Merge branch 'work.autofs' into for-linus

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

1 files changed, 29 insertions, 0 deletions

diff --git a/fs/namespace.c b/fs/namespace.c
index 9ad88a45b3e3..f7e28f8ea04d 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1159,6 +1159,35 @@ struct vfsmount *mntget(struct vfsmount *mnt)
 }
 EXPORT_SYMBOL(mntget);
 
+/* path_is_mountpoint() - Check if path is a mount in the current
+ *                          namespace.
+ *
+ *  d_mountpoint() can only be used reliably to establish if a dentry is
+ *  not mounted in any namespace and that common case is handled inline.
+ *  d_mountpoint() isn't aware of the possibility there may be multiple
+ *  mounts using a given dentry in a different namespace. This function
+ *  checks if the passed in path is a mountpoint rather than the dentry
+ *  alone.
+ */
+bool path_is_mountpoint(const struct path *path)
+{
+	unsigned seq;
+	bool res;
+
+	if (!d_mountpoint(path->dentry))
+		return false;
+
+	rcu_read_lock();
+	do {
+		seq = read_seqbegin(&mount_lock);
+		res = __path_is_mountpoint(path);
+	} while (read_seqretry(&mount_lock, seq));
+	rcu_read_unlock();
+
+	return res;
+}
+EXPORT_SYMBOL(path_is_mountpoint);
+
 struct vfsmount *mnt_clone_internal(const struct path *path)
 {
 	struct mount *p;