Context:
https://github.com/openshift/os/pull/1350#issuecomment-1708486101

1. Test manually with `-cdrom`, which is ide controller by default

- run `eject`, device `/dev/sr0` can not be removed
- run `device_del`, delete `/dev/sr0` failed as `Bus 'ide.1' does not support hotplugging`

# first boot
IGNITION_CONFIG="/home/fedora/ign/ssh.ign"
IGNITION_DEVICE_ARG="-fw_cfg name=opt/com.coreos/config,file=${IGNITION_CONFIG}"
qemu-kvm -m 4096 -cpu host -nographic \
  -drive if=virtio,file=qmp.qcow2 ${IGNITION_DEVICE_ARG}\
  -cdrom test.iso \
  -qmp-pretty tcp::8888,server,nowait
  
qemu-kvm -m 4096 -cpu host -nographic \
  -drive if=virtio,file=qmp.qcow2 \
  -cdrom test.iso \
  -qmp-pretty tcp::8888,server,nowait

$ telnet localhost 8888
# Issue the qmp_capabilities command, so that QMP enters command mode
{"execute":"qmp_capabilities"}

# Get a list of BlockInfo for all virtual block devices.
{ "execute": "query-block" }

{"execute":"eject","arguments":{"device":"ide1-cd0","force":true}}

# Remove a device from a guest
{ "execute": "device_del", "arguments": { "id": "/machine/unattached/device[24]" } }
{
    "error": {
        "class": "GenericError",
        "desc": "Bus 'ide.1' does not support hotplugging"
    }
}

2. Test manually with scsi cdrom,
- run `device_del`, delete `/dev/sr0` successfully
(maybe this is what we want?)

qemu-kvm -m 4096 -cpu host -nographic \
  -drive if=virtio,file=/home/fedora/data/qmp.qcow2 \
  -drive id=cdrom0,if=none,readonly=on,file=/home/fedora/data/test.iso \
  -device virtio-scsi-pci,id=scsi0 \
  -device scsi-cd,bus=scsi0.0,drive=cdrom0 \
  -qmp-pretty tcp::8888,server,nowait

telnet localhost 8888
{"execute":"qmp_capabilities"}

# This command will list any properties of a object given a path in the object model.
{ "execute": "qom-list", "arguments": { "path": "/machine/peripheral-anon" } }
{
    "return": [
        {
            "name": "type",
            "type": "string"
        },
        {
            "name": "device[0]",
            "type": "child<scsi-cd>"
        },
        {
            "name": "device[1]",
            "type": "child<virtio-blk-pci>"
        }
    ]
}
[core@localhost ~]$ ls /dev/sr0 
/dev/sr0

{ "execute": "device_del", "arguments": { "id": "/machine/peripheral-anon/device[0]" } }
{
    "return": {
    }
}
{
    "timestamp": {
        "seconds": 1694173073,
        "microseconds": 162006
    },
    "event": "DEVICE_DELETED",
    "data": {
        "path": "/machine/peripheral-anon/device[0]"
    }
}
[core@localhost ~]$ ls /dev/sr0 
ls: cannot access '/dev/sr0': No such file or directory

3. Make a little change, build and testing, will remove device `/dev/sr0`.

See https://github.com/coreos/coreos-assembler/commit/a1a00472b3070c87b68026828a259a789f0f6546

podman build -t localhost/coreos-assembler .
export COREOS_ASSEMBLER_CONTAINER=localhost/coreos-assembler
$ cosa shell
[coreos-assembler]$ env COSA_TEST_CDROM_UNPLUG=8s cosa run qemu.qcow2 --debug -- \
-drive id=cdrom0,if=none,readonly=on,file=/srv/test.iso \
-device virtio-scsi-pci,id=scsi0 \
-device scsi-cd,bus=scsi0.0,drive=cdrom0
...
2023-09-12T10:54:08Z platform: get cdrom id /machine/peripheral-anon/device[2]
[STARTUP] '2023-09-12T10:54:13Z platform: delete cdrom
...
[core@cosa-devsh ~]$ ls /dev/sr0
ls: cannot access '/dev/sr0': No such file or directory

Reference:
https://wiki.qemu.org/Documentation/QMP
https://qemu-project.gitlab.io/qemu/interop/qemu-qmp-ref.html