linux-kernel - Re: [PATCH] j1939: fix unable to send messages with data length zero

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Message-ID: <20250107-conscious-daring-lemming-c63aa8-mkl@pengutronix.de>
Date: Tue, 7 Jan 2025 14:48:17 +0100
From: Marc Kleine-Budde <mkl@...gutronix.de>
To: Alexander Hölzl <alexander.hoelzl@....net>
Cc: robin@...tonic.nl, socketcan@...tkopp.net, davem@...emloft.net, 
	edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com, corbet@....net, 
	kernel@...gutronix.de, linux-can@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] j1939: fix unable to send messages with data length zero

On 07.01.2025 14:32:17, Alexander Hölzl wrote:
> The J1939 standard requires the transmission of messages of length 0.
> For example the proprietary messages are specified with a data length
> of 0 to 1785. The transmission of such messages was not possible.
> Sending such a message resulted in no error being returned but no
> corresponding can frame being generated.

What does your patch do? Please describe it here.

Marc

> Signed-off-by: Alexander Hölzl <alexander.hoelzl@....net>
> ---
>  net/can/j1939/socket.c    | 4 ++--
>  net/can/j1939/transport.c | 5 +++--
>  2 files changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/net/can/j1939/socket.c b/net/can/j1939/socket.c
> index 305dd72c844c..17226b2341d0 100644
> --- a/net/can/j1939/socket.c
> +++ b/net/can/j1939/socket.c
> @@ -1132,7 +1132,7 @@ static int j1939_sk_send_loop(struct j1939_priv *priv,  struct sock *sk,
> 
>  	todo_size = size;
> 
> -	while (todo_size) {
> +	do {
>  		struct j1939_sk_buff_cb *skcb;
> 
>  		segment_size = min_t(size_t, J1939_MAX_TP_PACKET_SIZE,
> @@ -1177,7 +1177,7 @@ static int j1939_sk_send_loop(struct j1939_priv *priv,  struct sock *sk,
> 
>  		todo_size -= segment_size;
>  		session->total_queued_size += segment_size;
> -	}
> +	} while (todo_size);
> 
>  	switch (ret) {
>  	case 0: /* OK */
> diff --git a/net/can/j1939/transport.c b/net/can/j1939/transport.c
> index 319f47df3330..99832e60c08d 100644
> --- a/net/can/j1939/transport.c
> +++ b/net/can/j1939/transport.c
> @@ -382,8 +382,9 @@ sk_buff *j1939_session_skb_get_by_offset(struct j1939_session *session,
>  	skb_queue_walk(&session->skb_queue, do_skb) {
>  		do_skcb = j1939_skb_to_cb(do_skb);
> 
> -		if (offset_start >= do_skcb->offset &&
> -		    offset_start < (do_skcb->offset + do_skb->len)) {
> +		if ((offset_start >= do_skcb->offset &&
> +		     offset_start < (do_skcb->offset + do_skb->len)) ||
> +			(offset_start == 0 && do_skcb->offset == 0 && do_skb->len == 0)) {
>  			skb = do_skb;
>  		}
>  	}
> --
> 2.43.0
> 
> 
> 

-- 
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