bug#22633: Provide a kvm-less qemu / guix system vm

[Christopher Allan Webber <cwebber@dustycloud.org>]

Ludovic Courtès writes:

> Christopher Allan Webber <cwebber@dustycloud.org> skribis:
>
>> Christopher Allan Webber writes:
>>
>>> Ludovic Courtès writes:
>>>
>>>> Libkmod honors ‘modprobe.blacklist’ (in ‘kcmdline_parse_result’ in
>>>> libkmod-config.c) and eudev passes KMOD_PROBE_APPLY_BLACKLIST
>>>> unconditionally in udev-builtin-kmod.c (meaning it honors it too.)
>>>>
>>>> However, there’s a hyphen-vs-underscore issue, I think.  Namely, the
>>>> file is called ‘kvm-intel.ko’, but the normalized module name is
>>>> ‘kvm_intel’, and this is what libkmod expects (commit 5c7dd5a changes
>>>> our code to normalize module names similarly.)
>>>>
>>>> Could you try with “modprobe.blacklist=kvm_intel”?
>>>
>>> I tried it, and it works!  This does mean that /dev/kvm doesn't exist,
>>> so I should be able to write a patch to Guix that disables kvm for qemu
>>> when /dev/kvm is absent.  Great! :)
>>
>> This is slightly based off of Leo's preliminary patch, so I included him
>> in the copyright headers.  I've tested and it works (in terms of
>> disabling kvm if no /dev/kvm is present) here.
>
> Cool!  Can you just double-check whether -enable-kvm has any effect when
> /dev/kvm is missing?  If it has no effect when /dev/kvm is missing, then
> we don’t even need a patch.

I checked yes; qemu fails.

>> Let me know if I need to fix something or if I should push...
>>
>> From 852e0049213a0a80cacdcad4aba13ab242c3fbd8 Mon Sep 17 00:00:00 2001
>> From: Christopher Allan Webber <cwebber@dustycloud.org>
>> Date: Mon, 22 Feb 2016 11:23:14 -0800
>> Subject: [PATCH] vm: Only pass "-enable-kvm" to qemu if /dev/kvm is present.
>>
>> * gnu/build/vm.scm (load-in-linux-vm): Only pass "-enable-kvm" flag to qemu
>>   if "/dev/kvm" is present.
>> * gnu/system/vm.scm (common-kvm-options): Same as above.
>
> [...]
>
>> +                   ;; Only enable kvm if we see /dev/kvm exists.
>> +                   ;; This allows uers without hardware virtualization to still use these
>                                      ^^
> Typo.
>
> [...]
>
>> +     ;; Only enable kvm if we see /dev/kvm exists.
>> +     ;; This allows uers without hardware virtualization to still use these
>
> Ditto.

Okay, fixed those.

> Otherwise the patch LGTM.  Make sure to mention:
>
>   Fixes <http://bugs.gnu.org/22633>.
>
> in the commit log.

Mentioned, committed, pushed!