[{"id":3674898,"web_url":"http://patchwork.ozlabs.org/comment/3674898/","msgid":"","list_archive_url":null,"date":"2026-04-08T12:16:41","subject":"Re: [RFC v4 0/5] net/filter: Add AF_PACKET support for vhost-net","submitter":{"id":2694,"url":"http://patchwork.ozlabs.org/api/people/2694/","name":"Daniel P. Berrangé","email":"berrange@redhat.com"},"content":"On Tue, Apr 07, 2026 at 01:05:47PM +0800, Cindy Lu wrote:\n> Hi, All\n> \n> This series wires AF_PACKET-backed packet capture and inject support into\n> the existing socket chardev backend so filter-redirector can keep using exist\n> process\n> \n> Example Usage\n> =============\n> Users are expected to create the AF_PACKET socket in userspace, bind it\n> to the target tap device, and then pass the resulting fd to QEMU via\n> the existing FD_PLACEHOLDER mechanism.\n> \n> Creating such a socket requires CAP_NET_RAW (or running as root). A\n> typical setup looks like:\n> \n> sock = socket.socket(socket.AF_PACKET, socket.SOCK_RAW,\n> socket.htons(ETH_P_ALL))\n> sock.bind((ifname, ETH_P_ALL))\n\nWhile FD passing is certainly desirable, and indeed required, for\nlibvirt to manage QEMU, IMHO, the QIOChannelSocket should be made\ncapable of opening AF_PACKET sockets explicitly too.\n\nI generally only consider \"FD\" passing for QIOCHannelSocket to be\nsupported for address families that we can explicitly open - we\nshouldn't have address familys that are only supported via FD\npassing\n\n> \n> The bound fd can then be passed to QEMU with:\n> \n> -chardev socket,...,fd=${FD_PLACEHOLDER},...\n> \n> Primary VM (mirror incoming packets to secondary via chardev socket):\n> \n> -netdev \"tap,id=net0,ifname=${TAP}...vhost=on\"\n> -device \"${VIRTIO_NET_DEVICE}\"\n> -chardev \"socket,id=chain_out,fd=${FD_PLACEHOLDER},af-packet-mode=capture\"\n> -chardev \"socket,id=mirror0,host=${MIRROR_HOST},port=${MIRROR_PORT},reconnect-ms=${MIRROR_RECONNECT_MS}\"\n> -object \"filter-redirector,id=r1,netdev=net0,queue=tx,indev=chain_out,status=on,vnet_hdr_support=off,position=head\"\n> -object \"filter-redirector,id=r1_mirror,netdev=net0,queue=tx,outdev=mirror0,status=on,vnet_hdr_support=off,insert=behind\"\n> \n> Secondary VM (receive mirrored packets):\n> \n> -netdev \"tap,id=net0,ifname=${TAP}...vhost=on\"\n> -device \"${VIRTIO_NET_DEVICE}\"\n> -chardev \"socket,id=red0,host=${MIRROR_BIND_HOST},port=${MIRROR_PORT},server=on,wait=off\"\n> -chardev \"socket,id=chain_in,fd=${FD_PLACEHOLDER},af-packet-mode=inject\"\n> -object \"filter-redirector,id=r1,netdev=net0,queue=tx,indev=red0,status=off,vnet_hdr_support=off,position=head\"\n> -object \"filter-redirector,id=r1_inject,netdev=net0,queue=tx,outdev=chain_in,status=off,vnet_hdr_support=off,position=id=r1,insert=behind\"\n> \n> \n> changset\n> ===========\n> change in v2: \n> 1. add support for filter-buffer \n> 2. remove the in_netdev and out_netdev for AF_PACKET bind port, now only use netdev \n> when the vhost=on start use AF_PACKET to capture and inject, when use vhost=off will use\n> the existing code\n> 3. add CAP_NET_RAW check\n> 4. address the comment \n> \n> change in v3: \n> 1. reuse the exist Capture/inject process \n> \n> change in v4: \n> 1.move the capture/inject to chardev \n> 2.move the create/bind socket to user script\n> \n> Testing\n> =======\n> - Tested with vhost=on/off TAP device on x86_64\n> \n> \n> \n> Cindy Lu (5):\n> net/filter: allow filters on vhost netdevs\n> chardev/socket: add AF_PACKET initialization\n> io/channel-socket: tolerate AF_PACKET getpeername\n> chardev/socket: add AF_PACKET inject path\n> chardev/socket: add AF_PACKET capture path\n> \n> chardev/char-socket.c | 385 +++++++++++++++++++++++++++++++++-\n> chardev/char.c | 3 +\n> include/chardev/char-socket.h | 13 ++\n> io/channel-socket.c | 6 +-\n> net/filter.c | 6 -\n> qapi/char.json | 23 +-\n> qemu-options.hx | 5 +-\n> 7 files changed, 429 insertions(+), 12 deletions(-)\n> \n> -- \n> 2.52.0\n> \n> \n\nWith regards,\nDaniel","headers":{"Return-Path":"","X-Original-To":"incoming@patchwork.ozlabs.org","Delivered-To":"patchwork-incoming@legolas.ozlabs.org","Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (1024-bit key;\n unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256\n header.s=mimecast20190719 header.b=K0dMVC91;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=nongnu.org\n (client-ip=209.51.188.17; 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