udp: Share payload buffers between IPv4 and IPv6

Currently the IPv4 and IPv6 paths unnecessarily use different buffers for
the UDP payload.  Now that we're handling the various pieces of the UDP
packets with an iov, we can split the payload part of the buffers off into
its own array shared between IPv4 and IPv6.  As well as saving a little
memory, this allows the payload buffers to be neatly page aligned.

With the buffers merged, udp[46]_l2_iov_sock contain exactly the same thing
as each other and can also be merged.  Likewise udp[46]_iov_splice can be
merged together.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

1 files changed, 67 insertions, 59 deletions

diff --git a/udp.c b/udp.c
index cc938bb..adca819 100644
--- a/udp.c
+++ b/udp.c
@@ -172,13 +172,26 @@ static uint8_t udp_act[IP_VERSIONS][UDP_ACT_TYPE_MAX][DIV_ROUND_UP(NUM_PORTS, 8)
 /* Static buffers */
 
 /**
+ * struct udp_payload_t - UDP header and data for inbound messages
+ * @uh:		UDP header
+ * @data:	UDP data
+ */
+static struct udp_payload_t {
+	struct udphdr uh;
+	char data[USHRT_MAX - sizeof(struct udphdr)];
+#ifdef __AVX2__
+} __attribute__ ((packed, aligned(32)))
+#else
+} __attribute__ ((packed, aligned(__alignof__(unsigned int))))
+#endif
+udp_payload[UDP_MAX_FRAMES];
+
+/**
  * udp4_l2_buf_t - Pre-cooked IPv4 packet buffers for tap connections
  * @s_in:	Source socket address, filled in by recvmmsg()
  * @taph:	Tap backend specific header
  * @eh:		Prefilled ethernet header
  * @iph:	Pre-filled IP header (except for tot_len and saddr)
- * @uh:		Headroom for UDP header
- * @data:	Storage for UDP payload
  */
 static struct udp4_l2_buf_t {
 	struct sockaddr_in s_in;
@@ -186,9 +199,6 @@ static struct udp4_l2_buf_t {
 	struct tap_hdr taph;
 	struct ethhdr eh;
 	struct iphdr iph;
-	struct udphdr uh;
-	uint8_t data[USHRT_MAX -
-		     (sizeof(struct iphdr) + sizeof(struct udphdr))];
 } __attribute__ ((packed, aligned(__alignof__(unsigned int))))
 udp4_l2_buf[UDP_MAX_FRAMES];
 
@@ -198,8 +208,6 @@ udp4_l2_buf[UDP_MAX_FRAMES];
  * @taph:	Tap backend specific header
  * @eh:		Pre-filled ethernet header
  * @ip6h:	Pre-filled IP header (except for payload_len and addresses)
- * @uh:		Headroom for UDP header
- * @data:	Storage for UDP payload
  */
 struct udp6_l2_buf_t {
 	struct sockaddr_in6 s_in6;
@@ -212,9 +220,6 @@ struct udp6_l2_buf_t {
 	struct tap_hdr taph;
 	struct ethhdr eh;
 	struct ipv6hdr ip6h;
-	struct udphdr uh;
-	uint8_t data[USHRT_MAX -
-		     (sizeof(struct ipv6hdr) + sizeof(struct udphdr))];
 #ifdef __AVX2__
 } __attribute__ ((packed, aligned(32)))
 #else
@@ -239,8 +244,7 @@ enum udp_iov_idx {
 };
 
 /* recvmmsg()/sendmmsg() data for tap */
-static struct iovec	udp4_l2_iov_sock	[UDP_MAX_FRAMES];
-static struct iovec	udp6_l2_iov_sock	[UDP_MAX_FRAMES];
+static struct iovec	udp_l2_iov_sock		[UDP_MAX_FRAMES];
 
 static struct iovec	udp4_l2_iov_tap		[UDP_MAX_FRAMES][UDP_NUM_IOVS];
 static struct iovec	udp6_l2_iov_tap		[UDP_MAX_FRAMES][UDP_NUM_IOVS];
@@ -249,8 +253,7 @@ static struct mmsghdr	udp4_l2_mh_sock		[UDP_MAX_FRAMES];
 static struct mmsghdr	udp6_l2_mh_sock		[UDP_MAX_FRAMES];
 
