Re: [Xen-devel] [PATCH v6 22/26] xen: support console_switching between Dom0 and DomUs on ARM

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 03.11.18 at 00:45, <sstabellini@xxxxxxxxxx> wrote:
> Today Ctrl-AAA is used to switch between Xen and Dom0. Extend the
> mechanism to allow for switching between Xen, Dom0, and any of the
> initial DomU created from Xen alongside Dom0 out of information provided
> via device tree.
> 
> Rename xen_rx to console_rx to match the new behavior.
> 
> Clarify existing comment about "notify the guest", making it clear that
> it is only about the hardware domain.
> 
> Switching the console input to domUs started from Xen at boot is
> #ifdef'ed to 0 in this patch. The code will be enabled when
> vpl011_rx_char_xen is introduced. For now it is disabled for
> bisectability.
> 
> Signed-off-by: Stefano Stabellini <stefanos@xxxxxxxxxx>

Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
with two remarks (but the ack applies with or without either
taken care of):

> @@ -391,31 +394,82 @@ static void dump_console_ring_key(unsigned char key)
>      free_xenheap_pages(buf, order);
>  }
>  
> -/* CTRL-<switch_char> switches input direction between Xen and DOM0. */
> +/*
> + * CTRL-<switch_char> changes input direction, rotating among Xen, Dom0,
> + * and the DomUs started from Xen at boot.
> + */
>  #define switch_code (opt_conswitch[0]-'a'+1)
> -static int __read_mostly xen_rx = 1; /* FALSE => input passed to domain 0. */
> +/*
> + * console_rx=0 => input to xen
> + * console_rx=1 => input to dom0
> + * console_rx=N => input to dom(N-1)
> + */
> +static unsigned int __read_mostly console_rx = 0;
>  
>  static void switch_serial_input(void)
>  {
> -    static char *input_str[2] = { "DOM0", "Xen" };
> -    xen_rx = !xen_rx;
> -    printk("*** Serial input -> %s", input_str[xen_rx]);
> +    if ( console_rx == max_init_domid + 1 )

I generally consider it better to use >= in cases like this.

>  static void __serial_rx(char c, struct cpu_user_regs *regs)
>  {
> -    if ( xen_rx )
> +    switch ( console_rx )
> +    {
> +    case 0:
>          return handle_keypress(c, regs);
>  
> -    /* Deliver input to guest buffer, unless it is already full. */
> -    if ( (serial_rx_prod-serial_rx_cons) != SERIAL_RX_SIZE )
> -        serial_rx_ring[SERIAL_RX_MASK(serial_rx_prod++)] = c;
> -    /* Always notify the guest: prevents receive path from getting stuck. */
> -    send_global_virq(VIRQ_CONSOLE);
> +    case 1:
> +        /*
> +         * Deliver input to the hardware domain buffer, unless it is
> +         * already full.
> +         */
> +        if ( (serial_rx_prod - serial_rx_cons) != SERIAL_RX_SIZE )
> +            serial_rx_ring[SERIAL_RX_MASK(serial_rx_prod++)] = c;
> +
> +        /*
> +         * Always notify the hardware domain: prevents receive path from
> +         * getting stuck.
> +         */
> +        send_global_virq(VIRQ_CONSOLE);
> +        break;
> +
> +#if 0
> +    default:
> +    {
> +        struct domain *d = rcu_lock_domain_by_any_id(console_rx - 1);
> +
> +        /*
> +         * If we have a properly initialized vpl011 console for the
> +         * domain, without a full PV ring to Dom0 (in that case input
> +         * comes from the PV ring), then send the character to it.
> +         */
> +        if ( d != NULL &&
> +             !d->arch.vpl011.backend_in_domain &&
> +             d->arch.vpl011.backend.xen != NULL )
> +            vpl011_rx_char_xen(d, c);
> +        else
> +            printk("Cannot send chars to Dom%d: no UART available\n",
> +                   console_rx - 1);
> +
> +        if ( d != NULL )
> +            rcu_unlock_domain(d);
> +    }
> +#endif

As said before, I would have preferred if this code block was
introduced only with the patch making it usable, rather than
with the #if 0 here.

Jan



_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel