[PATCH RFC 03/11] um: Use a simple time travel handler for line interrupts

[Benjamin Beichler]

Am 06.11.2023 um 21:26 schrieb Johannes Berg:
> ________________________________
>
> On Fri, 2023-11-03 at 16:41 +0000, Benjamin Beichler wrote:
>> This change permits interrupts on serial lines in time travel mode,
>> especially in external mode. However, these interrupts are processed
>> with the simple handler that does not provide any acknowledgment.
>>
> Yeah... we had this discussion in the other thread.
>
> At least in my mental model this is broken because the sender of the
> event basically has to prepare the calendar for it happening, which
> feels ... odd.
Actually, for me, this would make kind of sense. Why couldn't we be more 
explicit in the time travel protocol to the calendar about interrupts?
We could use the ID from the start-msg to identify um instances and 
tell, in an additional msg, that we are going to trigger an interrupt at 
the current time to that instance from the device simulation.
Another way would be, to serve such information (if the device 
simulation really need it) over the facilities we already established. 
Why not send the ACK as MSG_OOB or ancillary data?
>
> But I can see where you're coming from, and switching to virtio console
> that does it all right might be tricky, so ... perhaps this still makes
> some sense.
>
> I'd still think we should put a warning into the code somewhere when you
> actually use line interrupts though?
>
> johannes
>
Benjamin