tcp: Pass TCP header and payload separately to tcp_update_check_tcp[46]()

Currently these expects both the TCP header and payload in a single IOV,
and goes to some trouble to locate the checksum field within it.  In the
current caller we've already know where the TCP header is, so we might as
well just pass it in.  This will need to work a bit differently for
vhost-user, but that code already needs to locate the TCP header for other
reasons, so again we can just pass it in.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

3 files changed, 34 insertions, 94 deletions

diff --git a/tcp.c b/tcp.c
index f334ca5..5c40e18 100644
--- a/tcp.c
+++ b/tcp.c
@@ -755,106 +755,42 @@ static void tcp_sock_set_bufsize(const struct ctx *c, int s)
 /**
  * tcp_update_check_tcp4() - Calculate TCP checksum for IPv4
  * @iph:	IPv4 header
- * @iov:	Pointer to the array of IO vectors
- * @iov_cnt:	Length of the array
- * @l4offset:	IPv4 payload offset in the iovec array
+ * @th:		TCP header (updated)
+ * @payload:	TCP payload
  */
-void tcp_update_check_tcp4(const struct iphdr *iph,
-			   const struct iovec *iov, int iov_cnt,
-			   size_t l4offset)
+void tcp_update_check_tcp4(const struct iphdr *iph, struct tcphdr *th,
+			   struct iov_tail *payload)
 {
 	uint16_t l4len = ntohs(iph->tot_len) - sizeof(struct iphdr);
-	struct iov_tail l4 = IOV_TAIL(iov, iov_cnt, l4offset);
 	struct in_addr saddr = { .s_addr = iph->saddr };
 	struct in_addr daddr = { .s_addr = iph->daddr };
-	size_t check_ofs;
-	uint16_t *check;
-	int check_idx;
 	uint32_t sum;
-	char *ptr;
 
 	sum = proto_ipv4_header_psum(l4len, IPPROTO_TCP, saddr, daddr);
 
-	check_idx = iov_skip_bytes(iov, iov_cnt,
-				   l4offset + offsetof(struct tcphdr, check),
-				   &check_ofs);
-
-	if (check_idx >= iov_cnt) {
-		err("TCP4 buffer is too small, iov size %zd, check offset %zd",
-		    iov_size(iov, iov_cnt),
-		    l4offset + offsetof(struct tcphdr, check));
-		return;
-	}
-
-	if (check_ofs + sizeof(*check) > iov[check_idx].iov_len) {
-		err("TCP4 checksum field memory is not contiguous "
-		    "check_ofs %zd check_idx %d iov_len %zd",
-		    check_ofs, check_idx, iov[check_idx].iov_len);
-		return;
-	}
-
-	ptr = (char *)iov[check_idx].iov_base + check_ofs;
-	if ((uintptr_t)ptr & (__alignof__(*check) - 1)) {
-		err("TCP4 checksum field is not correctly aligned in memory");
-		return;
-	}
-
-	check = (uint16_t *)ptr;
-
-	*check = 0;
-	*check = csum_iov_tail(&l4, sum);
+	th->check = 0;
+	sum = csum_unfolded(th, sizeof(*th), sum);
+	th->check = csum_iov_tail(payload, sum);
 }
 
 /**
  * tcp_update_check_tcp6() - Calculate TCP checksum for IPv6
  * @ip6h:	IPv6 header
- * @iov:	Pointer to the array of IO vectors
- * @iov_cnt:	Length of the array
- * @l4offset:	IPv6 payload offset in the iovec array
+ * @th:		TCP header (updated)
+ * @payload:	TCP payload
  */
-void tcp_update_check_tcp6(const struct ipv6hdr *ip6h,
-			   const struct iovec *iov, int iov_cnt,
-			   size_t l4offset)
+void tcp_update_check_tcp6(const struct ipv6hdr *ip6h, struct tcphdr *th,
+			   struct iov_tail *payload)
 {
-	struct iov_tail l4 = IOV_TAIL(iov, iov_cnt, l4offset);
 	uint16_t l4len = ntohs(ip6h->payload_len);
-	size_t check_ofs;
-	uint16_t *check;
-	int check_idx;
 	uint32_t sum;
-	char *ptr;
 
 	sum = proto_ipv6_header_psum(l4len, IPPROTO_TCP, &ip6h->saddr,
 				     &ip6h->daddr);
 
