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    SubjectRe: [PATCH v4 1/2] Provide in-kernel headers for making it easy to extend the kernel
    Hi Joel,

    On Fri, Mar 1, 2019 at 5:10 PM 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.
    >
    > 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.
    >
    > 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

    As the usage pattern will be accessing the individual files, what about
    implementing a file system that provides read-only access to the internal
    kheaders archive?

    mount kheaders $HOME/headers -t kheaders

    Gr{oetje,eeting}s,

    Geert

    --
    Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

    In personal conversations with technical people, I call myself a hacker. But
    when I'm talking to journalists I just say "programmer" or something like that.
    -- Linus Torvalds

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