Date:   Sun, 20 Jan 2019 13:58:15 -0800
From:   hpa@...or.com
To:     Joel Fernandes <joel@...lfernandes.org>
CC:     Greg KH <gregkh@...uxfoundation.org>,
        Christoph Hellwig <hch@...radead.org>,
        linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>, ast@...nel.org,
        atishp04@...il.com, Borislav Petkov <bp@...en8.de>,
        dancol@...gle.com, Ingo Molnar <mingo@...hat.com>,
        Jan Kara <jack@...e.cz>, Jonathan Corbet <corbet@....net>,
        karim.yaghmour@...rsys.com, Kees Cook <keescook@...omium.org>,
        kernel-team@...roid.com, linux-doc@...r.kernel.org,
        Manoj Rao <linux@...ojrajarao.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        paulmck@...ux.vnet.ibm.com,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        rdunlap@...radead.org, rostedt@...dmis.org,
        Thomas Gleixner <tglx@...utronix.de>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        yhs@...com
Subject: Re: [RFC] Provide in-kernel headers for making it easy to extend the kernel

On January 20, 2019 8:10:03 AM PST, Joel Fernandes <joel@...lfernandes.org> wrote:
>On Sat, Jan 19, 2019 at 11:01:13PM -0800, hpa@...or.com wrote:
>> On January 19, 2019 2:36:06 AM PST, Greg KH
><gregkh@...uxfoundation.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.

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