[PATCH v2 2/2] tcp: Allow checksum to be disabled

[Laurent Vivier <lvivier@redhat.com>]

We can need not to set TCP checksum. Add a parameter to
tcp_fill_headers4() and tcp_fill_headers6() to disable it.

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
---
 tcp.c          | 24 +++++++++++++++++-------
 tcp_buf.c      |  8 +++++---
 tcp_internal.h |  3 ++-
 3 files changed, 24 insertions(+), 11 deletions(-)

diff --git a/tcp.c b/tcp.c
index f9fe1b9a1330..a44d7b977214 100644
--- a/tcp.c
+++ b/tcp.c
@@ -903,6 +903,7 @@ static void tcp_fill_header(struct tcphdr *th,
  * @dlen:	TCP payload length
  * @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
  */
@@ -910,7 +911,7 @@ static size_t tcp_fill_headers4(const struct tcp_tap_conn *conn,
 				struct tap_hdr *taph,
 				struct iphdr *iph, struct tcphdr *th,
 				size_t dlen, const uint16_t *check,
-				uint32_t seq)
+				uint32_t seq, bool no_tcp_csum)
 {
 	const struct flowside *tapside = TAPFLOW(conn);
 	const struct in_addr *src4 = inany_v4(&tapside->oaddr);
@@ -929,7 +930,10 @@ static size_t tcp_fill_headers4(const struct tcp_tap_conn *conn,
 
 	tcp_fill_header(th, conn, seq);
 
-	tcp_update_check_tcp4(iph, th);
+	if (no_tcp_csum)
+		th->check = 0;
+	else
+		tcp_update_check_tcp4(iph, th);
 
 	tap_hdr_update(taph, l3len + sizeof(struct ethhdr));
 
@@ -945,13 +949,14 @@ static size_t tcp_fill_headers4(const struct tcp_tap_conn *conn,
  * @dlen:	TCP payload length
  * @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
  */
 static size_t tcp_fill_headers6(const struct tcp_tap_conn *conn,
 				struct tap_hdr *taph,
 				struct ipv6hdr *ip6h, struct tcphdr *th,
-				size_t dlen, uint32_t seq)
+				size_t dlen, uint32_t seq, bool no_tcp_csum)
 {
 	const struct flowside *tapside = TAPFLOW(conn);
 	size_t l4len = dlen + sizeof(*th);
@@ -970,7 +975,10 @@ static size_t tcp_fill_headers6(const struct tcp_tap_conn *conn,
 
 	tcp_fill_header(th, conn, seq);
 
-	tcp_update_check_tcp6(ip6h, th);
+	if (no_tcp_csum)
+		th->check = 0;
+	else
+		tcp_update_check_tcp6(ip6h, th);
 
 	tap_hdr_update(taph, l4len + sizeof(*ip6h) + sizeof(struct ethhdr));
 
@@ -984,12 +992,14 @@ static size_t tcp_fill_headers6(const struct tcp_tap_conn *conn,
  * @dlen:	TCP payload length
  * @check:	Checksum, if already known
  * @seq:	Sequence number for this segment
+ * @no_tcp_csum: Do not set TCP checksum
  *
  * Return: IP payload length, host order
  */
 size_t tcp_l2_buf_fill_headers(const struct tcp_tap_conn *conn,
 			       struct iovec *iov, size_t dlen,
-			       const uint16_t *check, uint32_t seq)
+			       const uint16_t *check, uint32_t seq,
+			       bool no_tcp_csum)
 {
 	const struct flowside *tapside = TAPFLOW(conn);
 	const struct in_addr *a4 = inany_v4(&tapside->oaddr);
@@ -998,13 +1008,13 @@ size_t tcp_l2_buf_fill_headers(const struct tcp_tap_conn *conn,
 		return tcp_fill_headers4(conn, iov[TCP_IOV_TAP].iov_base,
 					 iov[TCP_IOV_IP].iov_base,
 					 iov[TCP_IOV_PAYLOAD].iov_base, dlen,
-					 check, seq);
+					 check, seq, no_tcp_csum);
 	}
 
 	return tcp_fill_headers6(conn, iov[TCP_IOV_TAP].iov_base,
 				 iov[TCP_IOV_IP].iov_base,
 				 iov[TCP_IOV_PAYLOAD].iov_base, dlen,
-				 seq);
+				 seq, no_tcp_csum);
 }
 
