Add SocketCAN support

[jthomas-geotab]

My company is working on several embedded Linux projects and we would like to switch from running Ubuntu under VirtualBox to WSL. However, we need SocketCAN support along with the Virtual CAN (vcan) driver. Can you please add these to the WSL kernel?

[therealkenc]

I gather this is CONFIG_CAN_RAW et al.

[jthomas-geotab]

Yes, I think this is the minimum useful set:
CONFIG_CAN
CONFIG_CAN_RAW
CONFIG_CAN_BCM
CONFIG_CAN_VCAN
CONFIG_CAN_SLCAN
CONFIG_CAN_DEV
CONFIG_CAN_CALC_BITTIMING

Would also be good to get support for some CAN USB adapters. I am using CONFIG_CAN_PEAK_USB

[therealkenc]

In the interim between now and when those configs hypothetically became enabled in a stock release, you can try rolling your own kernel and see if it is viable.

Would also be good to get support for some CAN USB adapters

USB passthrough at the kernel level would be another kettle of fish.

[jthomas-geotab]

Oh cool, I didn't know you could run your own custom kernel with WSL 2!

[therealkenc]

You can also compile just the modules and insmod them, which is sometimes a safer approach because you are less likely to "break something else" in the process. YRMV caveats apply; custom kernels isn't really a supported scenario (if there is such a thing) but people have had some luck.

[windelbouwman]

For anyone trying this, these were my steps:

$ git clone https://github.com/microsoft/WSL2-Linux-Kernel
$ cd WSL2-Linux-Kernel
$ git checkout `uname -r`
$ cat /proc/config.gz | gunzip > .config
$ make prepare modules_prepare
$ make menuconfig  # select vcan and can here
$ make modules
# make modules_install
# modprobe vcan
# ip link add dev vcan0 type vcan
# ip link set up vcan0
# apt install can-utils

So far so good, however, candump does not cooperate: socket: Address family not supported by protocol

This is an interesting effect:

# modprobe can_raw  --> wsl dies

Update: building your own kernel for WSL works! You can enable CONFIG_CAN_VCAN=y and use it.

[windelbouwman]

I opened a proposal here:

https://github.com/microsoft/WSL2-Linux-Kernel/pull/242/files

[blackliner]

git checkout `uname -r`

Did not work for my current kernel (5.4.72-microsoft-standard-WSL2), but found the correct branch here: https://github.com/microsoft/WSL2-Linux-Kernel/releases/tag/linux-msft-5.4.72

linux-msft-5.4.72

but unfortunately, I did not get it installed with your steps, still getting:

$ modprobe vcan
modprobe: FATAL: Module vcan not found in directory /lib/modules/5.4.72-microsoft-standard-WSL2

maybe I have other issues with my install?

$ ll /lib/modules
total 44
drwxr-xr-x 11 root root 4096 Mar 20 09:32 ./
drwxr-xr-x 21 root root 4096 Dec 23 21:53 ../
drwxr-xr-x  2 root root 4096 Sep  4  2020 4.15.0-106-generic/
drwxr-xr-x  2 root root 4096 Sep  4  2020 4.15.0-112-generic/
drwxr-xr-x  2 root root 4096 Sep  4  2020 4.15.0-115-generic/
drwxr-xr-x  2 root root 4096 Sep 28 08:36 4.15.0-117-generic/
drwxr-xr-x  2 root root 4096 Sep 28 11:58 4.15.0-118-generic/
drwxr-xr-x  2 root root 4096 Nov 24 23:43 4.15.0-124-generic/
drwxr-xr-x  3 root root 4096 Mar  9 22:24 4.15.0-136-generic/
drwxr-xr-x  3 root root 4096 Mar 20 09:14 4.15.0-139-generic/
drwxr-xr-x  3 root root 4096 Mar 20 09:35 5.4.72-microsoft-standard-WSL2+/

[jeremitu]

The problem is in the +. After mv 5.4.72-microsoft-standard-WSL2+ 5.4.72-microsoft-standard-WSL2 I ran into the next problem:

# modprobe vcan
modprobe: ERROR: could not insert 'vcan': Invalid argument
$ dmesg | tail
[649362.799943] vcan: disagrees about version of symbol kfree_skb
[649362.799944] vcan: Unknown symbol kfree_skb (err -22)
... # and many more
# modprobe --dump-modversions 5.4.72-microsoft-standard-WSL2/kernel/drivers/net/can/vcan.ko
0x61040109      module_layout
...
0xf8604075      kfree_skb
...

I do not know what to compare it against, but I guess there are differences in the binary layout between the tagged and released version.

[therealkenc]

I should probably walk back the "sometimes a safer approach" comment in the sense it does introduce the potential for a symbol version conflict. There was no conflict last I tried checking out the correct linux-msft-[45].x.y, but can't strictly confirm or deny linux-msft-5.4.72 results in a conflict either, because I haven't tried. If in doubt, compile the modules you want in-kernel with =y.

[jeremitu]

I left the modules as =m, put + back in place in lib/modules/5.4.72-microsoft-standard-WSL2+ and compiled/set up the kernel with:

$ make -j8 # quick after modules are compiled
$ cp vmlinux /mnt/c/Users/<me>/

rem Windows: create C:\Users\<me>\.wslconfig:
[wsl2]
kernel=C:\\Users\\<me>\\vmlinux
cmd> wsl --shutdown
cmd> wsl
$  uname -r
5.4.72-microsoft-standard-WSL2+
# modprobe vcan # works!

[blackliner]

@microsoft can we get this as a default feature?