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

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Message-ID: <20141002104552.GC19748@quack.suse.cz>
Date:	Thu, 2 Oct 2014 12:45:52 +0200
From:	Jan Kara <jack@...e.cz>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Jan Kara <jack@...e.cz>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Heinrich Schuchardt <xypron.debian@....de>,
	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	John McCutchan <john@...nmccutchan.com>,
	Robert Love <rlove@...ve.org>,
	Eric Paris <eparis@...isplace.org>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	Pavel Emelyanov <xemul@...allels.com>,
	Andrey Vagin <avagin@...nvz.org>
Subject: Re: [PATCH] fs: don't remove inotify watchers from alive inode-s (v2)

On Thu 25-09-14 10:30:10, Jan Kara wrote:
> On Wed 24-09-14 13:19:47, Andrew Morton wrote:
> > On Wed, 24 Sep 2014 12:51:55 +0200 Jan Kara <jack@...e.cz> 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:
> 4       (IN_ATTRIB)
> 400     (IN_DELETE_SELF)
> 8000    (IN_IGNORED)
> 
> and sometimes you get events:
> 4       (IN_ATTRIB)
> <possibly more events happening for unlinked file>
> 8       (IN_CLOSE_WRITE)
> 400     (IN_DELETE_SELF)
> 8000    (IN_IGNORED)
> 
> 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).
  Ping Andrew? Do you still need more info or are you now OK to merge the
patch?

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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