[virt-tools-list] [virt-manager PATCH] Allow installation of i686 guests on x86_64 machines

[Martin Kletzander]

On Sat, Mar 03, 2018 at 03:53:59PM -0500, Cole Robinson wrote:
>On 03/01/2018 03:52 AM, Martin Kletzander wrote:
>> Do that by changing the code that was disabling it into code that just warns in
>> such case.
>>
>> Signed-off-by: Martin Kletzander <mkletzan at redhat.com>
>> ---
>>  virtManager/create.py | 10 ++++------
>>  1 file changed, 4 insertions(+), 6 deletions(-)
>>
>> diff --git a/virtManager/create.py b/virtManager/create.py
>> index 0a73309372d9..9a40aec4a068 100644
>> --- a/virtManager/create.py
>> +++ b/virtManager/create.py
>> @@ -495,6 +495,10 @@ class vmmCreate(vmmGObjectUI):
>>                  msg = _("Failed to setup UEFI for AArch64: %s\n"
>>                          "Install options are limited.") % e
>>                  self._show_arch_warning(msg)
>> +        elif (self._capsinfo.arch == "i686" and
>> +              self.conn.caps.host.cpu.arch == "x86_64"):
>> +            msg = _("You are installing 32bit guest on 64bit host")
>> +            self._show_arch_warning(msg)
>>
>>          # Install Options
>>          method_tree = self.widget("method-tree")
>> @@ -824,12 +828,6 @@ class vmmCreate(vmmGObjectUI):
>>              if guest.os_type == self._capsinfo.os_type:
>>                  archs.append(guest.arch)
>>
>> -        # Combine x86/i686 to avoid confusion
>> -        if (self.conn.caps.host.cpu.arch == "x86_64" and
>> -            "x86_64" in archs and "i686" in archs):
>> -            archs.remove("i686")
>> -        archs.sort()
>> -
>>          prios = ["x86_64", "i686", "aarch64", "armv7l", "ppc64", "ppc64le",
>>              "s390x"]
>>          if self.conn.caps.host.cpu.arch not in prios:
>>
>
>The idea behind hiding the option is 1) it should be rare that someone
>actually wants their VM to present a 32bit cpu on 64bit host, 2) hiding
>it means when only x86_64 qemu is installed we can entirely hide the
>'advanced options' expander.
>
>Example: on rhel7 x86_64, libvirt advertises arch=i686 and arch=x86_64
>for /usr/libexec/qemu-kvm. If we hide i686, there's only one arch option
>available, and virt-manager will hide the entire 'advanced options'
>expander. This is ideal IMO, otherwise users might go clicking, see the
>i686 option, misinterpret it to mean OS arch (which in the context of
>virt I've seen people mistake many times), set things to i686 needlessly.
>

Sure I get that, that's why I kept it as a warning.

>Are there benefits I'm missng of doing arch=i686 on an x86_64 host
>exactly? Doesn't it just map to using qemu32 as the default CPU?
>

To be honest, I'm not sure if qemu32 CPU type means also 32bit CPU or
just limited instruction set and how it looks from the guest OS POV.
The reason for this patch emerged simply when we needed to test libvirt
build failure on 32bit machine and it was just easier to install 32bit
VM than setting up a cross-build.  Or rather installing all 32bit
dependencies properly.  I'd love to hear how to do this properly, I'm
not saying this patch is needed =)

>Thanks,
>Cole
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