[PATCH v2] ratp: Fix retransmission for header-only packets

[Jules Maselbas]

On Wed, Jan 25, 2023 at 04:39:59PM +0100, Jules Maselbas wrote:
> Using sendmsg_current to detect if a packet needs to be retransmitted is
> brittle as only packets containing data will ever be considered, packets
> only containing a header (without data) were never being retransmitted.
> 
> The sendbuf_len is used to determine if a packets is being send or not,
> a non-zero length means that a packets is still being in the "try-send"
> state, the length is not set to zero when a valid SN is received.
> 
> Retransmission issue can be easily reproduced with a physical UART (not
> cdc_acm over USB), by running the following command:
> 
>     while ratp-barebox-cli -b 115200 -t /dev/ttyACMx -p; do :; done
> 
> Alternatively, it is possible to modify lib/ratp.c to force packets to
> be sent by the retransmission logic with the following change:
> 
>     @ int ratp_send_pkt(struct ratp_internal *ri, void *pkt, int length)
>                     ri->sendbuf_len = length;
>     -               ri->retransmission_timer_start = get_time_ns();
>     +               ri->retransmission_timer_start = get_time_ns() - ri->rto * MSECOND/2;
>                     ri->retransmission_count = 0;
>             }
>     -       return ri->ratp->send(ri->ratp, pkt, length);
>     +       return 0;
> 
> Signed-off-by: Jules Maselbas <jmaselbas at kalray.eu>
> ---
> changes in v2: reset sendbuf_len to zero where appropriated (in each behavior)
> 
> lib/ratp.c | 25 +++++++++++++++++--------
>  1 file changed, 17 insertions(+), 8 deletions(-)
> 
> diff --git a/lib/ratp.c b/lib/ratp.c
> index ce30223bac..b582e4e779 100644
> --- a/lib/ratp.c
> +++ b/lib/ratp.c
> @@ -738,7 +738,7 @@ static int ratp_behaviour_c2(struct ratp_internal *ri, void *pkt)
>  		control = RATP_CONTROL_RST | RATP_CONTROL_ACK |
>  			ratp_set_sn(ratp_an(hdr)) | ratp_set_next_an(ratp_sn(hdr));
>  		ratp_send_hdr(ri, control);
> -
> +		ri->sendbuf_len = 0;
>  		ratp_state_change(ri, RATP_STATE_CLOSED);
>  		return 1;
>  	}
> @@ -784,7 +784,7 @@ static int ratp_behaviour_d1(struct ratp_internal *ri, void *pkt)
>  	ri->status = -ECONNREFUSED;
>  
>  	pr_debug("Error: connection refused\n");
> -
> +	ri->sendbuf_len = 0;
>  	ratp_state_change(ri, RATP_STATE_CLOSED);
>  
>  	return 1;
> @@ -812,6 +812,8 @@ static int ratp_behaviour_d2(struct ratp_internal *ri, void *pkt)
>  	ri->status = -ECONNRESET;
>  
>  	pr_debug("connection reset\n");
> +	ri->sendbuf_len = 0;
> +	ratp_state_change(ri, RATP_STATE_CLOSED);
>  
>  	return 0;
>  }
> @@ -879,7 +881,7 @@ static int ratp_behaviour_e(struct ratp_internal *ri, void *pkt)
>  	ratp_send_hdr(ri, control);
>  
>  	pr_debug("connection reset\n");
> -
> +	ri->sendbuf_len = 0;
>  	ratp_state_change(ri, RATP_STATE_CLOSED);
>  
>  	return 1;
> @@ -924,8 +926,10 @@ static int ratp_behaviour_f1(struct ratp_internal *ri, void *pkt)
>  	if (!(hdr->control & RATP_CONTROL_ACK))
>  		return 1;
>  
> -	if (ratp_an_expected(ri, hdr))
> +	if (ratp_an_expected(ri, hdr)) {
> +		ri->sendbuf_len = 0; /* packet succesfully received */
>  		return 0;
> +	}
>  
>  	control = RATP_CONTROL_RST | ratp_set_sn(ratp_an(hdr));
>  	ratp_send_hdr(ri, control);
> @@ -971,6 +975,8 @@ static int ratp_behaviour_f2(struct ratp_internal *ri, void *pkt)
>  		if (ri->sendmsg_current)
>  			ratp_msg_done(ri, ri->sendmsg_current, 0);
>  		ri->sendmsg_current = NULL;
> +		ri->sendbuf_len = 0; /* packet succesfully received */
> +		pr_debug("Data succesfully sent 0\n");
This pr_debug line was not intended to be included.

>  		return 0;
>  	} else {
>  		pr_vdebug("%s: an not expected\n", __func__);
> @@ -1175,6 +1181,7 @@ static int ratp_behaviour_h3(struct ratp_internal *ri, void *pkt)
>  		ratp_send_hdr(ri, control);
>  		ri->status = -ECONNRESET;
>  		pr_debug("Error: Connection reset\n");
> +		ri->sendbuf_len = 0;
>  		ratp_state_change(ri, RATP_STATE_CLOSED);
>  		return 1;
>  	}
> @@ -1217,8 +1224,10 @@ static int ratp_behaviour_h4(struct ratp_internal *ri, void *pkt)
>  
>  	pr_debug("%s\n", __func__);
>  
> -	if (ratp_an_expected(ri, hdr))
> +	if (ratp_an_expected(ri, hdr)) {
> +		ri->sendbuf_len = 0; /* packet succesfully received */
>  		ratp_state_change(ri, RATP_STATE_CLOSED);
> +	}
>  
>  	return 1;
>  }
> @@ -1244,6 +1253,7 @@ static int ratp_behaviour_h5(struct ratp_internal *ri, void *pkt)
>  	pr_debug("%s\n", __func__);
>  
>  	if (ratp_an_expected(ri, hdr)) {
> +		ri->sendbuf_len = 0; /* packet succesfully received */
>  		ratp_state_change(ri, RATP_STATE_TIME_WAIT);
>  		ratp_start_time_wait_timer(ri);
>  	}
> @@ -1580,9 +1590,8 @@ int ratp_poll(struct ratp *ratp)
>  		}
>  	}
>  
> -	if (ri->sendmsg_current && is_timeout(ri->retransmission_timer_start,
> +	if (ri->sendbuf_len && is_timeout(ri->retransmission_timer_start,
>  	    ri->rto * MSECOND)) {
> -
>  		ri->retransmission_count++;
>  		if (ri->retransmission_count == ri->max_retransmission) {
>  			ri->status = ret = -ETIMEDOUT;
> @@ -1601,7 +1610,7 @@ int ratp_poll(struct ratp *ratp)
>  			goto out;
>  	}
>  
> -	if (!ri->sendmsg_current && !list_empty(&ri->sendmsg))
> +	if (ri->sendbuf_len == 0 && !list_empty(&ri->sendmsg))
>  		ratp_send_next_data(ri);
>  
>  	ret = 0;
> -- 
> 2.17.1
>