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[82.64.211.94]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-48e8f442129sm37308665e9.28.2026.05.13.02.17.12 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 13 May 2026 02:17:13 -0700 (PDT) Message-ID: <003a0da1-47b9-42fd-8a0a-bc07af0051f5@redhat.com> Date: Wed, 13 May 2026 11:17:12 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 10/10] vhost-user: Centralise Ethernet frame padding in vu_collect() and vu_pad() To: David Gibson References: <20260416155721.3807225-1-lvivier@redhat.com> <20260416155721.3807225-11-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: Tn42x6gYc0X0Wwym0sq-A7BopNHjw8XNfne5ymQZjH8_1778663835 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: P2RXI7EHE6H6BWVOMQUO553DDOMLFSVK X-Message-ID-Hash: P2RXI7EHE6H6BWVOMQUO553DDOMLFSVK 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 5/11/26 04:01, David Gibson wrote: > On Thu, Apr 16, 2026 at 05:57:21PM +0200, Laurent Vivier wrote: >> The previous per-protocol padding done by vu_pad() in tcp_vu.c and >> udp_vu.c was only correct for single-buffer frames: it assumed the >> padding area always fell within the first iov, writing past its end >> with a plain memset(). >> >> It also required each caller to compute MAX(..., ETH_ZLEN + VNET_HLEN) >> for vu_collect() and to call vu_pad() at the right point, duplicating >> the minimum-size logic across protocols. >> >> Move the Ethernet minimum size enforcement into vu_collect() itself, so >> that enough buffer space is always reserved for padding regardless of >> the requested frame size. >> >> Rewrite vu_pad() to take a full iovec array and use iov_memset(), >> making it safe for multi-buffer (mergeable rx buffer) frames. >> >> In tcp_vu_sock_recv(), replace iov_truncate() with iov_skip_bytes(): >> now that all consumers receive explicit data lengths, truncating the >> iovecs is no longer needed. In tcp_vu_data_from_sock(), cap each >> frame's data length against the remaining bytes actually received from >> the socket, so that the last partial frame gets correct headers and >> sequence number advancement. >> >> Signed-off-by: Laurent Vivier > > LGTM, except for what looks like one minor bug. > > [snip] >> index 704e908aa02c..d07f584f228a 100644 >> --- a/vu_common.c >> +++ b/vu_common.c >> @@ -74,6 +74,7 @@ int vu_collect(const struct vu_dev *vdev, struct vu_virtq *vq, >> size_t current_iov = 0; >> int elem_cnt = 0; >> >> + size = MAX(size, ETH_ZLEN /* Ethernet minimum size */ + VNET_HLEN); > > This seems to imply size should include the vnet header... size is the max of "size" provided below by vu_single() to vu_collect() (and you noted includes vnet header) and the the minimum frame size (Ethernet minimum + vnet header) > >> while (current_size < size && elem_cnt < max_elem && >> current_iov < max_in_sg) { >> int ret; >> @@ -261,29 +262,27 @@ int vu_send_single(const struct ctx *c, const void *buf, size_t size) >> return -1; >> } >> >> - size += VNET_HLEN; >> elem_cnt = vu_collect(vdev, vq, elem, ARRAY_SIZE(elem), in_sg, >> - ARRAY_SIZE(in_sg), &in_total, size, &total); >> - if (elem_cnt == 0 || total < size) { >> + ARRAY_SIZE(in_sg), &in_total, VNET_HLEN + size, &total); > > ...but this seems to imply it doesn't. This is not the same "size". Here "size" is without vnet header, but we need to provide a size with vnet header to vu_collect(). > >> + if (elem_cnt == 0 || total < VNET_HLEN + size) { >> debug("vu_send_single: no space to send the data " >> "elem_cnt %d size %zu", elem_cnt, total); >> goto err; >> } >> >> - total -= VNET_HLEN; >> - >> /* copy data from the buffer to the iovec */ >> - iov_from_buf(in_sg, in_total, VNET_HLEN, buf, total); >> + iov_from_buf(in_sg, in_total, VNET_HLEN, buf, size); >> >> if (*c->pcap) >> pcap_iov(in_sg, in_total, VNET_HLEN, size); >> >> + vu_pad(in_sg, in_total, VNET_HLEN + size); > > As does this. Same here (see vu_pad() comment header) > >> vu_flush(vdev, vq, elem, elem_cnt, VNET_HLEN + size); > > And this. See vu_flush() comment header > >> vu_queue_notify(vdev, vq); >> >> - trace("vhost-user sent %zu", total); >> + trace("vhost-user sent %zu", size); >> >> - return total; >> + return size; >> err: >> for (i = 0; i < elem_cnt; i++) >> vu_queue_detach_element(vq); >> @@ -292,15 +291,15 @@ err: >> } >> >> /** >> - * vu_pad() - Pad 802.3 frame to minimum length (60 bytes) if needed >> - * @iov: Buffer in iovec array where end of 802.3 frame is stored >> - * @l2len: Layer-2 length already filled in frame >> + * vu_pad() - Pad short frames to minimum Ethernet length and truncate iovec >> + * @iov: Pointer to iovec array >> + * @cnt: Number of entries in @iov >> + * @frame_len: Data length in @iov (including virtio-net header) >> */ >> -void vu_pad(struct iovec *iov, size_t l2len) >> +void vu_pad(const struct iovec *iov, size_t cnt, size_t frame_len) >> { >> - if (l2len >= ETH_ZLEN) >> - return; >> + size_t min_frame_len = ETH_ZLEN + VNET_HLEN; >> >> - memset((char *)iov->iov_base + iov->iov_len, 0, ETH_ZLEN - l2len); >> - iov->iov_len += ETH_ZLEN - l2len; >> + if (frame_len < min_frame_len) >> + iov_memset(iov, cnt, frame_len, 0, min_frame_len - frame_len); >> } >> diff --git a/vu_common.h b/vu_common.h >> index 77d1849e6115..51f70084a7cb 100644 >> --- a/vu_common.h >> +++ b/vu_common.h >> @@ -44,6 +44,6 @@ void vu_flush(const struct vu_dev *vdev, struct vu_virtq *vq, >> void vu_kick_cb(struct vu_dev *vdev, union epoll_ref ref, >> const struct timespec *now); >> int vu_send_single(const struct ctx *c, const void *buf, size_t size); >> -void vu_pad(struct iovec *iov, size_t l2len); >> +void vu_pad(const struct iovec *iov, size_t cnt, size_t frame_len); >> >> #endif /* VU_COMMON_H */ >> -- >> 2.53.0 >> > Thanks, Laurent