Re: [Qemu-devel] [RFC PATCH] hw/s390x: Allow to configure the consoles with the "-serial" parameter

[Thomas Huth <thuth@redhat.com>]

On 24.04.2018 13:49, Christian Borntraeger wrote:
> 
> 
> On 04/24/2018 01:44 PM, Thomas Huth wrote:
>> The consoles ("sclpconsole" and "sclplmconsole") can only be configured
>> with "-device" and "-chardev" so far. Other machines use the convenience
>> option "-serial" to configure the default consoles, too, even for virtual
>> consoles like spapr-vty on the pseries machine. So let's support this
>> option on s390x, too, so we can easily enable the serial console here
>> again with "-nodefaults", for example. Also map the second -serial
>> option to the "sclplmconsole", so that there is now an easy way to
>> configure this second console on s390x, too.
>> Additionally, the new code is also smaller than the old one and we have
>> less s390x-specific code in vl.c :-)
> 
> Can you show some new example command lines?

Sure. I'm mainly using this together with nodefaults:

qemu-system-s390x -no-shutdown -nographic -nodefaults -serial mon:stdio

That's way easier than typing:

qemu-system-s390x -no-shutdown -nographic -nodefaults \
  -chardev stdio,id=c1,mux=on -device sclpconsole,chardev=c1 \
  -mon chardev=c1

Another example: You only want to see the QEMU monitor on stdio, but not
the serial output, without using -nodefaults (i.e. you still want to
have the other default devices). AFAIK that's pretty impossible with the
current code. But once you've got this patch applied, you can do:

qemu-system-s390x -no-shutdown -nographic -serial none

And to view the sclplm console, you can now simply do:

qemu-system-s390x -no-shutdown -nographic -serial null -serial mon:stdio

> I read that as "the current command lines continue to work". Correct?

Right. I was a little bit afraid that this might break migration, but I
gave it a quick check and it still seems to work fine here.
"info qom-tree" and "info qtree" at the HMP monitor show slightly
different output, though ... not sure whether that's critical or not?

 Thomas