gitlab_runner: Fix broken "Running on ..." in the libvirt-executor

The prepare stage runs "echo "Running on $(hostname)...""[1], resulting
in "bash: line 7: hostname: command not found" and it outputting
"Running on ..." as the hostname command is provided by inetutils, which
is not installed.

Fix it by "monkey patching" it to use "hostnamectl hostname" and inject
the hostname with SMBIOS[2][3]. Injecting creds with SMBIOS may also be
useful in the future, e.g. for injecting an ephemeral SSH public key.

[1] https://gitlab.com/gitlab-org/gitlab-runner/-/blob/v17.5.2/shells/bash.go?ref_type=tags#L452-L456
[2] https://systemd.io/CREDENTIALS/
[3] https://github.com/systemd/systemd/pull/30814

roles/gitlab_runner/files/libvirt-executor

@@ -69,7 +69,13 @@ prepare() {
 run() {
   local ip
   ip="$(vm_ip "$(vm_name)")"
-  ssh "${ip}" bash < "${1}" || exit "${BUILD_FAILURE_EXIT_CODE:-1}"
+  if [[ ${2} == prepare_script ]]; then
+    # TODO: Get this fixed upstream or perhaps we should just install inetutils?
+    # https://gitlab.com/gitlab-org/gitlab-runner/-/blob/v17.5.2/shells/bash.go?ref_type=tags#L452-L456
+    ssh "${ip}" bash < <(sed 's/$(hostname)/$(hostnamectl hostname)/' "${1}") || exit "${BUILD_FAILURE_EXIT_CODE:-1}"
+  else
+    ssh "${ip}" bash < "${1}" || exit "${BUILD_FAILURE_EXIT_CODE:-1}"
+  fi
 }
 
 # https://docs.gitlab.com/runner/executors/custom.html#cleanup

roles/gitlab_runner/files/libvirt-executor-update-base-image

@@ -43,7 +43,9 @@ sed 's/^\(GRUB_CMDLINE_LINUX=".*\)"$/\1 lockdown=confidentiality"/' -i mnt/etc/d
 arch-chroot mnt /usr/bin/grub-mkconfig -o /boot/grub/grub.cfg
 install -d -m0700 mnt/root/.ssh
 install -m0600 /etc/libvirt-executor/id_ed25519.pub mnt/root/.ssh/authorized_keys
-rm -f mnt/etc/machine-id
+# We want to use the transient hostname
+# https://github.com/systemd/systemd/pull/30814
+rm -f mnt/etc/machine-id mnt/etc/hostname
 
 cp -a mnt/boot/{initramfs-linux-fallback.img,initramfs-linux.img}
 

roles/gitlab_runner/templates/domain_template.xml.j2

@@ -2,8 +2,14 @@
   <name>$vm_name</name>
   <memory unit='MiB'>{{ gitlab_runner_libvirt_vm_memory }}</memory>
   <vcpu>4</vcpu>
+  <sysinfo type='smbios'>
+    <oemStrings>
+      <entry>io.systemd.credential:system.hostname=$vm_name</entry>
+    </oemStrings>
+  </sysinfo>
   <os>
     <type arch='x86_64' machine='q35'>hvm</type>
+    <smbios mode='sysinfo'/>
   </os>
   <features>
     <acpi/>