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

[dmkhn@xxxxxxxxx]

On Wed, Jun 04, 2025 at 12:48:05PM +0200, Jan Beulich wrote:
> On 31.05.2025 02:04, dmkhn@xxxxxxxxx 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.

> 
> Jan