bug#42129: guix-install.sh does not add build users to kvm group

[Leo Famulari <leo@famulari.name>]

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On Thu, Apr 08, 2021 at 06:38:59PM -0400, Leo Famulari wrote:
> On Mon, Jun 29, 2020 at 10:01:54PM +0200, Marius Bakke wrote:
> > guix-install.sh should add the build users to the 'kvm' group if present
> > so that commands that require use of KVM can succeed.
> 
> Here is a patch (untested) that makes sure a 'kvm' group exists and adds
> it to the guixbuilders' groups.

I realized that you specified that the build users should be added to
the kvm group 'if' it is present. So, here is a revised patch.

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From 1a9fd7decd843f21c36d8ec4d1e218f478b983cf Mon Sep 17 00:00:00 2001
From: Leo Famulari <leo@famulari.name>
Date: Thu, 8 Apr 2021 18:34:43 -0400
Subject: [PATCH v2] guix-install.sh: Add the build users to the 'kvm' group.

* etc/guix-install.sh (sys_create_build_user): If a 'kvm' group exists,
add it to the guixbuilders' lists of supplementary groups.
---
 etc/guix-install.sh | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/etc/guix-install.sh b/etc/guix-install.sh
index c84e7b7577..f3fcbf5d05 100755
--- a/etc/guix-install.sh
+++ b/etc/guix-install.sh
@@ -330,15 +330,20 @@ sys_create_build_user()
         _msg "${PAS}group <guixbuild> created"
     fi
 
+    if [ $(getent group kvm) ]; then
+        _msg "${INF}group kvm exists and build users will be added to it"
+	local KVMGROUP=,kvm
+    fi
+
     for i in $(seq -w 1 10); do
         if id "guixbuilder${i}" &>/dev/null; then
             _msg "${INF}user is already in the system, reset"
-            usermod -g guixbuild -G guixbuild           \
+            usermod -g guixbuild -G guixbuild{$KVMGROUP}     \
                     -d /var/empty -s "$(which nologin)" \
                     -c "Guix build user $i"             \
                     "guixbuilder${i}";
         else
-            useradd -g guixbuild -G guixbuild           \
+            useradd -g guixbuild -G guixbuild{$KVMGROUP}     \
                     -d /var/empty -s "$(which nologin)" \
                     -c "Guix build user $i" --system    \
                     "guixbuilder${i}";
-- 
2.31.1


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