[PATCH 4/7] tcp: Don't use return value from tcp_fill_headers[46] to adjust iov_len

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

Currently tcp_fill_headers[46] return the size of the IP payload, which
we use to adjust the size of the last IOV entry for the frame, so that it
only includes the expected data.  This was originally done to isolate
knowledge of the header layout to the header building functions.  However,
we since reorganized from a single buffer for the frame to an IO vector of
pieces, which means we already know something about the layout in the
caller.

Use that knowledge to adjust iov_len *before* we call tcp_fill_headers*().
This means that the header building functions are called with the IOV
containing the frame and only the frame, which will be useful later on.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 tcp.c          | 24 ++++++++----------------
 tcp_buf.c      | 13 ++++++-------
 tcp_internal.h | 17 +++++++++--------
 3 files changed, 23 insertions(+), 31 deletions(-)

diff --git a/tcp.c b/tcp.c
index 7c6f51a..d1e71ec 100644
--- a/tcp.c
+++ b/tcp.c
@@ -919,13 +919,11 @@ static void tcp_fill_header(struct tcphdr *th,
  * @check:		Checksum, if already known
  * @seq:		Sequence number for this segment
  * @no_tcp_csum:	Do not set TCP checksum
- *
- * Return: The IPv4 payload length, host order
  */
-size_t tcp_fill_headers4(const struct tcp_tap_conn *conn,
-			 struct tap_hdr *taph, struct iphdr *iph,
-			 struct tcp_payload_t *bp, size_t dlen,
-			 const uint16_t *check, uint32_t seq, bool no_tcp_csum)
+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,
+		       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);
@@ -956,8 +954,6 @@ size_t tcp_fill_headers4(const struct tcp_tap_conn *conn,
 	}
 
 	tap_hdr_update(taph, l3len + sizeof(struct ethhdr));
-
-	return l4len;
 }
 
 /**
@@ -970,13 +966,11 @@ size_t tcp_fill_headers4(const struct tcp_tap_conn *conn,
  * @check:		Checksum, if already known
  * @seq:		Sequence number for this segment
  * @no_tcp_csum:	Do not set TCP checksum
- *
- * Return: The IPv6 payload length, host order
  */
-size_t tcp_fill_headers6(const struct tcp_tap_conn *conn,
-			 struct tap_hdr *taph, struct ipv6hdr *ip6h,
-			 struct tcp_payload_t *bp, size_t dlen,
-			 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,
+		       uint32_t seq, bool no_tcp_csum)
 {
 	const struct flowside *tapside = TAPFLOW(conn);
 	size_t l4len = dlen + sizeof(bp->th);
@@ -1007,8 +1001,6 @@ size_t tcp_fill_headers6(const struct tcp_tap_conn *conn,
 	}
 
 	tap_hdr_update(taph, l4len + sizeof(*ip6h) + sizeof(struct ethhdr));
-
-	return l4len;
 }
 
 /**
diff --git a/tcp_buf.c b/tcp_buf.c
index deb7be4..b2d806a 100644
--- a/tcp_buf.c
+++ b/tcp_buf.c
@@ -274,21 +274,20 @@ static void tcp_buf_make_frame(const struct tcp_tap_conn *conn,
 	struct tap_hdr *taph = iov[TCP_IOV_TAP].iov_base;
 	const struct flowside *tapside = TAPFLOW(conn);
 	const struct in_addr *a4 = inany_v4(&tapside->oaddr);
-	size_t l4len;
+
+	iov[TCP_IOV_PAYLOAD].iov_len = dlen + sizeof(struct tcphdr);
 
 	if (a4) {
 		struct iphdr *iph = iov[TCP_IOV_IP].iov_base;
 
-		l4len = tcp_fill_headers4(conn, taph, iph, payload, dlen,
-					  check, seq, no_tcp_csum);
+		tcp_fill_headers4(conn, taph, iph, payload, dlen,
+				  check, seq, no_tcp_csum);
 	} else {
 		struct ipv6hdr *ip6h = iov[TCP_IOV_IP].iov_base;
 
-		l4len = tcp_fill_headers6(conn, taph, ip6h, payload, dlen,
-					  seq, no_tcp_csum);
+		tcp_fill_headers6(conn, taph, ip6h, payload, dlen,
+				  seq, no_tcp_csum);
 	}
-
-	iov[TCP_IOV_PAYLOAD].iov_len = l4len;
 }
 
 /**
diff --git a/tcp_internal.h b/tcp_internal.h
index 0034b22..6cf5ad6 100644
--- a/tcp_internal.h
+++ b/tcp_internal.h
@@ -177,14 +177,15 @@ void tcp_rst_do(const struct ctx *c, struct tcp_tap_conn *conn);
 
 struct tcp_info_linux;
 
-size_t tcp_fill_headers4(const struct tcp_tap_conn *conn,
-			 struct tap_hdr *taph, struct iphdr *iph,
-			 struct tcp_payload_t *bp, size_t dlen,
-			 const uint16_t *check, uint32_t seq, bool no_tcp_csum);
-size_t tcp_fill_headers6(const struct tcp_tap_conn *conn,
-			 struct tap_hdr *taph, struct ipv6hdr *ip6h,
-			 struct tcp_payload_t *bp, size_t dlen,
-			 uint32_t seq, bool no_tcp_csum);
+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,
+		       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,
+		       uint32_t seq, bool no_tcp_csum);
+
 int tcp_update_seqack_wnd(const struct ctx *c, struct tcp_tap_conn *conn,
 			  bool force_seq, struct tcp_info_linux *tinfo);
 int tcp_prepare_flags(const struct ctx *c, struct tcp_tap_conn *conn,
-- 
@@ -177,14 +177,15 @@ void tcp_rst_do(const struct ctx *c, struct tcp_tap_conn *conn);
 
 struct tcp_info_linux;
 
-size_t tcp_fill_headers4(const struct tcp_tap_conn *conn,
-			 struct tap_hdr *taph, struct iphdr *iph,
-			 struct tcp_payload_t *bp, size_t dlen,
-			 const uint16_t *check, uint32_t seq, bool no_tcp_csum);
-size_t tcp_fill_headers6(const struct tcp_tap_conn *conn,
-			 struct tap_hdr *taph, struct ipv6hdr *ip6h,
-			 struct tcp_payload_t *bp, size_t dlen,
-			 uint32_t seq, bool no_tcp_csum);
+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,
+		       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,
+		       uint32_t seq, bool no_tcp_csum);
+
 int tcp_update_seqack_wnd(const struct ctx *c, struct tcp_tap_conn *conn,
 			  bool force_seq, struct tcp_info_linux *tinfo);
 int tcp_prepare_flags(const struct ctx *c, struct tcp_tap_conn *conn,
-- 
2.47.0