Re: OpenBSD 7.3 found a process with PID 0

Am 26.09.23 um 18:12 schrieb Alessandro Baggi:
>
>
> Il 26/09/23 17:30, Claudio Jeker ha scritto:
>> On Tue, Sep 26, 2023 at 05:13:46PM +0200, Andreas Kähäri wrote:
>>> On Tue, Sep 26, 2023 at 04:59:22PM +0200, Alessandro Baggi wrote:
>>>> Hi list,
>>>> running this python3 script:
>>>>
>>>> #!/usr/bin/env python3
>>>> import psutil
>>>>
>>>> pids = psutil.pids()
>>>> for i in pids:
>>>>      p = psutil.Process(i)
>>>>      with p.oneshot():
>>>>          print(str(i) + " " + p.name())
>>>>
>>>> The result start with:
>>>>
>>>> 0 swapper
>>>> 1 init
>>>> 536 smtpd
>>>> 868 ksh
>>>> ...
>>>>
>>>> This process does not appear in ps, top and htop.
>>>
>>> $ ps -p 0
>>>    PID TT  STAT        TIME COMMAND
>>>        0 ??  DK       0:02.19 (swapper)
>>>
>>> For top, you need to press S to show system processes.  I don't use
>>> htop, but I assume it has a similar capability to show system processes.
>>>
>>>>
>>>> How could be that there is a process with PID 0 before init?
>>>> Probably I'm missing something about OpenBSD core.
>>>>
>>>> Can someone point me in the right direction?
>>>>
>>>
>>> See uvm_init(9):
>>>
>>>           The swapper process swaps in runnable processes that are
>>>           currently swapped out, if there is room.
>>>
>>
>> ... and this is a lie. The swapper process does nothing.
>>
>
> Ok, but why it is running?
>
My guess without looking at the code is that it's an "idle" process,
it runs if there is nothing else to run and maybe does something like:

loop:
hlt ; wait for interrupt
jmp loop

It would make sense, but please correct me if I'm wrong.