 /* recvmmsg()/sendmmsg() data for "spliced" connections */
-static struct iovec	udp4_iov_splice		[UDP_MAX_FRAMES];
-static struct iovec	udp6_iov_splice		[UDP_MAX_FRAMES];
+static struct iovec	udp_iov_splice		[UDP_MAX_FRAMES];
 
 static struct sockaddr_in udp4_localname = {
 	.sin_family = AF_INET,
@@ -322,10 +325,14 @@ void udp_update_l2_buf(const unsigned char *eth_d, const unsigned char *eth_s)
  */
 static void udp_iov_init_one(const struct ctx *c, size_t i)
 {
+	struct udp_payload_t *payload = &udp_payload[i];
+	struct iovec *siov = &udp_l2_iov_sock[i];
+
+	*siov = IOV_OF_LVALUE(payload->data);
+
 	if (c->ifi4) {
 		struct msghdr *mh = &udp4_l2_mh_sock[i].msg_hdr;
 		struct udp4_l2_buf_t *buf = &udp4_l2_buf[i];
-		struct iovec *siov = &udp4_l2_iov_sock[i];
 		struct iovec *tiov = udp4_l2_iov_tap[i];
 
 		*buf = (struct udp4_l2_buf_t) {
@@ -333,8 +340,6 @@ static void udp_iov_init_one(const struct ctx *c, size_t i)
 			.iph = L2_BUF_IP4_INIT(IPPROTO_UDP)
 		};
 
-		*siov		= IOV_OF_LVALUE(buf->data);
-
 		mh->msg_name	= &buf->s_in;
 		mh->msg_namelen	= sizeof(buf->s_in);
 		mh->msg_iov	= siov;
@@ -343,13 +348,12 @@ static void udp_iov_init_one(const struct ctx *c, size_t i)
 		tiov[UDP_IOV_TAP] = tap_hdr_iov(c, &buf->taph);
 		tiov[UDP_IOV_ETH] = IOV_OF_LVALUE(buf->eh);
 		tiov[UDP_IOV_IP] = IOV_OF_LVALUE(buf->iph);
-		tiov[UDP_IOV_PAYLOAD].iov_base = &buf->uh;
+		tiov[UDP_IOV_PAYLOAD].iov_base = payload;
 	}
 
 	if (c->ifi6) {
 		struct msghdr *mh = &udp6_l2_mh_sock[i].msg_hdr;
 		struct udp6_l2_buf_t *buf = &udp6_l2_buf[i];
-		struct iovec *siov = &udp6_l2_iov_sock[i];
 		struct iovec *tiov = udp6_l2_iov_tap[i];
 
 		*buf = (struct udp6_l2_buf_t) {
@@ -357,8 +361,6 @@ static void udp_iov_init_one(const struct ctx *c, size_t i)
 			.ip6h = L2_BUF_IP6_INIT(IPPROTO_UDP)
 		};
 
-		*siov		 = IOV_OF_LVALUE(buf->data);
-
 		mh->msg_name	= &buf->s_in6;
 		mh->msg_namelen	= sizeof(buf->s_in6);
 		mh->msg_iov	= siov;
@@ -367,7 +369,7 @@ static void udp_iov_init_one(const struct ctx *c, size_t i)
 		tiov[UDP_IOV_TAP] = tap_hdr_iov(c, &buf->taph);
 		tiov[UDP_IOV_ETH] = IOV_OF_LVALUE(buf->eh);
 		tiov[UDP_IOV_IP] = IOV_OF_LVALUE(buf->ip6h);
-		tiov[UDP_IOV_PAYLOAD].iov_base = &buf->uh;
+		tiov[UDP_IOV_PAYLOAD].iov_base = payload;
 	}
 }
 
