Re: qemu and -vga vs. -device

[Daniel Henrique Barboza <danielhb413@gmail.com>]

Hi Adam,

On 9/26/22 06:26, Gerd Hoffmann wrote:
> On Sat, Sep 24, 2022 at 12:12:45AM -0700, Adam Williamson wrote:
>> On Mon, 2022-09-19 at 06:42 +0200, Gerd Hoffmann wrote:
>>> On Fri, Sep 16, 2022 at 10:02:17AM -0700, Adam Williamson wrote:
>>>> Hi Gerd!
>>>>
>>>> I'm working on a patch to revise how openQA sets video devices in qemu.
>>>> In that context, a question: if we always want to specify a single
>>>> video device with `-device` (e.g. `-device VGA` or `-device virtio-
>>>> vga`), should we also specify `-vga none` to ensure qemu doesn't also
>>>> include another adapter as a default for the -vga arg?
>>>
>>> Doesn't hurt to include it.  In theory it should not be needed, qemu has
>>> a list of vga devices and in case '-device $vga' is found on the command
>>> line will turn off the default vga device automatically.  In practice
>>> there are qemu versions where this list is not complete, so it
>>> sometimes doesn't work as intended.
>>>
>>> Alternatively use '-nodefaults' which will disable all automatically
>>> added devices (vga, nic, cdrom, ...).
>>
>> Thanks Gerd!
>>
>> So, I got around to testing this today, and found something
>> interesting. On ppc64le, adding `-vga none` seems to break things.
>> Booting a Fedora installer ISO, which should show the boot menu with a
>> 60 second timeout then boot to the installer, if we run the VM with `-
>> vga std`, we see the bootloader. If we run it with `-device VGA` and no
>> `-vga` arg, we see the bootloader. But if we run qemu with `-vga none -
>> device VGA`, we don't see the bootloader. The system just sits at the
>> OFW init screen apparently forever (I thought it might actually be
>> running in the background and recover to anaconda after the 60 second
>> boot timeout, but it doesn't seem to).
>>
>> Not sure what's going on there, but thought you might be interested.

Can you please send the full command line you're using?

I'm actually surprised that you can combo '-vga none -display VGA' together
in the command line is executed without a parse error.


This also works, which is also surprising to me:


(launches the process with the 'curses' display)
./qemu-system-ppc64 -M pseries -display none -display curses


(launches with the 'none' display)
./qemu-system-ppc64 -M pseries -display curses -display none


It seems that we're considering just the last entry as valid.

Should I send a patch to make QEMU error out when multiple '-display'
options are present in the command line?



Thanks,


Daniel

> 
> Hmm, no clue offhand.  Cc'ing qemu-ppc list (+ keeping full context).
> 
> I know ppc has some vga quirks in the machine init code path, switching
> framebuffer byteorder to bigendian for example, maybe more.  Possibly
> something goes wrong there.
> 
> take care,
>    Gerd
> 
>