getifaddrs and SocketCAN interfaces

getifaddrs and SocketCAN interfaces

[Paarvai Naai]

Hi,

I recently tried using getifaddrs to list all of the SocketCAN
interfaces on my system programmatically.

However, I found that the SocketCAN interfaces do not have their
ifa_addr field in the returned ifaddrs structure set.  This makes it
not possible to identifying the interface as type SocketCAN.
Presumably if the ifa_addr field was set, we could look at the
sa_family field and check if it is AF_CAN.

The other option is to use netlink to query the network devices, but
that is more involved.  Is there an easier way?

Thanks!
Paarvai

Re: getifaddrs and SocketCAN interfaces

[Oliver Hartkopp]

On 28.03.2015 21:30, Paarvai Naai wrote:
> I recently tried using getifaddrs to list all of the SocketCAN
> interfaces on my system programmatically.
> 
> However, I found that the SocketCAN interfaces do not have their
> ifa_addr field in the returned ifaddrs structure set.  This makes it
> not possible to identifying the interface as type SocketCAN.
> Presumably if the ifa_addr field was set, we could look at the
> sa_family field and check if it is AF_CAN.

Hi Paarvai,

on the CAN bus you don't have node addresses - so there's nothing comparable
to ethernet devices which have an IP-address bound to them.

The CAN netdevice stuff in linux/driver/net/can is currently separated from
the network layer stuff in linux/net/can pretty good.

So attaching a (useless) sock_addr from the network layer to the CAN
interface seems inappropriate.

Do you know about the network device ARPHRD definitions:

http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/include/uapi/linux/if_arp.h#n55

> The other option is to use netlink to query the network devices, but
> that is more involved.  Is there an easier way?

E.g. you can get this netdevice type information from

$ cat /sys/class/net/vcan0/type
280

Regards,
Oliver

Re: getifaddrs and SocketCAN interfaces

[dev.kurt]

On 29 March 2015 20:36:48 CEST, Oliver Hartkopp <socketcan@hartkopp.net> wrote:
>On 28.03.2015 21:30, Paarvai Naai wrote:
>> I recently tried using getifaddrs to list all of the SocketCAN
>> interfaces on my system programmatically.
>> 
>> However, I found that the SocketCAN interfaces do not have their
>> ifa_addr field in the returned ifaddrs structure set.  This makes it
>> not possible to identifying the interface as type SocketCAN.
>> Presumably if the ifa_addr field was set, we could look at the
>> sa_family field and check if it is AF_CAN.
>
>Hi Paarvai,
>
>on the CAN bus you don't have node addresses - so there's nothing
>comparable
>to ethernet devices which have an IP-address bound to them.
>
>The CAN netdevice stuff in linux/driver/net/can is currently separated
>from
>the network layer stuff in linux/net/can pretty good.
>
>So attaching a (useless) sock_addr from the network layer to the CAN
>interface seems inappropriate.
>
>Do you know about the network device ARPHRD definitions:
>
>http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/include/uapi/linux/if_arp.h#n55
>
>> The other option is to use netlink to query the network devices, but
>> that is more involved.  Is there an easier way?
>
>E.g. you can get this netdevice type information from

I created
https://github.com/kurt-vd/enumif
for this reason.
I'd explain if I was using my own computer

Kurt

Re: getifaddrs and SocketCAN interfaces

[Tom Evans]

On 29/03/15 07:30, Paarvai Naai wrote:
> Hi,
>
> I recently tried using getifaddrs to list all of the SocketCAN
> interfaces on my system programmatically.

root@triton1:/# find /sys -name "*can*"
/sys/bus/platform/devices/flexcan.0
/sys/bus/platform/devices/flexcan.1
/sys/bus/platform/drivers/flexcan
/sys/bus/platform/drivers/flexcan/flexcan.0
/sys/bus/platform/drivers/flexcan/flexcan.1
/sys/devices/soc.0/50000000.aips/flexcan.0
/sys/devices/soc.0/50000000.aips/flexcan.0/net/can0
/sys/devices/soc.0/50000000.aips/flexcan.1
/sys/devices/soc.0/50000000.aips/flexcan.1/net/can1
/sys/devices/virtual/net/vcan0
...
/sys/class/net/vcan0
/sys/class/net/can0
/sys/class/net/can1

Then I open them by name:

     struct ifreq ifr;
     strcpy(ifr.ifr_name, f_vnCanBusNames[a_eDevice]);
     /* ifr.ifr_ifindex gets filled
     rc = ioctl(pSkt->skt, SIOCGIFINDEX, &ifr);

Or was there something else you needed?

Tom

Re: getifaddrs and SocketCAN interfaces

[Paarvai Naai]

Hi Kurt,

Thanks for that pointer!  It's exactly what I'm looking for as it is
less complicated than libnetlink from iproute2.

(I see there was an earlier post about enumif too, but I missed it
during my earlier search:
http://permalink.gmane.org/gmane.linux.can/3351)

I see that your libenumif.cc has the following includes:
#include <linux/rtnetlink.h>
#include <linux/netlink.h>

Not being super familiar with netlink, what would you say are the
forward/backward compatibility guarantees for these kernel-level
includes?  I'm assuming the dependance on these kernel-level includes
is pretty stable?

Regarding, the other suggestions, these are good options too, but I'd
prefer not to use the /sys filesystem if possible.  Relying on /sys
can be brittle.

Thanks!
Paarvai

On Sun, Mar 29, 2015 at 12:40 PM,  <dev.kurt@vandijck-laurijssen.be> wrote:
> I created
> https://github.com/kurt-vd/enumif
> for this reason.
> I'd explain if I was using my own computer
>
> Kurt