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

[dmkhn@xxxxxxxxx]

On Sun, Jun 29, 2025 at 03:47:41PM +0200, Jan Beulich wrote:
> 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.

I will preserve the existing non-dom0less dom0 behavior for printouts.
Thanks for the patience and the feedback!

> 
> Jan