Fixes for pdrfork(2) and tests

[kib]

Summary

pdrfork(2): do require RFPROCDESC | RFPROC

when RFSPAWN is not specified, as stated in the man page.
rfork(2) cannot modify non-curproc, which is why RFPROC is required,
the syscall cannot act on arbitrary process descriptor.
If RFPROCDESC is not specified, the syscall does not make sense,
use rfork(2).

Reported and tested by: pho

pdfork.2: add EFAULT as possible error, explain some consequences of it


pdrfork(2) tests: RFPROCDESC|RFPROC are required


pdrfork(2) tests: do not rely on (int *)-1 being invalid address

Explicitly mmap guard and use it as the invalid address instead.


pdrfork(2) tests: catch runaway child for EFAULT test


pdrfork(2) tests: split basic_usage

into pdrfork(2) call itself, and basic_usage_tail() that checks the
pdrfork(2) results.


pdrfork(2) tests: should wait for the child to exit


pdrfork(2) tests: enable on x86

Use pfrfork_thread(3) instead of pdrfork(RFSPAWN) to make tests working
on x86.

[markj]

sys/kern/kern_fork.c

220

Indentation here is wrong.

Shouldn't the message be RFPROC and RFPRCDESC are required, passed %#jx or so?

tests/sys/kern/pdrfork.c

97 ↗

(On Diff #171967)

116 ↗

(On Diff #171967)

Why bother unmapping it?

120 ↗

(On Diff #171967)

[kib]

Remove munmap(guard).
Fix comments.
Fix style.