udp: Single buffer for IPv4, IPv6 headers and metadata

Currently we have separate arrays for IPv4 and IPv6 which contain the
headers for guest-bound packets, and also the originating socket address.
We can combine these into a single array of "metadata" structures with
space for both pre-cooked IPv4 and IPv6 headers, as well as shared space
for the tap specific header and socket address (using sockaddr_inany).

Because we're using IOVs to separately address the pieces of each frame,
these structures don't need to be packed to keep the headers contiguous
so we can more naturally arrange for the alignment we want.

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

1 files changed, 55 insertions, 77 deletions

diff --git a/udp.c b/udp.c
index c940749..3abafc9 100644
--- a/udp.c
+++ b/udp.c
@@ -189,44 +189,27 @@ udp_payload[UDP_MAX_FRAMES];
 /* Ethernet header for IPv4 frames */
 static struct ethhdr udp4_eth_hdr;
 
-/**
- * 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
- * @iph:	Pre-filled IP header (except for tot_len and saddr)
- */
-static struct udp4_l2_buf_t {
-	struct sockaddr_in s_in;
-
-	struct tap_hdr taph;
-	struct iphdr iph;
-} __attribute__ ((packed, aligned(__alignof__(unsigned int))))
-udp4_l2_buf[UDP_MAX_FRAMES];
-
 /* Ethernet header for IPv6 frames */
 static struct ethhdr udp6_eth_hdr;
 
 /**
- * udp6_l2_buf_t - Pre-cooked IPv6 packet buffers for tap connections
- * @s_in6:	Source socket address, filled in by recvmmsg()
+ * struct udp_meta_t - Pre-cooked headers and metadata for UDP packets
+ * @ip6h:	Pre-filled IPv6 header (except for payload_len and addresses)
+ * @ip4h:	Pre-filled IPv4 header (except for tot_len and saddr)
  * @taph:	Tap backend specific header
- * @ip6h:	Pre-filled IP header (except for payload_len and addresses)
+ * @s_in:	Source socket address, filled in by recvmmsg()
  */
-struct udp6_l2_buf_t {
-	struct sockaddr_in6 s_in6;
-#ifdef __AVX2__
-	/* Align ip6h to 32-byte boundary. */
-	uint8_t pad[64 - (sizeof(struct sockaddr_in6) + sizeof(struct tap_hdr))];
-#endif
-
-	struct tap_hdr taph;
+static struct udp_meta_t {
 	struct ipv6hdr ip6h;
+	struct iphdr ip4h;
+	struct tap_hdr taph;
+
+	union sockaddr_inany s_in;
+}
 #ifdef __AVX2__
-} __attribute__ ((packed, aligned(32)))
-#else
-} __attribute__ ((packed, aligned(__alignof__(unsigned int))))
+__attribute__ ((aligned(32)))
 #endif
-udp6_l2_buf[UDP_MAX_FRAMES];
+udp_meta[UDP_MAX_FRAMES];
 
 /**
  * enum udp_iov_idx - Indices for the buffers making up a single UDP frame
@@ -321,6 +304,12 @@ 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];
+	struct udp_meta_t *meta = &udp_meta[i];
+
+	*meta = (struct udp_meta_t) {
+		.ip4h = L2_BUF_IP4_INIT(IPPROTO_UDP),
+		.ip6h = L2_BUF_IP6_INIT(IPPROTO_UDP),
+	};
 
 	*siov = IOV_OF_LVALUE(payload->data);
 	udp4_eth_hdr.h_proto = htons_constant(ETH_P_IP);
@@ -328,41 +317,31 @@ static void udp_iov_init_one(const struct ctx *c, size_t i)
 
 	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 *tiov = udp4_l2_iov_tap[i];
 
-		*buf = (struct udp4_l2_buf_t) {
-			.iph = L2_BUF_IP4_INIT(IPPROTO_UDP)
-		};
-
-		mh->msg_name	= &buf->s_in;
-		mh->msg_namelen	= sizeof(buf->s_in);
+		mh->msg_name	= &meta->s_in;
+		mh->msg_namelen	= sizeof(struct sockaddr_in);
 		mh->msg_iov	= siov;
 		mh->msg_iovlen	= 1;
 
