL_HEAD(&s->s_anon);
 		INIT_LIST_HEAD(&s->s_inodes);
 		INIT_LIST_HEAD(&s->s_dentry_lru);
+		INIT_LIST_HEAD(&s->s_mounts);
 		init_rwsem(&s->s_umount);
 		mutex_init(&s->s_lock);
 		lockdep_set_class(&s->s_umount, &type->s_umount_key);
@@ -128,6 +129,7 @@ static inline void destroy_super(struct
 	free_percpu(s->s_files);
 #endif
 	security_sb_free(s);
+	WARN_ON(!list_empty(&s->s_mounts));
 	kfree(s->s_subtype);
 	kfree(s->s_options);
 	kfree(s);
@@ -1019,6 +1021,11 @@ vfs_kern_mount(struct file_system_type *
 	mnt->mnt_parent = mnt;
 	up_write(&mnt->mnt_sb->s_umount);
 	free_secdata(secdata);
+
+	br_write_lock(vfsmount_lock);
+	list_add_tail(&mnt->mnt_instance, &mnt->mnt_sb->s_mounts);
+	br_write_unlock(vfsmount_lock);
+
 	return mnt;
 out_sb:
 	dput(mnt->mnt_root);

--