From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: passt.top; dmarc=none (p=none dis=none) header.from=gibson.dropbear.id.au Authentication-Results: passt.top; dkim=pass (2048-bit key; secure) header.d=gibson.dropbear.id.au header.i=@gibson.dropbear.id.au header.a=rsa-sha256 header.s=202602 header.b=DW6Nu2hU; dkim-atps=neutral Received: from mail.ozlabs.org (mail.ozlabs.org [IPv6:2404:9400:2221:ea00::3]) by passt.top (Postfix) with ESMTPS id DD5D05A0262 for ; Mon, 11 May 2026 04:01:39 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gibson.dropbear.id.au; s=202602; t=1778464895; bh=lNAb5h8i2t/ciEzwnidg9EzK/HWKIzj10e0isWfDNTY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=DW6Nu2hUARANS1phLn6BOBwRrU+mhnDRdLEtWArlBlR+5PCwoigHfV/0cSTtbx+80 puaXPRAhCYWmEQZbtGcgo6AIdrgZM0WgXCpFHxRnFMk6iqa25C+7TcrGpvcV07iimu JTB1VnknQbow8u6DVSE7pve2vpK+5wb2TuG5+J1BUjBxiUOgOH7p9DKo1XpTHzbMzR D9bS5iXYCGVDYNMYD3fPSt09/CwO+Xv0AneoDTFt6CXEYq+sUEhgU4I8gPijQ0vegz Jn/HaXiAcnL9pZtp/ai9rpuc+LQvC9QM1KiIrCoGBWsUZ9xRXZCrL7V+310GC5XBHT IZVySYjqVqM5g== Received: by gandalf.ozlabs.org (Postfix, from userid 1007) id 4gDNHz6K9zz4wJS; Mon, 11 May 2026 12:01:35 +1000 (AEST) Date: Mon, 11 May 2026 12:01:27 +1000 From: David Gibson To: Laurent Vivier Subject: Re: [PATCH v3 10/10] vhost-user: Centralise Ethernet frame padding in vu_collect() and vu_pad() Message-ID: References: <20260416155721.3807225-1-lvivier@redhat.com> <20260416155721.3807225-11-lvivier@redhat.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="ZxsTyxVFbiZ/IPDw" Content-Disposition: inline In-Reply-To: <20260416155721.3807225-11-lvivier@redhat.com> Message-ID-Hash: RMHJIFWDSXJNWWIJFRHIIQUUZZDTYAGV X-Message-ID-Hash: RMHJIFWDSXJNWWIJFRHIIQUUZZDTYAGV X-MailFrom: dgibson@gandalf.ozlabs.org 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: --ZxsTyxVFbiZ/IPDw Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable 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(). >=20 > 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. >=20 > 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. >=20 > Rewrite vu_pad() to take a full iovec array and use iov_memset(), > making it safe for multi-buffer (mergeable rx buffer) frames. >=20 > 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. >=20 > 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_vir= tq *vq, > size_t current_iov =3D 0; > int elem_cnt =3D 0; > =20 > + size =3D MAX(size, ETH_ZLEN /* Ethernet minimum size */ + VNET_HLEN); This seems to imply size should include the 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; > } > =20 > - size +=3D VNET_HLEN; > elem_cnt =3D vu_collect(vdev, vq, elem, ARRAY_SIZE(elem), in_sg, > - ARRAY_SIZE(in_sg), &in_total, size, &total); > - if (elem_cnt =3D=3D 0 || total < size) { > + ARRAY_SIZE(in_sg), &in_total, VNET_HLEN + size, &total); =2E..but this seems to imply it doesn't. > + if (elem_cnt =3D=3D 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; > } > =20 > - total -=3D 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); > =20 > if (*c->pcap) > pcap_iov(in_sg, in_total, VNET_HLEN, size); > =20 > + vu_pad(in_sg, in_total, VNET_HLEN + size); As does this. > vu_flush(vdev, vq, elem, elem_cnt, VNET_HLEN + size); And this. > vu_queue_notify(vdev, vq); > =20 > - trace("vhost-user sent %zu", total); > + trace("vhost-user sent %zu", size); > =20 > - return total; > + return size; > err: > for (i =3D 0; i < elem_cnt; i++) > vu_queue_detach_element(vq); > @@ -292,15 +291,15 @@ err: > } > =20 > /** > - * 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 i= ovec > + * @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 >=3D ETH_ZLEN) > - return; > + size_t min_frame_len =3D ETH_ZLEN + VNET_HLEN; > =20 > - memset((char *)iov->iov_base + iov->iov_len, 0, ETH_ZLEN - l2len); > - iov->iov_len +=3D 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_virt= q *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); > =20 > #endif /* VU_COMMON_H */ > --=20 > 2.53.0 >=20 --=20 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 --ZxsTyxVFbiZ/IPDw Content-Type: application/pgp-signature; name=signature.asc -----BEGIN PGP SIGNATURE----- iQIyBAEBCgAdFiEEO+dNsU4E3yXUXRK2zQJF27ox2GcFAmoBOHYACgkQzQJF27ox 2Gdjsg/3ZBhKmA1/D14nDUmAwa9GGtzz3eeIQ3iO0tLrsXojaUC3Ieb56ytWDcEQ 5aZ358KAvjZkcRwVZYwTKNQeNZuBWQW67zW8PrJXZMtx1u6h1ecMg7LEBHGXPLKQ AtwE/qxWPvexGWKiUPF4rj1Ld1rngpYLA19CoDuuz+gkp3GSzBvDsaHl2WEab0pL FIdQrDF9yuOa5k60m+JjAkloliEV2J219+RSZU+RokJknU4ZHde/2w6WW4+Dg2EH eiuZxfHKFHS6ffcBen3rcJrGr3/WepVXwHthIhDLNu3x6cIxpXkaXHDAmnu8qlRw sSLaEeSHVjV0XxhZApfeN7eooWb/OStFvNefyIkN8+bH8wPaU2u/q30fv8wnKZdB i8ZEOyHE5XHCM4N+lbfhStcidK1qNKIBcrmvD7H7L2gWhC4HEPSw94qcJVE1DFS9 7Wqpm42fm71eFau/rB0p2hncqV3Lp1s6+GtCtCIXnYnYfma4U2bGjCQA3JJVa4n5 zcUQeNptujfHPFsQuBDlMsnt3UU/MMu8Qpeh0T1SaEGAuNgVjPz3kAxQUr8uBTUM uJVmEe+371jHf4eczFBDJQWcKUl6AS/3RDNZS+JiVtUVgk0pCh/c6mlJWGVqBjsJ StkbDbayPGtJjxQY9pqxD1B2jshj4Ll/b/9qP+bJnn1ukV9gZg== =JB7X -----END PGP SIGNATURE----- --ZxsTyxVFbiZ/IPDw--