[PATCH v3 8/8] udp: Pass iov_tail to udp_update_hdr4()/udp_update_hdr6()

[Laurent Vivier <lvivier@redhat.com>]

Change udp_update_hdr4() and udp_update_hdr6() to take an iov_tail
covering the full L3 frame (IP header + UDP header + data), instead of
separate IP header, udp_payload_t, and data-length parameters.  The
functions now use with_header() and IOV_DROP_HEADER() to access the IP
and UDP headers directly from the iov_tail, and derive sizes via
iov_tail_size() rather than an explicit length argument.

This decouples the header update functions from the udp_payload_t memory
layout, which assumes all headers and data sit in a single contiguous
buffer.  The vhost-user path uses virtqueue-provided scatter-gather
buffers where this assumption does not hold; passing an iov_tail lets
both the tap path and the vhost-user path share the same functions
without layout-specific helpers.

On the vhost-user side, udp_vu_prepare() likewise switches to
with_header() for the Ethernet header, and its caller now drops the
vnet header before calling udp_vu_prepare() instead of having the
function deal with it internally.

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
---
 iov.c          |   1 -
 udp.c          | 129 +++++++++++++++++++++++++++----------------------
 udp_internal.h |   6 +--
 udp_vu.c       |  51 +++++++++----------
 4 files changed, 97 insertions(+), 90 deletions(-)

diff --git a/iov.c b/iov.c
index 41e418aab2cc..d92f28995004 100644
--- a/iov.c
+++ b/iov.c
@@ -315,7 +315,6 @@ 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_(const struct iov_tail *tail, const void *v, size_t len)
 {
 	size_t l = len;
diff --git a/udp.c b/udp.c
index 2275c16b19f3..ec764a4a3969 100644
--- a/udp.c
+++ b/udp.c
@@ -254,42 +254,42 @@ static void udp_iov_init(const struct ctx *c)
 
 /**
  * udp_update_hdr4() - Update headers for one IPv4 datagram
- * @ip4h:		Pre-filled IPv4 header (except for tot_len and saddr)
- * @bp:			Pointer to udp_payload_t to update
+ * @payload:		UDP payload
  * @toside:		Flowside for destination side
- * @dlen:		Length of UDP payload
  * @no_udp_csum:	Do not set UDP checksum
  *
  * Return: size of IPv4 payload (UDP header + data)
  */
-size_t udp_update_hdr4(struct iphdr *ip4h, struct udp_payload_t *bp,
-		       const struct flowside *toside, size_t dlen,
+size_t udp_update_hdr4(struct iov_tail *payload, const struct flowside *toside,
 		       bool no_udp_csum)
 {
 	const struct in_addr *src = inany_v4(&toside->oaddr);
 	const struct in_addr *dst = inany_v4(&toside->eaddr);
-	size_t l4len = dlen + sizeof(bp->uh);
-	size_t l3len = l4len + sizeof(*ip4h);
+	size_t l3len = iov_tail_size(payload);
+	size_t l4len = l3len - sizeof(struct iphdr);
 
 	ASSERT(src && dst);
 
-	ip4h->tot_len = htons(l3len);
-	ip4h->daddr = dst->s_addr;
-	ip4h->saddr = src->s_addr;
-	ip4h->check = csum_ip4_header(l3len, IPPROTO_UDP, *src, *dst);
+	with_header(struct iphdr, ip4h, payload) {
+		ip4h->tot_len = htons(l3len);
+		ip4h->daddr = dst->s_addr;
+		ip4h->saddr = src->s_addr;
+		ip4h->check = csum_ip4_header(l3len, IPPROTO_UDP, *src, *dst);
+	}
+	IOV_DROP_HEADER(payload, struct iphdr);
+
+	with_header(struct udphdr, uh, payload) {
+		uh->source = htons(toside->oport);
+		uh->dest = htons(toside->eport);
+		uh->len = htons(l4len);
+		if (no_udp_csum) {
+			uh->check = 0;
+		} else {
+			struct iov_tail data = *payload;
 
-	bp->uh.source = htons(toside->oport);
-	bp->uh.dest = htons(toside->eport);
-	bp->uh.len = htons(l4len);
-	if (no_udp_csum) {
-		bp->uh.check = 0;
-	} else {
-		const struct iovec iov = {
-			.iov_base = bp->data,
-			.iov_len = dlen
-		};
-		struct iov_tail data = IOV_TAIL(&iov, 1, 0);
-		csum_udp4(&bp->uh, *src, *dst, &data);
+			IOV_DROP_HEADER(&data, struct udphdr);
+			csum_udp4(uh, *src, *dst, &data);
+		}
 	}
 
 	return l4len;
@@ -297,44 +297,45 @@ size_t udp_update_hdr4(struct iphdr *ip4h, struct udp_payload_t *bp,
 
