do_splice_to(): move the logics for limiting the read length in

Both callers have the identical logics limiting the amount of
data we try to read into pipe - no more than would fit into
that pipe.  Move that into do_splice_to() itself.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/splice.c

@@ -771,11 +771,16 @@ static long do_splice_to(struct file *in, loff_t *ppos,
 			 struct pipe_inode_info *pipe, size_t len,
 			 unsigned int flags)
 {
+	unsigned int p_space;
 	int ret;
 
 	if (unlikely(!(in->f_mode & FMODE_READ)))
 		return -EBADF;
 
+	/* Don't try to read more the pipe has space for. */
+	p_space = pipe->max_usage - pipe_occupancy(pipe->head, pipe->tail);
+	len = min_t(size_t, len, p_space << PAGE_SHIFT);
+
 	ret = rw_verify_area(READ, in, ppos, len);
 	if (unlikely(ret < 0))
 		return ret;
@@ -856,15 +861,10 @@ ssize_t splice_direct_to_actor(struct file *in, struct splice_desc *sd,
 	WARN_ON_ONCE(!pipe_empty(pipe->head, pipe->tail));
 
 	while (len) {
-		unsigned int p_space;
 		size_t read_len;
 		loff_t pos = sd->pos, prev_pos = pos;
 
-		/* Don't try to read more the pipe has space for. */
-		p_space = pipe->max_usage -
-			pipe_occupancy(pipe->head, pipe->tail);
-		read_len = min_t(size_t, len, p_space << PAGE_SHIFT);
-		ret = do_splice_to(in, &pos, pipe, read_len, flags);
+		ret = do_splice_to(in, &pos, pipe, len, flags);
 		if (unlikely(ret <= 0))
 			goto out_release;
 
@@ -1083,15 +1083,8 @@ long do_splice(struct file *in, loff_t *off_in, struct file *out,
 
 		pipe_lock(opipe);
 		ret = wait_for_space(opipe, flags);
-		if (!ret) {
-			unsigned int p_space;
-
-			/* Don't try to read more the pipe has space for. */
-			p_space = opipe->max_usage - pipe_occupancy(opipe->head, opipe->tail);
-			len = min_t(size_t, len, p_space << PAGE_SHIFT);
-
+		if (!ret)
 			ret = do_splice_to(in, &offset, opipe, len, flags);
-		}
 		pipe_unlock(opipe);
 		if (ret > 0)
 			wakeup_pipe_readers(opipe);