linux-kernel - Re: [PATCH 1/1] can: skb: add and set local

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Date:   Wed, 11 May 2022 14:38:32 +0200
From:   Oliver Hartkopp <socketcan@...tkopp.net>
To:     Oleksij Rempel <o.rempel@...gutronix.de>,
        Wolfgang Grandegger <wg@...ndegger.com>,
        Marc Kleine-Budde <mkl@...gutronix.de>
Cc:     Devid Antonio Filoni <devid.filoni@...uetechnologies.com>,
        kernel@...gutronix.de, linux-can@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        David Jander <david@...tonic.nl>
Subject: Re: [PATCH 1/1] can: skb: add and set local_origin flag

Hi Oleksij,

On 5/11/22 14:19, Oleksij Rempel wrote:
> Add new can_skb_priv::local_origin flag to be able detect egress
> packages even if they was sent directly from kernel and not assigned to
> some socket.
> 
> Signed-off-by: Oleksij Rempel <o.rempel@...gutronix.de>
> Cc: Devid Antonio Filoni <devid.filoni@...uetechnologies.com>
> ---
>   drivers/net/can/dev/skb.c | 3 +++
>   include/linux/can/skb.h   | 1 +
>   net/can/raw.c             | 2 +-
>   3 files changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/can/dev/skb.c b/drivers/net/can/dev/skb.c
> index 61660248c69e..3e2357fb387e 100644
> --- a/drivers/net/can/dev/skb.c
> +++ b/drivers/net/can/dev/skb.c
> @@ -63,6 +63,7 @@ int can_put_echo_skb(struct sk_buff *skb, struct net_device *dev,
>   
>   		/* save frame_len to reuse it when transmission is completed */
>   		can_skb_prv(skb)->frame_len = frame_len;
> +		can_skb_prv(skb)->local_origin = true;
>   
>   		skb_tx_timestamp(skb);
>   
> @@ -200,6 +201,7 @@ struct sk_buff *alloc_can_skb(struct net_device *dev, struct can_frame **cf)
>   	can_skb_reserve(skb);
>   	can_skb_prv(skb)->ifindex = dev->ifindex;
>   	can_skb_prv(skb)->skbcnt = 0;
> +	can_skb_prv(skb)->local_origin = false;
>   
>   	*cf = skb_put_zero(skb, sizeof(struct can_frame));
>   
> @@ -231,6 +233,7 @@ struct sk_buff *alloc_canfd_skb(struct net_device *dev,
>   	can_skb_reserve(skb);
>   	can_skb_prv(skb)->ifindex = dev->ifindex;
>   	can_skb_prv(skb)->skbcnt = 0;
> +	can_skb_prv(skb)->local_origin = false;

IMO this patch does not work as intended.

You probably need to revisit every place where can_skb_reserve() is 
used, e.g. in raw_sendmsg().

E.g. to make it work for virtual CAN and vxcan interfaces.

I'm a bit unsure why we should not stick with the simple skb->sk handling?

Regards,
Oliver

>   
>   	*cfd = skb_put_zero(skb, sizeof(struct canfd_frame));
>   
> diff --git a/include/linux/can/skb.h b/include/linux/can/skb.h
> index fdb22b00674a..1b8a8cf2b13b 100644
> --- a/include/linux/can/skb.h
> +++ b/include/linux/can/skb.h
> @@ -52,6 +52,7 @@ struct can_skb_priv {
>   	int ifindex;
>   	int skbcnt;
>   	unsigned int frame_len;
> +	bool local_origin;
>   	struct can_frame cf[];
>   };
>   
> diff --git a/net/can/raw.c b/net/can/raw.c
> index b7dbb57557f3..df2d9334b395 100644
> --- a/net/can/raw.c
> +++ b/net/can/raw.c
> @@ -173,7 +173,7 @@ static void raw_rcv(struct sk_buff *oskb, void *data)
>   	/* add CAN specific message flags for raw_recvmsg() */
>   	pflags = raw_flags(skb);
>   	*pflags = 0;
> -	if (oskb->sk)
> +	if (can_skb_prv(skb)->local_origin)
>   		*pflags |= MSG_DONTROUTE;
>   	if (oskb->sk == sk)
>   		*pflags |= MSG_CONFIRM;