-	check_idx = iov_skip_bytes(iov, iov_cnt,
-				   l4offset + offsetof(struct tcphdr, check),
-				   &check_ofs);
-
-	if (check_idx >= iov_cnt) {
-		err("TCP6 buffer is too small, iov size %zd, check offset %zd",
-		    iov_size(iov, iov_cnt),
-		    l4offset + offsetof(struct tcphdr, check));
-		return;
-	}
-
-	if (check_ofs + sizeof(*check) > iov[check_idx].iov_len) {
-		err("TCP6 checksum field memory is not contiguous "
-		    "check_ofs %zd check_idx %d iov_len %zd",
-		    check_ofs, check_idx, iov[check_idx].iov_len);
-		return;
-	}
-
-	ptr = (char *)iov[check_idx].iov_base + check_ofs;
-	if ((uintptr_t)ptr & (__alignof__(*check) - 1)) {
-		err("TCP6 checksum field is not correctly aligned in memory");
-		return;
-	}
-
-	check = (uint16_t *)ptr;
-
-	*check = 0;
-	*check = csum_iov_tail(&l4, sum);
+	th->check = 0;
+	sum = csum_unfolded(th, sizeof(*th), sum);
+	th->check = csum_iov_tail(payload, sum);
 }
 
 /**
@@ -1005,11 +941,12 @@ void tcp_fill_headers4(const struct tcp_tap_conn *conn,
 		bp->th.check = 0;
 	} else {
 		const struct iovec iov = {
-			.iov_base = bp,
-			.iov_len = ntohs(iph->tot_len) - sizeof(struct iphdr),
+			.iov_base = bp->data,
+			.iov_len = dlen,
 		};
+		struct iov_tail payload = IOV_TAIL(&iov, 1, 0);
 
-		tcp_update_check_tcp4(iph, &iov, 1, 0);
+		tcp_update_check_tcp4(iph, &bp->th, &payload);
 	}
 
 	tap_hdr_update(taph, l3len + sizeof(struct ethhdr));
@@ -1052,11 +989,12 @@ void tcp_fill_headers6(const struct tcp_tap_conn *conn,
 		bp->th.check = 0;
 	} else {
 		const struct iovec iov = {
-			.iov_base = bp,
-			.iov_len = ntohs(ip6h->payload_len)
+			.iov_base = bp->data,
+			.iov_len = dlen,
 		};
+		struct iov_tail payload = IOV_TAIL(&iov, 1, 0);
 
-		tcp_update_check_tcp6(ip6h, &iov, 1, 0);
+		tcp_update_check_tcp6(ip6h, &bp->th, &payload);
 	}
 
 	tap_hdr_update(taph, l4len + sizeof(*ip6h) + sizeof(struct ethhdr));
diff --git a/tcp_internal.h b/tcp_internal.h
index d7b125f..744c5c0 100644
--- a/tcp_internal.h
+++ b/tcp_internal.h
@@ -162,12 +162,10 @@ void tcp_rst_do(const struct ctx *c, struct tcp_tap_conn *conn);
 
 struct tcp_info_linux;
 
-void tcp_update_check_tcp4(const struct iphdr *iph,
-			   const struct iovec *iov, int iov_cnt,
-			   size_t l4offset);
-void tcp_update_check_tcp6(const struct ipv6hdr *ip6h,
-			   const struct iovec *iov, int iov_cnt,
-			   size_t l4offset);
+void tcp_update_check_tcp4(const struct iphdr *iph, struct tcphdr *th,
+			   struct iov_tail *payload);
+void tcp_update_check_tcp6(const struct ipv6hdr *ip6h, struct tcphdr *th,
+			   struct iov_tail *payload);
 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,
diff --git a/tcp_vu.c b/tcp_vu.c
index bbae918..134650e 100644
--- a/tcp_vu.c
+++ b/tcp_vu.c
@@ -73,15 +73,19 @@ static void tcp_vu_update_check(const struct flowside *tapside,
 	char *base = iov[0].iov_base;
 
 	if (inany_v4(&tapside->oaddr)) {
+		struct tcphdr *th = vu_payloadv4(base);
 		const struct iphdr *iph = vu_ip(base);
+		struct iov_tail payload = IOV_TAIL(iov, iov_cnt,
+						   (char *)(th + 1) - base);
 
-		tcp_update_check_tcp4(iph, iov, iov_cnt,
-				      (char *)vu_payloadv4(base) - base);
+		tcp_update_check_tcp4(iph, th, &payload);
 	} else {
+		struct tcphdr *th = vu_payloadv6(base);
 		const struct ipv6hdr *ip6h = vu_ip(base);
+		struct iov_tail payload = IOV_TAIL(iov, iov_cnt,
+						   (char *)(th + 1) - base);
 
-		tcp_update_check_tcp6(ip6h, iov, iov_cnt,
-				      (char *)vu_payloadv6(base) - base);
+		tcp_update_check_tcp6(ip6h, th, &payload);
 	}
 }