linux-kernel - Re: [PATCH v2 1/9] drm/vc4: Switch to container_of

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Date:   Tue, 21 Feb 2023 12:38:34 +0100
From:   Maxime Ripard <maxime@...no.tech>
To:     Hans Verkuil <hverkuil@...all.nl>
Cc:     Emma Anholt <emma@...olt.net>, David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Dave Stevenson <dave.stevenson@...pberrypi.com>,
        Thomas Zimmermann <tzimmermann@...e.de>
Subject: Re: [PATCH v2 1/9] drm/vc4: Switch to container_of_const

Hi Hans,

On Sat, Feb 18, 2023 at 11:45:04AM +0100, Hans Verkuil wrote:
> > diff --git a/drivers/gpu/drm/vc4/vc4_bo.c b/drivers/gpu/drm/vc4/vc4_bo.c
> > index 86d629e45307..d0a00ed42cb0 100644
> > --- a/drivers/gpu/drm/vc4/vc4_bo.c
> > +++ b/drivers/gpu/drm/vc4/vc4_bo.c
> > @@ -609,7 +609,7 @@ static void vc4_free_object(struct drm_gem_object *gem_bo)
> >  static void vc4_bo_cache_time_work(struct work_struct *work)
> >  {
> >  	struct vc4_dev *vc4 =
> > -		container_of(work, struct vc4_dev, bo_cache.time_work);
> > +		container_of_const(work, struct vc4_dev, bo_cache.time_work);
> 
> ...I think this is misleading. It's definitely not const, so switching to
> container_of_const suggests that there is some 'constness' involved, which
> isn't the case. I'd leave this just as 'container_of'. This also reduces the
> size of the patch, since this is done in quite a few places.

The name threw me off too, but it's supposed to keep the argument
pointer constness, not always take and return a const pointer. I still
believe that it's beneficial since, if the work pointer was ever to
change constness, we would have that additional check.

Maxime