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udev not on-demand-loading modules with custom kernel



Hi all.

I need help getting module on-demand-loading working with a custom kernel.

Currently I'm running Debian 11 for x86_64 on a Chromebook in developer mode directly via Coreboot/Depthcharge. Not having UEFI or classical BIOS boot code means that the default Debian kernel doesn't work, right? So I'm using a kernel from the chromiumOS project (ChromeOS 5.10) with a custom config.

I do need a patched kernel anyways as there's no UEFI/ACPI but a special Chromebook embedded controller for all those fancy sensors and a like.

The system is working fine, including wifi, rotation sensors, graphics and so on except the on demand kernel module loading doesn't work. Running "edevadm monitor" I do get many UEVENTs when plugging in an usb stick, for example. The event device system itself does work. But trying to mount the filesystem doesn't work as no vfat module gets loaded (as an example).

Likewise adding rules via iptables doesn't work, as the netfilter modules are missing. I have to manually load the nf* modules and _then_ I'm able to use iptables.

I can load all those modules by hand via modprobe, but autoloading via kernel/udev doesn't work.

Running "depmod -a" was fine. The files /lib/modules/[kernelversions]/modules.* seem(!) also to be ok. "find /sys/ -name "uevent" | wc -l" seems also fine with more than a thousand results.

When I try for example mounting the fat system without having the vfat module ready, on my standard desktop system "udevadm monitor" shows events and mount succeeds. But on the Chromebook with custom kernel there's no such event shown and mount fails with:
"mount: /mnt: unknown filesystem type 'vfat'."
After "modprobe vfat" everything is fine and mount succeeds. Indeed the udev events do show when manually running modprobe.

systemd-udevd.service is running. The files in /run/udev/* seem to be the same on the desktop (where everything is fine) and Chromebook (not working).

Does anyone has an idea how to solve this? Feel free to ask me further details of the system. I don't know how the module autoloading works so I have no idea which additional information is useful.

regards
hede


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