@@ -581,22 +583,24 @@ static void udp_splice_sendfrom(const struct ctx *c, unsigned start, unsigned n,
 /**
  * udp_update_hdr4() - Update headers for one IPv4 datagram
  * @c:		Execution context
- * @b:		Pointer to udp4_l2_buf to update
+ * @bh:		Pointer to udp4_l2_buf to update
+ * @bp:		Pointer to udp_payload_t to update
  * @dstport:	Destination port number
  * @dlen:	Length of UDP payload
  * @now:	Current timestamp
  *
  * Return: size of IPv4 payload (UDP header + data)
  */
-static size_t udp_update_hdr4(const struct ctx *c, struct udp4_l2_buf_t *b,
+static size_t udp_update_hdr4(const struct ctx *c, struct udp4_l2_buf_t *bh,
+			      struct udp_payload_t *bp,
 			      in_port_t dstport, size_t dlen,
 			      const struct timespec *now)
 {
+	in_port_t srcport = ntohs(bh->s_in.sin_port);
 	const struct in_addr dst = c->ip4.addr_seen;
-	size_t l4len = dlen + sizeof(b->uh);
-	size_t l3len = l4len + sizeof(b->iph);
-	in_port_t srcport = ntohs(b->s_in.sin_port);
-	struct in_addr src = b->s_in.sin_addr;
+	struct in_addr src = bh->s_in.sin_addr;
+	size_t l4len = dlen + sizeof(bp->uh);
+	size_t l3len = l4len + sizeof(bh->iph);
 
 	if (!IN4_IS_ADDR_UNSPECIFIED(&c->ip4.dns_match) &&
 	    IN4_ARE_ADDR_EQUAL(&src, &c->ip4.dns_host) && srcport == 53 &&
@@ -617,38 +621,40 @@ static size_t udp_update_hdr4(const struct ctx *c, struct udp4_l2_buf_t *b,
 		src = c->ip4.gw;
 	}
 
-	b->iph.tot_len = htons(l3len);
-	b->iph.daddr = dst.s_addr;
-	b->iph.saddr = src.s_addr;
-	b->iph.check = csum_ip4_header(l3len, IPPROTO_UDP, src, dst);
+	bh->iph.tot_len = htons(l3len);
+	bh->iph.daddr = dst.s_addr;
+	bh->iph.saddr = src.s_addr;
+	bh->iph.check = csum_ip4_header(l3len, IPPROTO_UDP, src, dst);
 
-	b->uh.source = b->s_in.sin_port;
-	b->uh.dest = htons(dstport);
-	b->uh.len = htons(l4len);
-	csum_udp4(&b->uh, src, dst, b->data, dlen);
+	bp->uh.source = bh->s_in.sin_port;
+	bp->uh.dest = htons(dstport);
+	bp->uh.len = htons(l4len);
+	csum_udp4(&bp->uh, src, dst, bp->data, dlen);
 
-	tap_hdr_update(&b->taph, l3len + sizeof(b->eh));
+	tap_hdr_update(&bh->taph, l3len + sizeof(bh->eh));
 	return l4len;
 }
 
 /**
  * udp_update_hdr6() - Update headers for one IPv6 datagram
  * @c:		Execution context
- * @b:		Pointer to udp6_l2_buf to update
+ * @bh:		Pointer to udp6_l2_buf to update
+ * @bp:		Pointer to udp_payload_t to update
  * @dstport:	Destination port number
  * @dlen:	Length of UDP payload
  * @now:	Current timestamp
  *
  * Return: size of IPv6 payload (UDP header + data)
  */
-static size_t udp_update_hdr6(const struct ctx *c, struct udp6_l2_buf_t *b,
+static size_t udp_update_hdr6(const struct ctx *c, struct udp6_l2_buf_t *bh,
+			      struct udp_payload_t *bp,
 			      in_port_t dstport, size_t dlen,
 			      const struct timespec *now)
 {
-	const struct in6_addr *src = &b->s_in6.sin6_addr;
+	const struct in6_addr *src = &bh->s_in6.sin6_addr;
 	const struct in6_addr *dst = &c->ip6.addr_seen;
-	in_port_t srcport = ntohs(b->s_in6.sin6_port);
-	uint16_t l4len = dlen + sizeof(b->uh);
+	in_port_t srcport = ntohs(bh->s_in6.sin6_port);
+	uint16_t l4len = dlen + sizeof(bp->uh);
 
