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

[Martin Nybo Andersen]

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@xxxxxxxx>
> > > ---
> > > 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