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

[Jules Maselbas <jmaselbas@kalray.eu>]

Hi Sascha,

On Fri, Feb 03, 2023 at 09:16:08AM +0100, Sascha Hauer wrote:
> Hi Jules,
> 
> 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@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(-)
> 
> Is this one still ok to be applied from your side?
No, I will send a new series with some additional patches.

> This doesn't fix the issue you are mentioning in the other thread,
> right?
It does fix an issue but it is not sufficient, but the RATP protcol needs
to fix as well

> Sascha
> 
> > 
> > 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");
> >  		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
> > 
> > 
> > 
> 
> -- 
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> 
> 
>