linux-kernel - Re: [PATCH 2/4] Staging: rtl8712: Use ether_addr

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Date:	Sat, 10 Oct 2015 12:34:54 -0500
From:	Larry Finger <Larry.Finger@...inger.net>
To:	Punit Vara <punitvara@...il.com>
Cc:	gregkh@...uxfoundation.org, stillcompiling@...il.com,
	sudipm.mukherjee@...il.com, dan.carpenter@...cle.com,
	dogukan.ergun@...il.com, Julia.Lawall@...6.fr,
	devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] Staging: rtl8712: Use ether_addr_equal() over
 memcmp()

On 10/10/2015 11:58 AM, Punit Vara wrote:
> This patch is to the rtl871x_ioctl_linux.c file that fixes up following
> warning reported by checkpatch.pl :
>
> -Prefer ether_addr_equal() or ether_addr_equal_unaligned() over memcmp()
>
> bssid has datatype u8 and pnetwork->network.MacAddress has data type
>   unsigned char.
>
> Signed-off-by: Punit Vara <punitvara@...il.com>
> ---
>   drivers/staging/rtl8712/rtl871x_ioctl_linux.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/staging/rtl8712/rtl871x_ioctl_linux.c b/drivers/staging/rtl8712/rtl871x_ioctl_linux.c
> index 2ba055d..1c9092e 100644
> --- a/drivers/staging/rtl8712/rtl871x_ioctl_linux.c
> +++ b/drivers/staging/rtl8712/rtl871x_ioctl_linux.c
> @@ -2007,7 +2007,7 @@ static int r871x_get_ap_info(struct net_device *dev,
>   			return -EINVAL;
>   		}
>   		netdev_info(dev, "r8712u: BSSID:%pM\n", bssid);
> -		if (!memcmp(bssid, pnetwork->network.MacAddress, ETH_ALEN)) {
> +		if (!ether_addr_equal(bssid, pnetwork->network)) {
>   			/* BSSID match, then check if supporting wpa/wpa2 */
>   			pbuf = r8712_get_wpa_ie(&pnetwork->network.IEs[12],
>   			       &wpa_ielen, pnetwork->network.IELength-12);
>

The types of the variables are not what is important - it is the alignment!

I suggest that you read the definition of ether_addr_equal() and consider what 
happens if either of the two addresses is not aligned to u16!

You also have a logic error. Routine memcmp() returns zero when the two 
arguments are equal. Thus !memcmp() will be true when they are equal. Routine 
ether_addr_equal() returns true when the arguments are equal. Whenever !memcmp() 
is correct and the arguments are aligned, then you need to replace it with 
ether_addr_equal().

The checkpatch script is a good tool for locating things to be changed; however, 
if the change is other than cosmetic, you *MUST THINK* about what is happening. 
Yes, rtl8712 is ugly code, but it works. Please do not break it.

NACK.

Larry

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