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

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Date:	Wed, 5 Aug 2009 17:46:16 +0100
From:	Tvrtko Ursulin <tvrtko.ursulin@...hos.com>
To:	Pavel Machek <pavel@....cz>
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>,
	"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>,
	Douglas Leeder <douglas.leeder@...hos.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>,
	"jack@...e.cz" <jack@...e.cz>,
	"a.p.zijlstra@...llo.nl" <a.p.zijlstra@...llo.nl>,
	"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 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?

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.

Tvrtko
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