[PATCH 5/7] tcp: Pass TCP header and payload separately to tcp_fill_headers[46]()

[David Gibson <david@gibson.dropbear.id.au>]

At the moment these take separate pointers to the tap specific and IP
headers, but expect the TCP header and payload as a single tcp_payload_t.
As well as being slightly inconsistent, this involves some slightly iffy
pointer shenanigans when called on the flags path with a tcp_flags_t
instead of a tcp_payload_t.

More importantly, it's inconvenient for the upcoming vhost-user case, where
the TCP header and payload might not be contiguous.  Furthermore, the
payload itself might not be contiguous.

So, pass the TCP header as its own pointer, and the TCP payload as an IO
vector.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 tcp.c          | 56 +++++++++++++++++++++++---------------------------
 tcp_buf.c      |  7 ++++---
 tcp_internal.h |  6 ++++--
 3 files changed, 34 insertions(+), 35 deletions(-)

diff --git a/tcp.c b/tcp.c
index d1e71ec..787bc19 100644
--- a/tcp.c
+++ b/tcp.c
@@ -914,21 +914,25 @@ static void tcp_fill_header(struct tcphdr *th,
  * @conn:		Connection pointer
  * @taph:		tap backend specific header
  * @iph:		Pointer to IPv4 header
- * @bp:			Pointer to TCP header followed by TCP payload
- * @dlen:		TCP payload length
+ * @th:			Pointer to TCP header
+ * @iov:		IO vector containing payload
+ * @iov_cnt:		Number of entries in @iov
+ * @doffset:		Offset of the TCP payload within @iov
  * @check:		Checksum, if already known
  * @seq:		Sequence number for this segment
  * @no_tcp_csum:	Do not set TCP checksum
  */
 void tcp_fill_headers4(const struct tcp_tap_conn *conn,
 		       struct tap_hdr *taph, struct iphdr *iph,
-		       struct tcp_payload_t *bp, size_t dlen,
+		       struct tcphdr *th,
+		       const struct iovec *iov, size_t iov_cnt, size_t doffset,
 		       const uint16_t *check, uint32_t seq, bool no_tcp_csum)
 {
 	const struct flowside *tapside = TAPFLOW(conn);
 	const struct in_addr *src4 = inany_v4(&tapside->oaddr);
 	const struct in_addr *dst4 = inany_v4(&tapside->eaddr);
-	size_t l4len = dlen + sizeof(bp->th);
+	size_t dlen = iov_size(iov, iov_cnt) - doffset;
+	size_t l4len = dlen + sizeof(*th);
 	size_t l3len = l4len + sizeof(*iph);
 
 	ASSERT(src4 && dst4);
@@ -940,18 +944,12 @@ 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(&bp->th, conn, seq);
+	tcp_fill_header(th, conn, seq);
 
-	if (no_tcp_csum) {
-		bp->th.check = 0;
-	} else {
-		const struct iovec iov = {
-			.iov_base = bp->data,
-			.iov_len = dlen,
-		};
-
-		tcp_update_check_tcp4(iph, &bp->th, &iov, 1, 0);
-	}
+	if (no_tcp_csum)
+		th->check = 0;
+	else
+		tcp_update_check_tcp4(iph, th, iov, iov_cnt, doffset);
 
 	tap_hdr_update(taph, l3len + sizeof(struct ethhdr));
 }
@@ -961,19 +959,23 @@ void tcp_fill_headers4(const struct tcp_tap_conn *conn,
  * @conn:		Connection pointer
  * @taph:		tap backend specific header
  * @ip6h:		Pointer to IPv6 header
- * @bp:			Pointer to TCP header followed by TCP payload
- * @dlen:		TCP payload length
+ * @th:			Pointer to TCP header
+ * @iov:		IO vector containing payload
+ * @iov_cnt:		Number of entries in @iov
+ * @doffset:		Offset of the TCP payload within @iov
  * @check:		Checksum, if already known
  * @seq:		Sequence number for this segment
  * @no_tcp_csum:	Do not set TCP checksum
  */
 void tcp_fill_headers6(const struct tcp_tap_conn *conn,
 		       struct tap_hdr *taph, struct ipv6hdr *ip6h,
-		       struct tcp_payload_t *bp, size_t dlen,
+		       struct tcphdr *th,
+		       const struct iovec *iov, size_t iov_cnt, size_t doffset,
 		       uint32_t seq, bool no_tcp_csum)
 {
 	const struct flowside *tapside = TAPFLOW(conn);
-	size_t l4len = dlen + sizeof(bp->th);
+	size_t dlen = iov_size(iov, iov_cnt) - doffset;
+	size_t l4len = dlen + sizeof(*th);
 
 	ip6h->payload_len = htons(l4len);
 	ip6h->saddr = tapside->oaddr.a6;
@@ -987,18 +989,12 @@ 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(&bp->th, conn, seq);
+	tcp_fill_header(th, conn, seq);
 
