Re: [RFC] Provide in-kernel headers for making it easy to extend the kernel

From: hpa@zytor.com
To: Joel Fernandes <joel@joelfernandes.org>
Cc: Greg KH <gregkh@linuxfoundation.org>,
	Christoph Hellwig <hch@infradead.org>,
	linux-kernel@vger.kernel.org,
	Andrew Morton <akpm@linux-foundation.org>,
	ast@kernel.org, atishp04@gmail.com,
	Borislav Petkov <bp@alien8.de>,
	dancol@google.com, Ingo Molnar <mingo@redhat.com>,
	Jan Kara <jack@suse.cz>, Jonathan Corbet <corbet@lwn.net>,
	karim.yaghmour@opersys.com, Kees Cook <keescook@chromium.org>,
	kernel-team@android.com, linux-doc@vger.kernel.org,
	Manoj Rao <linux@manojrajarao.com>,
	Masahiro Yamada <yamada.masahiro@socionext.com>,
	paulmck@linux.vnet.ibm.com,
	"Peter Zijlstra (Intel)" <peterz@infradead.org>,
	rdunlap@infradead.org, rostedt@goodmis.org,
	Thomas Gleixner <tglx@linutronix.de>,
	"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
	<x86@kernel.org>,
	yhs@fb.com
Subject: Re: [RFC] Provide in-kernel headers for making it easy to extend the kernel
Date: Sun, 20 Jan 2019 13:58:15 -0800	[thread overview]
Message-ID: <A40C22DF-B43F-44BA-8148-FC0881087315@zytor.com> (raw)
In-Reply-To: <20190120161003.GB23827@google.com>

On January 20, 2019 8:10:03 AM PST, Joel Fernandes <joel@joelfernandes.org> wrote:
>On Sat, Jan 19, 2019 at 11:01:13PM -0800, hpa@zytor.com wrote:
>> On January 19, 2019 2:36:06 AM PST, Greg KH
><gregkh@linuxfoundation.org> wrote:
>> >On Sat, Jan 19, 2019 at 02:28:00AM -0800, Christoph Hellwig wrote:
>> >> This seems like a pretty horrible idea and waste of kernel memory.
>> >
>> >It's only a waste if you want it to be a waste, i.e. if you load the
>> >kernel module.
>> >
>> >This really isn't any different from how /proc/config.gz works.
>> >
>> >> Just add support to kbuild to store a compressed archive in
>initramfs
>> >> and unpack it in the right place.
>> >
>> >I think the issue is that some devices do not use initramfs, or
>switch
>> >away from it after init happens or something like that.  Joel has
>all
>> >of
>> >the looney details that he can provide.
>> >
>> >thanks,
>> >
>> >greg k-h
>> 
>> Yeah, well... but it is kind of a losing game... the more in-kernel
>stuff there is the less smiley are things to actually be supported.
>
>It is better than nothing, and if this makes things a bit easier and
>solves
>real-world issues people have been having, and is optional, then I
>don't see
>why not.
>
>> Modularizing is it in some ways even crazier in the sense that at
>that point you are relying on the filesystem containing the module,
>which has to be loaded into the kernel by a root user. One could even
>wonder if a better way to do this would be to have "make
>modules_install" park an archive file – or even a directory as opposed
>to a symlink – with this stuff in /lib/modules. We could even provide a
>tmpfs shim which autoloads such an archive via the firmware loader;
>this might even be generically useful, who knows.
>
>All this seems to assume where the modules are located. In Android, we
>don't
>have /lib/modules. This patch generically fits into the grand scheme
>things
>and I think is just better made a part of the kernel since it is not
>that
>huge once compressed, as Dan also pointed. The more complex, and the
>more
>assumptions we make, the less likely people writing tools will get it
>right
>and be able to easily use it.
>
>> 
>> Note also that initramfs contents can be built into the kernel.
>Extracting such content into a single-instance tmpfs would again be a
>possibility
>
>Such an approach would bloat the kernel image size though, which may
>not work
>for everyone. The module based approach, on the other hand, gives an
>option
>to the user to enable the feature, but not have it loaded into memory
>or used
>until it is really needed.
>
>thanks,
>
> - Joel

Well, where are the modules? They must exist in the filesystem.
-- 
Sent from my Android device with K-9 Mail. Please excuse my brevity.