Re: [PATCH] fs: don't remove inotify watchers from alive inode-s (v2)

From: Jan Kara
Date: Thu Sep 25 2014 - 04:30:30 EST

On Wed 24-09-14 13:19:47, Andrew Morton wrote:
> On Wed, 24 Sep 2014 12:51:55 +0200 Jan Kara <jack@xxxxxxx> wrote:
> > Hello,
> >
> > Andrew, what do you think about the patch below? Al objected that it
> > changes userspace visible behavior some time ago and then he didn't react
> > to our explanations...
> Difficult situation. There's some really important information missing
> from the changelog:
> - Who cares? Is there some real application which is hurting from
> the current situation? If so, who, what, how and why. If not, then
> why change anything?
I believe Openvz guys hit this in their application but I'll defer to
them for more details.

> - A description of the userspace API change impact. How did the
> interface change? What is the risk of this change causing damage to
> real applications?
I believe this was covered in the changelog. Without the patch depending
on the order of unlinks for hardlinked file you sometimes get events:

and sometimes you get events:
<possibly more events happening for unlinked file>

With the patch you'll always have the second case. So without the patch you
don't receive some events if the file has at least 2 hardlinks and then
gets unlinked. I think the risk that some application relies on *not* getting
those events is pretty low (especially since in the common case of file
without hardlinks you will get all those events).

Jan Kara <jack@xxxxxxx>
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