Re: Proper use of daemonize()?

[Chris Wright <chrisw@osdl.org>]

* Stuart MacDonald (stuartm@connecttech.com) wrote:
> I've been looking at the kernel threads that use daemonize() and have
> some questions about the proper use of this call:

What kernel are you looking at?  Take a look at current 2.6 and you
should find it much more uniform.

> 1: Some threads use the lock_kernel() calls around the daemonize()
> call. Is this necessary? I thought the BKL was phasing out.

I don't see why it'd be necessary.

> 2: Some threads do their setup (like changing the comm string, setting
> the signal masks, etc) before daemonize(), some do it after. Is there
> any benefit to a particular order of operations? I can't see one.

Current daemonize api includes name.

> 3: Some threads set current->tty to NULL. Why would a thread *not* do
> this?

Current daemonize function does this.

> 4: Some threads grab the sigmask_lock before manipulating their masks.
> Is this necessary? If so, some threads have bugs. If not, why do some
> threads bother?

Yes it's required.

> 5: Some threads do flush_signals() or recalc_sigpending() before
> updating their blocked mask, some do it after. Does the order matter?
> I suspect not.

Current daemonize gets this right.

> 6: MOD_INC_USE_COUNT should be used by all threads that could be in
> drivers built as modules, correct?

Not necessarily, modules can handle this in other ways (killing thread
on unload, for example).

> 7: If you're not spawning a permanent kernel thread (like kswapd frex)
> is the any benefit to using reparent_to_init()? I can't see one.

To give thread proper security credentials.

thanks,
-chris
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