On 16.03.2023 23:59, Stefano Stabellini wrote:
> On Thu, 16 Mar 2023, Jan Beulich wrote:
>> On 16.03.2023 11:26, Michal Orzel wrote:
>>> --- a/xen/drivers/char/console.c
>>> +++ b/xen/drivers/char/console.c
>>> @@ -490,7 +490,24 @@ static void switch_serial_input(void)
>>> }
>>> else
>>> {
>>> - console_rx++;
>>> + unsigned int next_rx = console_rx + 1;
>>> +
>>> + /* Skip switching serial input to non existing domains */
>>> + while ( next_rx < max_init_domid + 1 )
>>> + {
>>> + struct domain *d = rcu_lock_domain_by_id(next_rx - 1);
>>> +
>>> + if ( d )
>>> + {
>>> + rcu_unlock_domain(d);
>>> + break;
>>> + }
>>> +
>>> + next_rx++;
>>> + }
>>> +
>>> + console_rx = next_rx;
>>> +
>>> printk("*** Serial input to DOM%d", console_rx - 1);
>>> }
>>
>> While at the first glance (when you sent it in reply to v1) it looked okay,
>> I'm afraid it really isn't: Please consider what happens when the last of
>> the DomU-s doesn't exist anymore. (You don't really check whether it still
>> exists, because the range check comes ahead of the existence one.) In that
>> case you want to move from second-to-last to Xen. I expect the entire
>> if/else construct wants to be inside the loop.
>
> I don't think we need another loop, just a check if we found a domain or
I didn't say "another loop", but I suggested that the loop needs to be
around the if/else. Of course this can be transformed into equivalent
forms, like ...
> not. E.g.:
>
>
> unsigned int next_rx = console_rx + 1;
>
> /* Skip switching serial input to non existing domains */
> while ( next_rx < max_init_domid + 1 )
> {
> struct domain *d = rcu_lock_domain_by_id(next_rx - 1);
>
> if ( d )
> {
> rcu_unlock_domain(d);
> console_rx = next_rx;
> printk("*** Serial input to DOM%d", console_rx - 1);
> break;
> }
>
> next_rx++;
> }
>
> /* no domain found */
> console_rx = 0;
> printk("*** Serial input to Xen");
... what you suggest (or at least almost, because the way it's written
we'd always switch to Xen).
Jan
