1 files changed, 40 insertions, 0 deletions

diff --git a/fs/namespace.c b/fs/namespace.c
index 22ae06ad751d..120b8a6b99ed 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -265,6 +265,46 @@ out:
 EXPORT_SYMBOL_GPL(mnt_want_write);
 
 /**
+ * mnt_clone_write - get write access to a mount
+ * @mnt: the mount on which to take a write
+ *
+ * This is effectively like mnt_want_write, except
+ * it must only be used to take an extra write reference
+ * on a mountpoint that we already know has a write reference
+ * on it. This allows some optimisation.
+ *
+ * After finished, mnt_drop_write must be called as usual to
+ * drop the reference.
+ */
+int mnt_clone_write(struct vfsmount *mnt)
+{
+        /* superblock may be r/o */
+        if (__mnt_is_readonly(mnt))
+                return -EROFS;
+        preempt_disable();
+        inc_mnt_writers(mnt);
+        preempt_enable();
+        return 0;
+}
+EXPORT_SYMBOL_GPL(mnt_clone_write);
+
+/**
+ * mnt_want_write_file - get write access to a file's mount
+ * @file: the file who's mount on which to take a write
+ *
+ * This is like mnt_want_write, but it takes a file and can
+ * do some optimisations if the file is open for write already
+ */
+int mnt_want_write_file(struct file *file)
+{
+        if (!(file->f_mode & FMODE_WRITE))
+                return mnt_want_write(file->f_path.mnt);
+        else
+                return mnt_clone_write(file->f_path.mnt);
+}
+EXPORT_SYMBOL_GPL(mnt_want_write_file);
+
+/**
  * mnt_drop_write - give up write access to a mount
  * @mnt: the mount on which to give up write access
  *