Hi Joel,
On Wed, 27 Feb 2019 14:37:47 -0500 "Joel Fernandes (Google)" joel@joelfernandes.org wrote:
Introduce in-kernel headers and other artifacts which are made available as an archive through proc (/proc/kheaders.tar.xz file). This archive makes it possible to build kernel modules, run eBPF programs, and other tracing programs that need to extend the kernel for tracing purposes without any dependency on the file system having headers and build artifacts.
On Android and embedded systems, it is common to switch kernels but not have kernel headers available on the file system. Raw kernel headers also cannot be copied into the filesystem like they can be on other distros, due to licensing and other issues. There's no linux-headers package on Android. Further once a different kernel is booted, any headers stored on the file system will no longer be useful. By storing the headers as a compressed archive within the kernel, we can avoid these issues that have been a hindrance for a long time.
Hmm, isn't it easier to add kernel-headers package on Android?
The feature is also buildable as a module just in case the user desires it not being part of the kernel image. This makes it possible to load and unload the headers on demand. A tracing program, or a kernel module builder can load the module, do its operations, and then unload the module to save kernel memory. The total memory needed is 3.8MB.
But it also requires to install build environment (tools etc.) on the target system...
The code to read the headers is based on /proc/config.gz code and uses the same technique to embed the headers.
To build a module, the below steps have been tested on an x86 machine: modprobe kheaders rm -rf $HOME/headers mkdir -p $HOME/headers tar -xvf /proc/kheaders.tar.xz -C $HOME/headers >/dev/null cd my-kernel-module make -C $HOME/headers M=$(pwd) modules rmmod kheaders
It seems a bit complex, but no difference from compared with carrying kheaders.tar.gz. I think we would better have a psudo filesystem which can mount this compressed header file directly :) Then it becomes simpler, like
modprobe headerfs mkdir $HOME/headers mount -t headerfs $HOME/headers
And this doesn't consume any disk-space.
Thank you,