-	if (no_tcp_csum) {
-		bp->th.check = 0;
-	} else {
-		const struct iovec iov = {
-			.iov_base = bp->data,
-			.iov_len = dlen,
-		};
-
-		tcp_update_check_tcp6(ip6h, &bp->th, &iov, 1, 0);
-	}
+	if (no_tcp_csum)
+		th->check = 0;
+	else
+		tcp_update_check_tcp6(ip6h, th, iov, iov_cnt, doffset);
 
 	tap_hdr_update(taph, l4len + sizeof(*ip6h) + sizeof(struct ethhdr));
 }
diff --git a/tcp_buf.c b/tcp_buf.c
index b2d806a..c03dd33 100644
--- a/tcp_buf.c
+++ b/tcp_buf.c
@@ -270,8 +270,9 @@ static void tcp_buf_make_frame(const struct tcp_tap_conn *conn,
 			       const uint16_t *check, uint32_t seq,
 			       bool no_tcp_csum)
 {
-	struct tcp_payload_t *payload = iov[TCP_IOV_PAYLOAD].iov_base;
+	struct tcphdr *th = iov[TCP_IOV_PAYLOAD].iov_base;
 	struct tap_hdr *taph = iov[TCP_IOV_TAP].iov_base;
+	const struct iovec *tail = &iov[TCP_IOV_PAYLOAD];
 	const struct flowside *tapside = TAPFLOW(conn);
 	const struct in_addr *a4 = inany_v4(&tapside->oaddr);
 
@@ -280,12 +281,12 @@ static void tcp_buf_make_frame(const struct tcp_tap_conn *conn,
 	if (a4) {
 		struct iphdr *iph = iov[TCP_IOV_IP].iov_base;
 
-		tcp_fill_headers4(conn, taph, iph, payload, dlen,
+		tcp_fill_headers4(conn, taph, iph, th, tail, 1, sizeof(*th),
 				  check, seq, no_tcp_csum);
 	} else {
 		struct ipv6hdr *ip6h = iov[TCP_IOV_IP].iov_base;
 
-		tcp_fill_headers6(conn, taph, ip6h, payload, dlen,
+		tcp_fill_headers6(conn, taph, ip6h, th, tail, 1, sizeof(*th),
 				  seq, no_tcp_csum);
 	}
 }
diff --git a/tcp_internal.h b/tcp_internal.h
index 6cf5ad6..8bdfc77 100644
--- a/tcp_internal.h
+++ b/tcp_internal.h
@@ -179,11 +179,13 @@ struct tcp_info_linux;
 
 void tcp_fill_headers4(const struct tcp_tap_conn *conn,
 		       struct tap_hdr *taph, struct iphdr *iph,
-		       struct tcp_payload_t *bp, size_t dlen,
+		       struct tcphdr *th,
+		       const struct iovec *iov, size_t iov_cnt, size_t doffset,
 		       const uint16_t *check, uint32_t seq, bool no_tcp_csum);
 void tcp_fill_headers6(const struct tcp_tap_conn *conn,
 		       struct tap_hdr *taph, struct ipv6hdr *ip6h,
-		       struct tcp_payload_t *bp, size_t dlen,
+		       struct tcphdr *th,
+		       const struct iovec *iov, size_t iov_cnt, size_t doffset,
 		       uint32_t seq, bool no_tcp_csum);
 
 int tcp_update_seqack_wnd(const struct ctx *c, struct tcp_tap_conn *conn,
-- 
@@ -179,11 +179,13 @@ struct tcp_info_linux;
 
 void tcp_fill_headers4(const struct tcp_tap_conn *conn,
 		       struct tap_hdr *taph, struct iphdr *iph,
-		       struct tcp_payload_t *bp, size_t dlen,
+		       struct tcphdr *th,
+		       const struct iovec *iov, size_t iov_cnt, size_t doffset,
 		       const uint16_t *check, uint32_t seq, bool no_tcp_csum);
 void tcp_fill_headers6(const struct tcp_tap_conn *conn,
 		       struct tap_hdr *taph, struct ipv6hdr *ip6h,
-		       struct tcp_payload_t *bp, size_t dlen,
+		       struct tcphdr *th,
+		       const struct iovec *iov, size_t iov_cnt, size_t doffset,
 		       uint32_t seq, bool no_tcp_csum);
 
 int tcp_update_seqack_wnd(const struct ctx *c, struct tcp_tap_conn *conn,
-- 
2.47.0