Re: [PATCH v6 4/8] init: add support for zstd compressed kernel

[Nick Terrell <terrelln@fb.com>]

> 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