netdev - Re: [PATCH v2 05/14] net: core: provide priv_to

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Message-Id: <20200511.134117.1336222619714836904.davem@davemloft.net>
Date:   Mon, 11 May 2020 13:41:17 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     brgl@...ev.pl
Cc:     robh+dt@...nel.org, matthias.bgg@...il.com, john@...ozen.org,
        sean.wang@...iatek.com, Mark-MC.Lee@...iatek.com, kuba@...nel.org,
        arnd@...db.de, fparent@...libre.com, hkallweit1@...il.com,
        edwin.peer@...adcom.com, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org,
        stephane.leprovost@...iatek.com, pedro.tsai@...iatek.com,
        andrew.perepech@...iatek.com, bgolaszewski@...libre.com
Subject: Re: [PATCH v2 05/14] net: core: provide priv_to_netdev()

From: Bartosz Golaszewski <brgl@...ev.pl>
Date: Mon, 11 May 2020 17:07:50 +0200

> From: Bartosz Golaszewski <bgolaszewski@...libre.com>
> 
> Appropriate amount of extra memory for private data is allocated at
> the end of struct net_device. We have a helper - netdev_priv() - that
> returns its address but we don't have the reverse: a function which
> given the address of the private data, returns the address of struct
> net_device.
> 
> This has caused many drivers to store the pointer to net_device in
> the private data structure, which basically means storing the pointer
> to a structure in this very structure.
> 
> This patch proposes to add priv_to_netdev() - a helper which converts
> the address of the private data to the address of the associated
> net_device.
> 
> Signed-off-by: Bartosz Golaszewski <bgolaszewski@...libre.com>

Sorry, please don't do this.  We had this almost two decades ago and
explicitly removed it intentionally.

Store the back pointer in your software state just like everyone else
does.