From: Joel Fernandes <joel@joelfernandes.org>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Alexei Starovoitov <ast@kernel.org>,
atishp04@gmail.com, dancol@google.com,
Dan Williams <dan.j.williams@intel.com>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Guenter Roeck <groeck@chromium.org>,
Jonathan Corbet <corbet@lwn.net>,
karim.yaghmour@opersys.com, Kees Cook <keescook@chromium.org>,
Android Kernel Team <kernel-team@android.com>,
"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
"open list:KERNEL SELFTEST FRAMEWORK"
<linux-kselftest@vger.kernel.org>,
linux-trace-devel@vger.kernel.org,
Manoj Rao <linux@manojrajarao.com>,
Masahiro Yamada <yamada.masahiro@socionext.com>,
Masami Hiramatsu <mhiramat@kernel.org>,
qais.yousef@arm.com, Randy Dunlap <rdunlap@infradead.org>,
Steven Rostedt <rostedt@goodmis.org>,
Shuah Khan <shuah@kernel.org>,
yhs@fb.com
Subject: Re: [PATCH v4 1/2] Provide in-kernel headers for making it easy to extend the kernel
Date: Thu, 7 Mar 2019 11:54:33 -0500 [thread overview]
Message-ID: <20190307165433.GA90983@google.com> (raw)
In-Reply-To: <20190307152303.GA9819@kroah.com>
On Thu, Mar 07, 2019 at 04:23:03PM +0100, Greg KH wrote:
> > > 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
> >
> > I thought about it already. This is easier said than done though. The archive
> > is compressed from 40MB to 3.6MB. If we leave it uncompressed in RAM, then it
> > will take up the entire 40MB of RAM and in Android we don't even use
> > disk-based swap.
> >
> > So we will need some kind of intra file compressed memory representation that
> > a filesystem can use for the backing store. I thought of RAM-backed squashfs
> > but it requires squashfs-tools to be installed at build time (which my host
> > distro itself didn't have).
> >
> > It is just so much easier to use tar + xz at build time, and leave the
> > decompression task to the user. After decompression, the files will live on
> > the disk and the page-cache mechanism will free memory when/if the files fall
> > off the LRUs.
> >
> > WDYT?
>
> I think the compressed tarball is much simpler/easier overall. If
> someone really wants the filesystem, they just uncompress it into a
> tmpfs mount. It's much less moving kernel code to worry about.
Agreed, I also feel the same. thanks,
- Joel
next prev parent reply other threads:[~2019-03-07 16:54 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-01 16:08 [PATCH v4 1/2] Provide in-kernel headers for making it easy to extend the kernel Joel Fernandes (Google)
2019-03-01 16:08 ` [PATCH v4 2/2] Add selftests for module build using in-kernel headers Joel Fernandes (Google)
2019-03-02 21:59 ` [PATCH v4 1/2] Provide in-kernel headers for making it easy to extend the kernel kbuild test robot
2019-03-03 16:11 ` Joel Fernandes
2019-03-06 12:26 ` Masahiro Yamada
2019-03-06 17:49 ` Joel Fernandes
2019-03-07 4:59 ` Masahiro Yamada
2019-03-07 14:54 ` Joel Fernandes
2019-03-07 23:23 ` Justin Capella
2019-03-06 18:16 ` Joel Fernandes
2019-03-07 4:54 ` Masahiro Yamada
2019-03-03 2:04 ` kbuild test robot
2019-03-04 14:00 ` Qais Yousef
2019-03-05 16:27 ` Joel Fernandes
2019-03-04 22:48 ` Dietmar Eggemann
2019-03-05 16:25 ` Joel Fernandes
2019-03-07 8:58 ` Geert Uytterhoeven
2019-03-07 15:03 ` Joel Fernandes
2019-03-07 15:23 ` Greg KH
2019-03-07 16:54 ` Joel Fernandes [this message]
[not found] ` <20190318185742.109dee5c@alans-desktop>
2019-03-18 21:11 ` Karim Yaghmour
2019-03-08 8:53 ` Geert Uytterhoeven
2019-03-08 13:42 ` Joel Fernandes
2019-03-08 13:57 ` Enrico Weigelt, metux IT consult
2019-03-08 14:04 ` Greg KH
2019-03-08 14:02 ` Greg KH
2019-03-08 17:58 ` Joel Fernandes
2019-03-08 17:59 ` Geert Uytterhoeven
2019-03-09 7:16 ` Greg KH
2019-03-09 11:40 ` Geert Uytterhoeven
2019-03-09 12:11 ` Greg KH
2019-03-09 16:51 ` Karim Yaghmour
2019-03-09 19:26 ` Geert Uytterhoeven
2019-03-09 21:44 ` Karim Yaghmour
2019-03-11 8:03 ` Geert Uytterhoeven
2019-03-12 15:15 ` Karim Yaghmour
2019-03-11 23:36 ` Steven Rostedt
2019-03-11 23:58 ` Daniel Colascione
2019-03-12 0:39 ` Joel Fernandes
2019-03-12 1:28 ` Steven Rostedt
2019-03-12 1:38 ` Joel Fernandes
2019-03-13 1:18 ` Masami Hiramatsu
2019-03-14 12:27 ` Joel Fernandes
2019-03-15 13:14 ` Masami Hiramatsu
2019-03-12 1:45 ` Alexei Starovoitov
2019-03-12 15:26 ` Steven Rostedt
2019-03-12 1:22 ` Steven Rostedt
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