Find qemu in /usr/libexec or via qemu-system-$(arch)

[cgwalters]

qemu-kvm is going away in Fedora; invoke qemu how libvirt does it.

Similarly on RHEL, it's in /usr/libexec as QEMU is an implementation
detail of libvirt (or something), so let's find it there.

[miabbott]

You have to appease the ShellCheck gods, otherwise LGTM

[r4f4]

Shouldn't you also update the qemu call inside the qemu_wrapper script in src/gf-oemid?

[cgwalters]

Shouldn't you also update the qemu call inside the qemu_wrapper script in src/gf-oemid?

Oh wow I forgot about that one. I think that one is mostly x86_64 specific for now, but yeah let's wrap it too.

[cgwalters]

Updated 🆕

[cgwalters]

This should fix #314
and #328
(But I didn't explicitly test either of those either)

[dustymabe]

(But I didn't explicitly test either of those either)

asked @r4f4 to review and also test this on other architectures

[r4f4]

It'll still fail on other arches because of some arch specific options, e.g, no KVM on aarch64 and the binary being qemu-system-ppc64 on ppc64le. I have a patch to fix those issues but testing on all arches takes a long time.

[dustymabe]

I have a patch to fix those issues but testing on all arches takes a long time.

in that case we can focus on x86_64 here and do a follow up for the others.

[miabbott]

FWIW, when using this patch in an EL7 cosa, the next papercut is:

+ exec /usr/libexec/qemu-kvm -name coreos -m 2048 -nographic -netdev user,id=eth0,hostname=coreos -device virtio-net-pci,netdev=eth0 -object rng-random,filename=/dev/urandom,id=rng0 -device virtio-rng-pci,rng=rng0 -drive if=virtio,cache=unsafe,file=builds/47.6-1/redhat-coreos-maipo
-47.6-1-qemu.qcow2 -snapshot -fw_cfg name=opt/com.coreos/config,file=/proc/self/fd/3 -machine accel=kvm -cpu host -smp 4
qemu-kvm: -fw_cfg: invalid option                                 

EL7 ships an embarassingly old version of qemu-kvm:

$ /usr/libexec/qemu-kvm --version
QEMU emulator version 1.5.3 (qemu-kvm-1.5.3-160.el7_6.1), Copyright (c) 2003-2008 Fabrice Bellard

And support for -fw_cfg was added in v2.4 - qemu/qemu@81b2b81

Me right now: 😭

[cgwalters]

And support for -fw_cfg was added in v2.4 - qemu/qemu@81b2b81

I would really hope we can focus on RHEL8 soon.

But if not remember there are actually two qemu packages/streams in RHEL7. The one that gets rebased regularly is called qemu-kvm-rhev.

[miabbott]

I would really hope we can focus on RHEL8 soon.

This papercut has put me over the edge...I'm refocusing on EL8 today.

[ashcrow]

As long as it works I'm fine with rhel 8 or 7.

[cgwalters]

Relatedly in RHEL7 (at least initially) libguestfs used qemu directly. In RHEL8 it defaults to running via libvirt. I think the reason they did this I suspect is maintaining the qemu abstraction (including which args are available on which architectures) is a nontrivial maintenance task.

The problem with this though is we really don't want a persistent daemon...but if we have to we can suck it up and try switching to libvirt across the board.

[miabbott]

Noting that we need additional fixes for non x86_64 arches, this helps the EL7 cause, and is required by #344...

Any reasons not to merge this?

[cgwalters]

Yeah, let's merge. Clearly not the end state as someone noted it's qemu-system-ppc64 and not ppc64le or something but at least we're converging.