linux-kernel - Re: [PATCH v2 03/13] can: slcan: use the alloc_can

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Date:   Thu, 9 Jun 2022 10:07:24 +0200
From:   Marc Kleine-Budde <mkl@...gutronix.de>
To:     Dario Binacchi <dario.binacchi@...rulasolutions.com>
Cc:     linux-kernel@...r.kernel.org,
        Amarula patchwork <linux-amarula@...rulasolutions.com>,
        michael@...rulasolutions.com,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Wolfgang Grandegger <wg@...ndegger.com>,
        linux-can@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH v2 03/13] can: slcan: use the alloc_can_skb() helper

On 08.06.2022 18:51:06, Dario Binacchi wrote:
> It is used successfully by most (if not all) CAN device drivers. It
> allows to remove replicated code.
> 
> Signed-off-by: Dario Binacchi <dario.binacchi@...rulasolutions.com>
> 
> ---
> 
> Changes in v2:
> - Put the data into the allocated skb directly instead of first
>   filling the "cf" on the stack and then doing a memcpy().
> 
>  drivers/net/can/slcan.c | 69 +++++++++++++++++++----------------------
>  1 file changed, 32 insertions(+), 37 deletions(-)
> 
> diff --git a/drivers/net/can/slcan.c b/drivers/net/can/slcan.c
> index 6162a9c21672..5d87e25e2285 100644
> --- a/drivers/net/can/slcan.c
> +++ b/drivers/net/can/slcan.c
> @@ -54,6 +54,7 @@
>  #include <linux/kernel.h>
>  #include <linux/workqueue.h>
>  #include <linux/can.h>
> +#include <linux/can/dev.h>
>  #include <linux/can/skb.h>
>  #include <linux/can/can-ml.h>
>  
> @@ -143,85 +144,79 @@ static struct net_device **slcan_devs;
>  static void slc_bump(struct slcan *sl)
>  {
>  	struct sk_buff *skb;
> -	struct can_frame cf;
> +	struct can_frame *cf;
>  	int i, tmp;
>  	u32 tmpid;
>  	char *cmd = sl->rbuff;
>  
> -	memset(&cf, 0, sizeof(cf));
> +	skb = alloc_can_skb(sl->dev, &cf);
> +	if (unlikely(!skb)) {
> +		sl->dev->stats.rx_dropped++;
> +		return;
> +	}
>  
>  	switch (*cmd) {
>  	case 'r':
> -		cf.can_id = CAN_RTR_FLAG;
> +		cf->can_id = CAN_RTR_FLAG;
>  		fallthrough;
>  	case 't':
>  		/* store dlc ASCII value and terminate SFF CAN ID string */
> -		cf.len = sl->rbuff[SLC_CMD_LEN + SLC_SFF_ID_LEN];
> +		cf->len = sl->rbuff[SLC_CMD_LEN + SLC_SFF_ID_LEN];
>  		sl->rbuff[SLC_CMD_LEN + SLC_SFF_ID_LEN] = 0;
>  		/* point to payload data behind the dlc */
>  		cmd += SLC_CMD_LEN + SLC_SFF_ID_LEN + 1;
>  		break;
>  	case 'R':
> -		cf.can_id = CAN_RTR_FLAG;
> +		cf->can_id = CAN_RTR_FLAG;
>  		fallthrough;
>  	case 'T':
> -		cf.can_id |= CAN_EFF_FLAG;
> +		cf->can_id |= CAN_EFF_FLAG;
>  		/* store dlc ASCII value and terminate EFF CAN ID string */
> -		cf.len = sl->rbuff[SLC_CMD_LEN + SLC_EFF_ID_LEN];
> +		cf->len = sl->rbuff[SLC_CMD_LEN + SLC_EFF_ID_LEN];
>  		sl->rbuff[SLC_CMD_LEN + SLC_EFF_ID_LEN] = 0;
>  		/* point to payload data behind the dlc */
>  		cmd += SLC_CMD_LEN + SLC_EFF_ID_LEN + 1;
>  		break;
>  	default:
> -		return;
> +		goto decode_failed;
>  	}
>  
>  	if (kstrtou32(sl->rbuff + SLC_CMD_LEN, 16, &tmpid))
> -		return;
> +		goto decode_failed;
>  
> -	cf.can_id |= tmpid;
> +	cf->can_id |= tmpid;
>  
>  	/* get len from sanitized ASCII value */
> -	if (cf.len >= '0' && cf.len < '9')
> -		cf.len -= '0';
> +	if (cf->len >= '0' && cf->len < '9')
> +		cf->len -= '0';
>  	else
> -		return;
> +		goto decode_failed;
>  
>  	/* RTR frames may have a dlc > 0 but they never have any data bytes */
> -	if (!(cf.can_id & CAN_RTR_FLAG)) {
> -		for (i = 0; i < cf.len; i++) {
> +	if (!(cf->can_id & CAN_RTR_FLAG)) {
> +		for (i = 0; i < cf->len; i++) {
>  			tmp = hex_to_bin(*cmd++);
>  			if (tmp < 0)
> -				return;
> -			cf.data[i] = (tmp << 4);
> +				goto decode_failed;
> +
> +			cf->data[i] = (tmp << 4);
>  			tmp = hex_to_bin(*cmd++);
>  			if (tmp < 0)
> -				return;
> -			cf.data[i] |= tmp;
> +				goto decode_failed;
> +
> +			cf->data[i] |= tmp;
>  		}
>  	}
>  
> -	skb = dev_alloc_skb(sizeof(struct can_frame) +
> -			    sizeof(struct can_skb_priv));
> -	if (!skb)
> -		return;
> -
> -	skb->dev = sl->dev;
> -	skb->protocol = htons(ETH_P_CAN);
> -	skb->pkt_type = PACKET_BROADCAST;
> -	skb->ip_summed = CHECKSUM_UNNECESSARY;
> -
> -	can_skb_reserve(skb);
> -	can_skb_prv(skb)->ifindex = sl->dev->ifindex;
> -	can_skb_prv(skb)->skbcnt = 0;
> -
> -	skb_put_data(skb, &cf, sizeof(struct can_frame));
> -
>  	sl->dev->stats.rx_packets++;
> -	if (!(cf.can_id & CAN_RTR_FLAG))
> -		sl->dev->stats.rx_bytes += cf.len;
> +	if (!(cf->can_id & CAN_RTR_FLAG))
> +		sl->dev->stats.rx_bytes += cf->len;
>  
>  	netif_rx(skb);
> +	return;
> +
> +decode_failed:
> +	dev_kfree_skb(skb);

Can you increase an error counter in this situation, too?

Marc

>  }
>  
>  /* parse tty input stream */
> -- 
> 2.32.0
> 
> 

-- 
Pengutronix e.K.                 | Marc Kleine-Budde           |
Embedded Linux                   | https://www.pengutronix.de  |
Vertretung West/Dortmund         | Phone: +49-231-2826-924     |
Amtsgericht Hildesheim, HRA 2686 | Fax:   +49-5121-206917-5555 |

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