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

[Christopher Allan Webber]

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.

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 <address@hidden>
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.
---
 gnu/build/vm.scm  | 19 ++++++++++++++-----
 gnu/system/vm.scm | 10 +++++++++-
 2 files changed, 23 insertions(+), 6 deletions(-)

diff --git a/gnu/build/vm.scm b/gnu/build/vm.scm
index a095f9d..823156d 100644
--- a/gnu/build/vm.scm
+++ b/gnu/build/vm.scm
@@ -1,5 +1,7 @@
 ;;; GNU Guix --- Functional package management for GNU
 ;;; Copyright © 2013, 2014, 2015 Ludovic Courtès <address@hidden>
+;;; Copyright © 2016 Christopher Allan Webber <address@hidden>
+;;; Copyright © 2016 Leo Famulari <address@hidden>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -97,7 +99,7 @@ the #:references-graphs parameter of 'derivation'."
     (_ #f))
 
   (unless (zero?
-           (apply system* qemu "-enable-kvm" "-nographic" "-no-reboot"
+           (apply system* qemu "-nographic" "-no-reboot"
                   "-m" (number->string memory-size)
                   "-net" "nic,model=virtio"
                   "-virtfs"
@@ -111,10 +113,17 @@ the #:references-graphs parameter of 'derivation'."
                   "-initrd" initrd
                   "-append" (string-append "console=ttyS0 --load="
                                            builder)
-                  (if make-disk-image?
-                      `("-drive" ,(string-append "file=" image-file
-                                                 ",if=virtio"))
-                      '())))
+                  (append
+                   (if make-disk-image?
+                       `("-drive" ,(string-append "file=" image-file
+                                                  ",if=virtio"))
+                       '())
+                   ;; Only enable kvm if we see /dev/kvm exists.
+                   ;; This allows uers without hardware virtualization to 
still use these
+                   ;; commands.
+                   (if (file-exists? "/dev/kvm")
+                       '("-enable-kvm")
+                       '()))))
     (error "qemu failed" qemu))
 
   (if make-disk-image?
diff --git a/gnu/system/vm.scm b/gnu/system/vm.scm
index a7c03bd..5235ee3 100644
--- a/gnu/system/vm.scm
+++ b/gnu/system/vm.scm
@@ -1,5 +1,7 @@
 ;;; GNU Guix --- Functional package management for GNU
 ;;; Copyright © 2013, 2014, 2015, 2016 Ludovic Courtès <address@hidden>
+;;; Copyright © 2016 Christopher Allan Webber <address@hidden>
+;;; Copyright © 2016 Leo Famulari <address@hidden>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -457,7 +459,13 @@ with '-virtfs' options for the host file systems listed in 
SHARED-FS."
                      "\" "))
 
   #~(string-append
-     " -enable-kvm -no-reboot -net nic,model=virtio \
+     ;; Only enable kvm if we see /dev/kvm exists.
+     ;; This allows uers without hardware virtualization to still use these
+     ;; commands.
+     #$(if (file-exists? "/dev/kvm")
+           " -enable-kvm "
+           "")
+     " -no-reboot -net nic,model=virtio \
   " #$@(map virtfs-option shared-fs) " \
   -net user \
   -serial stdio -vga std \
-- 
2.6.3