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([2a01:e0a:e10:ef90:4326:a36e:a7cb:624b]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-48541b6f708sm296516105e9.11.2026.03.12.01.19.53 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 12 Mar 2026 01:19:53 -0700 (PDT) Message-ID: <3f8ad2e8-55dc-4dc7-8fab-746bc9932c6b@redhat.com> Date: Thu, 12 Mar 2026 09:19:52 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 08/13] udp_vu: Use iov_tail in udp_vu_prepare() To: David Gibson References: <20260309094744.1907754-1-lvivier@redhat.com> <20260309094744.1907754-9-lvivier@redhat.com> From: Laurent Vivier Autocrypt: addr=lvivier@redhat.com; keydata= xsFNBFYFJhkBEAC2me7w2+RizYOKZM+vZCx69GTewOwqzHrrHSG07MUAxJ6AY29/+HYf6EY2 WoeuLWDmXE7A3oJoIsRecD6BXHTb0OYS20lS608anr3B0xn5g0BX7es9Mw+hV/pL+63EOCVm SUVTEQwbGQN62guOKnJJJfphbbv82glIC/Ei4Ky8BwZkUuXd7d5NFJKC9/GDrbWdj75cDNQx UZ9XXbXEKY9MHX83Uy7JFoiFDMOVHn55HnncflUncO0zDzY7CxFeQFwYRbsCXOUL9yBtqLer Ky8/yjBskIlNrp0uQSt9LMoMsdSjYLYhvk1StsNPg74+s4u0Q6z45+l8RAsgLw5OLtTa+ePM JyS7OIGNYxAX6eZk1+91a6tnqfyPcMbduxyBaYXn94HUG162BeuyBkbNoIDkB7pCByed1A7q q9/FbuTDwgVGVLYthYSfTtN0Y60OgNkWCMtFwKxRaXt1WFA5ceqinN/XkgA+vf2Ch72zBkJL RBIhfOPFv5f2Hkkj0MvsUXpOWaOjatiu0fpPo6Hw14UEpywke1zN4NKubApQOlNKZZC4hu6/ 8pv2t4HRi7s0K88jQYBRPObjrN5+owtI51xMaYzvPitHQ2053LmgsOdN9EKOqZeHAYG2SmRW LOxYWKX14YkZI5j/TXfKlTpwSMvXho+efN4kgFvFmP6WT+tPnwARAQABzSNMYXVyZW50IFZp dmllciA8bHZpdmllckByZWRoYXQuY29tPsLBeAQTAQIAIgUCVgVQgAIbAwYLCQgHAwIGFQgC CQoLBBYCAwECHgECF4AACgkQ8ww4vT8vvjwpgg//fSGy0Rs/t8cPFuzoY1cex4limJQfReLr SJXCANg9NOWy/bFK5wunj+h/RCFxIFhZcyXveurkBwYikDPUrBoBRoOJY/BHK0iZo7/WQkur 6H5losVZtrotmKOGnP/lJYZ3H6OWvXzdz8LL5hb3TvGOP68K8Bn8UsIaZJoeiKhaNR0sOJyI YYbgFQPWMHfVwHD/U+/gqRhD7apVysxv5by/pKDln1I5v0cRRH6hd8M8oXgKhF2+rAOL7gvh jEHSSWKUlMjC7YwwjSZmUkL+TQyE18e2XBk85X8Da3FznrLiHZFHQ/NzETYxRjnOzD7/kOVy gKD/o7asyWQVU65mh/ECrtjfhtCBSYmIIVkopoLaVJ/kEbVJQegT2P6NgERC/31kmTF69vn8 uQyW11Hk8tyubicByL3/XVBrq4jZdJW3cePNJbTNaT0d/bjMg5zCWHbMErUib2Nellnbg6bc 2HLDe0NLVPuRZhHUHM9hO/JNnHfvgiRQDh6loNOUnm9Iw2YiVgZNnT4soUehMZ7au8PwSl4I KYE4ulJ8RRiydN7fES3IZWmOPlyskp1QMQBD/w16o+lEtY6HSFEzsK3o0vuBRBVp2WKnssVH qeeV01ZHw0bvWKjxVNOksP98eJfWLfV9l9e7s6TaAeySKRRubtJ+21PRuYAxKsaueBfUE7ZT 7zfOwU0EVgUmGQEQALxSQRbl/QOnmssVDxWhHM5TGxl7oLNJms2zmBpcmlrIsn8nNz0rRyxT 460k2niaTwowSRK8KWVDeAW6ZAaWiYjLlTunoKwvF8vP3JyWpBz0diTxL5o+xpvy/Q6YU3BN efdq8Vy3rFsxgW7mMSrI/CxJ667y8ot5DVugeS2NyHfmZlPGE0Nsy7hlebS4liisXOrN3jFz