linux-kernel - Re: [PATCH] net: dsa: sja1105: Remove unneeded cast in sja1105

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Message-ID: <20210224224358.pysql5pu23zt7mtb@skbuf>
Date:   Thu, 25 Feb 2021 00:43:58 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Geert Uytterhoeven <geert+renesas@...der.be>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: dsa: sja1105: Remove unneeded cast in
 sja1105_crc32()

On Tue, Feb 23, 2021 at 12:20:03PM +0100, Geert Uytterhoeven wrote:
> sja1105_unpack() takes a "const void *buf" as its first parameter, so
> there is no need to cast away the "const" of the "buf" variable before
> calling it.
> 
> Drop the cast, as it prevents the compiler performing some checks.
> 
> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
> ---

Reviewed-by: Vladimir Oltean <olteanv@...il.com>

By the way, your email went straight to my spam box, I just found the
patch by mistake on patchwork.

    Why is this message in spam?
    It is in violation of Google's recommended email sender guidelines.

> Compile-tested only.
> 
> BTW, sja1105_packing() and packing() are really bad APIs, as the input
> pointer parameters cannot be const due to the direction depending on
> "op".  This means the compiler cannot do const checks.  Worse, callers
> are required to cast away constness to prevent the compiler from
> issueing warnings.  Please don't do this!
> ---

What const checks can the compiler not do?
Also, if you know of an existing kernel API which can replace packing(),
I'm all ears.