Re: [RFC PATCH 04/11] kvm tools: console: unconditionally output to any console

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On Fri, May 3, 2013 at 5:19 PM, Pekka Enberg <penberg@xxxxxxxxxx> wrote:
> On Wed, May 1, 2013 at 6:50 PM, Will Deacon <will.deacon@xxxxxxx> wrote:
>> From: Marc Zyngier <Marc.Zyngier@xxxxxxx>
>>
>> Kvmtool suppresses any output to a console that has not been elected
>> as *the* console.
>>
>> While this makes sense on the input side (we want the input to be sent
>> to one console driver only), it seems to be the wrong thing to do on
>> the output side, as it effectively prevents the guest from switching
>> from one console to another (think earlyprintk using 8250 to virtio
>> console).
>>
>> After all, the guest *does* poke this device and outputs something
>> there.
>>
>> Just remove the kvm->cfg.active_console test from the output paths.
>>
>> Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx>
>> Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
>
> Seems reasonable. Asias, Sasha?

This patch itself looks good to me.

But we have more issues for the console devices and termials with
regard to multiple console support:

1) All the console outputs (spapr_hvcons.c, spapr_rtas.c
virtio/console.c) are redirected to term 0.
2) With multiple console support, the cfg.active_console logic is not
very useful at all.
3) Four serial devices ttyS0-3 are initialized unconditionally and
mapped to term 0-3.
4) Using --tty option, we can map a term to /dev/pts/N on host. I
think we can merge --tty option to --console option.

I have something like this in my mind:

--console type=serial,backend=stdio
--console type=virtio,backend=pts
--console type=hv,backend=pts

e.g to add two serial consoles ttyS0 and ttyS1 and one virtio console
hvc0, ttyS0 is mapped the stdio and ttyS1 and hvc0 are mapped to pts,
we use this:

--console type=serial,backend=stdio  --console type=serial,backend=pts
 --console type=virtio,backend=pts


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