Jan Engelhardt <jengelh at linux01.gwdg.de> writes:
>>> +static inline pid_t pid_nr(struct pid *pid)
>>> +{
>>> + pid_t nr = 0;
>>> + if (pid)
>>> + nr = pid->nr;
>>> + return nr;
>>> +}
>>
>>When is it valid to be passing around a NULL 'struct pid *'?
>
> Is 0 even the right thing to return in the rare case that pid == NULL?
> -1 maybe?
I believe 0 is what we have used elsewhere.
A negative value for a pid is likely to be taken as the group of all
processes, or -EPERM, and it does really confusing things when fed through
the current f_getown implementation, with PIDTYPE_PGRP.
The only other possible interpretations of 0 are the idle process and
yourself. There is still some potential there, but largely 0 is much
less likely to be confused than -1. Especially as it doesn't change
when you negate it.
Eric
