Re: [PATCH v1 2/2] xen/console: unify printout behavior for UART emulators

[dmkhn@proton.me]

On Thu, Jun 05, 2025 at 08:15:15AM +0200, Jan Beulich wrote:
> On 05.06.2025 02:57, dmkhn@proton.me wrote:
> > On Wed, Jun 04, 2025 at 12:48:05PM +0200, Jan Beulich wrote:
> >> On 31.05.2025 02:04, dmkhn@proton.me wrote:
> >>> --- a/xen/arch/x86/hvm/hvm.c
> >>> +++ b/xen/arch/x86/hvm/hvm.c
> >>> @@ -577,7 +577,7 @@ static int cf_check hvm_print_line(
> >>>      if ( (cd->pbuf_idx == (DOMAIN_PBUF_SIZE - 1)) || (c == '\n') )
> >>>      {
> >>>          cd->pbuf[cd->pbuf_idx] = '\0';
> >>> -        guest_printk(cd, XENLOG_G_DEBUG "%s\n", cd->pbuf);
> >>> +        guest_printk(cd, "%s\n", cd->pbuf);
> >>>          cd->pbuf_idx = 0;
> >>>      }
> >>
> >> Why this and ...
> >>
> >>> @@ -755,7 +765,7 @@ static long guest_console_write(XEN_GUEST_HANDLE_PARAM(char) buffer,
> >>>              else
> >>>              {
> >>>                  cd->pbuf[cd->pbuf_idx] = '\0';
> >>> -                guest_printk(cd, XENLOG_G_DEBUG "%s%s\n", cd->pbuf, kbuf);
> >>> +                guest_printk(cd, "%s%s\n", cd->pbuf, kbuf);
> >>>                  cd->pbuf_idx = 0;
> >>>              }
> >>
> >> ... this change? There's no compensation for it ...
> >>
> >>> @@ -1013,12 +1023,21 @@ void printk(const char *fmt, ...)
> >>>      va_end(args);
> >>>  }
> >>>
> >>> +/*
> >>> + * Print message from the guest on the diagnostic console.
> >>> + * Prefixes all messages w/ "(dX)" if domain X does not own physical console
> >>> + * focus.
> >>> + */
> >>>  void guest_printk(const struct domain *d, const char *fmt, ...)
> >>>  {
> >>>      va_list args;
> >>> -    char prefix[16];
> >>> +    char prefix[16] = "";
> >>> +    struct domain *consd;
> >>>
> >>> -    snprintf(prefix, sizeof(prefix), "(d%d) ", d->domain_id);
> >>> +    consd = console_get_domain();
> >>> +    if ( consd != d )
> >>> +        snprintf(prefix, sizeof(prefix), "(d%d) ", d->domain_id);
> >>> +    console_put_domain(consd);
> >>>
> >>>      va_start(args, fmt);
> >>>      vprintk_common(fmt, args, prefix);
> >>
> >> ... here afaics, so it looks like you're undermining rate-limiting of
> >> those messages.
> >
> > I droppped behavior change for I/O debug port on x86 and HYPERVISOR_console_io
> > hypercall.
> >
> > But my understanding is that all guest debugging facilities, if enabled, should
> > not be rate-limited.
> 
> I certainly disagree there. How much rate limiting to apply to guest output is a
> matter of the guest_loglvl= command line option. Its default settings are the way
> they are for a reason.

Oh, I see!
Thanks for clarification!

> 
> Jan
>