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From:   "Fabio M. De Francesco" <fmdefrancesco@gmail.com>
To:     Jaehee Park <jhpark1013@gmail.com>, Kalle Valo <kvalo@kernel.org>
Cc:     =?ISO-8859-1?Q?J=E9r=F4me?= Pouiller <jerome.pouiller@silabs.com>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        linux-wireless@vger.kernel.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-staging@lists.linux.dev,
        outreachy@lists.linux.dev, Stefano Brivio <sbrivio@redhat.com>
Subject: Re: [PATCH] wfx: use container_of() to get vif
Date:   Wed, 20 Apr 2022 18:53:39 +0200
Message-ID: <2258432.bcXerOTE6V@leap>
In-Reply-To: <87y200nf0a.fsf@kernel.org>
References: <20220418035110.GA937332@jaehee-ThinkPad-X1-Extreme> <87y200nf0a.fsf@kernel.org>
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On mercoled=C3=AC 20 aprile 2022 13:57:57 CEST Kalle Valo wrote:
> Jaehee Park <jhpark1013@gmail.com> writes:
>=20
> > Currently, upon virtual interface creation, wfx_add_interface() stores
> > a reference to the corresponding struct ieee80211_vif in private data,
> > for later usage. This is not needed when using the container_of
> > construct. This construct already has all the info it needs to retrieve
> > the reference to the corresponding struct from the offset that is
> > already available, inherent in container_of(), between its type and
> > member inputs (struct ieee80211_vif and drv_priv, respectively).
> > Remove vif (which was previously storing the reference to the struct
> > ieee80211_vif) from the struct wfx_vif, define a function
> > wvif_to_vif(wvif) for container_of(), and replace all wvif->vif with
> > the newly defined container_of construct.
> >
> > Signed-off-by: Jaehee Park <jhpark1013@gmail.com>
>=20
> [...]
>=20
> > +static inline struct ieee80211_vif *wvif_to_vif(struct wfx_vif *wvif)
> > +{
> > +	return container_of((void *)wvif, struct ieee80211_vif,=20
drv_priv);
> > +}
>=20
> Why the void pointer cast? Avoid casts as much possible.

In a previous email Jaehee wrote that she could compile her changes only by=
=20
using that "(void *)" cast.

I replied that probably this is a hint that something is broken, although=20
my argument is not necessarily a "proof". Might very well be that this cast=
=20
was needed in this particular situation but I cannot see why.

@Jaehee, please try to explain why this "(void *)" cast is actually=20
necessary and why your changes cannot avoid it.

Thanks,

=46abio M. De Francesco