Re: [PATCH v3 2/2] xen/console: unify printout behavior for UART emulators

[Jan Beulich <jbeulich@xxxxxxxx>]

On 27.06.2025 23:58, Stefano Stabellini wrote:
> On Fri, 27 Jun 2025, Julien Grall wrote:
>> Hi Stefano,
>>
>> On 19/06/2025 01:45, Stefano Stabellini wrote:
>>> On Wed, 18 Jun 2025, Jan Beulich wrote:
>>>> On 18.06.2025 02:39, Stefano Stabellini wrote:
>>>>> On Thu, 12 Jun 2025, Jan Beulich wrote:
>>>>>> On 11.06.2025 21:07, Stefano Stabellini wrote:
>>>>>>> On Wed, 11 Jun 2025, Jan Beulich wrote:
>>>>>>>> On 11.06.2025 02:07, dmkhn@xxxxxxxxx wrote:
>>>>>>>>> On Tue, Jun 10, 2025 at 10:21:40AM +0200, Jan Beulich wrote:
>>>>>>>>>> On 06.06.2025 22:11, dmkhn@xxxxxxxxx wrote:
>>>>>>>>>>> From: Denis Mukhin <dmukhin@xxxxxxxx>
>>>>> If I understood correctly I like your proposal. Let me rephrase it to
>>>>> make sure we are aligned. You are suggesting that:
>>>>>
>>>>> - domains without input focus will print with a (d<N>) prefix
>>>>> - the domain with input focus will print without a (d<N>) prefix
>>>>> - this applies to both DomUs and Dom0
>>>>
>>>> Except in the non-dom0less case, at least up and until there's at least
>>>> one other domain. I.e. I'd like to keep Dom0 boot output as it is today,
>>>> regardless of the presence of e.g. "conswitch=".
>>>
>>> In the non-dom0less case, since dom0 has focus, it would naturally be
>>> without (d<N>) prefix. Unless the user passes "conswitch=". Honestly, I
>>> wouldn't special-case conswitch= that way and would prefer keep things
>>> simple and consistent without corner cases. I don't think conswitch= is
>>> so widely used that it is worth the complexity to special-case it.
>>
>> I am a bit confused with the wording. Before I can provide another opinion, I
>> want to understand a bit more the concern.
>>
>> From my understanding the command line option "conswitch" is to allow the
>> admin to change with key is used to switch between Dom0 and Xen. By default
>> this is 'a'. So are you referring to the fact a trailing "x" (to not switch 
>> to
>> dom0 console) can be added?
> 
> Yes, conswitch can also be used to ask Xen to keep the input focus to
> itself, instead of giving it away to Dom0. I think this is the specific
> feature Jan was referring to when he said he is using conswitch and the
> proposal would change the way the output looks like for him, which is
> true.
> 
> Today, dom0 would still print without any prefix.
> 
> Tomorrow with this proposal, dom0 would print with a "(d0)" prefix
> because it doesn't have input focus.
> 
> The question is, with the new policy in place, whether this is worth the
> trouble of having a special case to remove the "(d0)" prefix in the
> conswitch=x case. I think it is not worth it, Jan thinks it is.

Just to clarify: Along with this mode being entered by conswitch=, I also
expect the behavior to remain unaltered when booting (non-dom0less)
without that option, and later flipping focus between Xen and Dom0 by
using triple Ctrl-a. I'm saying this just to make sure that an eventual
change to the patch wouldn't be keyed to the use of the command line
option.

Jan