linux-kernel - Re: Linux 2.6.36-rc7

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Message-ID: <201010081717.25940.tvrtko.ursulin@sophos.com>
Date:	Fri, 8 Oct 2010 17:17:25 +0100
From:	Tvrtko Ursulin <tvrtko.ursulin@...hos.com>
To:	John Stoffel <john@...ffel.org>
CC:	Eric Paris <eparis@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"agruen@...e.de" <agruen@...e.de>
Subject: Re: Linux 2.6.36-rc7

On Friday 08 Oct 2010 16:42:06 John Stoffel wrote:
> >>>>> "Eric" == Eric Paris <eparis@...hat.com> writes:
> Eric> I will tell you that the way I envision it working (and being
> Eric> backwards compatible) is that priority 0 is the last thing to be
> Eric> serviced.  If 2 things register at the same priority the order
> Eric> between them getting events is unpredictable.  So when an HSM
> Eric> uses the interface it would use the highest priority.  An AV
> Eric> vendor might use (highest priority / 2) while normal inotify
> Eric> like listeners would all be happy using priority 0.
>
> Ugh, I'd prefer that priority 0 is first (highest), but I can see how
> that would make ABI problems, assuming we don't punt on releasing the
> ABI now.
>
> So if the order is undefined now, that's not good.  Well... maybe it's
> acceptable, but I can see all kinds of problems cropping up.
> Hopefully they're processed in order of notifier creation instead.  So
> if I insert a notifier, anyone who inserts a notifier after me gets
> serviced after my notifier gets run.  That would seem to be the
> logical and sane semantics to use here.
>
> Again, I'm really approaching this as a SysAdmin who'd love to use
> this in an HSM environment, so ordering is a *key* requirement.

Ordering by time of registration? I thought of that but it falls flat once any
service needs to restart or be restarted.

Priority is also not that great concept. I may have proposed classes or
something similar at some point, don't remember any more. It would be
equivalent to having allocated priority ranges, like:

>1000 - pre-content
>=100 - access-control
<100 - content

Doesn't really solve ordering inside groups so maybe we do not need priorities
at all just these three classes?

Tvrtko

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