Re: proced: ppid of process ID 0 can be 0

[Giorgos Keramidas <keramida@ceid.upatras.gr>]

On Tue, 23 Dec 2008 15:41:56 -0500, Stefan Monnier <monnier@IRO.UMontreal.CA> wrote:
>>> >> Indeed, it should be in system-process-attributes which is already
>>> >> OS-dependent.
>>> > If you mean by having no ppid attribute, then that's ambiguous, since
>>> > an attribute can be missing because it is inaccessible for some
>>> > reason, like some kind of failure unrelated to the fact that the
>>> > process is really a root of a tree.
>>>
>>> Seems very hypothetical.
>>
>> It's not hypothetical, I've seen such cases and reported them to
>> Roland.
>
> What were those cases?
>
>>> More to the point: even if we could distinguish the "no ppid" from
>>> "unkown ppid", it's unclear how Elisp code could make use of it.
>> Lisp code cannot, but a primitive written in C can.
>
> Like what can it do?

It can differentiate between FreeBSD 4.3 and FreeBSD 7.2 if they use a
different style of `process root', or between Linux 1.2.X, 2.4.X and
2.6.X.  Right now, Emacs sets `system-type' to "berkeley-unix" on more
than one BSD system.  They might be easier to detect at C level.