 /**
diff --git a/tcp_buf.c b/tcp_buf.c
index 1a398461a34b..10a663bdfc26 100644
--- a/tcp_buf.c
+++ b/tcp_buf.c
@@ -320,7 +320,7 @@ int tcp_buf_send_flag(struct ctx *c, struct tcp_tap_conn *conn, int flags)
 		return ret;
 	}
 
-	l4len = tcp_l2_buf_fill_headers(conn, iov, optlen, NULL, seq);
+	l4len = tcp_l2_buf_fill_headers(conn, iov, optlen, NULL, seq, false);
 	iov[TCP_IOV_PAYLOAD].iov_len = l4len;
 
 	if (flags & DUP_ACK) {
@@ -381,7 +381,8 @@ static void tcp_data_to_tap(struct ctx *c, struct tcp_tap_conn *conn,
 		tcp4_frame_conns[tcp4_payload_used] = conn;
 
 		iov = tcp4_l2_iov[tcp4_payload_used++];
-		l4len = tcp_l2_buf_fill_headers(conn, iov, dlen, check, seq);
+		l4len = tcp_l2_buf_fill_headers(conn, iov, dlen, check, seq,
+						false);
 		iov[TCP_IOV_PAYLOAD].iov_len = l4len;
 		if (tcp4_payload_used > TCP_FRAMES_MEM - 1)
 			tcp_payload_flush(c);
@@ -389,7 +390,8 @@ static void tcp_data_to_tap(struct ctx *c, struct tcp_tap_conn *conn,
 		tcp6_frame_conns[tcp6_payload_used] = conn;
 
 		iov = tcp6_l2_iov[tcp6_payload_used++];
-		l4len = tcp_l2_buf_fill_headers(conn, iov, dlen, NULL, seq);
+		l4len = tcp_l2_buf_fill_headers(conn, iov, dlen, NULL, seq,
+						false);
 		iov[TCP_IOV_PAYLOAD].iov_len = l4len;
 		if (tcp6_payload_used > TCP_FRAMES_MEM - 1)
 			tcp_payload_flush(c);
diff --git a/tcp_internal.h b/tcp_internal.h
index aa8bb64f1f33..e7fe735bfcb4 100644
--- a/tcp_internal.h
+++ b/tcp_internal.h
@@ -91,7 +91,8 @@ void tcp_rst_do(struct ctx *c, struct tcp_tap_conn *conn);
 
 size_t tcp_l2_buf_fill_headers(const struct tcp_tap_conn *conn,
 			       struct iovec *iov, size_t dlen,
-			       const uint16_t *check, uint32_t seq);
+			       const uint16_t *check, uint32_t seq,
+			       bool no_tcp_csum);
 int tcp_update_seqack_wnd(const struct ctx *c, struct tcp_tap_conn *conn,
 			  int force_seq, struct tcp_info *tinfo);
 int tcp_prepare_flags(struct ctx *c, struct tcp_tap_conn *conn, int flags,
-- 
@@ -91,7 +91,8 @@ void tcp_rst_do(struct ctx *c, struct tcp_tap_conn *conn);
 
 size_t tcp_l2_buf_fill_headers(const struct tcp_tap_conn *conn,
 			       struct iovec *iov, size_t dlen,
-			       const uint16_t *check, uint32_t seq);
+			       const uint16_t *check, uint32_t seq,
+			       bool no_tcp_csum);
 int tcp_update_seqack_wnd(const struct ctx *c, struct tcp_tap_conn *conn,
 			  int force_seq, struct tcp_info *tinfo);
 int tcp_prepare_flags(struct ctx *c, struct tcp_tap_conn *conn, int flags,
-- 
2.46.0