API between modules

API between modules

[Lucas Tanure]

Hi,

I have two kernel modules that need to talk over an API, and right
now, they are statically linked together, but I am looking for a
better way to separate them and share an API between them.

A few years ago, I did the HDA component:
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/sound/pci/hda/hda_component.h

Using the component API:
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/include/linux/component.h

Are there other ways for a module to wait for another module to load
and use its API?
Is there a default way to do that?

I know that with MFD devices, you can have children, but that's not
the case. My modules are not related in that way.

Thanks
Lucas

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Re: API between modules

[Greg KH]

On Thu, May 18, 2023 at 08:16:18AM +0100, Lucas Tanure wrote:
> Hi,
> 
> I have two kernel modules that need to talk over an API, and right
> now, they are statically linked together, but I am looking for a
> better way to separate them and share an API between them.
> 
> A few years ago, I did the HDA component:
> https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/sound/pci/hda/hda_component.h
> 
> Using the component API:
> https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/include/linux/component.h
> 
> Are there other ways for a module to wait for another module to load
> and use its API?
> Is there a default way to do that?

Yes, just call a function in that other module and it will be loaded
properly before your module can call it.  That's how all in-kernel apis
work.

thanks,

greg k-h

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Re: API between modules

[Prathu Baronia]

On Thu, May 18, 2023 at 08:16:18AM +0100, Lucas Tanure wrote:
> Are there other ways for a module to wait for another module to load
> and use its API?
> Is there a default way to do that?
Hi Lucas,
IIUC you can use MODULE_SOFTDEP macro to establish loading dependencies.
This stack overflow explains it:-
https://stackoverflow.com/questions/29717761/how-do-i-define-dependency-among-kernel-modules

Prathu

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Release of my Kernel Development Tool

[Lucas Tanure]

Hi,

I have been working with Kernel development and single-board computers
for a few years now, and to help me with my development, I created
this tool:

https://github.com/lucastanure/kernel_dev_tools  (GPLv2)

It helps me to build and test the kernel in a faster and easy way. But
it also helps me to switch between boards (Rpi4, Vim4, Vim3, rk399) in
a reliable way.
The aim of this tool is to centralize the configuration of a
particular board (cross-compiler, kernel configuration, make targets,
etc.) in a config file and expose a simple workflow.
Example:

I have my VIM4 board configuration:
[vim4_arm64]
cc                      = aarch64-none-linux-gnu-
cc_path             =
~/.local/bin/gcc-arm-10.3-2021.07-x86_64-aarch64-none-linux-gnu/bin
kernel_target     = Image
kernel_file          = Image-devel
dtb_path            = dtbs_devel
config_file          = $kdt_boards/vim4_arm64_defconfig
ramfs_file           = initramfs-linux-devel.img
update_ramfs    = mkinitcpio -k $version -g $ramfs_file
on                       = kasa --alias Strip_9BA6 --type strip on --name P2
off                       = kasa --alias Strip_9BA6 --type strip off --name P2

And my workflow to develop the kernel is as follows:
$ export board=vim4
# Do some kernel changes
$ kb config        # Configures the kernel
$ kb build          # Builds the kernel
$ kb scp vim4   # Copy the kernel, modules and device trees to my VIM4
board using rsync and scp
# Reboot the board using ssh or issue:
$ kb off ; sleep 2 ; kb on    # Power cycle the board if reboot by ssh
is not available

This tool has many more features, like updating kernels in image files
and removing Gerrit "Change-id" from patch files.
In the near future, I will add the following:
- Check a series of patches before upstreaming. Build the kernel with
every patch in a patch series and check for building warnings,
checkpatch, sparse, etc.
- Device tree tool to help to upstream new boards to the kernel
mainline. Like, find device nodes from a device tree that don't have a
driver for it and list Kernel configs needed by the device tree.

Happy coding

Thanks
Lucas

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