[PATCH] tcp: Move tap header update out of tcp_fill_headers()

[Laurent Vivier <lvivier@redhat.com>]

tcp_fill_headers() currently calls tap_hdr_update() to set the frame
length in the tap-specific header.  This is backend-specific: the tap
backend needs this for its frame length header, but the vhost-user
backend passes NULL for the tap header and doesn't use it at all.

Remove the tap_hdr parameter from tcp_fill_headers() and instead return
the computed L2 frame length.  The tap backend caller,
tcp_l2_buf_fill_headers(), now calls tap_hdr_update() itself with the
returned length.  The vhost-user callers, tcp_vu_send_flag() and
tcp_vu_prepare(), no longer need to pass a NULL tap header.

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
---
 tap.h          |  3 +--
 tcp.c          | 16 +++++++++-------
 tcp_buf.c      |  6 ++++--
 tcp_internal.h | 11 ++++++-----
 tcp_vu.c       |  4 ++--
 5 files changed, 22 insertions(+), 18 deletions(-)

diff --git a/tap.h b/tap.h
index ee22a9d78c44..cc780d168941 100644
--- a/tap.h
+++ b/tap.h
@@ -65,8 +65,7 @@ static inline struct iovec tap_hdr_iov(const struct ctx *c,
  */
 static inline void tap_hdr_update(struct tap_hdr *thdr, size_t l2len)
 {
-	if (thdr)
-		thdr->vnet_len = htonl(l2len);
+	thdr->vnet_len = htonl(l2len);
 }
 
 unsigned long tap_l2_max_len(const struct ctx *c);
diff --git a/tcp.c b/tcp.c
index 0a64892afbaf..048da2ab59bc 100644
--- a/tcp.c
+++ b/tcp.c
@@ -924,7 +924,6 @@ static void tcp_fill_header(struct tcphdr *th,
  * tcp_fill_headers() - Fill 802.3, IP, TCP headers
  * @c:			Execution context
  * @conn:		Connection pointer
- * @taph:		tap backend specific header
  * @eh:		Pointer to Ethernet header
  * @ip4h:		Pointer to IPv4 header, or NULL
  * @ip6h:		Pointer to IPv6 header, or NULL
@@ -933,12 +932,15 @@ static void tcp_fill_header(struct tcphdr *th,
  * @ip4_check:		IPv4 checksum, if already known
  * @seq:		Sequence number for this segment
  * @no_tcp_csum:	Do not set TCP checksum
+ *
+ * Return: frame length (including L2 headers)
  */
-void tcp_fill_headers(const struct ctx *c, struct tcp_tap_conn *conn,
-		      struct tap_hdr *taph, struct ethhdr *eh,
-		      struct iphdr *ip4h, struct ipv6hdr *ip6h,
-		      struct tcphdr *th, struct iov_tail *payload,
-		      const uint16_t *ip4_check, uint32_t seq, bool no_tcp_csum)
+size_t tcp_fill_headers(const struct ctx *c, struct tcp_tap_conn *conn,
+			struct ethhdr *eh,
+			struct iphdr *ip4h, struct ipv6hdr *ip6h,
+			struct tcphdr *th, struct iov_tail *payload,
+			const uint16_t *ip4_check, uint32_t seq,
+			bool no_tcp_csum)
 {
 	const struct flowside *tapside = TAPFLOW(conn);
 	size_t l4len = iov_tail_size(payload) + sizeof(*th);
@@ -1004,7 +1006,7 @@ void tcp_fill_headers(const struct ctx *c, struct tcp_tap_conn *conn,
 	else
 		tcp_update_csum(psum, th, payload);
 
-	tap_hdr_update(taph, MAX(l3len + sizeof(struct ethhdr), ETH_ZLEN));
+	return MAX(l3len + sizeof(struct ethhdr), ETH_ZLEN);
 }
 
 /**
diff --git a/tcp_buf.c b/tcp_buf.c
index d29254103364..675ec138c460 100644
--- a/tcp_buf.c
+++ b/tcp_buf.c
@@ -183,14 +183,16 @@ static void tcp_l2_buf_fill_headers(const struct ctx *c,
 	struct ethhdr *eh = iov[TCP_IOV_ETH].iov_base;
 	struct ipv6hdr *ip6h = NULL;
 	struct iphdr *ip4h = NULL;
+	size_t l2len;
 
 	if (a4)
 		ip4h = iov[TCP_IOV_IP].iov_base;
 	else
 		ip6h = iov[TCP_IOV_IP].iov_base;
 
-	tcp_fill_headers(c, conn, taph, eh, ip4h, ip6h, th, &tail,
-			 check, seq, no_tcp_csum);
+	l2len = tcp_fill_headers(c, conn, eh, ip4h, ip6h, th, &tail, check, seq,
+				 no_tcp_csum);
+	tap_hdr_update(taph, l2len);
 }
 
 /**
diff --git a/tcp_internal.h b/tcp_internal.h
index 5f8fb3584355..518913b5bc03 100644
--- a/tcp_internal.h
+++ b/tcp_internal.h
@@ -176,11 +176,12 @@ void tcp_rst_do(const struct ctx *c, struct tcp_tap_conn *conn);
 
 struct tcp_info_linux;
 
-void tcp_fill_headers(const struct ctx *c, struct tcp_tap_conn *conn,
-		      struct tap_hdr *taph, struct ethhdr *eh,
-		      struct iphdr *ip4h, struct ipv6hdr *ip6h,
-		      struct tcphdr *th, struct iov_tail *payload,
-		      const uint16_t *ip4_check, uint32_t seq, bool no_tcp_csum);
+size_t tcp_fill_headers(const struct ctx *c, struct tcp_tap_conn *conn,
+			struct ethhdr *eh,
+			struct iphdr *ip4h, struct ipv6hdr *ip6h,
+			struct tcphdr *th, struct iov_tail *payload,
+			const uint16_t *ip4_check, 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);
diff --git a/tcp_vu.c b/tcp_vu.c
index b9e9b55ed3d3..f654f3193bd7 100644
--- a/tcp_vu.c
+++ b/tcp_vu.c
@@ -135,7 +135,7 @@ int tcp_vu_send_flag(const struct ctx *c, struct tcp_tap_conn *conn, int flags)
 	flags_elem[0].in_sg[0].iov_len = hdrlen + optlen;
 	payload = IOV_TAIL(flags_elem[0].in_sg, 1, hdrlen);
 
-	tcp_fill_headers(c, conn, NULL, eh, ip4h, ip6h, th, &payload,
+	tcp_fill_headers(c, conn, eh, ip4h, ip6h, th, &payload,
 			 NULL, seq, !*c->pcap);
 
 	vu_pad(&flags_elem[0].in_sg[0], hdrlen + optlen);
@@ -335,7 +335,7 @@ static void tcp_vu_prepare(const struct ctx *c, struct tcp_tap_conn *conn,
 	th->ack = 1;
 	th->psh = push;
 
-	tcp_fill_headers(c, conn, NULL, eh, ip4h, ip6h, th, &payload,
+	tcp_fill_headers(c, conn, eh, ip4h, ip6h, th, &payload,
 			 *check, conn->seq_to_tap, no_tcp_csum);
 	if (ip4h)
 		*check = &ip4h->check;
-- 
2.52.0