how to instrument/debug module loading

[Cliff Brake]

Hi,

I'm trying to better understand the kernel module loading mechanism
(for example when you plug in a USB device and a kernel module
autoloads).  It appears that depmod creates a module.alias map that
maps USB info to modules.  Is there any way to instrument or observe
the actual loading process?  I've looking into udev debug logging, and
udevadm, but have not found anything yet that shows when this device
is installed, this module loads.  I'd also be interested in
understanding which program is run to do the loading.  I assume udev
runs this, but again, I'd like to understand the details better.

It seems some of the documentation is out of date --
kernel:Documentation/usb/hotplug.txt refers to
/proc/sys/kernel/hotplug and /sbin/hotplug -- neither exist on my
system.

Appreciate any pointers to documentation, etc.  My test system is Arch
Linux with systemd.

Thanks,
Cliff