[PATCH 7/7] tcp: Fold tcp_update_csum() into tcp_fill_header()

tcp_update_csum() is now simple enough that it makes sense to just fold it
into tcp_fill_header(), meaning the latter now really does fill all the
header fields.

Signed-off-by: David Gibson <david(a)gibson.dropbear.id.au>
---
 tcp.c | 66 ++++++++++++++++++++++++++---------------------------------
 1 file changed, 29 insertions(+), 37 deletions(-)

diff --git a/tcp.c b/tcp.c
index e9f62a4..88a285b 100644
--- a/tcp.c
+++ b/tcp.c
@@ -750,23 +750,6 @@ static void tcp_sock_set_bufsize(const struct ctx *c, int s)
 		trace("TCP: failed to set SO_SNDBUF to %i", v);
 }
 
-/**
- * tcp_update_csum() - Calculate TCP checksum
- * @psum:	Unfolded partial checksum of the IPv4 or IPv6 pseudo-header
- * @th:		TCP header (updated)
- * @iov:	IO vector containing the TCP payload
- * @iov_cnt:	Length of @iov
- * @doffset:	TCP payload offset in @iov
- */
-static void tcp_update_csum(uint32_t psum, struct tcphdr *th,
-			    const struct iovec *iov, int iov_cnt,
-			    size_t doffset)
-{
-	th->check = 0;
-	psum = csum_unfolded(th, sizeof(*th), psum);
-	th->check = csum_iov(iov, iov_cnt, doffset, psum);
-}
-
 /**
  * tcp_opt_get() - Get option, and value if any, from TCP header
  * @opts:	Pointer to start of TCP options in header
@@ -860,9 +843,16 @@ void tcp_defer_handler(struct ctx *c)
  * @th:		Pointer to the TCP header structure
  * @conn:	Pointer to the TCP connection structure
  * @seq:	Sequence number
+ * @ppsum:	Pointer to pseudo-header checksum, or NULL to omit checksum
+ * @iov:	IO vector containing the TCP payload
+ * @iov_cnt:	Length of @iov
+ * @doffset:	TCP payload offset in @iov
  */
 static void tcp_fill_header(struct tcphdr *th,
-			    const struct tcp_tap_conn *conn, uint32_t seq)
+			    const struct tcp_tap_conn *conn, uint32_t seq,
+			    const uint32_t *ppsum,
+			    const struct iovec *iov, size_t iov_cnt,
+			    size_t doffset)
 {
 	const struct flowside *tapside = TAPFLOW(conn);
 
@@ -877,6 +867,11 @@ static void tcp_fill_header(struct tcphdr *th,
 
 		th->window = htons(MIN(wnd, USHRT_MAX));
 	}
+	th->check = 0;
+	if (ppsum) {
+		uint32_t sum = csum_unfolded(th, sizeof(*th), *ppsum);
+		th->check = csum_iov(iov, iov_cnt, doffset, sum);
+	}
 }
 
 /**
@@ -904,6 +899,8 @@ void tcp_fill_headers4(const struct tcp_tap_conn *conn,
 	size_t dlen = iov_size(iov, iov_cnt) - doffset;
 	size_t l4len = dlen + sizeof(*th);
 	size_t l3len = l4len + sizeof(*iph);
+	const uint32_t *ppsum = NULL;
+	uint32_t psum;
 
 	ASSERT(src4 && dst4);
 
@@ -914,17 +911,13 @@ void tcp_fill_headers4(const struct tcp_tap_conn *conn,
 	iph->check = check ? *check :
 			     csum_ip4_header(l3len, IPPROTO_TCP, *src4, *dst4);
 
-	tcp_fill_header(th, conn, seq);
-
-	if (no_tcp_csum) {
-		th->check = 0;
-	} else {
-		uint32_t psum = proto_ipv4_header_psum(l4len, IPPROTO_TCP,
-						       *src4, *dst4);
-
-		tcp_update_csum(psum, th, iov, iov_cnt, doffset);
+	if (!no_tcp_csum) {
+		psum = proto_ipv4_header_psum(l4len, IPPROTO_TCP, *src4, *dst4);
+		ppsum = &psum;
 	}
 
+	tcp_fill_header(th, conn, seq, ppsum, iov, iov_cnt, doffset);
+
 	tap_hdr_update(taph, l3len + sizeof(struct ethhdr));
 }
 
@@ -950,6 +943,8 @@ void tcp_fill_headers6(const struct tcp_tap_conn *conn,
 	const struct flowside *tapside = TAPFLOW(conn);
 	size_t dlen = iov_size(iov, iov_cnt) - doffset;
 	size_t l4len = dlen + sizeof(*th);
+	const uint32_t *ppsum = NULL;
+	uint32_t psum;
 
 	ip6h->payload_len = htons(l4len);
 	ip6h->saddr = tapside->oaddr.a6;
@@ -963,18 +958,15 @@ void tcp_fill_headers6(const struct tcp_tap_conn *conn,
 	ip6h->flow_lbl[1] = (conn->sock >> 8) & 0xff;
 	ip6h->flow_lbl[2] = (conn->sock >> 0) & 0xff;
 
-	tcp_fill_header(th, conn, seq);
-
-	if (no_tcp_csum) {
-		th->check = 0;
-	} else {
-		uint32_t psum = proto_ipv6_header_psum(l4len, IPPROTO_TCP,
-						       &ip6h->saddr,
-						       &ip6h->daddr);
-
-		tcp_update_csum(psum, th, iov, iov_cnt, doffset);
+	if (!no_tcp_csum) {
+		psum = proto_ipv6_header_psum(l4len, IPPROTO_TCP,
+					      &ip6h->saddr,
+					      &ip6h->daddr);
+		ppsum = &psum;
 	}
 
+	tcp_fill_header(th, conn, seq, ppsum, iov, iov_cnt, doffset);
+
 	tap_hdr_update(taph, l4len + sizeof(*ip6h) + sizeof(struct ethhdr));
 }
 
-- 
2.47.0