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

[dmkhn@xxxxxxxxx]

On Mon, Jun 30, 2025 at 03:27:32PM -0700, Stefano Stabellini wrote:
> On Mon, 30 Jun 2025, Stefano Stabellini wrote:
> > On Sun, 28 Jun 2025, 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.
> >
> > Oh, I see now where the difference of opinion lies. This is the policy
> > as written above:
> >
> > - 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
> >
> > Which means that when you move around with Ctrl-AAA or conswitch, no
> > matter if it is dom0less or not, Dom0 would end up printing the prefix
> > (d0).
> >
> > Jan, and now also Julien are saying that prefer to retain the old
> > behavior. I defer to the will of the majority. So then the policy would
> > be:
> >
> > Dom0less:
> > - 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
> >
> > Dom0:
> > - same as today
> > - the domain with input focus will print without a (d<N>) prefix
> 
> Sorry this last line was an editing error. I'll write it again for
> clarity.
> 
> Dom0less:
> - 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
> 
> Dom0:
> - same as today (with or without conswitch)

Thanks!

>