kthread: Add a wrapper macro KPROC_START

[zlei]

Summary

kthread: Add a wrapper macro KPROC_START

The function kproc_start(const void *) requires passing an argument
with type `struct kproc_desc *`. The compilers are not able to report
error when passing wrong typed arguments.

Add a wrapper macro KPROC_START so that we no longer worry about that
when using the macro instead of plain SYSINIT.

MFC after:      2 weeks


kthread: Migrate to use the macro KPROC_START to start kernel threads

No functional change intended.

MFC after:      2 weeks

[zlei]

sys/kern/kern_alq.c

418

Hi @jeff, I'm not quite sure if the name matters, but I do not find "ALQ Daemon" used elsewhere except here.

Will the change of thread name from "ALQ Daemon" to "alq_daemon" breaks anything ?

[olce]

sys/kern/kern_alq.c

418

I don't think that name matters, and would prefer the names to have no spaces. Let's see if @jeff says something (based on the past few years, I'd say it's unlikely, but perhaps wait for a few days or a little more).

sys/sys/kthread.h

62

Perhaps expand the generated name to decrease the chances of collision with explicit variables?

67

If changed above, to be changed here.

[kib]

sys/sys/kthread.h

61

The simple macro argument names have high chance of interfere with names locally visible.
C standard reserves the identifiers namespace '^_[A-Z]' (i.e. all identifiers starting with underscore, then upper-case letter) to file-local preprocessor tokens.

I suggest to use that convention for such global macro args, and also I suggest to use much more descriptive names for them. If I need to write another KPROC_START(), I would need to spend more time than I want figuring out what these n/s/o/f/gp mean.