From mboxrd@z Thu Jan  1 00:00:00 1970
From: Mike Snitzer <snitzer@redhat.com>
Subject: Re: dm: remove pointless comparison
Date: Tue, 7 Jan 2014 10:52:52 -0500
Message-ID: <20140107155252.GB7983@redhat.com>
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	<20140107103930.GA11734@debian>
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To: device-mapper development <dm-devel@redhat.com>, "Alasdair G. Kergon" <agk@redhat.com>
Cc: ejt@redhat.com, Mikulas Patocka <mpatocka@redhat.com>
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On Tue, Jan 07 2014 at  5:39am -0500,
Joe Thornber <thornber@redhat.com> wrote:

> On Mon, Jan 06, 2014 at 10:53:28PM -0500, Mikulas Patocka wrote:
> > Remove pointless comparison in dm_get_from_kobject. The comparison is
> > always true and the compiler optimizes it out anyway.
> > 
> > Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
> > 
> > ---
> >  drivers/md/dm.c |    2 --
> >  1 file changed, 2 deletions(-)
> > 
> > Index: linux-3.13-rc7/drivers/md/dm.c
> > ===================================================================
> > --- linux-3.13-rc7.orig/drivers/md/dm.c	2014-01-07 01:28:27.000000000 +0100
> > +++ linux-3.13-rc7/drivers/md/dm.c	2014-01-07 01:28:39.000000000 +0100
> > @@ -2922,8 +2922,6 @@ struct mapped_device *dm_get_from_kobjec
> >  	struct mapped_device *md;
> >  
> >  	md = container_of(kobj, struct mapped_device, kobj);
> > -	if (&md->kobj != kobj)
> > -		return NULL;
> 
> What were they trying to check?  The compiler?
> 

Milan's commit 784aae735d, and the current dm.c code, offers this
comment above dm_get_from_kobject:

/*
 * struct mapped_device should not be exported outside of dm.c
 * so use this check to verify that kobj is part of md structure
 */

I'm lacking the vision to _know_ why the kobject would suddenly be
outside of the mapped_device without us knowing via code change..

The check does seem overly cautious/useless (if we remove it the above
comment should be removed too).