1 files changed, 38 insertions, 1 deletions

diff --git a/fs/mount.h b/fs/mount.h
index 79c85639a7ba..f13a28752d0b 100644
--- a/fs/mount.h
+++ b/fs/mount.h
@@ -58,7 +58,10 @@ struct mount {
 #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 */
+	struct mount *mnt_next_for_sb;	/* the next two fields are hlist_node, */
+	struct mount * __aligned(1) *mnt_pprev_for_sb;
+					/* except that LSB of pprev is stolen */
+#define WRITE_HOLD 1			/* ... for use by mnt_hold_writers() */
 	const char *mnt_devname;	/* Name of device e.g. /dev/dsk/hda1 */
 	struct list_head mnt_list;
 	struct list_head mnt_expire;	/* link in fs-specific expiry list */
@@ -148,6 +151,11 @@ static inline void get_mnt_ns(struct mnt_namespace *ns)
 
 extern seqlock_t mount_lock;
 
+DEFINE_LOCK_GUARD_0(mount_writer, write_seqlock(&mount_lock),
+		    write_sequnlock(&mount_lock))
+DEFINE_LOCK_GUARD_0(mount_locked_reader, read_seqlock_excl(&mount_lock),
+		    read_sequnlock_excl(&mount_lock))
+
 struct proc_mounts {
 	struct mnt_namespace *ns;
 	struct path root;
@@ -224,4 +232,33 @@ static inline void mnt_notify_add(struct mount *m)
 }
 #endif
 
+static inline struct mount *topmost_overmount(struct mount *m)
+{
+	while (m->overmount)
+		m = m->overmount;
+	return m;
+}
+
+static inline bool __test_write_hold(struct mount * __aligned(1) *val)
+{
+	return (unsigned long)val & WRITE_HOLD;
+}
+
+static inline bool test_write_hold(const struct mount *m)
+{
+	return __test_write_hold(m->mnt_pprev_for_sb);
+}
+
+static inline void set_write_hold(struct mount *m)
+{
+	m->mnt_pprev_for_sb = (void *)((unsigned long)m->mnt_pprev_for_sb
+				       | WRITE_HOLD);
+}
+
+static inline void clear_write_hold(struct mount *m)
+{
+	m->mnt_pprev_for_sb = (void *)((unsigned long)m->mnt_pprev_for_sb
+				       & ~WRITE_HOLD);
+}
+
 struct mnt_namespace *mnt_ns_from_dentry(struct dentry *dentry);