pipe: add pipe_buf_steal() helper

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

drivers/char/virtio_console.c

@@ -889,7 +889,7 @@ static int pipe_to_sg(struct pipe_inode_info *pipe, struct pipe_buffer *buf,
 		return 0;
 
 	/* Try lock this page */
-	if (buf->ops->steal(pipe, buf) == 0) {
+	if (pipe_buf_steal(pipe, buf) == 0) {
 		/* Get reference and unlock page for moving */
 		get_page(buf->page);
 		unlock_page(buf->page);

fs/fuse/dev.c

@@ -841,7 +841,7 @@ static int fuse_try_move_page(struct fuse_copy_state *cs, struct page **pagep)
 	if (cs->len != PAGE_SIZE)
 		goto out_fallback;
 
-	if (buf->ops->steal(cs->pipe, buf) != 0)
+	if (pipe_buf_steal(cs->pipe, buf) != 0)
 		goto out_fallback;
 
 	newpage = buf->page;

include/linux/pipe_fs_i.h

@@ -151,6 +151,17 @@ static inline int pipe_buf_confirm(struct pipe_inode_info *pipe,
 	return buf->ops->confirm(pipe, buf);
 }
 
+/**
+ * pipe_buf_steal - attempt to take ownership of a pipe_buffer
+ * @pipe:	the pipe that the buffer belongs to
+ * @buf:	the buffer to attempt to steal
+ */
+static inline int pipe_buf_steal(struct pipe_inode_info *pipe,
+				 struct pipe_buffer *buf)
+{
+	return buf->ops->steal(pipe, buf);
+}
+
 /* Differs from PIPE_BUF in that PIPE_SIZE is the length of the actual
    memory allocation, whereas PIPE_BUF makes atomicity guarantees.  */
 #define PIPE_SIZE		PAGE_SIZE