linux-kernel - Re: [GIT PULL] notification tree

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Message-ID: <201008171112.42097.tvrtko.ursulin@sophos.com>
Date:	Tue, 17 Aug 2010 11:12:41 +0100
From:	Tvrtko Ursulin <tvrtko.ursulin@...hos.com>
To:	Andreas Gruenbacher <agruen@...e.de>
CC:	Eric Paris <eparis@...hat.com>,
	Christoph Hellwig <hch@...radead.org>,
	Matt Helsley <matthltc@...ibm.com>,
	"torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	Michael Kerrisk <michael.kerrisk@...il.com>
Subject: Re: [GIT PULL] notification tree - try 37!

On Tuesday 17 Aug 2010 11:01:09 Andreas Gruenbacher wrote:
> On Tuesday 17 August 2010 11:45:25 Tvrtko Ursulin wrote:
> > Why no timeouts? It sounds like a feasible way to work around listeners
> > which have stopped working. (Timeout and -ETIME for example to be clear,
> > not allowing access).
>
> From the kernel's point of view, there is no way to guess how long those
> timeouts should be.  Watching for progress can be implemented in user space
> though.

That is why I said the timeout can be configurable. But I agree (and raise you
double :) that not only the kernel can not guess how long the timeout should
be, but the application can not know as well. One possible way to let fanotify
know that listeners is making progress is via some sort of a heartbeat
message.  Then application can set the timeout as a fail safe and perm events
can take as long as needed and we still prevent clogging the system.

How would you create a robust solution purely from userspace? With the current
interface?

> Setting errno to ETIME as a result of trying to access a file is likely to
> break some applications which are not prepared to receive this error
> condition; we cannot do that.

Why you think EPERM will be handled better?

> I'm quite sure that both of these issues have been discussed already.

Ok, I obviosuly missed it. Do you have a pointer perhaps?

Tvrtko

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