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[2a10:fc81:a806:d6a9::1]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-46e619c396esm9280665e9.8.2025.09.30.14.29.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 30 Sep 2025 14:29:44 -0700 (PDT) Date: Tue, 30 Sep 2025 23:29:42 +0200 From: Stefano Brivio To: Jon Maloy Subject: Re: [PATCH v11 6/9] udp: forward external source MAC address through tap interface Message-ID: <20250930232942.36ba5bf0@elisabeth> In-Reply-To: <20250927192522.3024554-7-jmaloy@redhat.com> References: <20250927192522.3024554-1-jmaloy@redhat.com> <20250927192522.3024554-7-jmaloy@redhat.com> Organization: Red Hat X-Mailer: Claws Mail 4.2.0 (GTK 3.24.49; x86_64-pc-linux-gnu) MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: TjiCKSJD42XhboW2anQLPGFSb_M8Lm4K_JukSVh2k4w_1759267786 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Message-ID-Hash: YGHERVYTMJRGMO7XK43P3QMX4KX7NA6O X-Message-ID-Hash: YGHERVYTMJRGMO7XK43P3QMX4KX7NA6O X-MailFrom: sbrivio@redhat.com X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header CC: dgibson@redhat.com, david@gibson.dropbear.id.au, passt-dev@passt.top X-Mailman-Version: 3.3.8 Precedence: list List-Id: Development discussion and patches for passt Archived-At: Archived-At: List-Archive: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: On Sat, 27 Sep 2025 15:25:19 -0400 Jon Maloy wrote: > We forward the incoming MAC address through the tap interface when > receiving incoming packets from network local hosts. > > This is a part of the solution to bug > https://bugs.passt.top/show_bug.cgi?id=120 > > Signed-off-by: Jon Maloy > Reviewed-by: David Gibson > > --- > v3: - Adapted to the move of external MAC address from struct flowside > to struct flow_common > v4: - Changed signature of udp_tap_prepare() to take a MAC address > instead of a flow. > - Eliminated initialization of MAC source address in all frames, > since those now are set per send occasion anyway. > v5: - Added lookup in ARP/NDP table on incoming messages in > case flow->tap_omac wasn't initialized at flow creation, > i.e., the flow was initiated from the guest. > v6: - Using MAC_ZERO > --- > passt.c | 2 +- > udp.c | 45 +++++++++++++++++++++++++-------------------- > udp.h | 2 +- > 3 files changed, 27 insertions(+), 22 deletions(-) > > diff --git a/passt.c b/passt.c > index e20bbad..fdd275a 100644 > --- a/passt.c > +++ b/passt.c > @@ -164,7 +164,7 @@ static void timer_init(struct ctx *c, const struct timespec *now) > void proto_update_l2_buf(const unsigned char *eth_d, const unsigned char *eth_s) > { > tcp_update_l2_buf(eth_d, eth_s); > - udp_update_l2_buf(eth_d, eth_s); > + udp_update_l2_buf(eth_d); > } > > /** > diff --git a/udp.c b/udp.c > index 86585b7..eb57f05 100644 > --- a/udp.c > +++ b/udp.c > @@ -133,11 +133,8 @@ static int udp_splice_init[IP_VERSIONS][NUM_PORTS]; > /* UDP header and data for inbound messages */ > static struct udp_payload_t udp_payload[UDP_MAX_FRAMES]; > > -/* Ethernet header for IPv4 frames */ > -static struct ethhdr udp4_eth_hdr; > - > -/* Ethernet header for IPv6 frames */ > -static struct ethhdr udp6_eth_hdr; > +/* Ethernet headers for IPv4 and IPv6 frames */ > +static struct ethhdr udp_eth_hdr[UDP_MAX_FRAMES]; > > /** > * struct udp_meta_t - Pre-cooked headers for UDP packets > @@ -210,12 +207,13 @@ void udp_portmap_clear(void) > /** > * udp_update_l2_buf() - Update L2 buffers with Ethernet and IPv4 addresses > * @eth_d: Ethernet destination address, NULL if unchanged > - * @eth_s: Ethernet source address, NULL if unchanged > */ > -void udp_update_l2_buf(const unsigned char *eth_d, const unsigned char *eth_s) > +void udp_update_l2_buf(const unsigned char *eth_d) > { > - eth_update_mac(&udp4_eth_hdr, eth_d, eth_s); > - eth_update_mac(&udp6_eth_hdr, eth_d, eth_s); > + int i; > + > + for (i = 0; i < UDP_MAX_FRAMES; i++) > + eth_update_mac(&udp_eth_hdr[i], eth_d, NULL); > } > > /** > @@ -238,6 +236,7 @@ static void udp_iov_init_one(const struct ctx *c, size_t i) > > *siov = IOV_OF_LVALUE(payload->data); > > + tiov[UDP_IOV_ETH] = IOV_OF_LVALUE(udp_eth_hdr[i]); > tiov[UDP_IOV_TAP] = tap_hdr_iov(c, &meta->taph); > tiov[UDP_IOV_PAYLOAD].iov_base = payload; > > @@ -253,9 +252,6 @@ static void udp_iov_init(const struct ctx *c) > { > size_t i; > > - udp4_eth_hdr.h_proto = htons_constant(ETH_P_IP); > - udp6_eth_hdr.h_proto = htons_constant(ETH_P_IPV6); > - > for (i = 0; i < UDP_MAX_FRAMES; i++) > udp_iov_init_one(c, i); > } > @@ -352,31 +348,34 @@ size_t udp_update_hdr6(struct ipv6hdr *ip6h, struct udp_payload_t *bp, > * udp_tap_prepare() - Convert one datagram into a tap frame > * @mmh: Receiving mmsghdr array > * @idx: Index of the datagram to prepare > + * @tap_omac: MAC address of remote endpoint as seen from the guest > * @toside: Flowside for destination side > * @no_udp_csum: Do not set UDP checksum > */ > static void udp_tap_prepare(const struct mmsghdr *mmh, > - unsigned idx, const struct flowside *toside, > + unsigned int idx, > + const uint8_t *tap_omac, > + const struct flowside *toside, > bool no_udp_csum) > { > struct iovec (*tap_iov)[UDP_NUM_IOVS] = &udp_l2_iov[idx]; > struct udp_payload_t *bp = &udp_payload[idx]; > struct udp_meta_t *bm = &udp_meta[idx]; > + struct ethhdr *eh = (*tap_iov)[UDP_IOV_ETH].iov_base; Nit: this should be moved as second declaration. > size_t l4len; > > + 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); > - tap_hdr_update(&bm->taph, l4len + sizeof(bm->ip6h) + > - sizeof(udp6_eth_hdr)); > - (*tap_iov)[UDP_IOV_ETH] = IOV_OF_LVALUE(udp6_eth_hdr); > + tap_hdr_update(&bm->taph, l4len + sizeof(bm->ip6h) + ETH_HLEN); > + 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); > - tap_hdr_update(&bm->taph, l4len + sizeof(bm->ip4h) + > - sizeof(udp4_eth_hdr)); > - (*tap_iov)[UDP_IOV_ETH] = IOV_OF_LVALUE(udp4_eth_hdr); > + tap_hdr_update(&bm->taph, l4len + sizeof(bm->ip4h) + ETH_HLEN); > + eh->h_proto = htons_constant(ETH_P_IP); > (*tap_iov)[UDP_IOV_IP] = IOV_OF_LVALUE(bm->ip4h); > } > (*tap_iov)[UDP_IOV_PAYLOAD].iov_len = l4len; > @@ -801,13 +800,19 @@ static void udp_buf_sock_to_tap(const struct ctx *c, int s, int n, > flow_sidx_t tosidx) > { > const struct flowside *toside = flowside_at_sidx(tosidx); > + struct udp_flow *uflow = udp_at_sidx(tosidx); > + uint8_t *omac = uflow->f.tap_omac; > int i; > > if ((n = udp_sock_recv(c, s, udp_mh_recv, n)) <= 0) > return; > > + /* Make one attempt to find true MAC address in ARP/NDP table */ > + if (MAC_IS_ZERO(omac)) > + fwd_neigh_mac_get(c, &toside->oaddr, omac); > + > for (i = 0; i < n; i++) > - udp_tap_prepare(udp_mh_recv, i, toside, false); > + udp_tap_prepare(udp_mh_recv, i, omac, toside, false); > > tap_send_frames(c, &udp_l2_iov[0][0], UDP_NUM_IOVS, n); > } > diff --git a/udp.h b/udp.h > index 8f8531a..dd6e5ad 100644 > --- a/udp.h > +++ b/udp.h > @@ -21,7 +21,7 @@ int udp_sock_init(const struct ctx *c, int ns, const union inany_addr *addr, > const char *ifname, in_port_t port); > int udp_init(struct ctx *c); > void udp_timer(struct ctx *c, const struct timespec *now); > -void udp_update_l2_buf(const unsigned char *eth_d, const unsigned char *eth_s); > +void udp_update_l2_buf(const unsigned char *eth_d); > > /** > * union udp_listen_epoll_ref - epoll reference for "listening" UDP sockets -- Stefano