get rid of full-hash scan on detaching vfsmounts

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/mount.h

@@ -18,6 +18,12 @@ struct mnt_pcp {
 	int mnt_writers;
 };
 
+struct mountpoint {
+	struct list_head m_hash;
+	struct dentry *m_dentry;
+	int m_count;
+};
+
 struct mount {
 	struct list_head mnt_hash;
 	struct mount *mnt_parent;
@@ -40,6 +46,7 @@ struct mount {
 	struct list_head mnt_slave;	/* slave list entry */
 	struct mount *mnt_master;	/* slave is on master->mnt_slave_list */
 	struct mnt_namespace *mnt_ns;	/* containing namespace */
+	struct mountpoint *mnt_mp;	/* where is it mounted */
 #ifdef CONFIG_FSNOTIFY
 	struct hlist_head mnt_fsnotify_marks;
 	__u32 mnt_fsnotify_mask;

fs/pnode.c

@@ -217,7 +217,7 @@ static struct mount *get_source(struct mount *dest,
  * @source_mnt: source mount.
  * @tree_list : list of heads of trees to be attached.
  */
-int propagate_mnt(struct mount *dest_mnt, struct dentry *dest_dentry,
+int propagate_mnt(struct mount *dest_mnt, struct mountpoint *dest_mp,
 		    struct mount *source_mnt, struct list_head *tree_list)
 {
 	struct mount *m, *child;
@@ -244,8 +244,8 @@ int propagate_mnt(struct mount *dest_mnt, struct dentry *dest_dentry,
 			goto out;
 		}
 
-		if (is_subdir(dest_dentry, m->mnt.mnt_root)) {
-			mnt_set_mountpoint(m, dest_dentry, child);
+		if (is_subdir(dest_mp->m_dentry, m->mnt.mnt_root)) {
+			mnt_set_mountpoint(m, dest_mp, child);
 			list_add_tail(&child->mnt_hash, tree_list);
 		} else {
 			/*

fs/pnode.h

@@ -31,14 +31,14 @@ static inline void set_mnt_shared(struct mount *mnt)
 }
 
 void change_mnt_propagation(struct mount *, int);
-int propagate_mnt(struct mount *, struct dentry *, struct mount *,
+int propagate_mnt(struct mount *, struct mountpoint *, struct mount *,
 		struct list_head *);
 int propagate_umount(struct list_head *);
 int propagate_mount_busy(struct mount *, int);
 void mnt_release_group_id(struct mount *);
 int get_dominating_id(struct mount *mnt, const struct path *root);
 unsigned int mnt_get_count(struct mount *mnt);
-void mnt_set_mountpoint(struct mount *, struct dentry *,
+void mnt_set_mountpoint(struct mount *, struct mountpoint *,
 			struct mount *);
 void release_mounts(struct list_head *);
 void umount_tree(struct mount *, int, struct list_head *);