From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: passt.top; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: passt.top; dkim=pass (1024-bit key; unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256 header.s=mimecast20190719 header.b=benpuKTa; dkim-atps=neutral Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by passt.top (Postfix) with ESMTPS id 36F205A0274 for ; Fri, 27 Mar 2026 18:58:45 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1774634324; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=axx9zYURfetJdeqhKouIwd9VmLSf2mRaNRqsQMt4Elw=; b=benpuKTadKJwhNIerWwfEeX317mBfHNtCgQ8ZsTGK1GeQc8fgcQvS5/sm422Ux612cvmdO n7VV5niiz5fDUAFOACaFVjicdfAe+LZN/XYBBP1CD91uv146mDEYTGnS5hQLq5qPWxSwH5 DPWhNz7W1i/IERTlOpRQA5tEjNHxRf0= Received: from mx-prod-mc-05.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-214-Szpm3Va6P6KS1Q5GPC6QAg-1; Fri, 27 Mar 2026 13:58:42 -0400 X-MC-Unique: Szpm3Va6P6KS1Q5GPC6QAg-1 X-Mimecast-MFC-AGG-ID: Szpm3Va6P6KS1Q5GPC6QAg_1774634322 Received: from mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.111]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 01AD0195609D for ; Fri, 27 Mar 2026 17:58:42 +0000 (UTC) Received: from lenovo-t14s.redhat.com (unknown [10.44.32.96]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id F1902180035F; Fri, 27 Mar 2026 17:58:40 +0000 (UTC) From: Laurent Vivier To: passt-dev@passt.top Subject: [PATCH v5 3/8] vhost-user: Centralise Ethernet frame padding in vu_collect(), vu_pad() and vu_flush() Date: Fri, 27 Mar 2026 18:58:29 +0100 Message-ID: <20260327175834.831995-4-lvivier@redhat.com> In-Reply-To: <20260327175834.831995-1-lvivier@redhat.com> References: <20260327175834.831995-1-lvivier@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: 71ZOLMga3dbWxEbF4uOJMbad7P6KtsM-7tHb4W24ZJ8_1774634322 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: 8bit content-type: text/plain; charset="US-ASCII"; x-default=true Message-ID-Hash: 77BPBXDRWQCELX2IHI7BDBLMZPJEIEGH X-Message-ID-Hash: 77BPBXDRWQCELX2IHI7BDBLMZPJEIEGH 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: Laurent Vivier 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: The per-protocol padding done by vu_pad() in tcp_vu.c and udp_vu.c was only correct for single-buffer frames, and assumed the padding area always fell within the first iov. It also relied on each caller computing the right MAX(..., ETH_ZLEN + VNET_HLEN) size for vu_collect() and calling vu_pad() at the right point. Centralise padding logic into three shared vhost-user helpers instead: - vu_collect() now ensures at least ETH_ZLEN + VNET_HLEN bytes of buffer space are collected, so there is always room for a minimum-sized frame. - vu_pad() replaces the old single-iov helper with a new implementation that takes a full iovec array plus a 'skipped' byte count. It uses a new iov_memset() helper in iov.c to zero-fill the padding area across iovec boundaries, then calls iov_truncate() to set the logical frame size. - vu_flush() computes the actual frame length (accounting for VIRTIO_NET_F_MRG_RXBUF multi-buffer frames) and passes the padded length to vu_queue_fill(). Callers in tcp_vu.c, udp_vu.c and vu_send_single() now use the new vu_pad() in place of the old pad-then-truncate sequences and the MAX(..., ETH_ZLEN + VNET_HLEN) size calculations passed to vu_collect(). Centralising padding here will also ease the move to multi-iovec per element support, since there will be a single place to update. In vu_send_single(), fix padding, truncation and data copy to use the requested frame size rather than the total available buffer space from vu_collect(), which could be larger. Also add matching padding, truncation and explicit size to vu_collect() for the DUP_ACK path in tcp_vu_send_flag(). Signed-off-by: Laurent Vivier --- iov.c | 1 - tcp_vu.c | 23 ++++++------------- udp_vu.c | 9 ++------ vu_common.c | 63 ++++++++++++++++++++++++++++++++++------------------- vu_common.h | 2 +- 5 files changed, 50 insertions(+), 48 deletions(-) diff --git a/iov.c b/iov.c index 0188acdf5eba..8134b8c9f988 