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<markdown> # Patcher du debian ! how to ? Avec des vrais morceaux de LXD dedans ## 1. Contexte : du LXD & du qemu-system - pour une machine toute neuve debian sous Bookworm (testing à l'époque), qui nécessite de faire fonctionner des machines virtuelles (dites « vm/VM ») grâce au logiciel de Canonical « LXD » (sorte de remplacant de lxc), il fallait patcher le paquet qemu-system. - en passant du côté de `irc.libera.chat#qemu` et `irc.libera.chat#lxc` j'ai été redirigé []sur l'issue qui va bien](https://gitlab.com/qemu-project/qemu/-/issues/1486) mais vu que ça n'avançait pas : l'idée a été de patcher w00t ! ## 2. Reproduction du pépin (/¯◡ ‿ ◡)/¯ ~ ┻━┻ ### 2.1 Install machine de base ``` sudo apt update sudo apt install –no-install-recommends sudo vim etckeeper tig lnav screen htop borgbackup tcpstat nmap lsof iftop tcpdump tldr ncdu ripgrep unattended-upgrades gnupg debian-goodies apticron apt-listchanges ssmtp python3-pip sudo apt install lxd sudo apt install qemu-base qemu-utils qemu-system sudo apt upgrade ```

### 2.2 Étapes avant le bug - lancement du bridge et création de la vm ``` lxd –version 5.0.2 lxc network create UPLINK –type=physical parent=lxdbr0 +—————–+———-+———+————–+—————————+————-+———+———+

+—————–+———-+———+————–+—————————+————-+———+———+

lxc launch images:debian/bullseye test0 –vm Error: Failed setting up device via monitor: Failed setting up device “eth0”: Failed adding NIC netdev: Monitor is disconnected ``` - erreur, liée à qemu-system ( https://gitlab.com/qemu-project/qemu/-/issues/1486 ) ``` root@Selachimorpha:~# lxc info –show-log local:test0 Name: test0 Status: STOPPED Type: virtual-machine Architecture: x86_64 Created: 2023/03/13 17:06 CET Log: warning: tap: open vhost char device failed: Permission denied warning: tap: open vhost char device failed: Permission denied qemu-system-x86_64: ../../net/net.c:1106: net_client_init1: Assertion `nc' failed. ``` ## 3. Tentative de résolution : patcher du paquet debian（○゜ε＾○） - utilisation d'[]une ressource (maigre) de chez debian](https://wiki.debian.org/BuildingTutorial) - install des quelques paquets nécessaire à la (re)compilation ``` sudo apt install build-essential fakeroot devscripts dpkg-dev gcc make automake pbuilder cd /home/roz/ && mkdir pkg-qemu-patching && cd pkg-qemu-patching/ sudo apt source qemu-system ``` - création du patch, []téléchargé depuis la liste mail](https://www.mail-archive.com/qemu-devel@nongnu.org/msg924611.html) `vim debian/patches/0001-net-net.c-do-not-assert-nc-as-hotplug-vhost-net-may-.patch` : ``` From b2bca483212f04b9b021753aec1fcaeaf41385d1 Mon Sep 17 00:00:00 2001 From: Ming Yang yangming73@huawei.com Date: Fri, 25 Nov 2022 10:45:52 +0800 Subject: [PATCH] net/net.c: Fix qemu crash when hot-pluging a vhost-net failed.

Hot-pluging a vhost-net may cause virtual machine crash in following steps: 1. Starting a vm without net devices. 2. Hot-pluging 70 memory devices. 3. Hot-pluging a vhost-net device.

The reason is : if hotplug a vhost-net failed, the nc cannot be found via function qemu_find_netdev, as it has been cleaned up through function qemu_cleanup_net_client. Which leads to the result that assert(nc) failed, then qemu crashed.

While, the root reason is that, in commit 46d4d36d0bf2 if not both has_vhostforce and vhostforce flags are true, the errp would not be set. Then net_init_tap would not return a negative value, fallowed by founding nc and assert nc.

In this patch, asserting nc is replaced with setting an error message.

Fixes: 46d4d36d0bf2(“tap: setting error appropriately when calling net_init_tap_one()”) Signed-off-by: Ming Yang yangming73@huawei.com Signed-off-by: Liang Zhang zhangliang5@huawei.com https://gitlab.com/qemu-project/qemu/-/issues/1486 — net/net.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-)

diff –git a/net/net.c b/net/net.c index 840ad9dca5..1d1d7e54c4 100644 — a/net/net.c +++ b/net/net.c @@ -1103,7 +1103,16 @@ static int net_client_init1(const Netdev *netdev, bool is_netdev, Error **errp)

if (is_netdev) {

       nc = qemu_find_netdev(netdev->id);

- assert(nc); + /* + * If the tap of hotpluged net device do not has both has_vhostforce flag and vhostforce flags, + * when error occurs, the error messags will be report but not set to errp. Thus net_client_init_fun + * will not return a negatave value. Therefore the value of nc might be NULL. To make qemu robust, + * it is better to judge if nc is NULL. + */ + if (!nc) { + error_setg(errp, “Device '%s' could not be initialized”, netdev→id); + return -1; + }

