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

[Jan Beulich <jbeulich@xxxxxxxx>]

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.

Jan