-		tiov[UDP_IOV_TAP] = tap_hdr_iov(c, &buf->taph);
+		tiov[UDP_IOV_TAP] = tap_hdr_iov(c, &meta->taph);
 		tiov[UDP_IOV_ETH] = IOV_OF_LVALUE(udp4_eth_hdr);
-		tiov[UDP_IOV_IP] = IOV_OF_LVALUE(buf->iph);
+		tiov[UDP_IOV_IP] = IOV_OF_LVALUE(meta->ip4h);
 		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 *tiov = udp6_l2_iov_tap[i];
 
-		*buf = (struct udp6_l2_buf_t) {
-			.ip6h = L2_BUF_IP6_INIT(IPPROTO_UDP)
-		};
-
-		mh->msg_name	= &buf->s_in6;
-		mh->msg_namelen	= sizeof(buf->s_in6);
+		mh->msg_name	= &meta->s_in;
+		mh->msg_namelen	= sizeof(struct sockaddr_in6);
 		mh->msg_iov	= siov;
 		mh->msg_iovlen	= 1;
 
-		tiov[UDP_IOV_TAP] = tap_hdr_iov(c, &buf->taph);
+		tiov[UDP_IOV_TAP] = tap_hdr_iov(c, &meta->taph);
 		tiov[UDP_IOV_ETH] = IOV_OF_LVALUE(udp6_eth_hdr);
-		tiov[UDP_IOV_IP] = IOV_OF_LVALUE(buf->ip6h);
+		tiov[UDP_IOV_IP] = IOV_OF_LVALUE(meta->ip6h);
 		tiov[UDP_IOV_PAYLOAD].iov_base = payload;
 	}
 }
@@ -577,7 +556,7 @@ 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
- * @bh:		Pointer to udp4_l2_buf to update
+ * @bm:		Pointer to udp_meta_t to update
  * @bp:		Pointer to udp_payload_t to update
  * @dstport:	Destination port number
  * @dlen:	Length of UDP payload
@@ -585,16 +564,16 @@ static void udp_splice_sendfrom(const struct ctx *c, unsigned start, unsigned n,
  *
  * Return: size of IPv4 payload (UDP header + data)
  */
-static size_t udp_update_hdr4(const struct ctx *c, struct udp4_l2_buf_t *bh,
-			      struct udp_payload_t *bp,
+static size_t udp_update_hdr4(const struct ctx *c,
+			      struct udp_meta_t *bm, 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);
+	in_port_t srcport = ntohs(bm->s_in.sa4.sin_port);
 	const struct in_addr dst = c->ip4.addr_seen;
-	struct in_addr src = bh->s_in.sin_addr;
+	struct in_addr src = bm->s_in.sa4.sin_addr;
 	size_t l4len = dlen + sizeof(bp->uh);
-	size_t l3len = l4len + sizeof(bh->iph);
+	size_t l3len = l4len + sizeof(bm->ip4h);
 
 	if (!IN4_IS_ADDR_UNSPECIFIED(&c->ip4.dns_match) &&
 	    IN4_ARE_ADDR_EQUAL(&src, &c->ip4.dns_host) && srcport == 53 &&
@@ -615,24 +594,24 @@ static size_t udp_update_hdr4(const struct ctx *c, struct udp4_l2_buf_t *bh,
 		src = c->ip4.gw;
 	}
 
-	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);
+	bm->ip4h.tot_len = htons(l3len);
+	bm->ip4h.daddr = dst.s_addr;
+	bm->ip4h.saddr = src.s_addr;
+	bm->ip4h.check = csum_ip4_header(l3len, IPPROTO_UDP, src, dst);
 
