linux-kernel - Re: [PATCH] Add device addition/removal notifier

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Message-Id: <1161322979.10524.143.camel@localhost.localdomain>
Date:	Fri, 20 Oct 2006 15:42:59 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Greg KH <greg@...ah.com>
Cc:	Linux Kernel list <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...l.org>, Len Brown <len.brown@...el.com>,
	Deepak Saxena <dsaxena@...xity.net>
Subject: Re: [PATCH] Add device addition/removal notifier

> Ok, as long as you all agree that this does change the behavior, it's
> fine with me :)

I should probably split the patch in two: One that does that behaviour
change (I already have an Acked-by: Len Brown for that one even :) and
one adding that notifier.

> Ok, then perhaps you just want a bus specific callback for the devices
> on that bus?  That would be much simpler and keep you from having to do
> that mess with the different tests of bus type.
>
> Actually, that's the only thing that really makes sense here, now that I
> think about it, the platform_notify doesn't really make any sense...

Well... people already use it and go check the bus types :)

Having a notifier queue per bus type is a bit harder though because bus
types are generally allocated statically and thus we would need to find
them all in the kernel to add a proper static initialisation for the
notifier queue... bus_register() is not a good spot to do it because
platform code might want to register for bus types before those bus
types have been registered (it's not always easy to find a place to
"hook" between a bus is registered and things get added to it).

In fact, the whole bus type thing is a mess :) We can't easily register
for bus types that are in modules. 

For example, if I want to use the notifier to catch USB devices in order
to, for example, link them to firmware nodes, I'm lost if the USB
subsystem is modular ... unless I use a global notifier and strcmp the
bus type name in there.

So at this point, I'd rather stay on a global notifier.

Ben.

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