[PATCH 1/3 RESEND] namei: add follow_up_bind()

[Christian Brauner <christian.brauner@ubuntu.com>]

This adds a new helper for resolving bind-mounts.

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
---
 fs/namei.c            | 10 ++++++++++
 include/linux/namei.h |  1 +
 2 files changed, 11 insertions(+)

diff --git a/fs/namei.c b/fs/namei.c
index a09419379f5d..4fa56ec78f63 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1085,6 +1085,16 @@ int follow_up(struct path *path)
 }
 EXPORT_SYMBOL(follow_up);
 
+/*
+ * follow_up_bind - Resolve bind-mounts to mountpoint of path's vfsmount
+ */
+inline void follow_up_bind(struct path *path)
+{
+	while (path->mnt->mnt_root == path->dentry && follow_up(path))
+		;
+}
+EXPORT_SYMBOL(follow_up_bind);
+
 /*
  * Perform an automount
  * - return -EISDIR to tell follow_managed() to stop and return the path we
diff --git a/include/linux/namei.h b/include/linux/namei.h
index a982bb7cd480..ea93127be26c 100644
--- a/include/linux/namei.h
+++ b/include/linux/namei.h
@@ -87,6 +87,7 @@ extern struct dentry *lookup_one_len_unlocked(const char *, struct dentry *, int
 extern int follow_down_one(struct path *);
 extern int follow_down(struct path *);
 extern int follow_up(struct path *);
+extern void follow_up_bind(struct path *path);
 
 extern struct dentry *lock_rename(struct dentry *, struct dentry *);
 extern void unlock_rename(struct dentry *, struct dentry *);
-- 
2.15.1