asKyUws3VXek4V65lHwB23BVzsnFMn/bw/rPliqXGcwl8CoJu8dSyrCcd1Ibs0/Inq9S9+t0 VmWiQWfQkz4rvEeTQkp/VfgZ6z98JRW7S6l6eophoWs0/ZyRfOm+QVSqRfFZdxdP2PlGeIFM C3fXJgygXJkFPyWkVElr76JTbtSHsGWbt6xUlYHKXWo+xf9WgtLeby3cfSkEchACrxDrQpj+ Jt/JFP+q997dybkyZ5IoHWuPkn7uZGBrKIHmBunTco1+cKSuRiSCYpBIXZMHCzPgVDjk4viP brV9NwRkmaOxVvye0vctJeWvJ6KA7NoAURplIGCqkCRwg0MmLrfoZnK/gRqVJ/f6adhU1oo6 z4p2/z3PemA0C0ANatgHgBb90cd16AUxpdEQmOCmdNnNJF/3Zt3inzF+NFzHoM5Vwq6rc1JP jfC3oqRLJzqAEHBDjQFlqNR3IFCIAo4SYQRBdAHBCzkM4rWyRhuVABEBAAHCwV8EGAECAAkF AlYFJhkCGwwACgkQ8ww4vT8vvjwg9w//VQrcnVg3TsjEybxDEUBm8dBmnKqcnTBFmxN5FFtI WlEuY8+YMiWRykd8Ln9RJ/98/ghABHz9TN8TRo2b6WimV64FmlVn17Ri6FgFU3xNt9TTEChq AcNg88eYryKsYpFwegGpwUlaUaaGh1m9OrTzcQy+klVfZWaVJ9Nw0keoGRGb8j4XjVpL8+2x OhXKrM1fzzb8JtAuSbuzZSQPDwQEI5CKKxp7zf76J21YeRrEW4WDznPyVcDTa+tz++q2S/Bp P4W98bXCBIuQgs2m+OflERv5c3Ojldp04/S4NEjXEYRWdiCxN7ca5iPml5gLtuvhJMSy36gl U6IW9kn30IWuSoBpTkgV7rLUEhh9Ms82VWW/h2TxL8enfx40PrfbDtWwqRID3WY8jLrjKfTd R3LW8BnUDNkG+c4FzvvGUs8AvuqxxyHbXAfDx9o/jXfPHVRmJVhSmd+hC3mcQ+4iX5bBPBPM oDqSoLt5w9GoQQ6gDVP2ZjTWqwSRMLzNr37rJjZ1pt0DCMMTbiYIUcrhX8eveCJtY7NGWNyx FCRkhxRuGcpwPmRVDwOl39MB3iTsRighiMnijkbLXiKoJ5CDVvX5yicNqYJPKh5MFXN1bvsB kmYiStMRbrD0HoY1kx5/VozBtc70OU0EB8Wrv9hZD+Ofp0T3KOr1RUHvCZoLURfFhSQ= In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: Yh9N_hrDmi3S1SjvC0cN7PczUvcnwLRMPFO9ag6fK60_1773303595 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Message-ID-Hash: FDE5DABXXVGWGTDJAC3DR6WJCLDP7JFM X-Message-ID-Hash: FDE5DABXXVGWGTDJAC3DR6WJCLDP7JFM X-MailFrom: lvivier@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: 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 3/12/26 05:30, David Gibson wrote: > On Mon, Mar 09, 2026 at 10:47:39AM +0100, Laurent Vivier wrote: >> Rework udp_vu_prepare() to use IOV_REMOVE_HEADER() and IOV_PUT_HEADER() >> to walk through Ethernet, IP and UDP headers instead of the layout-specific >> helpers (vu_eth(), vu_ip(), vu_payloadv4(), vu_payloadv6()) that assume a >> contiguous buffer. The payload length is now implicit in the iov_tail, so >> drop the dlen parameter. >> >> Signed-off-by: Laurent Vivier >> --- >> iov.c | 1 - >> udp_vu.c | 64 ++++++++++++++++++++++++++++++-------------------------- >> 2 files changed, 34 insertions(+), 31 deletions(-) >> >> diff --git a/iov.c b/iov.c >> index 296f24b61067..1f554f5ac297 100644 >> --- a/iov.c >> +++ b/iov.c >> @@ -313,7 +313,6 @@ void *iov_peek_header_(struct iov_tail *tail, void *v, size_t len, size_t