Building custom kernel modules (e.g. VHBA for CDEmu)

Building custom kernel modules (e.g. VHBA for CDEmu)

[Pierre Neidhardt]

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Hi!

The question of building custom Linux kernel modules was recently
brought up in bug #35758 (packaging CDEmu).

I'll summarize: a typical Makefile to build a kernel module looks like
this:

 --8<---------------cut here---------------start------------->8---
 VHBA_VERSION := 20170610

 KERNELRELEASE ?= $(shell uname -r)
 KDIR ?= /lib/modules/$(KERNELRELEASE)/build
 PWD ?= $(shell pwd)

 obj-m := vhba.o
 ccflags-y := -DVHBA_VERSION=\"$(VHBA_VERSION)\" -Werror

 default: modules
 install: modules_install

 modules modules_install clean:
	 $(MAKE) -C $(KDIR) M=$(PWD) $@
 --8<---------------cut here---------------end--------------->8---

The only thing we need, beside a C compiler, is this KDIR, which on Guix
_could_ be found at

  /gnu/store/…-linux-libre-5.0.1/lib/modules/5.0.1/build

Sadly, for us it's a dangling link to
/tmp/guix-build-linux-libre-5.0.1.drv-0/linux-5.0.1.

I presume that the answer is simple: replace the link with the folder.
But that would eat up significantly more disk space.  So we could
replace the link with a link to a new "build" output of the linux-libre
package, which would contain this "build" folder.

Thoughts?

-- 
Pierre Neidhardt
https://ambrevar.xyz/

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Re: Building custom kernel modules (e.g. VHBA for CDEmu)

[Chris Marusich]

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Pierre Neidhardt <mail@ambrevar.xyz> writes:

> The only thing we need, beside a C compiler, is this KDIR, which on Guix
> _could_ be found at
>
>   /gnu/store/…-linux-libre-5.0.1/lib/modules/5.0.1/build
>
> Sadly, for us it's a dangling link to
> /tmp/guix-build-linux-libre-5.0.1.drv-0/linux-5.0.1.
>
> I presume that the answer is simple: replace the link with the folder.
> But that would eat up significantly more disk space.  So we could
> replace the link with a link to a new "build" output of the linux-libre
> package, which would contain this "build" folder.

If that's all it takes, then it makes sense to me.  Do we have any
experienced kernel hackers on the list who can comment more on this?

-- 
Chris

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Re: Building custom kernel modules (e.g. VHBA for CDEmu)

[Pierre Neidhardt]

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Actually yesterday Danny posted patch 35110 which implements
`make-linux-module', which answers this issue!

Hurray to Danny! :D

-- 
Pierre Neidhardt
https://ambrevar.xyz/

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