Built and tested basic functionality 👍

Hey,

thanks for this!
I have had some issues when using a local nixpkgs checkout with this PR applied and trying to switch to a system configuration with boot.binfmt.emulatedSystems = [ "aarch64-linux" ]; enabled.

I have investigated it a bit and here are my findings:

When enabling the emulatedSystems option, a special overridden version of the QEMU package is built which has the following hardcoded flags:

This sets, in my case, --target-list=aarch64-linux-user.

Since at least 2019, QEMU disables the guest agent when no system emulation is required, and I am fairly certain this is what happens when passing a target which ends with -user. However, this package always exports the guest agent as an output:

https://github.com/NixOS/nixpkgs/blob/85aafb5ed958e71fd2c073acf99b37ea88f65584/pkgs/applications/virtualization/qemu/default.nix#L74

This causes my build to fail during the fixup phase, as it's expecting a binary in the ga output directory. I fixed it by temporarily removing the ga output, but I'm unsure if my issues derive from something I am doing wrong or if this is an actual problem.

Moreover, I am not sure what would be the best (and most idiomatic) way to solve this. What do you think?

I can confirm that using the existing derivation (4.2.0) the guest agent is built, even if not necessary/used at all:

configuring
configure flags: --disable-dependency-tracking --prefix=/nix/store/s8cv8wa06d16w77ws1fnjf3f1amfq92l-qemu-4.2.0 --bindir=/nix/store/s8cv8wa06d16w77ws1fnjf3f1amfq92l-qemu-4.2.0/bin --sbindir=/nix/store/s8cv8wa06d16w77ws1fnjf3f1amfq92l-qemu-4.2.0/sbin --includedir=/nix/store/s8cv8wa06d16w77ws1fnjf3f1amfq92l-qemu-4.2.0/include --oldincludedir=/nix/store/s8cv8wa06d16w77ws1fnjf3f1amfq92l-qemu-4.2.0/include --mandir=/nix/store/s8cv8wa06d16w77ws1fnjf3f1amfq92l-qemu-4.2.0/share/man --infodir=/nix/store/s8cv8wa06d16w77ws1fnjf3f1amfq92l-qemu-4.2.0/share/info --docdir=/nix/store/s8cv8wa06d16w77ws1fnjf3f1amfq92l-qemu-4.2.0/share/doc/ --libdir=/nix/store/s8cv8wa06d16w77ws1fnjf3f1amfq92l-qemu-4.2.0/lib --libexecdir=/nix/store/s8cv8wa06d16w77ws1fnjf3f1amfq92l-qemu-4.2.0/libexec --localedir=/nix/store/s8cv8wa06d16w77ws1fnjf3f1amfq92l-qemu-4.2.0/share/locale --audio-drv-list=alsa\, --sysconfdir=/etc --localstatedir=/var --enable-docs --enable-numa --target-list=aarch64-linux-user --enable-linux-aio
[...]
build guest agent yes

So either we always build the guest agent even if unneeded or add some logic which detects when it's built and when not.

Hey there! I've tried to run nixpkgs-review on macOS to help with the unset check, but either I've used the tool incorrectly (first time I've tried that) or there is some issue with building:

Result of nixpkgs-review pr 86291 1

Hey there! I've tried to run nixpkgs-review on macOS to help with the unset check, but either I've used the tool incorrectly (first time I've tried that) or there is some issue with building:

Result of nixpkgs-review pr 86291 1

11 package marked as broken and skipped:
4 package failed to build:

Hey, thanks for testing! Can you upload the build log for the qemu package on some pastebin service?

Can we add "--enable-guest-agent" to the configure flags to always build the guest agent? That would allow us to not change too many things about the current assumptions of the derivation. @Robertof can you test whether your build problems go away when you add that flag to the array around line 105?

@clefru I can confirm that this diff:

diff --git a/pkgs/applications/virtualization/qemu/default.nix b/pkgs/applications/virtualization/qemu/default.nix
index 9ff2f06d..62a9e533 100644
--- a/pkgs/applications/virtualization/qemu/default.nix
+++ b/pkgs/applications/virtualization/qemu/default.nix
@@ -107,6 +107,8 @@ stdenv.mkDerivation rec {
       "--sysconfdir=/etc"
       "--localstatedir=/var"
       "--enable-docs"
+      "--enable-tools"
+      "--enable-guest-agent"
     ]
     # disable sysctl check on darwin.
     ++ optional stdenv.isDarwin "--cpu=x86_64"

fixes the issue with boot.binfmt.emulatedSystems = [ "aarch64-linux" ]; 👍

There is this weird (non-fatal) "no such file or directory":

patching script interpreter paths in /nix/store/b2k55yi7gz9ymq7bfgwx8zl64pww9zpz-qemu-5.0.0
checking for references to /build/ in /nix/store/b2k55yi7gz9ymq7bfgwx8zl64pww9zpz-qemu-5.0.0...
cannot find section .dynamic
cannot find section .dynamic
cannot find section .dynamic
cannot find section .dynamic
cannot find section .dynamic
cannot find section .dynamic
find: '/nix/store/zlqhgxwz0klwh7xpb6waqy0p3xdwiqyn-qemu-5.0.0-ga': No such file or directory
strip is /nix/store/1zf4cnaaidjajwb4gx4mnkqc5dypkcdy-binutils-2.31.1/bin/strip
building '/nix/store/nkn0nlk68p8a0nyf9kzafv0cn2zch3ik-dbus-1.drv'..

but it was there even with qemu-4.2.0 so I'd say it's ok.

NOTE: --enable-tools is required as it was made non-default a while ago, and guest-agent is automatically disabled if tools are disabled and QEMU is compiling user-only

Successfully built on macOS!

reviewer tool is trying to build linux-only packages for some reason (maybe it is designed this way and it's my bad I was trying to use it on macOS), so I've built it manually.

When will this hit master? I'd like to add virtiofsd support and I don't want to work on top of staging.

It's already in staging-next if you don't want to work on top of staging
But yeah, I wait for it to hit master too.

@clefru I've been using virtiofsd on this commit -- what do you mean by that? The only issue is that the daemon is in libexec instead of bin.

Thanks @JJJollyjim. When I commented, I haven't seen that yet. Sorry for the noise.

For the record, virtiofsd is working fine for me. I manually spawn it via this systemd unit:

  systemd.services.virtiofsd-siona = {
    wantedBy = [ "multi-user.target" ];
    before = [ "libvirtd.service" ];
    path = [ pkgs.qemu ];
    serviceConfig =
      { ExecStart = pkgs.writeScript "virtiofsd-loop" ''#!/bin/sh
            while true; do ${pkgs.qemu}/libexec/virtiofsd --socket-path=/var/lib/libvirt/siona-vhost-socket -o no_flock -o no_posix_lock -o source=/z/siona -o cache=always; done
'';         
        User = "root";
        Restart = "always";
      };
  };