Re: [PATCH RFC] can-dev: fix real payload length return value for RTR frames - Marc Kleine-Budde

From: Marc Kleine-Budde <mkl@pengutronix.de>
To: Oliver Hartkopp <socketcan@hartkopp.net>, linux-can@vger.kernel.org
Cc: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Subject: Re: [PATCH RFC] can-dev: fix real payload length return value for RTR frames
Date: Tue, 20 Oct 2020 09:07:45 +0200	[thread overview]
Message-ID: <0e382596-9f05-5af7-e2bb-4d74c507eabb@pengutronix.de> (raw)
In-Reply-To: <20201020064443.80164-1-socketcan@hartkopp.net>

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On 10/20/20 8:44 AM, Oliver Hartkopp wrote:
> The can_get_echo_skb() function returns the number of received bytes to
> be used for netdev statistics. In the case of RTR frames we get a valid
> (potential non-zero) data length value which has to be passed for further
> operations. But on the wire RTR frames have no payload length. Therefore
> the value to be used in the statistics has to be zero for RTR frames.
> 
> Reported-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
> Link: https://lore.kernel.org/r/20201002154219.4887-4-mailhol.vincent@wanadoo.fr
> Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
> ---
>  drivers/net/can/dev.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/can/dev.c b/drivers/net/can/dev.c
> index b70ded3760f2..64c8cb27154b 100644
> --- a/drivers/net/can/dev.c
> +++ b/drivers/net/can/dev.c
> @@ -510,13 +510,17 @@ __can_get_echo_skb(struct net_device *dev, unsigned int idx, u8 *len_ptr)
>  		/* Using "struct canfd_frame::len" for the frame
>  		 * length is supported on both CAN and CANFD frames.
>  		 */
>  		struct sk_buff *skb = priv->echo_skb[idx];
>  		struct canfd_frame *cf = (struct canfd_frame *)skb->data;
> -		u8 len = cf->len;
>  
> -		*len_ptr = len;
> +		/* get the real payload length for netdev statistics */
> +		if (cf->can_id & CAN_RTR_FLAG)
> +			*len_ptr = 0;
> +		else
> +			*len_ptr = cf->len;
> +
>  		priv->echo_skb[idx] = NULL;
>  
>  		return skb;
>  	}

Looks good. I've replaced patches 4 and 5 by this one.

tnx,
Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde           |
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