remove qemu:commandline after first start (at least give a hint in documentation)

[pampelmuse76]

Describe the bug

Creating a CoreOS VM with kickstart using an ign file, the ign file must not be removed.

Reproduction steps

1. Create a CoreOs VM with an ignition file:
   virt-install
   --name core1
   [...]
   --qemu-commandline="-fw_cfg name=opt/com.coreos/config,file=/tmp/coreos_5988.ign"
2. Stop the VM (with login and shutdown)
3. Remove the ignition file: rm /tmp/coreos_5988.ign
4. Tring to restart the VM

virsh start core1
gives:
error: Failed to start domain 'core1'
error: internal error: qemu unexpectedly closed the monitor: 2023-02-04T17:40:10.657128Z qemu-system-x86_64: -fw_cfg name=opt/com.coreos/config,file=/tmp/coreos_5988.ign: can't load /tmp/coreos_5988.ign: Failed to open file “/tmp/coreos_5988.ign”: No such file or directory

Expected behavior

Removing of the ign file should be possible.

Actual behavior

There must be a manual interaction.
(see Additional information)

System details

virt-install
--name core1
--vcpus 2
--memory 4096
--disk vol=m2ssd/core1
--os-variant fedora-coreos-stable
--network bridge=virbr0
--mac=${MAC}
--import
--graphics none
--noautoconsole
--qemu-commandline="-fw_cfg name=opt/com.coreos/config,file=/tmp/coreos_5988.ign"

Ignition config

variant: fcos
version: 1.4.0
passwd:
users:
- name: core
ssh_authorized_keys:
- ssh-rsa [...]

Additional information

I can "solve" this problem by using

virsh edit core1
and than removing the following part at the end of the file:
qemu:commandline
<qemu:arg value='-fw_cfg'/>
<qemu:arg value='name=opt/com.coreos/config,file=/tmp/coreos_5988.ign'/>
</qemu:commandline>

[dustymabe]

Right. There's no way to make it optional. As you found out you must review it from the machine definition.

We can improve our docs around this. We'd probably need to edit https://github.com/coreos/fedora-coreos-docs/blob/main/modules/ROOT/pages/getting-started-libvirt.adoc

[pampelmuse76]

I suggest adding the following hint:

virt-xml core1 --edit --xml xpath.delete=./qemu:commandline