100644 --- a/iov.c +++ b/iov.c @@ -180,7 +180,6 @@ size_t iov_truncate(struct iovec *iov, size_t iov_cnt, size_t size) * Will write less than @length bytes if it runs out of space in * the iov */ -/* cppcheck-suppress unusedFunction */ void iov_memset(const struct iovec *iov, size_t iov_cnt, size_t offset, int c, size_t length) { diff --git a/tcp_vu.c b/tcp_vu.c index 0cd01190d612..7d3285152ad9 100644 --- a/tcp_vu.c +++ b/tcp_vu.c @@ -72,12 +72,12 @@ int tcp_vu_send_flag(const struct ctx *c, struct tcp_tap_conn *conn, int flags) struct vu_dev *vdev = c->vdev; struct vu_virtq *vq = &vdev->vq[VHOST_USER_RX_QUEUE]; struct vu_virtq_element flags_elem[2]; - size_t optlen, hdrlen, l2len; struct ipv6hdr *ip6h = NULL; struct iphdr *ip4h = NULL; struct iovec flags_iov[2]; struct tcp_syn_opts *opts; struct iov_tail payload; + size_t optlen, hdrlen; struct tcphdr *th; struct ethhdr *eh; uint32_t seq; @@ -88,7 +88,7 @@ int tcp_vu_send_flag(const struct ctx *c, struct tcp_tap_conn *conn, int flags) elem_cnt = vu_collect(vdev, vq, &flags_elem[0], 1, &flags_iov[0], 1, NULL, - MAX(hdrlen + sizeof(*opts), ETH_ZLEN + VNET_HLEN), NULL); + hdrlen + sizeof(*opts), NULL); if (elem_cnt != 1) return -1; @@ -128,7 +128,7 @@ int tcp_vu_send_flag(const struct ctx *c, struct tcp_tap_conn *conn, int flags) return ret; } - iov_truncate(&flags_iov[0], 1, hdrlen + optlen); + vu_pad(&flags_iov[0], 1, 0, hdrlen + optlen); payload = IOV_TAIL(flags_elem[0].in_sg, 1, hdrlen); if (flags & KEEPALIVE) @@ -137,9 +137,6 @@ int tcp_vu_send_flag(const struct ctx *c, struct tcp_tap_conn *conn, int flags) tcp_fill_headers(c, conn, eh, ip4h, ip6h, th, &payload, NULL, seq, !*c->pcap); - l2len = optlen + hdrlen - VNET_HLEN; - vu_pad(&flags_elem[0].in_sg[0], l2len); - vu_flush(vdev, vq, flags_elem, 1); if (*c->pcap) @@ -148,14 +145,14 @@ int tcp_vu_send_flag(const struct ctx *c, struct tcp_tap_conn *conn, int flags) if (flags & DUP_ACK) { elem_cnt = vu_collect(vdev, vq, &flags_elem[1], 1, &flags_iov[1], 1, NULL, - flags_elem[0].in_sg[0].iov_len, NULL); + hdrlen + optlen, NULL); if (elem_cnt == 1 && flags_elem[1].in_sg[0].iov_len >= flags_elem[0].in_sg[0].iov_len) { + vu_pad(&flags_iov[1], 1, 0, hdrlen + optlen); memcpy(flags_elem[1].in_sg[0].iov_base, flags_elem[0].in_sg[0].iov_base, flags_elem[0].in_sg[0].iov_len); - vu_flush(vdev, vq, &flags_elem[1], 1); if (*c->pcap) @@ -211,7 +208,7 @@ static ssize_t tcp_vu_sock_recv(const struct ctx *c, struct vu_virtq *vq, ARRAY_SIZE(elem) - elem_cnt, &iov_vu[DISCARD_IOV_NUM + iov_used], VIRTQUEUE_MAX_SIZE - iov_used, &in_total, - MAX(MIN(mss, fillsize) + hdrlen, ETH_ZLEN + VNET_HLEN), + MIN(mss, fillsize) + hdrlen, &frame_size); if (cnt == 0) break; @@ -247,8 +244,7 @@ static ssize_t tcp_vu_sock_recv(const struct ctx *c, struct vu_virtq *vq, if (!peek_offset_cap) ret -= already_sent; - /* adjust iov number and length of the last iov */ - i = iov_truncate(&iov_vu[DISCARD_IOV_NUM], iov_used, ret); + i = vu_pad(&iov_vu[DISCARD_IOV_NUM], iov_used, hdrlen, ret); /* adjust head count */ while (*head_cnt > 0 && head[*head_cnt - 1] >= i) @@ -444,7 +440,6 @@ int tcp_vu_data_from_sock(const struct ctx *c, struct tcp_tap_conn *conn) size_t frame_size = iov_size(iov, buf_cnt); bool push = i == head_cnt - 1; ssize_t dlen; - size_t l2len; assert(frame_size >= hdrlen); @@ -457,10 +452,6 @@ int tcp_vu_data_from_sock(const struct ctx *c, struct tcp_tap_conn *conn) tcp_vu_prepare(c, conn, iov, buf_cnt, &check, !*c->pcap, push); - /* Pad first/single buffer only, it's at least ETH_ZLEN long */ - l2len = dlen + hdrlen - VNET_HLEN; - vu_pad(iov, l2len); - vu_flush(vdev, vq, &elem[head[i]], buf_cnt); if (*c->pcap) diff --git a/udp_vu.c b/udp_vu.c index f8629af58ab5..537e9c92cfa6 100644 --- a/udp_vu.c +++ b/udp_vu.c @@ -73,8 +73,7 @@ static int udp_vu_sock_recv(const struct ctx *c, struct vu_virtq *vq, int s, const struct vu_dev *vdev = c->vdev; int elem_cnt, elem_used, iov_used; struct msghdr msg = { 0 }; - size_t hdrlen, l2len; - size_t iov_cnt; + size_t iov_cnt, hdrlen; assert(!c->no_udp); @@ -117,13 +116,9 @@ static int