linux-kernel - Re: [PATCH] wfx: use container

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Date:   Mon, 2 May 2022 14:34:03 -0400
From:   Jaehee Park <jhpark1013@...il.com>
To:     Kalle Valo <kvalo@...nel.org>
Cc:     Jérôme Pouiller <jerome.pouiller@...abs.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-staging@...ts.linux.dev,
        Outreachy Linux Kernel <outreachy@...ts.linux.dev>,
        Stefano Brivio <sbrivio@...hat.com>
Subject: Re: [PATCH] wfx: use container_of() to get vif

On Mon, May 02, 2022 at 02:10:07PM -0400, Jaehee wrote:
> On Wed, Apr 20, 2022 at 7:58 AM Kalle Valo <kvalo@...nel.org> wrote:
> >
> > Jaehee Park <jhpark1013@...il.com> writes:
> >
> > > 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@...il.com>
> >
> > [...]
> >
> > > +static inline struct ieee80211_vif *wvif_to_vif(struct wfx_vif *wvif)
> > > +{
> > > +     return container_of((void *)wvif, struct ieee80211_vif, drv_priv);
> > > +}
> >
> > Why the void pointer cast? Avoid casts as much possible.
> >
> 
> Hi Kalle,
> 
> Sorry for the delay in getting back to you about why the void pointer
> cast was used.
> 
> In essence, I'm taking private data with a driver-specific pointer
> and that needs to be resolved back to a generic pointer.
> 
> The private data (drv_priv) is declared as a generic u8 array in struct
> ieee80211_vif, but wvif is a more specific type.
> 
> I wanted to also point to existing, reasonable examples such as:
> static void iwl_mvm_tcm_uapsd_nonagg_detected_wk(struct work_struct *wk)
> {
>         struct iwl_mvm *mvm;
>         struct iwl_mvm_vif *mvmvif;
>         struct ieee80211_vif *vif;
> 
>         mvmvif = container_of(wk, struct iwl_mvm_vif,
>                               uapsd_nonagg_detected_wk.work);
>         vif = container_of((void *)mvmvif, struct ieee80211_vif, drv_priv);
> 
> in drivers/net/wireless$ less intel/iwlwifi/mvm/utils.c, which does the
> same thing.
> 
> There are fifteen of them throughout:
> wireless-next/drivers/net/wireless$ grep -rn "container_of(.* ieee80211_vif"
> intel/iwlwifi/mvm/utils.c:794:  vif = container_of((void *)mvmvif,
> struct ieee80211_vif, drv_priv);
> intel/iwlwifi/mvm/mac80211.c:1347:      vif = container_of((void
> *)mvmvif, struct ieee80211_vif, drv_priv);
> mediatek/mt76/mt76x02_mmio.c:415:               vif =
> container_of(priv, struct ieee80211_vif, drv_priv);
> mediatek/mt76/mt7615/mac.c:275: vif = container_of((void *)msta->vif,
> struct ieee80211_vif, drv_priv);
> mediatek/mt76/mt7915/mac.c:416: vif = container_of((void *)msta->vif,
> struct ieee80211_vif, drv_priv);
> mediatek/mt76/mt7915/mac.c:2327:                vif =
> container_of((void *)msta->vif, struct ieee80211_vif, drv_priv);
> mediatek/mt76/mt7915/debugfs.c:1026:    vif = container_of((void
> *)msta->vif, struct ieee80211_vif, drv_priv);
> mediatek/mt76/mt7921/mac.c:425: vif = container_of((void *)msta->vif,
> struct ieee80211_vif, drv_priv);
> ti/wlcore/wlcore_i.h:502:       return container_of((void *)wlvif,
> struct ieee80211_vif, drv_priv);
> realtek/rtl818x/rtl8187/dev.c:1068:             container_of((void
> *)vif_priv, struct ieee80211_vif, drv_priv);
> realtek/rtl818x/rtl8180/dev.c:1293:             container_of((void
> *)vif_priv, struct ieee80211_vif, drv_priv);
> realtek/rtw88/main.h:2075:      return container_of(p, struct
> ieee80211_vif, drv_priv);
> realtek/rtw89/core.h:3440:      return container_of(p, struct
> ieee80211_vif, drv_priv);
> ath/carl9170/carl9170.h:641:    return container_of((void *)priv,
> struct ieee80211_vif, drv_priv);
> ath/wcn36xx/wcn36xx.h:329:      return container_of((void *) vif_priv,
> struct ieee80211_vif, drv_priv);
> 

Sorry -- here's the last portion of the email without wrapping.

wireless-next/drivers/net/wireless$ grep -rn "container_of(.* ieee80211_vif"
intel/iwlwifi/mvm/utils.c:794:  vif = container_of((void *)mvmvif, struct ieee80211_vif, drv_priv);
intel/iwlwifi/mvm/mac80211.c:1347:      vif = container_of((void *)mvmvif, struct ieee80211_vif, drv_priv);
mediatek/mt76/mt76x02_mmio.c:415:               vif = container_of(priv, struct ieee80211_vif, drv_priv);
mediatek/mt76/mt7615/mac.c:275: vif = container_of((void *)msta->vif, struct ieee80211_vif, drv_priv);
mediatek/mt76/mt7915/mac.c:416: vif = container_of((void *)msta->vif, struct ieee80211_vif, drv_priv);
mediatek/mt76/mt7915/mac.c:2327:                vif = container_of((void *)msta->vif, struct ieee80211_vif, drv_priv);
mediatek/mt76/mt7915/debugfs.c:1026:    vif = container_of((void *)msta->vif, struct ieee80211_vif, drv_priv);
mediatek/mt76/mt7921/mac.c:425: vif = container_of((void *)msta->vif, struct ieee80211_vif, drv_priv);
ti/wlcore/wlcore_i.h:502:       return container_of((void *)wlvif, struct ieee80211_vif, drv_priv);
realtek/rtl818x/rtl8187/dev.c:1068:             container_of((void *)vif_priv, struct ieee80211_vif, drv_priv);
realtek/rtl818x/rtl8180/dev.c:1293:             container_of((void *)vif_priv, struct ieee80211_vif, drv_priv);
realtek/rtw88/main.h:2075:      return container_of(p, struct ieee80211_vif, drv_priv);
realtek/rtw89/core.h:3440:      return container_of(p, struct ieee80211_vif, drv_priv);
ath/carl9170/carl9170.h:641:    return container_of((void *)priv, struct ieee80211_vif, drv_priv);
ath/wcn36xx/wcn36xx.h:329:      return container_of((void *) vif_priv, struct ieee80211_vif, drv_priv);

> Thanks,
> Jaehee
> 
> 
> > --
> > https://patchwork.kernel.org/project/linux-wireless/list/
> >
> > https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches