linux-kernel - Re: [PATCH v2] kbuild: switch from lz4c to lz4 for compression

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Message-ID: <CAK7LNAS0VzqcKDz_1ds5qJcASqxVizE3kkdRk1Yiidch9KMxEQ@mail.gmail.com>
Date: Sat, 16 Nov 2024 16:51:48 +0900
From: Masahiro Yamada <masahiroy@...nel.org>
To: Francesco Dolcini <francesco@...cini.it>
Cc: Greg KH <gregkh@...uxfoundation.org>, Parth Pancholi <parth105105@...il.com>, 
	Nathan Chancellor <nathan@...nel.org>, Nicolas Schier <nicolas@...sle.eu>, 
	Parth Pancholi <parth.pancholi@...adex.com>, linux-kbuild@...r.kernel.org, 
	linux-kernel@...r.kernel.org, stable@...r.kernel.org, 
	Francesco Dolcini <francesco.dolcini@...adex.com>
Subject: Re: [PATCH v2] kbuild: switch from lz4c to lz4 for compression

On Fri, Nov 15, 2024 at 6:45 PM Francesco Dolcini <francesco@...cini.it> wrote:
>
> On Fri, Nov 15, 2024 at 10:22:13AM +0100, Greg KH wrote:
> > On Fri, Nov 15, 2024 at 09:39:40AM +0100, Francesco Dolcini wrote:
> > > On Thu, Nov 14, 2024 at 05:02:01PM +0100, Greg KH wrote:
> > > > On Thu, Nov 14, 2024 at 03:56:44PM +0100, Parth Pancholi wrote:
> > > > > From: Parth Pancholi <parth.pancholi@...adex.com>
> > > > >
> > > > > Replace lz4c with lz4 for kernel image compression.
> > > > > Although lz4 and lz4c are functionally similar, lz4c has been deprecated
> > > > > upstream since 2018. Since as early as Ubuntu 16.04 and Fedora 25, lz4
> > > > > and lz4c have been packaged together, making it safe to update the
> > > > > requirement from lz4c to lz4.
> > > > >
> > > > > Consequently, some distributions and build systems, such as OpenEmbedded,
> > > > > have fully transitioned to using lz4. OpenEmbedded core adopted this
> > > > > change in commit fe167e082cbd ("bitbake.conf: require lz4 instead of
> > > > > lz4c"), causing compatibility issues when building the mainline kernel
> > > > > in the latest OpenEmbedded environment, as seen in the errors below.
> > > > >
> > > > > This change also updates the LZ4 compression commands to make it backward
> > > > > compatible by replacing stdin and stdout with the '-' option, due to some
> > > > > unclear reason, the stdout keyword does not work for lz4 and '-' works for
> > > > > both. In addition, this modifies the legacy '-c1' with '-9' which is also
> > > > > compatible with both. This fixes the mainline kernel build failures with
> > > > > the latest master OpenEmbedded builds associated with the mentioned
> > > > > compatibility issues.
> > > > >
> > > > > LZ4     arch/arm/boot/compressed/piggy_data
> > > > > /bin/sh: 1: lz4c: not found
> > > > > ...
> > > > > ...
> > > > > ERROR: oe_runmake failed
> > > > >
> > > > > Cc: stable@...r.kernel.org
> > > >
> > > > What bug does this resolve that it needs to be backported to stable
> > > > kernels?
> > >
> > > This is not solving any existing actual bug, and therefore there is no
> > > fixes tag.
> > >
> > > The issue here is that the kernel build system is using lz4c, that is
> > > deprecated since 2018, and now distributions are actively moving away from it.
> > >
> > > openSUSE Tumbleweed and OE already removed it, so you would not be able
> > > to compile a stable kernel on such distribution when using lz4 unless we
> > > backport such a patch.
> > >
> > > Everything should be properly documented in the commit message already.
> > >
> > > My understanding is that something like that would be a reason for
> > > backporting to stable, if my understanding is not correct we'll remove
> > > the cc:stable and send a v3.
> >
> > Please read:
> >     https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
> > for what meets stable kernel requirements.  I don't think that this
> > patch is that.
>
> Greg, ack.
>
> Masahiro, can you please let me know if we should send a v3 with the stable
> tag removed or you can remove it yourself when applying?
>

I applied this with the stable tag removed.
Thanks.

(I guess someone may want to backport this eventually,
as such distros cannot build stable kernels with ld4 compression.)



-- 
Best Regards
Masahiro Yamada