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

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Date:	Thu, 6 Aug 2009 12:10:59 +0200
From:	Pavel Machek <pavel@....cz>
To:	Tvrtko Ursulin <tvrtko.ursulin@...hos.com>
Cc:	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>,
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	"Valdis.Kletnieks@...edu" <Valdis.Kletnieks@...edu>,
	"greg@...ah.com" <greg@...ah.com>,
	"jcm@...hat.com" <jcm@...hat.com>,
	Douglas Leeder <douglas.leeder@...hos.com>,
	"tytso@....edu" <tytso@....edu>,
	"arjan@...radead.org" <arjan@...radead.org>,
	"david@...g.hm" <david@...g.hm>,
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	"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 Wed 2009-08-05 17:46:16, Tvrtko Ursulin wrote:
> On Wednesday 05 August 2009 03:05:34 Pavel Machek wrote:
> > BTW my -@...e.cz address no longer works. pavel@....cz should be ok.
> >
> > > If a FAN_ACCESS_PERM or FAN_OPEN_PERM event is received the listener
> > > must send a response before the 5 second timeout.  If no response is
> > > sent before the 5 second timeout the original operation is allowed.  If
> > > this happens too many times (10 in a row) the fanotify group is evicted
> > > from the kernel and will not get any new events.  Sending a response is
> > > done using the setsockopt() call with the socket options set to
> > > FANOTIFY_ACCESS_RESPONSE.  The buffer should contain a structure like:
> >
> > The timeout part of interface is very ugly. Will fanotify users have
> > to be realtime/mlocked?
> 
> Why do you think it is very ugly?

Do I need to explain?

> 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.
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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