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How to get the kernel module imm to autoload

An introduction to autoloading

If you want to get a module to autoload when a device is accessed you can often add a file to /etc/modutils and run update-modules to generate /etc/modules.conf . When the kernel receives a request to open a device file that it does not have capabilities for it issues a request to modprobe for the module `char-major-n' or `block-major-n' depending on whether the device is a character or block device, and the device's major number, n. For example, my sound devices have major number 14, and my sound module is emu10k1 so added the alias below to my /etc/modutils directory.

$ ls -l /dev/dsp
crw-rw----    1 root     audio     14,   3 Jul  5  2000 /dev/dsp
$ cat /etc/modutils/sound
alias char-major-14 emu10k1

Why attempts to autoload imm failed

I added the file below to /etc/modutils , but try as I might, it just would not let imm autoload.

$ cat /etc/modutils/zip
alias block-major-8 imm

After an hour or so of browsing the kernel source I discovered the reason: When a device file is opened the kernel checks to see if the driver associated with that device is registered. If not, it asks modprobe to load it as a module. The kernel registers new device drivers either on boot if they are compiled in, or when the relevant module is loaded. It remembers that they are registered, and won't try to register them again.

If the SCSI subsystem is compiled into the kernel it will be registered at boot. Requests to open /dev/sda1 , say, will therefore not trigger registration again. In this situation modprobe never gets asked for char-major-8, and therefore never loads imm .

The solution

The solution that I found was to compile both scsi_mod.o (CONFIG_SCSI) and sd_mod.o (CONFIG_BLK_DEV_SD) as modules. This introduces a second problem: depmod does not know that imm needs sd_mod.o . The second line in the file below sorts that out.

$ cat /etc/modutils/zip
alias block-major-8 imm
below imm sd_mod

Don't forget to run update-modules to generate /etc/modules.conf .

Further information

The kernel source. I can't remember which files I found the information in. I should have noted it down. If I find it again I'll put it here.

If you still can't get imm to autoload, then mail me for some extra help.

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