[RFC PATCH 1/3] vu_common: Stick to size of input buffer in vu_send_single()

[Stefano Brivio <sbrivio@redhat.com>]

...instead of copying, from the input buffer, the amount of available
bytes in the buffer provided via vhost-user.

The existing behaviour should be harmless due to the fact that we
don't request overly large buffers from vhost-user, but it doesn't
look correct to me.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
---
 vu_common.c | 22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/vu_common.c b/vu_common.c
index b13b7c3..21cfb2a 100644
--- a/vu_common.c
+++ b/vu_common.c
@@ -238,7 +238,7 @@ void vu_kick_cb(struct vu_dev *vdev, union epoll_ref ref,
  * vu_send_single() - Send a buffer to the front-end using the RX virtqueue
  * @c:		execution context
  * @buf:	address of the buffer
- * @size:	size of the buffer
+ * @size:	size of the input buffer
  *
  * Return: number of bytes sent, -1 if there is an error
  */
@@ -248,7 +248,7 @@ int vu_send_single(const struct ctx *c, const void *buf, size_t size)
 	struct vu_virtq *vq = &vdev->vq[VHOST_USER_RX_QUEUE];
 	struct vu_virtq_element elem[VIRTQUEUE_MAX_SIZE];
 	struct iovec in_sg[VIRTQUEUE_MAX_SIZE];
-	size_t total;
+	size_t vu_buf_size;
 	int elem_cnt;
 	int i;
 
@@ -261,21 +261,20 @@ int vu_send_single(const struct ctx *c, const void *buf, size_t size)
 
 	vu_init_elem(elem, in_sg, VIRTQUEUE_MAX_SIZE);
 
-	size += sizeof(struct virtio_net_hdr_mrg_rxbuf);
-	elem_cnt = vu_collect(vdev, vq, elem, VIRTQUEUE_MAX_SIZE, size, &total);
-	if (total < size) {
+	elem_cnt = vu_collect(vdev, vq, elem, VIRTQUEUE_MAX_SIZE,
+			      size + sizeof(struct virtio_net_hdr_mrg_rxbuf),
+			      &vu_buf_size);
+	if (vu_buf_size < size + sizeof(struct virtio_net_hdr_mrg_rxbuf)) {
 		debug("vu_send_single: no space to send the data "
-		      "elem_cnt %d size %zd", elem_cnt, total);
+		      "elem_cnt %d size %zd", elem_cnt, size);
 		goto err;
 	}
 
 	vu_set_vnethdr(vdev, in_sg[0].iov_base, elem_cnt);
 
-	total -= sizeof(struct virtio_net_hdr_mrg_rxbuf);
-
 	/* copy data from the buffer to the iovec */
 	iov_from_buf(in_sg, elem_cnt, sizeof(struct virtio_net_hdr_mrg_rxbuf),
-		     buf, total);
+		     buf, size);
 
 	if (*c->pcap) {
 		pcap_iov(in_sg, elem_cnt,
@@ -284,9 +283,10 @@ int vu_send_single(const struct ctx *c, const void *buf, size_t size)
 
 	vu_flush(vdev, vq, elem, elem_cnt);
 
-	trace("vhost-user sent %zu", total);
+	trace("vhost-user sent %zu",
+	      vu_buf_size - sizeof(struct virtio_net_hdr_mrg_rxbuf));
 
-	return total;
+	return size;
 err:
 	for (i = 0; i < elem_cnt; i++)
 		vu_queue_detach_element(vq);
-- 
2.43.0