linux-kernel - Re: [PATCH] mac80211: Make addr const in SET_IEEE80211_PERM

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Message-ID: <CAJAp7Oinz993CQgA81SifcJoeHicD9YNhBv0HHkiav3rD5=M4Q@mail.gmail.com>
Date:	Wed, 30 Dec 2015 09:05:32 -0800
From:	Bjorn Andersson <bjorn@...o.se>
To:	Souptick Joarder <jrdr.linux@...il.com>
Cc:	Johannes Berg <johannes@...solutions.net>,
	"David S. Miller" <davem@...emloft.net>,
	linux-wireless <linux-wireless@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mac80211: Make addr const in SET_IEEE80211_PERM_ADDR()

On Wed, Dec 30, 2015 at 8:47 AM, Souptick Joarder <jrdr.linux@...il.com> wrote:
>
> HI Bjorn,
>
> On Thu, Dec 24, 2015 at 2:03 PM, Bjorn Andersson <bjorn@...o.se> wrote:
> > Make the addr parameter const in SET_IEEE80211_PERM_ADDR() to save
> > clients from having to cast away a const qualifier.
> >
> > Signed-off-by: Bjorn Andersson <bjorn.andersson@...ymobile.com>
> > ---
> >  include/net/mac80211.h | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/include/net/mac80211.h b/include/net/mac80211.h
> > index 7c30faff245f..a6f3c9c4b7c2 100644
> > --- a/include/net/mac80211.h
> > +++ b/include/net/mac80211.h
> > @@ -2167,7 +2167,7 @@ static inline void SET_IEEE80211_DEV(struct ieee80211_hw *hw, struct device *dev
> >   * @hw: the &struct ieee80211_hw to set the MAC address for
> >   * @addr: the address to set
> >   */
> > -static inline void SET_IEEE80211_PERM_ADDR(struct ieee80211_hw *hw, u8 *addr)
> > +static inline void SET_IEEE80211_PERM_ADDR(struct ieee80211_hw *hw, const u8 *addr)
>
> I guess without const or with const doesn't make much difference here.
> Correct me if I am wrong.

For most cases it doesn't make any difference, but in my driver I
acquire the mac address as a const u8 *. Therefor I need to cast away
the const part when calling this API.

There's an existing example of this in
drivers/net/wireless/st/cw1200/main.c line 601.


I think it's safe to assume that this API won't ever modify the passed
addr buffer, so there would be no future issues of marking the
parameter const either.

>
> >  {
> >         memcpy(hw->wiphy->perm_addr, addr, ETH_ALEN);
> >  }
>

Regards,
Bjorn
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