linux-kernel - Re: [take2] Inotify: nested attributes support.

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Message-Id: <20081126003825.2b9a92be.akpm@linux-foundation.org>
Date:	Wed, 26 Nov 2008 00:38:25 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Evgeniy Polyakov <zbr@...emap.net>
Cc:	john@...nmccutchan.com, arnd@...db.de, mtk.manpages@...il.com,
	hch@....de, rlove@...ve.org, linux-api@...r.kernel.org,
	linux-kernel@...r.kernel.org, pavel@...e.cz,
	davidn@...idnewall.com, Eric Paris <eparis@...hat.com>
Subject: Re: [take2] Inotify: nested attributes support.

On Wed, 26 Nov 2008 11:29:36 +0300 Evgeniy Polyakov <zbr@...emap.net> wrote:

> On Wed, Nov 26, 2008 at 12:15:38AM -0800, Andrew Morton (akpm@...ux-foundation.org) wrote:
> > OK, so we have a super-duper framework which will allow us to add pids
> > (and other things) to inotify messages.
> 
> Yup :)
> 
> > This still doesn't provide a reason for anyone to be interested in the
> > code!  Why do we want pids in inotify messages?
>  
> I actually cared only about myself :)
> I started the thread and implementation, because my application has to
> differentiate IO made by itself and any IO made by system (another
> users, crons, whatever else), inotify did not give me that info, so I
> extended it. As of others: PID/TID may be used by watching applications
> to reduce own load to not process own IO, things like beagle may show
> who actually made changes into the file.

hrm.  Well this is the sort of information which reviewers want to know
all about before looking at an implementation.

> > And how does this work give that pids are (no longer) system-wide unique?
> 
> It gets pids from the caller's task_struct (via current), so its data is
> as unique as process calling getpid() or syscall(__NR_gettid).

That means that the code delivers non-unique process identifiers to
userspace.  A client gets pid=42 but there are seven processes on the
machine with that pid.  Problem.


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