"most interesting" process in w(1)

[Yuri Pankov]

Benjamin Kaduk wrote:
> On Wed, Apr 22, 2020 at 12:09:48AM +0300, Yuri Pankov wrote:
>> Looking at how w(1) finds "most interesting" process for terminal, I
>> noticed the following code which looks strange to me (usr.bin/w/w.c,
>> line 360 in HEAD)
>>
>> for (ep = ehead; ep != NULL; ep = ep->next) {
>>       if (ep->tdev == kp->ki_tdev) {
>>           /*
>>            * proc is associated with this terminal
>>            */
>>           if (ep->kp == NULL && kp->ki_pgid == kp->ki_tpgid) {
>>               /*
>>                * Proc is 'most interesting'
>>                */
>>               if (proc_compare(ep->kp, kp))
>>                   ep->kp = kp;
>>               ...
>>           }
>>       }
>> }
>>
>> Given the (ep->kp == NULL) check, proc_compare() becomes no-op, it will
>> always select kp, and that's the only place we ever set ep->kp, so the
>> first matching process is always "most interesting".  If that's really
>> what we want, we could do without the proc_compare() call.  What am I
>> missing here?
> 
> I suspect it makes more sense as a "!=" than a "==" (with ep->kp = kp;
> always occurring for the "== NULL" case).

(ep->kp == NULL) check seems to be unrelated addition in r29310 (!), the 
code around it gives no hints on why it was added.