linux-kernel - Re: [PATCH v2 11/11] test_firmware: test three firmware kernel configs using a proc knob

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Message-ID: <20180301003816.GR14069@wotan.suse.de>
Date:   Thu, 1 Mar 2018 00:38:16 +0000
From:   "Luis R. Rodriguez" <mcgrof@...nel.org>
To:     Josh Triplett <josh@...htriplett.org>
Cc:     "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shuah Khan <shuah@...nel.org>,
        Martin Fuzzey <mfuzzey@...keon.com>,
        Mimi Zohar <zohar@...ux.vnet.ibm.com>,
        David Howells <dhowells@...hat.com>, pali.rohar@...il.com,
        Takashi Iwai <tiwai@...e.de>, arend.vanspriel@...adcom.com,
        Rafał Miłecki <zajec5@...il.com>,
        nbroeking@...com, Vikram Mulukutla <markivx@...eaurora.org>,
        stephen.boyd@...aro.org, Mark Brown <broonie@...nel.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Abhay_Salunke@...l.com, bjorn.andersson@...aro.org,
        jewalt@...innovations.com, LKML <linux-kernel@...r.kernel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH v2 11/11] test_firmware: test three firmware kernel
 configs using a proc knob

On Wed, Feb 28, 2018 at 04:00:58PM -0800, Josh Triplett wrote:
> On Wed, Feb 28, 2018 at 06:26:03PM +0000, Luis R. Rodriguez wrote:
> > So for folks who enable CONFIG_FW_LOADER=y, they'd now be forced to gain an
> > extra 13436 bytes broken down as follows:
> 
> Ah, I see.
> 
> If you have CONFIG_FW_LOADER and not CONFIG_FW_LOADER_USER_HELPER, then
> you only have the in-kernel firmware loading mechanism?

Right, we don't have the old fallback mechanism (which BTW used to be
the default way back in the hayday).

> Given the
> *substantial* size difference between the two, it seems useful to have
> that option.

That's what I wanted to get to, is 13436 bytes is*substantial* enough to
merit a kernel configuration option? It seems like that is the case.

> What would it gain to combine the two?

Well Android enables CONFIG_FW_LOADER_USER_HELPER, and if they do, I was trying
to think if there really was any point in having CONFIG_FW_LOADER_USER_HELPER
as an option. Who would enable CONFIG_FW_LOADER but not
CONFIG_FW_LOADER_USER_HELPER?

You see other than
CONFIG_FW_LOADER_USER_HELPER
we also have
CONFIG_FW_LOADER_USER_HELPER_FALLBACK
and Android defaults that to y too.

It used to be that CONFIG_FW_LOADER_USER_HELPER_FALLBACK was a mess to
understand in code, and this series has reduced it to simple bool now.

I started wondering if trimming kconfig options may be worth it. Sadly
I don't think we can remove CONFIG_FW_LOADER_USER_HELPER_FALLBACK, and
we'll have to just deal with it mapping to switching a sysctl option.

But I figured it was a good time to also reconsider also if we even had
any need for CONFIG_FW_LOADER_USER_HELPER.

The less hairball of mess of kconfig options the better to test. Even
though this series has reduced being able to consolidating being
able to make a kernel now which lets us test all configurations in
one build.

Who would save some 13436 bytes in the real world?

  Luis