Re: Semantics of command_id, process_id, process_to_com, process_tree

[Valdis.Kletnieks () vt edu]

On Fri, 23 Jun 2006 15:16:08 EDT, "Frank S Posluszny, III" said:

> > There are also some processes absent from process_to_com entirely,
> > like processes 7 and 12:
>
> Sorry, don't know about that one.

Number *that* low on a Linuxoid kernel is almost certainly a kernel
thread (see kernel/pid.c and the use of RESERVED_PIDS in alloc_pidmap()
for all the gory details, but basically, all PIDs under 300 (by default)
are reserved for kernel threads).   It's quite possible that 7 and 12
were threads created during boot to do things like scsi initialization
and so on (on my laptop, PID 8 is kblockd, and 9 is kacpid, then a
big jump to 117 cqueue and 120 khubd (USB support)).

If you're *really* curious to identify it, you'd have to add instrumentation to
kthread_create() in kernel/kthread.c and/or the kernel_thread() function in
arch/<mumble>/kernel/process.c - kernel_thread() calls do_fork() which is
what will end up assigning the PID to the thread....  You probably don't
want to instrument do_fork() itself unless you plan to spam yourself with
printk output for *every* fork() you do.. ;)

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