proc extension request: p_sched

[Peter Kadau]

Hi !

    I will commit the pointer to sys/proc.h so your proc
    size doesn't change. 
That's a good starting point, yes, thanks. :-)

...You'll have to maintain the
    rest of the stuff as a patch set for now... it looks
    like the structural topology needs some work so I'd rather
    not commit it all now.  For example, it is more likely that
    either p_sched would not be allocated and freed,  or
    there would be two pointers hanging off the proc...
    one describing the scheduler and another describing
    per-process extension info.
I'd rather think the userland scheduler would be fixed
at boot-time so why bother with a pointer in proc ?
Are you thinking of switching the scheduler in mid-air or
do I miss some other point entirely ?
I wasn't talking about userspace threading schedulers, e.g.
...  I would prefer that no
    dynamic allocations be necessary for the default 
    scheduler  but I can see their use for module-loaded
    schedulers... perhaps a union is a good compromise:

    struct proc {
	...
	struct scheduler *p_scheduler;	/* (static) describe scheduler */
	union sched	     p_sched; 		/* per-process scheduler info */
    }
    Then union sched would be:

    union sched {
	void	*s_ext;
	struct fubar_sched *s_fubar;
	struct {
	     ... embedded elements ...
	} bat_sched;
	struct {
	     ... embedded elements ...
	} bar_sched;
    }
    That is, it could accomodate both built-in non-dynamic schedulers
    and KLD schedulers, which would give us the flexibility of coming to
    a final decision later on down the line without sacrificing flexibility
    now.
Yes, but the opaque pointer gives us all the flexibility we need for now
and we don't have other examples (yet).
And what about proc0 and forking ? Since IMO the scheduler is fixed
at boot-time at least struct sched should be known at boot-time
to fill in proc0. Any hooks that could be used here ?
Cheers
Peter
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