 /**
  * udp_update_hdr6() - Update headers for one IPv6 datagram
- * @ip6h:		Pre-filled IPv6 header (except for payload_len and
- * 			addresses)
- * @bp:			Pointer to udp_payload_t to update
+ * @payload:		UDP payload
  * @toside:		Flowside for destination side
- * @dlen:		Length of UDP payload
  * @no_udp_csum:	Do not set UDP checksum
  *
  * Return: size of IPv6 payload (UDP header + data)
  */
-size_t udp_update_hdr6(struct ipv6hdr *ip6h, struct udp_payload_t *bp,
-		       const struct flowside *toside, size_t dlen,
+size_t udp_update_hdr6(struct iov_tail *payload, const struct flowside *toside,
 		       bool no_udp_csum)
 {
-	uint16_t l4len = dlen + sizeof(bp->uh);
-
-	ip6h->payload_len = htons(l4len);
-	ip6h->daddr = toside->eaddr.a6;
-	ip6h->saddr = toside->oaddr.a6;
-	ip6h->version = 6;
-	ip6h->nexthdr = IPPROTO_UDP;
-	ip6h->hop_limit = 255;
-
-	bp->uh.source = htons(toside->oport);
-	bp->uh.dest = htons(toside->eport);
-	bp->uh.len = ip6h->payload_len;
-	if (no_udp_csum) {
-		/* 0 is an invalid checksum for UDP IPv6 and dropped by
-		 * the kernel stack, even if the checksum is disabled by virtio
-		 * flags. We need to put any non-zero value here.
-		 */
-		bp->uh.check = 0xffff;
-	} else {
-		const struct iovec iov = {
-			.iov_base = bp->data,
-			.iov_len = dlen
-		};
-		struct iov_tail data = IOV_TAIL(&iov, 1, 0);
-		csum_udp6(&bp->uh, &toside->oaddr.a6, &toside->eaddr.a6, &data);
+	uint16_t l4len = iov_tail_size(payload) - sizeof(struct ipv6hdr);
+
+	with_header(struct ipv6hdr, ip6h, payload) {
+		ip6h->payload_len = htons(l4len);
+		ip6h->daddr = toside->eaddr.a6;
+		ip6h->saddr = toside->oaddr.a6;
+		ip6h->version = 6;
+		ip6h->nexthdr = IPPROTO_UDP;
+		ip6h->hop_limit = 255;
+	}
+	IOV_DROP_HEADER(payload, struct ipv6hdr);
+
+	with_header(struct udphdr, uh, payload) {
+		uh->source = htons(toside->oport);
+		uh->dest = htons(toside->eport);
+		uh->len = htons(l4len);
+		if (no_udp_csum) {
+			/* 0 is an invalid checksum for UDP IPv6 and dropped by
+			 * the kernel stack, even if the checksum is disabled
+			 * by virtio flags. We need to put any non-zero value
+			 * here.
+			 */
+			uh->check = 0xffff;
+		} else {
+			struct iov_tail data = *payload;
+
+			IOV_DROP_HEADER(&data, struct udphdr);
+			csum_udp6(uh, &toside->oaddr.a6, &toside->eaddr.a6,
+				  &data);
+		}
 	}
 
 	return l4len;
@@ -374,12 +375,22 @@ static void udp_tap_prepare(const struct mmsghdr *mmh,
 	struct ethhdr *eh = (*tap_iov)[UDP_IOV_ETH].iov_base;
 	struct udp_payload_t *bp = &udp_payload[idx];
 	struct udp_meta_t *bm = &udp_meta[idx];
+	struct iovec iov[3];
+	struct iov_tail payload = IOV_TAIL(iov, ARRAY_SIZE(iov), 0);
 	size_t l4len, l2len;
 
+	iov[1].iov_base = &bp->uh;
+	iov[1].iov_len = sizeof(bp->uh);
+	iov[2].iov_base = bp->data;
+	iov[2].iov_len = mmh[idx].msg_len;
+
 	eth_update_mac(eh, NULL, tap_omac);
 	if (!inany_v4(&toside->eaddr) || !inany_v4(&toside->oaddr)) {
-		l4len = udp_update_hdr6(&bm->ip6h, bp, toside,
-					mmh[idx].msg_len, no_udp_csum);
+
+		iov[0].iov_base = &bm->ip6h;
+		iov[0].iov_len = sizeof(bm->ip6h);
+
+		l4len = udp_update_hdr6(&payload, toside, no_udp_csum);
 
 		l2len = MAX(l4len + sizeof(bm->ip6h) + ETH_HLEN, ETH_ZLEN);
 		tap_hdr_update(&bm->taph, l2len);
@@ -387,8 +398,10 @@ static void udp_tap_prepare(const struct mmsghdr *mmh,
 		eh->h_proto = htons_constant(ETH_P_IPV6);
 		(*tap_iov)[UDP_IOV_IP] = IOV_OF_LVALUE(bm->ip6h);
 	} else {
-		l4len = udp_update_hdr4(&bm->ip4h, bp, toside,
-					mmh[idx].msg_len, no_udp_csum);
+		iov[0].iov_base = &bm->ip4h;
+		iov[0].iov_len = sizeof(bm->ip4h);
+
+		l4len = udp_update_hdr4(&payload, toside, no_udp_csum);
 
 		l2len = MAX(l4len + sizeof(bm->ip4h) + ETH_HLEN, ETH_ZLEN);
 		tap_hdr_update(&bm->taph, l2len);
diff --git a/udp_internal.h b/udp_internal.h
index 64e457748324..fb3017ae3251 100644
--- a/udp_internal.h
+++ b/udp_internal.h
@@ -25,11 +25,9 @@ struct udp_payload_t {
 } __attribute__ ((packed, aligned(__alignof__(unsigned int))));
 #endif
 
