On Fri, Feb 27, 2026 at 03:03:24PM +0100, Laurent Vivier wrote:
Change udp_update_hdr4() and udp_update_hdr6() to take a separate struct udphdr pointer and an iov_tail for the payload, instead of a struct udp_payload_t pointer and an explicit data length.
This decouples the header update functions from the udp_payload_t memory layout, which assumes all headers and data sit in a single contiguous buffer. The vhost-user path uses virtqueue-provided scatter-gather buffers where this assumption does not hold; passing an iov_tail lets both the tap path and the vhost-user path share the same functions without casting through layout-specific helpers.
Signed-off-by: Laurent Vivier
Concept looks good, a couple of nits below.
--- udp.c | 65 ++++++++++++++++++++++---------------------------- udp_internal.h | 10 ++++---- udp_vu.c | 14 +++++++++-- 3 files changed, 47 insertions(+), 42 deletions(-)
diff --git a/udp.c b/udp.c index 19adda065f44..52e93e357a94 100644 --- a/udp.c +++ b/udp.c @@ -257,18 +257,17 @@ static void udp_iov_init(const struct ctx *c) * @ip4h: Pre-filled IPv4 header (except for tot_len and saddr) * @bp: Pointer to udp_payload_t to update
Needs to be replaced with @payload description.
* @toside: Flowside for destination side - * @dlen: Length of UDP payload * @no_udp_csum: Do not set UDP checksum * * Return: size of IPv4 payload (UDP header + data) */ -size_t udp_update_hdr4(struct iphdr *ip4h, struct udp_payload_t *bp, - const struct flowside *toside, size_t dlen, - bool no_udp_csum) +size_t udp_update_hdr4(struct iphdr *ip4h, struct udphdr *uh, + struct iov_tail *payload, + const struct flowside *toside, bool no_udp_csum) { const struct in_addr *src = inany_v4(&toside->oaddr); const struct in_addr *dst = inany_v4(&toside->eaddr); - size_t l4len = dlen + sizeof(bp->uh); + size_t l4len = iov_tail_size(payload) + sizeof(*uh); size_t l3len = l4len + sizeof(*ip4h);
ASSERT(src && dst); @@ -278,19 +277,13 @@ size_t udp_update_hdr4(struct iphdr *ip4h, struct udp_payload_t *bp, ip4h->saddr = src->s_addr; ip4h->check = csum_ip4_header(l3len, IPPROTO_UDP, *src, *dst);
- bp->uh.source = htons(toside->oport); - bp->uh.dest = htons(toside->eport); - bp->uh.len = htons(l4len); - if (no_udp_csum) { - bp->uh.check = 0; - } else { - const struct iovec iov = { - .iov_base = bp->data, - .iov_len = dlen - }; - struct iov_tail data = IOV_TAIL(&iov, 1, 0); - csum_udp4(&bp->uh, *src, *dst, &data); - } + uh->source = htons(toside->oport); + uh->dest = htons(toside->eport); + uh->len = htons(l4len); + if (no_udp_csum) + uh->check = 0; + else + csum_udp4(uh, *src, *dst, payload);
return l4len; } @@ -306,11 +299,11 @@ size_t udp_update_hdr4(struct iphdr *ip4h, struct udp_payload_t *bp, *
This comment also needs updates for the changed parameters.
* Return: size of IPv6 payload (UDP header + data) */ -size_t udp_update_hdr6(struct ipv6hdr *ip6h, struct udp_payload_t *bp, - const struct flowside *toside, size_t dlen, - bool no_udp_csum) +size_t udp_update_hdr6(struct ipv6hdr *ip6h, struct udphdr *uh, + struct iov_tail *payload, + const struct flowside *toside, bool no_udp_csum) { - uint16_t l4len = dlen + sizeof(bp->uh); + uint16_t l4len = iov_tail_size(payload) + sizeof(*uh);
ip6h->payload_len = htons(l4len); ip6h->daddr = toside->eaddr.a6; @@ -319,22 +312,17 @@ size_t udp_update_hdr6(struct ipv6hdr *ip6h, struct udp_payload_t *bp, ip6h->nexthdr = IPPROTO_UDP; ip6h->hop_limit = 255;
