On 17.03.2023 10:32, Michal Orzel wrote:
>
>
> On 17/03/2023 09:36, Jan Beulich wrote:
>>
>>
>> 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).
>
> I would prefer a loop with if/else inside. If you are ok with the following
> code
> that handles all the cases, I will push a patch in a minute:
Looks roughly okay, but recall I said so also when you "pre-posted" the
previous version.
Jan