-size_t udp_update_hdr4(struct iphdr *ip4h, struct udp_payload_t *bp,
-		       const struct flowside *toside, size_t dlen,
+size_t udp_update_hdr4(struct iov_tail *payload, const struct flowside *toside,
 		       bool no_udp_csum);
-size_t udp_update_hdr6(struct ipv6hdr *ip6h, struct udp_payload_t *bp,
-		       const struct flowside *toside, size_t dlen,
+size_t udp_update_hdr6(struct iov_tail *payload, const struct flowside *toside,
 		       bool no_udp_csum);
 void udp_sock_fwd(const struct ctx *c, int s, int rule_hint,
 		  uint8_t frompif, in_port_t port, const struct timespec *now);
diff --git a/udp_vu.c b/udp_vu.c
index 7f6561f83505..f4023c765b6b 100644
--- a/udp_vu.c
+++ b/udp_vu.c
@@ -93,42 +93,39 @@ static ssize_t udp_vu_sock_recv(struct iovec *iov, size_t *cnt, 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;
+	bool ipv4 = inany_v4(&toside->eaddr) && inany_v4(&toside->oaddr);
+	struct iov_tail payload = *data;
 	size_t l4len;
 
 	/* ethernet header */
-	eh = vu_eth(iov[0].iov_base);
-
-	memcpy(eh->h_dest, c->guest_mac, sizeof(eh->h_dest));
-	memcpy(eh->h_source, c->our_tap_mac, sizeof(eh->h_source));
+	with_header(struct ethhdr, eh, &payload) {
+		memcpy(eh->h_dest, c->guest_mac, sizeof(eh->h_dest));
+		memcpy(eh->h_source, c->our_tap_mac, sizeof(eh->h_source));
+
+		if (ipv4)
+			eh->h_proto = htons(ETH_P_IP);
+		else
+			eh->h_proto = htons(ETH_P_IPV6);
+	}
+	IOV_DROP_HEADER(&payload, struct ethhdr);
 
 	/* 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);
+	if (ipv4) {
+		with_header(struct iphdr, iph, &payload)
+			*iph = (struct iphdr)L2_BUF_IP4_INIT(IPPROTO_UDP);
 
-		eh->h_proto = htons(ETH_P_IP);
-
-		*iph = (struct iphdr)L2_BUF_IP4_INIT(IPPROTO_UDP);
-
-		l4len = udp_update_hdr4(iph, bp, toside, dlen, true);
+		l4len = udp_update_hdr4(&payload, toside, true);
 	} else {
-		struct ipv6hdr *ip6h = vu_ip(iov[0].iov_base);
-		struct udp_payload_t *bp = vu_payloadv6(iov[0].iov_base);
-
-		eh->h_proto = htons(ETH_P_IPV6);
-
-		*ip6h = (struct ipv6hdr)L2_BUF_IP6_INIT(IPPROTO_UDP);
+		with_header(struct ipv6hdr, ip6h, &payload)
+			*ip6h = (struct ipv6hdr)L2_BUF_IP6_INIT(IPPROTO_UDP);
 
-		l4len = udp_update_hdr6(ip6h, bp, toside, dlen, true);
+		l4len = udp_update_hdr6(&payload, toside, true);
 	}
 
 	return l4len;
@@ -137,7 +134,7 @@ static size_t udp_vu_prepare(const struct ctx *c, const struct iov_tail *data,
 /**
  * udp_vu_csum() - Calculate and set checksum for a UDP packet
  * @toside:	Address information for one side of the flow
- * @data:	IO vector tail for the frame (including vnet header)
+ * @data:	IO vector tail for the L2 frame
  */
 static void udp_vu_csum(const struct flowside *toside,
 			const struct iov_tail *data)
@@ -148,7 +145,6 @@ static void udp_vu_csum(const struct flowside *toside,
 	struct udphdr *uh, uh_storage;
 	bool ipv4 = src4 && dst4;
 
-	IOV_DROP_HEADER(&payload, struct virtio_net_hdr_mrg_rxbuf);
 	IOV_DROP_HEADER(&payload, struct ethhdr);
 	if (ipv4)
 		IOV_DROP_HEADER(&payload, struct iphdr);
@@ -225,10 +221,11 @@ void udp_vu_sock_to_tap(const struct ctx *c, int s, int n, flow_sidx_t tosidx)
 		if (iov_cnt > 0) {
 			struct iov_tail data = IOV_TAIL(iov_vu, iov_cnt, 0);
 			vu_set_vnethdr(iov_vu[0].iov_base, elem_used);
-			udp_vu_prepare(c, &data, toside, dlen);
+			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, data.off);
 			}
 			vu_flush(vdev, vq, elem, elem_used);
 		}
-- 
2.53.0