tcp: Consolidate calculation of total frame size

tcp_l2_buf_fill_headers() returns the size of the generated frame including
the ethernet header.  The caller then adds on the size of the vnet_len
field to get the total frame size to be passed to the tap device.

Outside the tap code, though, we never care about the ethernet header size
only the final total size we need to put into an iovec.  So, consolidate
the total frame size calculation within tcp_l2_buf_fill_headers().

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

1 files changed, 16 insertions, 19 deletions

diff --git a/tcp.c b/tcp.c
index 052e38f..f812143 100644
--- a/tcp.c
+++ b/tcp.c
@@ -1451,7 +1451,7 @@ void tcp_defer_handler(struct ctx *c)
  * @check:	Checksum, if already known
  * @seq:	Sequence number for this segment
  *
- * Return: 802.3 length, host order
+ * Return: frame length including L2 headers, host order
  */
 static size_t tcp_l2_buf_fill_headers(const struct ctx *c,
 				      const struct tcp_tap_conn *conn,
@@ -1459,7 +1459,7 @@ static size_t tcp_l2_buf_fill_headers(const struct ctx *c,
 				      const uint16_t *check, uint32_t seq)
 {
 	const struct in_addr *a4 = inany_v4(&conn->addr);
-	size_t ip_len, eth_len;
+	size_t ip_len, tlen;
 
 #define SET_TCP_HEADER_COMMON_V4_V6(b, conn, seq)			\
 do {									\
@@ -1493,9 +1493,10 @@ do {									\
 
 		tcp_update_check_tcp4(b);
 
-		eth_len = ip_len + sizeof(struct ethhdr);
+		tlen = ip_len + sizeof(struct ethhdr);
 		if (c->mode == MODE_PASST)
-			b->vnet_len = htonl(eth_len);
+			b->vnet_len = htonl(tlen);
+		tlen += sizeof(b->vnet_len);
 	} else {
 		struct tcp6_l2_buf_t *b = (struct tcp6_l2_buf_t *)p;
 
@@ -1518,14 +1519,14 @@ do {									\
 		b->ip6h.flow_lbl[1] = (conn->sock >> 8) & 0xff;
 		b->ip6h.flow_lbl[2] = (conn->sock >> 0) & 0xff;
 
-		eth_len = ip_len + sizeof(struct ethhdr);
+		tlen = ip_len + sizeof(struct ethhdr);
 		if (c->mode == MODE_PASST)
-			b->vnet_len = htonl(eth_len);
+			b->vnet_len = htonl(tlen);
+		tlen += sizeof(b->vnet_len);
 	}
-
 #undef SET_TCP_HEADER_COMMON_V4_V6
 
-	return eth_len;
+	return tlen;
 }
 
 /**
@@ -1631,8 +1632,8 @@ static int tcp_send_flag(struct ctx *c, struct tcp_tap_conn *conn, int flags)
 	struct tcp6_l2_flags_buf_t *b6 = NULL;
 	struct tcp_info tinfo = { 0 };
 	socklen_t sl = sizeof(tinfo);
-	size_t optlen = 0, eth_len;
 	int s = conn->sock;
+	size_t optlen = 0;
 	struct iovec *iov;
 	struct tcphdr *th;
 	char *data;
@@ -1721,9 +1722,8 @@ static int tcp_send_flag(struct ctx *c, struct tcp_tap_conn *conn, int flags)
 	th->syn = !!(flags & SYN);
 	th->fin = !!(flags & FIN);
 
-	eth_len = tcp_l2_buf_fill_headers(c, conn, p, optlen,
-					  NULL, conn->seq_to_tap);
-	iov->iov_len = eth_len + sizeof(uint32_t);
+	iov->iov_len = tcp_l2_buf_fill_headers(c, conn, p, optlen,
+					       NULL, conn->seq_to_tap);
 
 	if (th->ack)
 		conn_flag(c, conn, ~ACK_TO_TAP_DUE);
@@ -2083,25 +2083,22 @@ static void tcp_data_to_tap(struct ctx *c, struct tcp_tap_conn *conn,
 			    ssize_t plen, int no_csum, uint32_t seq)
 {
 	struct iovec *iov;
-	size_t len;
 
 	if (CONN_V4(conn)) {
 		struct tcp4_l2_buf_t *b = &tcp4_l2_buf[tcp4_l2_buf_used];
 		uint16_t *check = no_csum ? &(b - 1)->iph.check : NULL;
 
-		len = tcp_l2_buf_fill_headers(c, conn, b, plen, check, seq);
-
 		iov = tcp4_l2_iov + tcp4_l2_buf_used++;
-		iov->iov_len = len + sizeof(b->vnet_len);
+		iov->iov_len = tcp_l2_buf_fill_headers(c, conn, b, plen,
+						       check, seq);
 		if (tcp4_l2_buf_used > ARRAY_SIZE(tcp4_l2_buf) - 1)
 			tcp_l2_data_buf_flush(c);
 	} else if (CONN_V6(conn)) {
 		struct tcp6_l2_buf_t *b = &tcp6_l2_buf[tcp6_l2_buf_used];
 
-		len = tcp_l2_buf_fill_headers(c, conn, b, plen, NULL, seq);
-
 		iov = tcp6_l2_iov + tcp6_l2_buf_used++;
-		iov->iov_len = len + sizeof(b->vnet_len);
+		iov->iov_len = tcp_l2_buf_fill_headers(c, conn, b, plen,
+						       NULL, seq);
 		if (tcp6_l2_buf_used > ARRAY_SIZE(tcp6_l2_buf) - 1)
 			tcp_l2_data_buf_flush(c);
 	}