linux-kernel - Re: fanotify - overall design before I start sending patches

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Message-Id: <1249554548.32113.137.camel@twins>
Date:	Thu, 06 Aug 2009 12:29:08 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Douglas Leeder <douglas.leeder@...hos.com>
Cc:	Pavel Machek <pavel@....cz>,
	Tvrtko Ursulin <tvrtko.ursulin@...hos.com>,
	Eric Paris <eparis@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"malware-list@...sg.printk.net" <malware-list@...sg.printk.net>,
	"Valdis.Kletnieks@...edu" <Valdis.Kletnieks@...edu>,
	"greg@...ah.com" <greg@...ah.com>,
	"jcm@...hat.com" <jcm@...hat.com>, "tytso@....edu" <tytso@....edu>,
	"arjan@...radead.org" <arjan@...radead.org>,
	"david@...g.hm" <david@...g.hm>,
	"jengelh@...ozas.de" <jengelh@...ozas.de>,
	"aviro@...hat.com" <aviro@...hat.com>,
	"mrkafk@...il.com" <mrkafk@...il.com>,
	"alexl@...hat.com" <alexl@...hat.com>,
	"hch@...radead.org" <hch@...radead.org>,
	"alan@...rguk.ukuu.org.uk" <alan@...rguk.ukuu.org.uk>,
	"mmorley@....in" <mmorley@....in>
Subject: Re: fanotify - overall design before I start sending patches

On Thu, 2009-08-06 at 11:20 +0100, Douglas Leeder wrote:
> Pavel Machek wrote:
> > On Wed 2009-08-05 17:46:16, Tvrtko Ursulin wrote:
> >> On Wednesday 05 August 2009 03:05:34 Pavel Machek wrote:
> 
> >> Just to make sure you haven't missed this - it is not that they have to 
> >> complete the whole operation before the timeout period (since you mention 
> >> realtime/mlock I suspect this is what you think?), but _during_ the operation 
> >> they have to show that they are active by sending something like keep alive 
> >> messages.
> >>
> >> Or you are worried about failing to meet even that on a loaded system? There 
> >> has to be something like this otherwise hung userspace client would kill the 
> >> whole system.
> > 
> > Of course, I'm worried about failing to meet this on loaded
> > system. And the fact that I _have_ to worry about that means that
> > interface is ugly/broken.
> 
> You mean that in 5 seconds, you won't have any point when you can tell
> the kernel, "I'm still working"?

I have to agree with Pavel here, either you demand the monitor process
is RT/mlock and can respond in time, in which case the interface doesn't
need a 5 second timeout, or you cannot and you have a hole somewhere.

Now having the kernel depend on any user task to guarantee process is of
course utterly insane too.

Sounds like a bad place to be, and I'd rather not have it.

If you really need the intermediate you might as well use a FUSE
filesystem, but I suspect there's plenty of problems there as well.

It all reeks of ugly though..

/me craws back from whence he came.

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