Oliver Hartkopp wrote: > Hi Matthias, > > Matthias Fuchs wrote: >> I played a little with various ways to manipulate tx/rxqueuesizes with >> SocketCAN. >> I ended up with some questions: >> >> 1) Does setsockopt(... ,SOL_SOCKET, SO_SNDBUF, ....) have any impact on >> CAN_RAW sockets? >> My result: no! > > Ack. > >> 2) Does setsockopt(... ,SOL_SOCKET, SO_RCVBUF, ....) have any impact on >> CAN_RAW sockets? >> Yes, that's also used by candump to prevent losing rx frames. >> >> 1+2 brings me to the conclusion that setsockopt(..., SO_RCVBUF, ...) >> configures receive >> behavior and "ip link set can0 txqueuelen <whatever>" configures tx >> behavior. Did I miss >> anything? > > No. That's the current behaviour. > >> 3) Do we have a way to make write() on CAN_RAW sockets block when there is >> no more buffer space? Typical behavior is returning ENOBUFS. I haven't tried >> to >> use select() for sending. Does this work? > > Yes. That should work. > > We had a discussion on this recently. > > http://old.nabble.com/-PATCH-0-2--add-support-for-Janz-MODULbus-devices-tp27662172p27715072.html > > Due to that discussion, i added the poll support to the 'cangen' tool: > > http://svn.berlios.de/wsvn/socketcan/?op=comp&compare[]=%2ftrunk%2fcan-ut...@1149&compare[]=%2ftrunk%2fcan-ut...@1146
I short, it does work but the poll/slect seems not to block as expected. >> 4) Do we have a way to flush the txqueue and block until all messages are on >> the bus? >> fsync() does not seem to be the right choice. > > AFAIK there's no way from the userspace to flush the txqueue - only set the > interface state to "down" ... > >> 5) Is there any special reason why read/write can only handle single >> messages? >> Is it just because nobody asked? It should be possible with our >> fixed size stuct can_frame. It could even speed thing up. > > This is an interesting idea. BUT the problem is that all the drivers and > especially the echo_skb handling deals with single skb's. For a good reason. > > But i could imagine to implement a multi-frame handling inside the CAN_RAW > socket. This could be done with a loop that splits it into single skb's in > raw_sendmsg() quite easily. > > At least this would reduce the number of userspace->kernelspace copies. > > But you would need to check the return code to check how many frames have been > written (when the txqueue is getting full). > > Interested? It should be done via sendmsg/recvmsg, I think. But it needs to be supported by the protocol. Here is an example: http://lxr.linux.no/#linux+v2.6.33/net/ipv4/tcp.c#L929 Wolfgang. _______________________________________________ Socketcan-users mailing list [email protected] https://lists.berlios.de/mailman/listinfo/socketcan-users
