[PATCH] vmsplice: restrict stealing a little more

Apply the same rules as the anon pipe pages, only allow stealing
if no one else is using the page.

Signed-off-by: Jens Axboe <axboe@suse.de>
diff --git a/include/linux/pipe_fs_i.h b/include/linux/pipe_fs_i.h
index 070954f..ba73108 100644
--- a/include/linux/pipe_fs_i.h
+++ b/include/linux/pipe_fs_i.h
@@ -69,6 +69,7 @@
 void generic_pipe_buf_unmap(struct pipe_inode_info *, struct pipe_buffer *, void *);
 void generic_pipe_buf_get(struct pipe_inode_info *, struct pipe_buffer *);
 int generic_pipe_buf_pin(struct pipe_inode_info *, struct pipe_buffer *);
+int generic_pipe_buf_steal(struct pipe_inode_info *, struct pipe_buffer *);
 
 /*
  * splice is tied to pipes as a transport (at least for now), so we'll just