-	bp->uh.source = bh->s_in.sin_port;
+	bp->uh.source = bm->s_in.sa4.sin_port;
 	bp->uh.dest = htons(dstport);
 	bp->uh.len = htons(l4len);
 	csum_udp4(&bp->uh, src, dst, bp->data, dlen);
 
-	tap_hdr_update(&bh->taph, l3len + sizeof(udp4_eth_hdr));
+	tap_hdr_update(&bm->taph, l3len + sizeof(udp4_eth_hdr));
 	return l4len;
 }
 
 /**
  * udp_update_hdr6() - Update headers for one IPv6 datagram
  * @c:		Execution context
- * @bh:		Pointer to udp6_l2_buf to update
+ * @bm:		Pointer to udp_meta_t to update
  * @bp:		Pointer to udp_payload_t to update
  * @dstport:	Destination port number
  * @dlen:	Length of UDP payload
@@ -640,14 +619,14 @@ static size_t udp_update_hdr4(const struct ctx *c, struct udp4_l2_buf_t *bh,
  *
  * Return: size of IPv6 payload (UDP header + data)
  */
-static size_t udp_update_hdr6(const struct ctx *c, struct udp6_l2_buf_t *bh,
-			      struct udp_payload_t *bp,
+static size_t udp_update_hdr6(const struct ctx *c,
+			      struct udp_meta_t *bm, struct udp_payload_t *bp,
 			      in_port_t dstport, size_t dlen,
 			      const struct timespec *now)
 {
-	const struct in6_addr *src = &bh->s_in6.sin6_addr;
+	const struct in6_addr *src = &bm->s_in.sa6.sin6_addr;
 	const struct in6_addr *dst = &c->ip6.addr_seen;
-	in_port_t srcport = ntohs(bh->s_in6.sin6_port);
+	in_port_t srcport = ntohs(bm->s_in.sa6.sin6_port);
 	uint16_t l4len = dlen + sizeof(bp->uh);
 
 	if (IN6_IS_ADDR_LINKLOCAL(src)) {
@@ -684,19 +663,19 @@ static size_t udp_update_hdr6(const struct ctx *c, struct udp6_l2_buf_t *bh,
 
 	}
 
-	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;
+	bm->ip6h.payload_len = htons(l4len);
+	bm->ip6h.daddr = *dst;
+	bm->ip6h.saddr = *src;
+	bm->ip6h.version = 6;
+	bm->ip6h.nexthdr = IPPROTO_UDP;
+	bm->ip6h.hop_limit = 255;
 
-	bp->uh.source = bh->s_in6.sin6_port;
+	bp->uh.source = bm->s_in.sa6.sin6_port;
 	bp->uh.dest = htons(dstport);
-	bp->uh.len = bh->ip6h.payload_len;
+	bp->uh.len = bm->ip6h.payload_len;
 	csum_udp6(&bp->uh, src, dst, bp->data, dlen);
 
-	tap_hdr_update(&bh->taph, l4len + sizeof(bh->ip6h) + sizeof(udp6_eth_hdr));
+	tap_hdr_update(&bm->taph, l4len + sizeof(bm->ip6h) + sizeof(udp6_eth_hdr));
 	return l4len;
 }
 
@@ -725,15 +704,14 @@ static void udp_tap_send(const struct ctx *c,
 
 	for (i = start; i < start + n; i++) {
 		struct udp_payload_t *bp = &udp_payload[i];
+		struct udp_meta_t *bm = &udp_meta[i];
 		size_t l4len;
 
 		if (v6) {
-			l4len = udp_update_hdr6(c, &udp6_l2_buf[i], bp,
-						dstport,
+			l4len = udp_update_hdr6(c, bm, bp, dstport,
 						udp6_l2_mh_sock[i].msg_len, now);
 		} else {
-			l4len = udp_update_hdr4(c, &udp4_l2_buf[i], bp,
-						dstport,
+			l4len = udp_update_hdr4(c, bm, bp, dstport,
 						udp4_l2_mh_sock[i].msg_len, now);
 		}
 		tap_iov[i][UDP_IOV_PAYLOAD].iov_len = l4len;