[PATCH 07/12] udp_vu: Use iov_tail in udp_vu_prepare()

[Laurent Vivier <lvivier@redhat.com>]

Rework udp_vu_prepare() to use IOV_REMOVE_HEADER() and IOV_PUT_HEADER()
to walk through Ethernet, IP and UDP headers instead of the layout-specific
helpers (vu_eth(), vu_ip(), vu_payloadv4(), vu_payloadv6()) that assume a
contiguous buffer.  The payload length is now implicit in the iov_tail, so
drop the dlen parameter.

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
---
 iov.c    |  1 -
 udp_vu.c | 63 ++++++++++++++++++++++++++++++--------------------------
 2 files changed, 34 insertions(+), 30 deletions(-)

diff --git a/iov.c b/iov.c
index 2cf23d284e4a..7c9641968271 100644
--- a/iov.c
+++ b/iov.c
@@ -304,7 +304,6 @@ void *iov_peek_header_(struct iov_tail *tail, void *v, size_t len, size_t align)
  *
  * Return: number of bytes written
  */
-/* cppcheck-suppress unusedFunction */
 size_t iov_put_header_(struct iov_tail *tail, const void *v, size_t len)
 {
 	size_t l = len;
diff --git a/udp_vu.c b/udp_vu.c
index dd8904d65a38..6d87f4872268 100644
--- a/udp_vu.c
+++ b/udp_vu.c
@@ -101,52 +101,54 @@ static ssize_t udp_vu_sock_recv(struct iov_tail *data, int s, bool v6)
  * @c:		Execution context
  * @data:	IO vector tail for the frame
  * @toside:	Address information for one side of the flow
- * @dlen:	Packet data length
  *
  * Return: Layer-4 length
  */
 static size_t udp_vu_prepare(const struct ctx *c, const struct iov_tail *data,
-			     const struct flowside *toside, ssize_t dlen)
+			     const struct flowside *toside)
 {
-	const struct iovec *iov = data->iov;
-	struct ethhdr *eh;
+	struct iov_tail current = *data;
+	struct ethhdr *eh, eh_storage;
+	struct udphdr *uh, uh_storage;
 	size_t l4len;
 
 	/* ethernet header */
-	eh = vu_eth(iov[0].iov_base);
+	eh = IOV_REMOVE_HEADER(&current, eh_storage);
 
 	memcpy(eh->h_dest, c->guest_mac, sizeof(eh->h_dest));
 	memcpy(eh->h_source, c->our_tap_mac, sizeof(eh->h_source));
 
 	/* initialize header */
 	if (inany_v4(&toside->eaddr) && inany_v4(&toside->oaddr)) {
-		struct iphdr *iph = vu_ip(iov[0].iov_base);
-		struct udp_payload_t *bp = vu_payloadv4(iov[0].iov_base);
-		const struct iovec payload_iov = {
-			.iov_base = bp->data,
-			.iov_len = dlen,
-		};
-		struct iov_tail payload = IOV_TAIL(&payload_iov, 1, 0);
+		struct iphdr *iph, iph_storage;
 
 		eh->h_proto = htons(ETH_P_IP);
 
+		iph = IOV_REMOVE_HEADER(&current, iph_storage);
 		*iph = (struct iphdr)L2_BUF_IP4_INIT(IPPROTO_UDP);
 
-		l4len = udp_update_hdr4(iph, &bp->uh, &payload, toside, true);
+		uh = IOV_REMOVE_HEADER(&current, uh_storage);
+		l4len = udp_update_hdr4(iph, uh, &current, toside, true);
+
+		current = *data;
+		IOV_PUT_HEADER(&current, eh);
+		IOV_PUT_HEADER(&current, iph);
+		IOV_PUT_HEADER(&current, uh);
 	} else {
-		struct ipv6hdr *ip6h = vu_ip(iov[0].iov_base);
-		struct udp_payload_t *bp = vu_payloadv6(iov[0].iov_base);
-		const struct iovec payload_iov = {
-			.iov_base = bp->data,
-			.iov_len = dlen,
-		};
-		struct iov_tail payload = IOV_TAIL(&payload_iov, 1, 0);
+		struct ipv6hdr *ip6h, ip6h_storage;
 
 		eh->h_proto = htons(ETH_P_IPV6);
 
+		ip6h = IOV_REMOVE_HEADER(&current, ip6h_storage);
 		*ip6h = (struct ipv6hdr)L2_BUF_IP6_INIT(IPPROTO_UDP);
 
-		l4len = udp_update_hdr6(ip6h, &bp->uh, &payload, toside, true);
+		uh = IOV_REMOVE_HEADER(&current, uh_storage);
+		l4len = udp_update_hdr6(ip6h, uh, &current, toside, true);
+
+		current = *data;
+		IOV_PUT_HEADER(&current, eh);
+		IOV_PUT_HEADER(&current, ip6h);
+		IOV_PUT_HEADER(&current, uh);
 	}
 
 	return l4len;
@@ -165,9 +167,10 @@ static void udp_vu_csum(const struct flowside *toside,
 	struct iov_tail payload = *data;
 	struct udphdr *uh, uh_storage;
 	bool ipv4 = src4 && dst4;
+	int hdrlen = sizeof(struct ethhdr) +
+		     (ipv4 ? sizeof(struct iphdr) : sizeof(struct ipv6hdr));
 
-	iov_drop_header(&payload,
-			udp_vu_hdrlen(!ipv4) - sizeof(struct udphdr));
+	iov_drop_header(&payload, hdrlen);
 	uh = IOV_REMOVE_HEADER(&payload, uh_storage);
 
 	if (ipv4)
@@ -208,8 +211,8 @@ void udp_vu_sock_to_tap(const struct ctx *c, int s, int n, flow_sidx_t tosidx)
 	}
 
 	for (i = 0; i < n; i++) {
+		int elem_cnt, elem_used;
 		ssize_t dlen;
-		int elem_cnt;
 
 		vu_init_elem(elem, iov_vu, ARRAY_SIZE(elem));
 
@@ -225,18 +228,20 @@ void udp_vu_sock_to_tap(const struct ctx *c, int s, int n, flow_sidx_t tosidx)
 			vu_queue_rewind(vq, elem_cnt);
 			continue;
 		}
+		elem_used = data.cnt;
 
 		/* release unused buffers */
-		vu_queue_rewind(vq, elem_cnt - data.cnt);
+		vu_queue_rewind(vq, elem_cnt - elem_used);
 
 		if (data.cnt > 0) {
-			vu_set_vnethdr(vdev, data.iov[0].iov_base, data.cnt);
-			udp_vu_prepare(c, &data, toside, dlen);
+			vu_set_vnethdr(vdev, data.iov[0].iov_base, elem_used);
+			iov_drop_header(&data, VNET_HLEN);
+			udp_vu_prepare(c, &data, toside);
 			if (*c->pcap) {
 				udp_vu_csum(toside, &data);
-				pcap_iov(data.iov, data.cnt, VNET_HLEN);
+				pcap_iov(data.iov, data.cnt, 0);
 			}
-			vu_flush(vdev, vq, elem, data.cnt);
+			vu_flush(vdev, vq, elem, elem_used);
 		}
 	}
 }
-- 
2.53.0