- bp->uh.source = htons(toside->oport); - bp->uh.dest = htons(toside->eport); - bp->uh.len = ip6h->payload_len; + uh->source = htons(toside->oport); + uh->dest = htons(toside->eport); + uh->len = ip6h->payload_len; if (no_udp_csum) { /* 0 is an invalid checksum for UDP IPv6 and dropped by * the kernel stack, even if the checksum is disabled by virtio * flags. We need to put any non-zero value here. */ - bp->uh.check = 0xffff; + uh->check = 0xffff; } else { - const struct iovec iov = { - .iov_base = bp->data, - .iov_len = dlen - }; - struct iov_tail data = IOV_TAIL(&iov, 1, 0); - csum_udp6(&bp->uh, &toside->oaddr.a6, &toside->eaddr.a6, &data); + csum_udp6(uh, &toside->oaddr.a6, &toside->eaddr.a6, payload); }
return l4len; @@ -374,12 +362,17 @@ static void udp_tap_prepare(const struct mmsghdr *mmh, struct ethhdr *eh = (*tap_iov)[UDP_IOV_ETH].iov_base; struct udp_payload_t *bp = &udp_payload[idx]; struct udp_meta_t *bm = &udp_meta[idx]; + const struct iovec iov = { + .iov_base = bp->data, + .iov_len = mmh[idx].msg_len, + }; + struct iov_tail payload = IOV_TAIL(&iov, 1, 0); size_t l4len, l2len;
eth_update_mac(eh, NULL, tap_omac); if (!inany_v4(&toside->eaddr) || !inany_v4(&toside->oaddr)) { - l4len = udp_update_hdr6(&bm->ip6h, bp, toside, - mmh[idx].msg_len, no_udp_csum); + l4len = udp_update_hdr6(&bm->ip6h, &bp->uh, &payload, toside, + no_udp_csum);
l2len = MAX(l4len + sizeof(bm->ip6h) + ETH_HLEN, ETH_ZLEN); tap_hdr_update(&bm->taph, l2len); @@ -387,8 +380,8 @@ static void udp_tap_prepare(const struct mmsghdr *mmh, eh->h_proto = htons_constant(ETH_P_IPV6); (*tap_iov)[UDP_IOV_IP] = IOV_OF_LVALUE(bm->ip6h); } else { - l4len = udp_update_hdr4(&bm->ip4h, bp, toside, - mmh[idx].msg_len, no_udp_csum); + l4len = udp_update_hdr4(&bm->ip4h, &bp->uh, &payload, toside, + no_udp_csum);
l2len = MAX(l4len + sizeof(bm->ip4h) + ETH_HLEN, ETH_ZLEN); tap_hdr_update(&bm->taph, l2len); diff --git a/udp_internal.h b/udp_internal.h index 0a8fe490b07e..aca831808ab4 100644 --- a/udp_internal.h +++ b/udp_internal.h @@ -22,11 +22,13 @@ struct udp_payload_t { } __attribute__ ((packed, aligned(__alignof__(unsigned int)))); #endif
-size_t udp_update_hdr4(struct iphdr *ip4h, struct udp_payload_t *bp, - const struct flowside *toside, size_t dlen, +size_t udp_update_hdr4(struct iphdr *ip4h, struct udphdr *uh, + struct iov_tail *payload, + const struct flowside *toside, bool no_udp_csum); -size_t udp_update_hdr6(struct ipv6hdr *ip6h, struct udp_payload_t *bp, - const struct flowside *toside, size_t dlen, +size_t udp_update_hdr6(struct ipv6hdr *ip6h, struct udphdr *uh, + struct iov_tail *payload, + const struct flowside *toside, bool no_udp_csum); void udp_sock_fwd(const struct ctx *c, int s, int rule_hint, uint8_t frompif, in_port_t port, const struct timespec *now); diff --git a/udp_vu.c b/udp_vu.c index aefcab0b86c2..dd8904d65a38 100644 --- a/udp_vu.c +++ b/udp_vu.c @@ -122,21 +122,31 @@ static size_t udp_vu_prepare(const struct ctx *c, const struct iov_tail *data, if (inany_v4(&toside->eaddr) && inany_v4(&toside->oaddr)) { struct iphdr *iph = vu_ip(iov[0].iov_base); struct udp_payload_t *bp = vu_payloadv4(iov[0].iov_base); + const struct iovec payload_iov = { + .iov_base = bp->data, + .iov_len = dlen, + }; + struct iov_tail payload = IOV_TAIL(&payload_iov, 1, 0);
eh->h_proto = htons(ETH_P_IP);
*iph = (struct iphdr)L2_BUF_IP4_INIT(IPPROTO_UDP);
- l4len = udp_update_hdr4(iph, bp, toside, dlen, true); + l4len = udp_update_hdr4(iph, &bp->uh, &payload, toside, true); } else { struct ipv6hdr *ip6h = vu_ip(iov[0].iov_base); struct udp_payload_t *bp = vu_payloadv6(iov[0].iov_base); + const struct iovec payload_iov = { + .iov_base = bp->data, + .iov_len = dlen, + }; + struct iov_tail payload = IOV_TAIL(&payload_iov, 1, 0);
eh->h_proto = htons(ETH_P_IPV6);
*ip6h = (struct ipv6hdr)L2_BUF_IP6_INIT(IPPROTO_UDP);
- l4len = udp_update_hdr6(ip6h, bp, toside, dlen, true); + l4len = udp_update_hdr6(ip6h, &bp->uh, &payload, toside, true); }
return l4len; -- 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