On Mon, Mar 23, 2026 at 05:52:55PM +0100, Laurent Vivier wrote:
Replace direct pointer arithmetic using vu_eth(), vu_ip(), vu_payloadv4() and vu_payloadv6() with the iov_tail abstraction to build Ethernet, IP and TCP headers in tcp_vu_prepare().
This removes the assumption that all headers reside in a single contiguous iov entry.
Signed-off-by: Laurent Vivier
LGTM, with the exception of my general concerns about with_header().
--- tcp_vu.c | 61 ++++++++++++++++++++++++++------------------------------ 1 file changed, 28 insertions(+), 33 deletions(-)
diff --git a/tcp_vu.c b/tcp_vu.c index c6206b7a689c..a39f6ea018e9 100644 --- a/tcp_vu.c +++ b/tcp_vu.c @@ -222,6 +222,7 @@ static ssize_t tcp_vu_sock_recv(const struct ctx *c, struct vu_virtq *vq, /* reserve space for headers in iov */ iov = &elem[elem_cnt].in_sg[0]; assert(iov->iov_len >= hdrlen); +
Unrelated change (usually I don't mind if it's a reasonable change adjacent to what you're doing, but this is an entirely different function).
iov->iov_base = (char *)iov->iov_base + hdrlen; iov->iov_len -= hdrlen; head[(*head_cnt)++] = elem_cnt; @@ -285,51 +286,45 @@ static void tcp_vu_prepare(const struct ctx *c, struct tcp_tap_conn *conn, int *check, bool no_tcp_csum, bool push) { const struct flowside *toside = TAPFLOW(conn); - bool v6 = !(inany_v4(&toside->eaddr) && inany_v4(&toside->oaddr)); - size_t hdrlen = tcp_vu_hdrlen(v6); - char *base = iov[0].iov_base; - struct ipv6hdr *ip6h = NULL; - struct iphdr *ip4h = NULL; + bool ipv4 = inany_v4(&toside->eaddr) && inany_v4(&toside->oaddr); struct iov_tail payload; - struct tcphdr *th; - struct ethhdr *eh; - - /* we guess the first iovec provided by the guest can embed - * all the headers needed by L2 frame, including any padding - */ - assert(iov[0].iov_len >= hdrlen); - - eh = vu_eth(base);
- memcpy(eh->h_dest, c->guest_mac, sizeof(eh->h_dest)); + payload = IOV_TAIL(iov, iov_cnt, VNET_HLEN); + with_header(struct ethhdr, eh, &payload) + memcpy(eh->h_dest, c->guest_mac, sizeof(eh->h_dest)); + IOV_DROP_HEADER(&payload, struct ethhdr);
/* initialize header */
- if (!v6) { - eh->h_proto = htons(ETH_P_IP); - - ip4h = vu_ip(base); - *ip4h = (struct iphdr)L2_BUF_IP4_INIT(IPPROTO_TCP); - th = vu_payloadv4(base); + if (ipv4) { + with_header(struct iphdr, ip4h, &payload) + *ip4h = (struct iphdr)L2_BUF_IP4_INIT(IPPROTO_TCP); + IOV_DROP_HEADER(&payload, struct iphdr); } else { - eh->h_proto = htons(ETH_P_IPV6); - - ip6h = vu_ip(base); - *ip6h = (struct ipv6hdr)L2_BUF_IP6_INIT(IPPROTO_TCP); - - th = vu_payloadv6(base); + with_header(struct ipv6hdr, ip6h, &payload) + *ip6h = (struct ipv6hdr)L2_BUF_IP6_INIT(IPPROTO_TCP); + IOV_DROP_HEADER(&payload, struct ipv6hdr); }
- memset(th, 0, sizeof(*th)); - th->doff = sizeof(*th) / 4; - th->ack = 1; - th->psh = push; + with_header(struct tcphdr, th, &payload) { + memset(th, 0, sizeof(*th)); + th->doff = sizeof(*th) / 4; + th->ack = 1; + th->psh = push; + }
payload = IOV_TAIL(iov, iov_cnt, VNET_HLEN); - tcp_fill_headers(c, conn, !v6, &payload, *check, conn->seq_to_tap, + tcp_fill_headers(c, conn, ipv4, &payload, *check, conn->seq_to_tap, no_tcp_csum); - if (ip4h) + if (ipv4) { + struct iphdr ip4h_storage; + const struct iphdr *ip4h; + + IOV_DROP_HEADER(&payload, struct ethhdr); + ip4h = IOV_PEEK_HEADER(&payload, ip4h_storage); + *check = ip4h->check; + } }
/** -- 2.53.0
-- David Gibson (he or they) | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you, not the other way | around. http://www.ozlabs.org/~dgibson