align) >> * >> * Return: number of bytes written >> */ >> -/* cppcheck-suppress unusedFunction */ >> size_t iov_put_header_(struct iov_tail *tail, const void *v, size_t len) >> { >> size_t l = len; >> diff --git a/udp_vu.c b/udp_vu.c >> index 2a5d3f822bf6..a21a03dbf23e 100644 >> --- a/udp_vu.c >> +++ b/udp_vu.c >> @@ -101,52 +101,54 @@ static ssize_t udp_vu_sock_recv(struct iovec *iov, size_t *cnt, int s, bool v6) >> * @c: Execution context >> * @data: IO vector tail for the frame >> * @toside: Address information for one side of the flow >> - * @dlen: Packet data length >> * >> * Return: Layer-4 length >> */ >> static size_t udp_vu_prepare(const struct ctx *c, const struct iov_tail *data, >> - const struct flowside *toside, ssize_t dlen) >> + const struct flowside *toside) >> { >> - const struct iovec *iov = data->iov; >> - struct ethhdr *eh; >> + struct iov_tail current = *data; >> + struct ethhdr *eh, eh_storage; >> + struct udphdr *uh, uh_storage; >> size_t l4len; >> >> /* ethernet header */ >> - eh = vu_eth(iov[0].iov_base); >> + eh = IOV_REMOVE_HEADER(¤t, eh_storage); >> >> memcpy(eh->h_dest, c->guest_mac, sizeof(eh->h_dest)); >> memcpy(eh->h_source, c->our_tap_mac, sizeof(eh->h_source)); >> >> /* initialize header */ >> 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); >> + struct iphdr *iph, iph_storage; >> >> eh->h_proto = htons(ETH_P_IP); >> >> + iph = IOV_REMOVE_HEADER(¤t, iph_storage); >> *iph = (struct iphdr)L2_BUF_IP4_INIT(IPPROTO_UDP); >> >> - l4len = udp_update_hdr4(iph, &bp->uh, &payload, toside, true); >> + uh = IOV_REMOVE_HEADER(¤t, uh_storage); >> + l4len = udp_update_hdr4(iph, uh, ¤t, toside, true); >> + >> + current = *data; > > Oof, having to reset the tail to the original position in order to > replay the PUTs in the right order seems kind of fragile. I'm > beginning to wonder if for writing (not reading) headers, trying to > use an in-place pointer is more trouble than it's worth. It would > certainly be easier to reason about this, if you always construct the > header in an external buffer, then there's just a sequence of > IOV_PUT_HEADER()s to stack them into the iov tail. I can use one PEEK and PUT with something like: struct { struct ethhdr eh; struct struct iphdr struct udphdr *uh } __attribute__((__packed__)) *hdr4, hdr4_storage; hdr4 = IOV_PEEK_HEADER(¤t, hdr4_storage); ... IOV_PUT_HEADER(¤t, hdr4); or as you proposed: with_header(hdr4, ¤t) { .... } Thanks, Laurent