Re: [Socketcan-users] increase buffer size

[Oliver Hartkopp <socketcan@hartkopp.net>]

On 24.01.2012 17:50, Steffen Rose wrote:

> Am Dienstag, 24. Januar 2012, 17:31:56 schrieb Heinz-Juergen Oertel:
>> Von meinem iPhone gesendet
>>
>> Am 24.01.2012 um 16:36 schrieb Steffen Rose <ro@emtas.de>:
>>> Du liest sicher mit...
>>
>> Ja, werde trotzdem nicht schlau wer die  Puffer, bes. RX verwaltet.
> 
> Wenn Du mich fragts:
> 
> RX Buffer: Hier wird die Socket Quere genutzt.


Yes. When a CAN frame is received the frame is delivered to the per-socket
receive queue due to the socket specific selected filter (default: receive
everything from the given CAN netdevice). See can.txt

http://lxr.linux.no/#linux+v3.2.1/Documentation/networking/can.txt#L245

and for the filters:

http://lxr.linux.no/#linux+v3.2.1/Documentation/networking/can.txt#L377

You can play with the filters using 'candump' that allows to set up multiple
filters.

> TX Buffer: Hierfür ist der CAN Treiber verantwortlich. Die Socket Quere könnte 
> genutzt werden, wird aber typ. nicht genutzt.


Writing to a CAN_RAW socket leads directly to the can_send() function that
put's the CAN frame to the CAN netdevice specific tx queue.

See:

http://lxr.linux.no/#linux+v3.2.1/net/can/raw.c#L640

http://lxr.linux.no/#linux+v3.2.1/net/can/raw.c#L690

If there's space in the queue it is stored into the FIFO.
If the tx queue is full, you directly get an error for the write() or
send[msg]() system call.

http://lxr.linux.no/#linux+v3.2.1/net/can/af_can.c#L209

Regards,
Oliver