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From:   Arvind Sankar <nivedita@alum.mit.edu>
Date:   Tue, 7 Jul 2020 23:09:39 -0400
To:     Nick Terrell <terrelln@fb.com>
Cc:     Arvind Sankar <nivedita@alum.mit.edu>,
        Nick Terrell <nickrterrell@gmail.com>,
        Borislav Petkov <bp@alien8.de>,
        Thomas Gleixner <tglx@linutronix.de>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Chris Mason <clm@fb.com>,
        "linux-kbuild@vger.kernel.org" <linux-kbuild@vger.kernel.org>,
        "x86@kernel.org" <x86@kernel.org>,
        "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
        Petr Malat <oss@malat.biz>, Kees Cook <keescook@chromium.org>,
        Kernel Team <Kernel-team@fb.com>,
        Adam Borowski <kilobyte@angband.pl>,
        Patrick Williams <patrickw3@fb.com>,
        Michael van der Westhuizen <rmikey@fb.com>,
        "mingo@kernel.org" <mingo@kernel.org>,
        Patrick Williams <patrick@stwcx.xyz>,
        Sedat Dilek <sedat.dilek@gmail.com>,
        Norbert Lange <nolange79@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH v6 4/8] init: add support for zstd compressed kernel
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On Wed, Jul 08, 2020 at 02:01:50AM +0000, Nick Terrell wrote:
> 
> 
> > On Jul 7, 2020, at 6:11 PM, Arvind Sankar <nivedita@alum.mit.edu> wrote:
> > 
> > On Mon, Jul 06, 2020 at 08:46:00PM -0700, Nick Terrell wrote:
> >> From: Nick Terrell <terrelln@fb.com>
> >> 
> >> * Adds the zstd cmd to scripts/Makefile.lib
> >> * Adds the HAVE_KERNEL_ZSTD and KERNEL_ZSTD options
> >> 
> >> Architecture specific support is still needed for decompression.
> >> 
> >> diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
> >> index 916b2f7f7098..d960f8815f87 100644
> >> --- a/scripts/Makefile.lib
> >> +++ b/scripts/Makefile.lib
> >> @@ -413,6 +413,21 @@ quiet_cmd_xzkern = XZKERN  $@
> >> quiet_cmd_xzmisc = XZMISC  $@
> >>       cmd_xzmisc = cat $(real-prereqs) | $(XZ) --check=crc32 --lzma2=dict=1MiB > $@
> >> 
> >> +# ZSTD
> >> +# ---------------------------------------------------------------------------
> >> +# Appends the uncompressed size of the data using size_append. The .zst
> >> +# format has the size information available at the beginning of the file too,
> >> +# but it's in a more complex format and it's good to avoid changing the part
> >> +# of the boot code that reads the uncompressed size.
> >> +# Note that the bytes added by size_append will make the zstd tool think that
> >> +# the file is corrupt. This is expected.
> >> +
> >> +quiet_cmd_zstd = ZSTD    $@
> >> +cmd_zstd = (cat $(filter-out FORCE,$^) | \
> > 		   ^^ should just be $(real-prereqs)
> >> +	zstd -19 && \
> >> +        $(call size_append, $(filter-out FORCE,$^))) > $@ || \
> > 	   ^^ size_append does not take arguments. It's used as just
> > 	   $(size_append) and will always output shell code to print the
> > 	   total size of $(real-prereqs) -- see other compressor command
> > 	   definitions.
> 
> Yeah, when I wrote this code, this was how the rest of the compressors were implemented.
> I noticed that they had all been updated when I was responding to Norbert Lange earlier.
> I will submit a v7 shortly with the updated command.
> 
> Thanks for the review,
> Nick
> 
> 

Looks like it changed in 5.1. I guess this patch has been floating
around for quite some time :) Here's hoping v8 is the last one!