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

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Message-ID: <ZzcYLAFqTSlFm2uF@gaggiata.pivistrello.it>
Date: Fri, 15 Nov 2024 10:45:16 +0100
From: Francesco Dolcini <francesco@...cini.it>
To: Greg KH <gregkh@...uxfoundation.org>,
	Masahiro Yamada <masahiroy@...nel.org>
Cc: Francesco Dolcini <francesco@...cini.it>,
	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 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?

Francesco