udp_vu_sock_recv(const struct ctx *c, struct vu_virtq *vq, int s, iov_vu[0].iov_base = (char *)iov_vu[0].iov_base - hdrlen; iov_vu[0].iov_len += hdrlen; - iov_used = iov_truncate(iov_vu, iov_cnt, *dlen + hdrlen); + iov_used = vu_pad(iov_vu, iov_cnt, 0, *dlen + hdrlen); elem_used = iov_used; /* one iovec per element */ - /* pad frame to 60 bytes: first buffer is at least ETH_ZLEN long */ - l2len = *dlen + hdrlen - VNET_HLEN; - vu_pad(&iov_vu[0], l2len); - /* release unused buffers */ vu_queue_rewind(vq, elem_cnt - elem_used); diff --git a/vu_common.c b/vu_common.c index 7627fad5976b..3bc6f1f42a8e 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 + VNET_HLEN); /* Ethernet minimum size */ while (current_size < size && elem_cnt < max_elem && current_iov < max_in_sg) { int ret; @@ -113,13 +114,31 @@ int vu_collect(const struct vu_dev *vdev, struct vu_virtq *vq, return elem_cnt; } +/** + * vu_pad() - Pad short frames to minimum Ethernet length and truncate iovec + * @iov: Pointer to iovec array + * @cnt: Number of entries in @iov + * @skipped: Bytes already accounted for in the frame but not in @iov + * @size: Data length in @iov + * + * Return: number of iovec entries after truncation + */ +size_t vu_pad(struct iovec *iov, size_t cnt, size_t skipped, size_t size) +{ + if (skipped + size < ETH_ZLEN + VNET_HLEN) { + iov_memset(iov, cnt, size, 0, + ETH_ZLEN + VNET_HLEN - (skipped + size)); + } + + return iov_truncate(iov, cnt, size); +} + /** * vu_set_vnethdr() - set virtio-net headers * @vnethdr: Address of the header to set * @num_buffers: Number of guest buffers of the frame */ -static void vu_set_vnethdr(struct virtio_net_hdr_mrg_rxbuf *vnethdr, - int num_buffers) +static void vu_set_vnethdr(struct virtio_net_hdr_mrg_rxbuf *vnethdr, int num_buffers) { vnethdr->hdr = VU_HEADER; /* Note: if VIRTIO_NET_F_MRG_RXBUF is not negotiated, @@ -138,15 +157,25 @@ static void vu_set_vnethdr(struct virtio_net_hdr_mrg_rxbuf *vnethdr, void vu_flush(const struct vu_dev *vdev, struct vu_virtq *vq, struct vu_virtq_element *elem, int elem_cnt) { + size_t len, padding, elem_size; int i; vu_set_vnethdr(elem[0].in_sg[0].iov_base, elem_cnt); - for (i = 0; i < elem_cnt; i++) { - size_t elem_size = iov_size(elem[i].in_sg, elem[i].in_num); - + len = 0; + for (i = 0; i < elem_cnt - 1; i++) { + elem_size = iov_size(elem[i].in_sg, elem[i].in_num); vu_queue_fill(vdev, vq, &elem[i], elem_size, i); + len += elem_size; } + /* pad the last element to have an Ethernet minimum size */ + elem_size = iov_size(elem[i].in_sg, elem[i].in_num); + if (ETH_ZLEN + VNET_HLEN > len + elem_size) + padding = ETH_ZLEN + VNET_HLEN - (len + elem_size); + else + padding = 0; + + vu_queue_fill(vdev, vq, &elem[i], elem_size + padding, i); vu_queue_flush(vdev, vq, elem_cnt); } @@ -262,10 +291,12 @@ int vu_send_single(const struct ctx *c, const void *buf, size_t size) goto err; } - total -= VNET_HLEN; + in_total = vu_pad(in_sg, in_total, 0, size); + + size -= 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); @@ -273,26 +304,12 @@ int vu_send_single(const struct ctx *c, const void *buf, size_t size) vu_flush(vdev, vq, elem, elem_cnt); 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); return -1; } - -/** - * 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 - */ -void vu_pad(struct iovec *iov, size_t l2len) -{ - if (l2len >= ETH_ZLEN) - return; - - memset((char *)iov->iov_base + iov->iov_len, 0, ETH_ZLEN - l2len); - iov->iov_len += ETH_ZLEN - l2len; -} diff --git a/vu_common.h b/vu_common.h index 4037ab765b7d..13e0126fb16c 100644 --- a/vu_common.h +++ b/vu_common.h @@ -39,11 +39,11 @@ int vu_collect(const struct vu_dev *vdev, struct vu_virtq *vq, struct vu_virtq_element *elem, int max_elem, struct iovec *in_sg, size_t max_in_sg, size_t *in_total, size_t size, size_t *collected); +size_t vu_pad(struct iovec *iov, size_t cnt, size_t skipped, size_t size); void vu_flush(const struct vu_dev *vdev, struct vu_virtq *vq, struct vu_virtq_element *elem, int elem_cnt); 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); #endif /* VU_COMMON_H */ -- 2.53.0