 	if (IN6_IS_ADDR_LINKLOCAL(src)) {
 		dst = &c->ip6.addr_ll_seen;
@@ -684,19 +690,19 @@ static size_t udp_update_hdr6(const struct ctx *c, struct udp6_l2_buf_t *b,
 
 	}
 
-	b->ip6h.payload_len = htons(l4len);
-	b->ip6h.daddr = *dst;
-	b->ip6h.saddr = *src;
-	b->ip6h.version = 6;
-	b->ip6h.nexthdr = IPPROTO_UDP;
-	b->ip6h.hop_limit = 255;
+	bh->ip6h.payload_len = htons(l4len);
+	bh->ip6h.daddr = *dst;
+	bh->ip6h.saddr = *src;
+	bh->ip6h.version = 6;
+	bh->ip6h.nexthdr = IPPROTO_UDP;
+	bh->ip6h.hop_limit = 255;
 
-	b->uh.source = b->s_in6.sin6_port;
-	b->uh.dest = htons(dstport);
-	b->uh.len = b->ip6h.payload_len;
-	csum_udp6(&b->uh, src, dst, b->data, dlen);
+	bp->uh.source = bh->s_in6.sin6_port;
+	bp->uh.dest = htons(dstport);
+	bp->uh.len = bh->ip6h.payload_len;
+	csum_udp6(&bp->uh, src, dst, bp->data, dlen);
 
-	tap_hdr_update(&b->taph, l4len + sizeof(b->ip6h) + sizeof(b->eh));
+	tap_hdr_update(&bh->taph, l4len + sizeof(bh->ip6h) + sizeof(bh->eh));
 	return l4len;
 }
 
@@ -724,13 +730,16 @@ static void udp_tap_send(const struct ctx *c,
 		tap_iov = udp4_l2_iov_tap;
 
 	for (i = start; i < start + n; i++) {
+		struct udp_payload_t *bp = &udp_payload[i];
 		size_t l4len;
 
 		if (v6) {
-			l4len = udp_update_hdr6(c, &udp6_l2_buf[i], dstport,
+			l4len = udp_update_hdr6(c, &udp6_l2_buf[i], bp,
+						dstport,
 						udp6_l2_mh_sock[i].msg_len, now);
 		} else {
-			l4len = udp_update_hdr4(c, &udp4_l2_buf[i], dstport,
+			l4len = udp_update_hdr4(c, &udp4_l2_buf[i], bp,
+						dstport,
 						udp4_l2_mh_sock[i].msg_len, now);
 		}
 		tap_iov[i][UDP_IOV_PAYLOAD].iov_len = l4len;
@@ -1077,11 +1086,10 @@ static void udp_splice_iov_init(void)
 		mh6->msg_name = &udp6_localname;
 		mh6->msg_namelen = sizeof(udp6_localname);
 
-		udp4_iov_splice[i].iov_base = udp4_l2_buf[i].data;
-		udp6_iov_splice[i].iov_base = udp6_l2_buf[i].data;
+		udp_iov_splice[i].iov_base = udp_payload[i].data;
 
-		mh4->msg_iov = &udp4_iov_splice[i];
-		mh6->msg_iov = &udp6_iov_splice[i];
+		mh4->msg_iov = &udp_iov_splice[i];
+		mh6->msg_iov = &udp_iov_splice[i];
 		mh4->msg_iovlen = mh6->msg_iovlen = 1;
 	}
 }