linux-kernel - Re: [PATCH -next 2/2] kbuild: fix for updated LZ4 tool with the new streaming format

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Date:	Tue, 16 Jul 2013 10:13:24 +0100
From:	Florian Fainelli <florian@...nwrt.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
	Kyungsik Lee <kyungsik.lee@....com>,
	Michal Marek <mmarek@...e.cz>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-kbuild@...r.kernel.org, x86@...nel.org,
	celinux-dev@...ts.celinuxforum.org,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>, hyojun.im@....com,
	chan.jeong@....com, Andy Lee <raphael.andy.lee@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Russell King <rmk@....linux.org.uk>,
	Borislav Petkov <bp@...en8.de>,
	Yann Collet <yann.collet.73@...il.com>,
	Chanho Min <chanho.min@....com>
Subject: Re: [PATCH -next 2/2] kbuild: fix for updated LZ4 tool with the new
 streaming format

2013/7/16 Andrew Morton <akpm@...ux-foundation.org>:
> On Tue, 16 Jul 2013 00:47:27 -0700 Andrew Morton <akpm@...ux-foundation.org> wrote:
>
>> On Mon, 15 Jul 2013 15:08:20 -0700 "H. Peter Anvin" <hpa@...or.com> wrote:
>>
>> > On 07/15/2013 03:03 PM, Andrew Morton wrote:
>> > >
>> > > I don't know how to do this.  Any suggestions?
>> > >
>> > > It has to be done at `make config' time.  We'd need to probe for the
>> > > presence of lz4c and then....  what?
>> > >
>> > > Is there any precedent for this?
>> > >
>> > > I don't think we can just ignore the absence of lz4c - the user has
>> > > selected a config which his system cannot build.  The problem lies
>> > > within randconfig itself.
>> > >
>> >
>> > We keep running over the need to be able to have kconfig run tests on
>> > the build system (for toolchain support or for optional tools needed);
>> > running them in the Makefiles (i.e. at Kbuild time) is simply too late.
>> >
>>
>> Would it make sense to extend Kconfig's `depends'?
>>
>>       depends on $(shell-command)
>>
>> I don't know how practical that would be to implement...
>
> Or, easier and faster, run some front-end script which generates
> once-off Kconfig symbols.
>
>         if [ -x /bin/lz4c ]
>         then
>                 echo CONFIG_HAVE_LZ4C
>         fi
>
> then munge the output of that script into the Kconfig run and do
>
>         depends on HAVE_LZ4C

That does sound nice to avoid the build error, but will eventually
make it harder to diagnose why the kernel has not been compressed with
the specific compression tool, some kind of warning should also be
emitted maybe?
--
Florian
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