       nc->is_netdev = true;
   }

– 2.33.0 ``` - ajout du patch au fichier de conf' des trucs à compiler : `vim qemu-7.2+dfsg/debian/patches/series` : ``` # Assertion failed au moment du lxc-start/launch 0001-net-net.c-do-not-assert-nc-as-hotplug-vhost-net-may-.patch ``` - Compilation avec le patch, celui-ci devrait apparaître clairement via son nom (ici `0001-net-net.c-do-not-assert-nc-as-hotplug-vhost-net-may-.patch`) en début de compilation ``` cd /home/roz/pkg-qemu-patching/qemu-7.2+dfsg/ dpkg-buildpackage -us -uc ``` - Vérification : ``` root@Selachimorpha:/home/roz/pkg-qemu-patching# ls -la total 864740 drwxr-xr-x 3 root root 4096 Mar 12 00:56 . drwx—— 4 roz roz 4096 Mar 11 23:40 .. drwxr-xr-x 60 root root 4096 Mar 12 00:56 qemu-7.2+dfsg -rw-r–r– 1 root root 30315205 Mar 12 01:01 qemu_7.2+dfsg-4_amd64.build -rw-r–r– 1 root root 32454 Mar 12 00:55 qemu_7.2+dfsg-4_amd64.buildinfo -rw-r–r– 1 root root 12577 Mar 12 00:56 qemu_7.2+dfsg-4_amd64.changes -rw-r–r– 1 root root 121624 Mar 11 23:51 qemu_7.2+dfsg-4.debian.tar.xz -rw-r–r– 1 root root 5892 Mar 11 23:51 qemu_7.2+dfsg-4.dsc -rw-r–r– 1 root root 23523172 Dec 15 15:32 qemu_7.2+dfsg.orig.tar.xz -rw-r–r– 1 root root 86428 Mar 12 00:52 qemu-block-extra_7.2+dfsg-4_amd64.deb -rw-r–r– 1 root root 292220 Mar 12 00:52 qemu-block-extra-dbgsym_7.2+dfsg-4_amd64.deb -rw-r–r– 1 root root 324884 Mar 12 00:53 qemu-guest-agent_7.2+dfsg-4_amd64.deb -rw-r–r– 1 root root 949128 Mar 12 00:53 qemu-guest-agent-dbgsym_7.2+dfsg-4_amd64.deb -rw-r–r– 1 root root 31504 Mar 12 00:52 qemu-system_7.2+dfsg-4_amd64.deb -rw-r–r– 1 root root 8981796 Mar 12 00:55 qemu-system-arm_7.2+dfsg-4_amd64.deb -rw-r–r– 1 root root 39860352 Mar 12 00:55 qemu-system-arm-dbgsym_7.2+dfsg-4_amd64.deb -rw-r–r– 1 root root 2138480 Mar 12 00:53 qemu-system-common_7.2+dfsg-4_amd64.deb -rw-r–r– 1 root root 7371508 Mar 12 00:53 qemu-system-common-dbgsym_7.2+dfsg-4_amd64.deb -rw-r–r– 1 root root 1276368 Mar 12 00:52 qemu-system-data_7.2+dfsg-4_all.deb -rw-r–r– 1 root root 297904 Mar 12 00:53 qemu-system-gui_7.2+dfsg-4_amd64.deb -rw-r–r– 1 root root 1041592 Mar 12 00:53 qemu-system-gui-dbgsym_7.2+dfsg-4_amd64.deb -rw-r–r– 1 root root 13307612 Mar 12 00:53 qemu-system-mips_7.2+dfsg-4_amd64.deb -rw-r–r– 1 root root 55224640 Mar 12 00:54 qemu-system-mips-dbgsym_7.2+dfsg-4_amd64.deb -rw-r–r– 1 root root 46229776 Mar 12 00:54 qemu-system-misc_7.2+dfsg-4_amd64.deb -rw-r–r– 1 root root 193547560 Mar 12 00:55 qemu-system-misc-dbgsym_7.2+dfsg-4_amd64.deb -rw-r–r– 1 root root 7538304 Mar 12 00:55 qemu-system-ppc_7.2+dfsg-4_amd64.deb -rw-r–r– 1 root root 31417836 Mar 12 00:55 qemu-system-ppc-dbgsym_7.2+dfsg-4_amd64.deb -rw-r–r– 1 root root 5175268 Mar 12 00:53 qemu-system-sparc_7.2+dfsg-4_amd64.deb -rw-r–r– 1 root root 20431008 Mar 12 00:54 qemu-system-sparc-dbgsym_7.2+dfsg-4_amd64.deb -rw-r–r– 1 root root 9255868 Mar 12 00:55 qemu-system-x86_7.2+dfsg-4_amd64.deb -rw-r–r– 1 root root 37281972 Mar 12 00:55 qemu-system-x86-dbgsym_7.2+dfsg-4_amd64.deb -rw-r–r– 1 root root 2685276 Mar 12 00:53 qemu-system-xen_7.2+dfsg-4_amd64.deb -rw-r–r– 1 root root 10742216 Mar 12 00:53 qemu-system-xen-dbgsym_7.2+dfsg-4_amd64.deb -rw-r–r– 1 root root 12706240 Mar 12 00:54 qemu-user_7.2+dfsg-4_amd64.deb -rw-r–r– 1 root root 5344 Mar 12 00:55 qemu-user-binfmt_7.2+dfsg-4_amd64.deb -rw-r–r– 1 root root 135493288 Mar 12 00:55 qemu-user-dbgsym_7.2+dfsg-4_amd64.deb -rw-r–r– 1 root root 46142944 Mar 12 00:54 qemu-user-static_7.2+dfsg-4_amd64.deb -rw-r–r– 1 root root 132001404 Mar 12 00:55 qemu-user-static-dbgsym_7.2+dfsg-4_amd64.deb -rw-r–r– 1 root root 1281392 Mar 12 00:55 qemu-utils_7.2+dfsg-4_amd64.deb -rw-r–r– 1 root root 8260576 Mar 12 00:52 qemu-utils-dbgsym_7.2+dfsg-4_amd64.deb ``` ## 4. Test ! ``` cd /home/roz/pkg-qemu-patching dpkg -i *.deb ``` </markdown>