Load kernel modules

[terlar]

WSL now supports kernel modules and come with a bunch configured as m and can be loaded this way. For example vhci-hcd used by usbip has changed from y to m and hence need to be explicitly loaded.

dorssel/usbipd-win#995
microsoft/WSL#11789 (comment)

Unfortunately we cannot use boot.kernelModules since it is gated behind boot.kernel.enable.

[K900]

Why can't we reuse boot.kernelModules here?

[terlar]

Since it is gated behind boot.kernel.enable which we don't want to enable.

Another option is to have something like a boolean wsl.loadKernelModules. That will write the file with the value based on boot.kernelModules. What do you prefer?

[K900]

Wait, how does this even work. Isn't our modprobe looking in the wrong path for this?

[nzbr]

Just wanted to ask this, because if I run insmod vhci-hcd it does not find the module file

  root@pulsar
ZS /home/nzbr> insmod vhci-hcd
insmod: ERROR: could not load module vhci-hcd: No such file or directory

[K900]

You want modprobe.

[terlar]

Systemd will do the loading based on config files located in this directory /etc/modules-load.d.

https://www.freedesktop.org/software/systemd/man/latest/modules-load.d.html

For NixOS it works like this:

• https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/system/boot/kernel.nix#L11
• https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/system/boot/kernel.nix#L321
• https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/system/boot/kernel.nix#L370

[K900]

But how does it know where to find the WSL modules

[terlar]

It is bundled with the kernel as loadable modules as I understand it and this change happened in the latest WSL kernel release (6.6). See release notes

[nzbr]

You want modprobe.

It seems that modprobe does not report if it failed though. It'll just run through but then lsmod will still show that no modules are loaded

[K900]

WSL also rolled back to 5.15 for now. I really want to see a test at this point to actually verify it does what it says.

[nzbr]

Ah, i have 5.15, that might be why this doesn't work

[terlar]

Yes, that is a bit confusing, just discovered they reverted to the older kernel again now when I was looking into it. I have tested this on WSL with the 6.6 kernel and verified it works. But I guess we might as well wait looking into it since the latest WSL went back to the older kernel.

[Stinjul]

WSL 2.5.7 switched to the 6.6 kernel, can this PR get merged now?