linux-kernel - Re: [PATCH] dpaa_eth: Fix comparing pointer to 0

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Date:   Mon, 27 Apr 2020 13:26:45 +0200
From:   Markus Elfring <Markus.Elfring@....de>
To:     Aishwarya Ramakrishnan <aishwaryarj100@...il.com>,
        netdev@...r.kernel.org, Coccinelle <cocci@...teme.lip6.fr>
Cc:     linux-kernel@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Madalin Bucur <madalin.bucur@....com>
Subject: Re: [PATCH] dpaa_eth: Fix comparing pointer to 0

> Fixes coccicheck warning:
> ./drivers/net/ethernet/freescale/dpaa/dpaa_eth.c:2110:30-31:
> WARNING comparing pointer to 0

Such information is actually provided by a known script for
the semantic patch language.
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/log/scripts/coccinelle/null/badzero.cocci

> Avoid pointer type value compared to 0.

But I suggest to reconsider corresponding software development consequences
also around mentioned implementation details.

…
> +++ b/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
> @@ -2107,7 +2107,7 @@ static int dpaa_a050385_wa(struct net_device *net_dev, struct sk_buff **s)
…
>  	start = PTR_ALIGN(new_skb->data, DPAA_A050385_ALIGN);
> -	if (start - new_skb->data != 0)
> +	if (start - new_skb->data)
>  		skb_reserve(new_skb, start - new_skb->data);
…

I interpret the source code in the way that a subtraction is performed
with two pointers. I would expect that such a pointer difference
has got an integral data type.
Will this view trigger any further software evolution?

Regards,
Markus