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

["Roger Pau Monné" <roger.pau@citrix.com>]

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@ford.com>
> >>
> >> 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).

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?

Thanks, Roger.