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Re: [dm-devel] dm: remove pointless comparison



On Tue, Jan 07 2014 at 12:28pm -0500,
Milan Broz <gmazyland gmail com> wrote:

> On 01/07/2014 04:52 PM, Mike Snitzer wrote:
> > 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.
> >>>gmane.linux.kernel.device-mapper.devel
> >>> 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).
> 
> Yes, please remove both :) The check doesn't make sense.

Ok, I'll take that as your Acked-by, thanks.


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