linux-kernel - Re: [PATCH] Use CRC32 and a 1MiB dictionary for XZ compressed modules

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Date:   Fri, 22 Sep 2023 10:52:02 +0200 (CEST)
From:   Martin Nybo Andersen <tweek@...ek.dk>
To:     Tor Vic <torvic9@...lbox.org>
cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nicolas Schier <nicolas@...sle.eu>,
        Nick Terrell <terrelln@...com>, linux-kbuild@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Use CRC32 and a 1MiB dictionary for XZ compressed
 modules

On Fri, 22 Sep 2023, Tor Vic wrote:

>> 
>> Hello?
>
> Hello,

:)

>> Anyone?
>> 
>> Best regards,
>> - Martin
>> 
>> On Fri, 15 Sep 2023, Martin Nybo Andersen wrote:
>> 
>>> Kmod is now using the kernel decompressor which doesn't handle CRC64
>>> and dictionaries larger than 1MiB.
>>> 
>>> Fixes: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1050582
>>> Signed-off-by: Martin Nybo Andersen <tweek@...ek.dk>
>>> ---
>>> scripts/Makefile.modinst | 2 +-
>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>> 
>>> diff --git a/scripts/Makefile.modinst b/scripts/Makefile.modinst
>>> index c59cc57286ba..ffbafbd3aeea 100644
>>> --- a/scripts/Makefile.modinst
>>> +++ b/scripts/Makefile.modinst
>>> @@ -144,7 +144,7 @@ endif
>>> quiet_cmd_gzip = GZIP    $@
>>>       cmd_gzip = $(KGZIP) -n -f $<
>>> quiet_cmd_xz = XZ      $@
>>> -      cmd_xz = $(XZ) --lzma2=dict=2MiB -f $<
>>> +      cmd_xz = $(XZ) --check=crc32 --lzma2=dict=1MiB -f $<
>
> I wonder whether it should be guarded with
>    ifdef CONFIG_MODULE_DECOMPRESS
>
> But on the other hand, the difference between 1M and 2M is likely very small 
> in terms of compression ratio.

That would work, since kmod decompress the modules in userspace if 
CONFIG_MODULE_DECOMPRESS if off.

What I'm aiming for is just that the kernel should be able to decompress 
its own modules, when it advertises it.

Cheers,
Martin

> Cheers,
> Tor Vic
>
>>> quiet_cmd_zstd = ZSTD    $@
>>>       cmd_zstd = $(ZSTD) -T0 --rm -f -q $<
>>> 
>>> -- 
>>> 2.40.1
>>> 
>>> 
>> 
>
>