Re: [PATCH v2 16/35] xen/console: introduce printk_common()

[Denis Mukhin <dmkhn@xxxxxxxxx>]

On Thursday, December 12th, 2024 at 5:03 PM, Stefano Stabellini 
<sstabellini@xxxxxxxxxx> wrote:

>
>
> On Thu, 12 Dec 2024, Jan Beulich wrote:
>
> > On 12.12.2024 13:15, Roger Pau Monné wrote:
> >
> > > On Thu, Dec 12, 2024 at 12:57:25PM +0100, Jan Beulich wrote:
> > >
> > > > On 12.12.2024 10:14, Roger Pau Monné wrote:
> > > >
> > > > > On Thu, Dec 05, 2024 at 08:41:46PM -0800, Denis Mukhin via B4 Relay 
> > > > > wrote:
> > > > >
> > > > > > From: Denis Mukhin dmukhin@xxxxxxxx
> > > > > >
> > > > > > Introduce new printk() variant for convenient printouts which skip 
> > > > > > '(XEN)'
> > > > > > prefix on xen console. This is needed for the case when physical 
> > > > > > console is
> > > > > > owned by a domain w/ in-hypervisor UART emulation enabled.
> > > > >
> > > > > IIRC the ns8250 can only send or receive one byte (character) at a
> > > > > time, so you should likely put that on the console as soon as it's
> > > > > received?
> > > > >
> > > > > For the hardware domain we explicitly don't buffer writes to the
> > > > > console (see guest_console_write() hardware domain special handling).
> > > > >
> > > > > I wonder however how you deal with domains that don't have the console
> > > > > focus (ie: != console_rx), as for those I think you still want to use
> > > > > the (d<domid>) prefix?
> > > >
> > > > Imo no matter what domain has the focus, the (d<domid>) prefix should
> > > > always be logged. Just to avoid possible confusion.
> > >
> > > WE don't do that currently for the hardware domain, because we avoid
> > > doing any kind of line processing, as characters from the hardware
> > > domain are send straight to the console without waiting for the
> > > newline terminator (like we do for other domains).
> >
> > Right, and that's kind of special, and aiui intentionally so. These are
> > the only un-prefixed lines logged.
>
>
> I think we should provide a consistent behavior across architectures.
> The current behavior with vpl011 and dom0less on ARM is the following:
>
> - no prefix for Dom0 output
> - DOM$NUM for DomUs when not in focus, otherwise no prefix
>
> It is OK to change this behavior, but in that case I would ask that we
> change it consistently also for ARM.

Addressed in v3.

>
> > > Are you suggesting that in case of the console input being shared
> > > between multiple domains they should all be treated as plain domUs and
> > > thus lines should be buffered?
> >
> > No, I'm actually not suggesting anything here beyond perhaps reducing
> > the scope of this series to just what the equivalent of vpl011 would be
> > for the 8250 / 16550 case.
>
>
> I agree with this