vcan multithreaded problem testing

vcan multithreaded problem testing

[John Whitmore]

Hello all, I'll try keep this short. I'm using vcan to test code I'm porting
from my embedded hardware. My embedded code has a simple dispatcher which
process all messages received from the Network. Higher layers of the
Application register an interest in certain CAN ids or ranges.

I don't need this dispatcher as Socket CAN filters already so in porting my
application the higher layers now simply create a new linux thread and socket
to listen for CAN Frames that they have an interest in.

My problem is that in testing with vcan if my core process thead sends a CAN
id which a child thread is filtering on then the child thread receives the
message. I've looked at vcan code and it simply consumes the sent frames back
into the linux networking stack.

At present a single process will not receive a CAN Frame which is sends but
it's child threads will recive the frame. Is there a way to restrict this? I
might have to wait until I get back to Hardware and test there but it would be
very handy to be able to use vcan.

John

Re: vcan multithreaded problem testing

[Marc Kleine-Budde]

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On 02/16/2014 11:04 AM, John Whitmore wrote:
> Hello all, I'll try keep this short. I'm using vcan to test code I'm porting
> from my embedded hardware. My embedded code has a simple dispatcher which
> process all messages received from the Network. Higher layers of the
> Application register an interest in certain CAN ids or ranges.
> 
> I don't need this dispatcher as Socket CAN filters already so in porting my
> application the higher layers now simply create a new linux thread and socket
> to listen for CAN Frames that they have an interest in.
> 
> My problem is that in testing with vcan if my core process thead sends a CAN
> id which a child thread is filtering on then the child thread receives the
> message. I've looked at vcan code and it simply consumes the sent frames back
> into the linux networking stack.
> 
> At present a single process will not receive a CAN Frame which is sends but
> it's child threads will recive the frame. Is there a way to restrict this? I
> might have to wait until I get back to Hardware and test there but it would be
> very handy to be able to use vcan.

The CAN stack doesn't care about thread or processes, it's all about
sockets.

By default a socket doesn't receive the CAN frame it sends. When a CAN
frame is successfully send, by default all other sockets receive the
locally created CAN frames, too. You can change both defaults. Have a
look at the can.txt documentation in the Linux kernel:

http://lxr.free-electrons.com/source/Documentation/networking/can.txt#L184
http://lxr.free-electrons.com/source/Documentation/networking/can.txt#L502
http://lxr.free-electrons.com/source/Documentation/networking/can.txt#L513

Feel free to ask, if you need more information.

cheers,
Marc

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