new helper: alloc_file_clone()

alloc_file_clone(old_file, mode, ops): create a new struct file with
->f_path equal to that of old_file.  pipe converted.

Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/pipe.c b/fs/pipe.c
index 9701bd3..5f50070 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -761,15 +761,13 @@
 
 	f->private_data = inode->i_pipe;
 
-	res[0] = alloc_file(&f->f_path, O_RDONLY | (flags & O_NONBLOCK),
-			&pipefifo_fops);
+	res[0] = alloc_file_clone(f, O_RDONLY | (flags & O_NONBLOCK),
+				  &pipefifo_fops);
 	if (IS_ERR(res[0])) {
 		put_pipe_info(inode, inode->i_pipe);
 		fput(f);
 		return PTR_ERR(res[0]);
 	}
-
-	path_get(&f->f_path);
 	res[0]->private_data = inode->i_pipe;
 	res[1] = f;
 	return 0;