udp: Split tap-bound UDP packets into multiple buffers using io vector

When sending to the tap device, currently we assemble the headers and
payload into a single contiguous buffer.  Those are described by a single
struct iovec, then a batch of frames is sent to the device with
tap_send_frames().

In order to better integrate the IPv4 and IPv6 paths, we want the IP
header in a different buffer that might not be contiguous with the
payload.  To prepare for that, split the UDP packet into an iovec of
buffers.  We use the same split that Laurent recently introduced for
TCP for convenience.

This removes the last use of tap_hdr_len_(), tap_frame_base() and
tap_frame_len(), so remove those too.

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

1 files changed, 49 insertions, 25 deletions

diff --git a/udp.c b/udp.c
index 7186fae..d293bc5 100644
--- a/udp.c
+++ b/udp.c
@@ -222,12 +222,28 @@ struct udp6_l2_buf_t {
 #endif
 udp6_l2_buf[UDP_MAX_FRAMES];
 
+/**
+ * enum udp_iov_idx - Indices for the buffers making up a single UDP frame
+ * @UDP_IOV_TAP         tap specific header
+ * @UDP_IOV_ETH         Ethernet header
+ * @UDP_IOV_IP          IP (v4/v6) header
+ * @UDP_IOV_PAYLOAD     IP payload (UDP header + data)
+ * @UDP_NUM_IOVS        the number of entries in the iovec array
+ */
+enum udp_iov_idx {
+	UDP_IOV_TAP	= 0,
+	UDP_IOV_ETH	= 1,
+	UDP_IOV_IP	= 2,
+	UDP_IOV_PAYLOAD	= 3,
+	UDP_NUM_IOVS
+};
+
 /* 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	udp4_l2_iov_tap		[UDP_MAX_FRAMES];
-static struct iovec	udp6_l2_iov_tap		[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];
 
 static struct mmsghdr	udp4_l2_mh_sock		[UDP_MAX_FRAMES];
 static struct mmsghdr	udp6_l2_mh_sock		[UDP_MAX_FRAMES];
@@ -309,7 +325,7 @@ static void udp_sock4_iov_init_one(const struct ctx *c, size_t i)
 	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];
+	struct iovec *tiov = udp4_l2_iov_tap[i];
 
 	*buf = (struct udp4_l2_buf_t) {
 		.eh  = ETH_HDR_INIT(ETH_P_IP),
@@ -323,7 +339,10 @@ static void udp_sock4_iov_init_one(const struct ctx *c, size_t i)
 	mh->msg_iov	= siov;
 	mh->msg_iovlen	= 1;
 
-	tiov->iov_base	= tap_frame_base(c, &buf->taph);
+	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;
 }
 
 /**
@@ -336,7 +355,7 @@ static void udp_sock6_iov_init_one(const struct ctx *c, size_t i)
 	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];
+	struct iovec *tiov = udp6_l2_iov_tap[i];
 
 	*buf = (struct udp6_l2_buf_t) {
 		.eh   = ETH_HDR_INIT(ETH_P_IPV6),
@@ -350,7 +369,10 @@ static void udp_sock6_iov_init_one(const struct ctx *c, size_t i)
 	mh->msg_iov	= siov;
 	mh->msg_iovlen	= 1;
 
-	tiov->iov_base	= tap_frame_base(c, &buf->taph);
+	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;
 }
 
 /**
@@ -572,13 +594,14 @@ static void udp_splice_sendfrom(const struct ctx *c, unsigned start, unsigned n,
  * @dlen:	Length of UDP payload
  * @now:	Current timestamp
  *
- * Return: size of tap frame with headers
+ * Return: size of IPv4 payload (UDP header + data)
  */
 static size_t udp_update_hdr4(const struct ctx *c, struct udp4_l2_buf_t *b,
 			      in_port_t dstport, size_t dlen,
 			      const struct timespec *now)
 {
-	size_t l3len = dlen + sizeof(b->iph) + sizeof(b->uh);
+	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;
 
@@ -609,9 +632,10 @@ static size_t udp_update_hdr4(const struct ctx *c, struct udp4_l2_buf_t *b,
 
 	b->uh.source = b->s_in.sin_port;
 	b->uh.dest = htons(dstport);
-	b->uh.len = htons(dlen + sizeof(b->uh));
+	b->uh.len = htons(l4len);
 
-	return tap_frame_len(c, &b->taph, l3len + sizeof(b->eh));
+	tap_hdr_update(&b->taph, l3len + sizeof(b->eh));
+	return l4len;
 }
 
 /**
@@ -622,7 +646,7 @@ static size_t udp_update_hdr4(const struct ctx *c, struct udp4_l2_buf_t *b,
  * @dlen:	Length of UDP payload
  * @now:	Current timestamp
  *
- * Return: size of tap frame with headers
+ * Return: size of IPv6 payload (UDP header + data)
  */
 static size_t udp_update_hdr6(const struct ctx *c, struct udp6_l2_buf_t *b,
 			      in_port_t dstport, size_t dlen,
@@ -679,8 +703,8 @@ static size_t udp_update_hdr6(const struct ctx *c, struct udp6_l2_buf_t *b,
 	b->uh.len = b->ip6h.payload_len;
 	csum_udp6(&b->uh, src, dst, b->data, dlen);
 
-	return tap_frame_len(c, &b->taph, l4len +
-			                  sizeof(b->ip6h) + sizeof(b->eh));
+	tap_hdr_update(&b->taph, l4len + sizeof(b->ip6h) + sizeof(b->eh));
+	return l4len;
 }
 
 /**
@@ -698,8 +722,8 @@ static void udp_tap_send(const struct ctx *c,
 			 unsigned int start, unsigned int n,
 			 in_port_t dstport, bool v6, const struct timespec *now)
 {
-	struct iovec *tap_iov;
-	unsigned int i;
+	struct iovec (*tap_iov)[UDP_NUM_IOVS];
+	size_t i;
 
 	if (v6)
 		tap_iov = udp6_l2_iov_tap;
@@ -707,19 +731,19 @@ static void udp_tap_send(const struct ctx *c,
 		tap_iov = udp4_l2_iov_tap;
 
 	for (i = start; i < start + n; i++) {
-		size_t buf_len;
-
-		if (v6)
-			buf_len = udp_update_hdr6(c, &udp6_l2_buf[i], dstport,
-						  udp6_l2_mh_sock[i].msg_len, now);
-		else
-			buf_len = udp_update_hdr4(c, &udp4_l2_buf[i], dstport,
-						  udp4_l2_mh_sock[i].msg_len, now);
+		size_t l4len;
 
-		tap_iov[i].iov_len = buf_len;
+		if (v6) {
+			l4len = udp_update_hdr6(c, &udp6_l2_buf[i], dstport,
+						udp6_l2_mh_sock[i].msg_len, now);
+		} else {
+			l4len = udp_update_hdr4(c, &udp4_l2_buf[i], dstport,
+						udp4_l2_mh_sock[i].msg_len, now);
+		}
+		tap_iov[i][UDP_IOV_PAYLOAD].iov_len = l4len;
 	}
 
-	tap_send_frames(c, tap_iov + start, 1, n);
+	tap_send_frames(c, &tap_iov[start][0], UDP_NUM_IOVS, n);
 }
 
 /**