linux-kernel - Re: [PATCH] staging: r8188eu: simplify complex pointer casting

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Date:   Sun, 6 Nov 2022 17:43:38 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Deepak R Varma <drv@...lo.com>
Cc:     Larry Finger <Larry.Finger@...inger.net>,
        Phillip Potter <phil@...lpotter.co.uk>,
        Pavel Skripkin <paskripkin@...il.com>,
        linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] staging: r8188eu: simplify complex pointer casting

On Sun, Nov 06, 2022 at 01:56:01PM +0530, Deepak R Varma wrote:
> Pointers to structures udphdr and dhcpMessage are derived by casting
> adjacent pointers with size_t. Such typecast of pointer using size_t
> is not preferred. The code looks complex and delicate. Simplify such
> casting by utilizing generic "void *" casting.
> While at this change, remove the unnecessary __be32 casting for member
> variable "cookie".

Wait, why is that unecessary?

And why is that part of this change, that should be a separate one, so
that it can be reverted when it's found to be buggy :)

> 
> Suggested-by: Joe Perches <joe@...ches.com>
> Signed-off-by: Deepak R Varma <drv@...lo.com>
> ---
>  drivers/staging/r8188eu/core/rtw_br_ext.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/staging/r8188eu/core/rtw_br_ext.c b/drivers/staging/r8188eu/core/rtw_br_ext.c
> index a23f7df373ed..e9b0906d0d74 100644
> --- a/drivers/staging/r8188eu/core/rtw_br_ext.c
> +++ b/drivers/staging/r8188eu/core/rtw_br_ext.c
> @@ -610,13 +610,15 @@ void dhcp_flag_bcast(struct adapter *priv, struct sk_buff *skb)
>  			struct iphdr *iph = (struct iphdr *)(skb->data + ETH_HLEN);
> 
>  			if (iph->protocol == IPPROTO_UDP) { /*  UDP */
> -				struct udphdr *udph = (struct udphdr *)((size_t)iph + (iph->ihl << 2));
> +				struct udphdr *udph = (void *)iph + (iph->ihl << 2);
> 
>  				if ((udph->source == htons(CLIENT_PORT)) &&
>  				    (udph->dest == htons(SERVER_PORT))) { /*  DHCP request */
> -					struct dhcpMessage *dhcph =
> -						(struct dhcpMessage *)((size_t)udph + sizeof(struct udphdr));
> -					u32 cookie = be32_to_cpu((__be32)dhcph->cookie);
> +					u32 cookie;
> +					struct dhcpMessage *dhcph;

Why reorder these variables?

> +
> +					dhcph = (void *)udph + sizeof(struct udphdr);
> +					cookie = be32_to_cpu(dhcph->cookie);

The cookie change should be separate please.

thanks,

greg k-h