[PATCH v2 13/13] vhost-user,udp: Use 2 iovec entries per element

[Laurent Vivier <lvivier@redhat.com>]

iPXE places the vnet header in one virtqueue descriptor and the payload
in another. When passt maps these descriptors, it needs two iovecs per
virtqueue element to handle this layout.

Without this, passt crashes with:

  ASSERTION FAILED in virtqueue_map_desc (virtio.c:403): num_sg < max_num_sg

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
---
 udp_vu.c    |  8 ++++----
 vu_common.c | 15 +++++++++++----
 2 files changed, 15 insertions(+), 8 deletions(-)

diff --git a/udp_vu.c b/udp_vu.c
index cb5274aa1d81..47659b0402fd 100644
--- a/udp_vu.c
+++ b/udp_vu.c
@@ -34,7 +34,7 @@
 #include "vu_common.h"
 
 static struct iovec     iov_vu		[VIRTQUEUE_MAX_SIZE];
-static struct vu_virtq_element	elem		[VIRTQUEUE_MAX_SIZE];
+static struct vu_virtq_element	elem	[VIRTQUEUE_MAX_SIZE / IOV_PER_ELEM];
 
 /**
  * udp_vu_hdrlen() - Sum size of all headers, from UDP to virtio-net
@@ -214,20 +214,20 @@ void udp_vu_sock_to_tap(const struct ctx *c, int s, int n, flow_sidx_t tosidx)
 		size_t iov_cnt;
 		ssize_t dlen;
 
-		vu_init_elem(elem, iov_vu, ARRAY_SIZE(elem), 1);
+		vu_init_elem(elem, iov_vu, ARRAY_SIZE(elem), IOV_PER_ELEM);
 
 		elem_cnt = vu_collect(vdev, vq, elem, ARRAY_SIZE(elem),
 				      IP_MAX_MTU + ETH_HLEN + VNET_HLEN, NULL);
 		if (elem_cnt == 0)
 			break;
 
-		iov_cnt = elem_cnt;
+		iov_cnt = (size_t)elem_cnt * IOV_PER_ELEM;
 		dlen = udp_vu_sock_recv(iov_vu, &iov_cnt, s, v6);
 		if (dlen < 0) {
 			vu_queue_rewind(vq, elem_cnt);
 			break;
 		}
-		elem_used = iov_cnt;
+		elem_used = DIV_ROUND_UP(iov_cnt, IOV_PER_ELEM);
 
 		/* release unused buffers */
 		vu_queue_rewind(vq, elem_cnt - elem_used);
diff --git a/vu_common.c b/vu_common.c
index 3225aca53ea6..a2867a293184 100644
--- a/vu_common.c
+++ b/vu_common.c
@@ -63,8 +63,15 @@ void vu_init_elem(struct vu_virtq_element *elem, struct iovec *iov,
 {
 	int i, j;
 
-	for (i = 0, j = 0; i < elem_cnt; i++, j += iov_per_elem)
+	for (i = 0, j = 0; i < elem_cnt; i++, j += iov_per_elem) {
+		int k;
+
+		for (k = 0; k < iov_per_elem; k++) {
+			iov[j + k].iov_base = NULL;
+			iov[j + k].iov_len = 0;
+		}
 		vu_set_element(&elem[i], 0, NULL, iov_per_elem, &iov[j]);
+	}
 }
 
 /**
@@ -272,7 +279,7 @@ int vu_send_single(const struct ctx *c, const void *buf, size_t size)
 {
 	struct vu_dev *vdev = c->vdev;
 	struct vu_virtq *vq = &vdev->vq[VHOST_USER_RX_QUEUE];
-	struct vu_virtq_element elem[VIRTQUEUE_MAX_SIZE];
+	struct vu_virtq_element elem[VIRTQUEUE_MAX_SIZE / IOV_PER_ELEM];
 	struct iovec in_sg[VIRTQUEUE_MAX_SIZE];
 	struct iov_tail data;
 	size_t total;
@@ -286,7 +293,7 @@ int vu_send_single(const struct ctx *c, const void *buf, size_t size)
 		return -1;
 	}
 
-	vu_init_elem(elem, in_sg, ARRAY_SIZE(elem), 1);
+	vu_init_elem(elem, in_sg, ARRAY_SIZE(elem), IOV_PER_ELEM);
 
 	size += VNET_HLEN;
 	elem_cnt = vu_collect(vdev, vq, elem, ARRAY_SIZE(elem), size, &total);
@@ -303,7 +310,7 @@ int vu_send_single(const struct ctx *c, const void *buf, size_t size)
 	}
 	elem_cnt = iov_truncate(in_sg, elem_cnt, size);
 
-	data = IOV_TAIL(&in_sg[0], elem_cnt, 0);
+	data = IOV_TAIL(&in_sg[0], (size_t)(elem_cnt * IOV_PER_ELEM), 0);
 	vu_set_vnethdr(&data, elem_cnt);
 
 	size -= VNET_HLEN;
-- 
2.53.0