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 11:25:14 +0200
From:	"Yann E. MORIN" <yann.morin.1998@...e.fr>
To:	Florian Fainelli <florian@...nwrt.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"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

Florian, All,

On Tuesday 16 July 2013 11:13:24 Florian Fainelli wrote:
> 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?

Either a warning at check-time, or a comment in Kconfig, such as:
    config COMPRESS_LZ4
        depends on HAVE_LZ4
    comment "'lz4' missing, LZ4 compression not available"
        depends on !HAVE_LZ4

Either way is fine with me. ;-)

Regards,
Yann E. MORIN.

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