dkms built modules may be compressed in a way unsupported by the kernel #386

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1. evelikov commented on Jan 25, 2024

   

   evelikov

   on Jan 25, 2024

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   The only thing that comes off the top of my head is the --ultra compressionsoption.

   Kernel supports up-to level 14 (or was it 20), where for 20+ you need to use zstd --ultra, which in itself requires more RAM, as far as decompression is concerned, which is perhaps why the kernel does not support it.

   IIRC newer versions of kmod will pass the compressed module directly to the kernel. Older ones will decompress it before hand.

   Perhaps kmod could (or should?) callback and uncompress if the kernel cannot load the compressed module?
2. anbe42 commented on Jan 25, 2024

   

   anbe42

   on Jan 25, 2024

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   this is about xz not zstd

   the relevant option here should be --check=crc32

   but then again, why can't module compression be delegated to kbuild? the kernel probably knows best how it wants its modules ... does dkms really have to reinvent that?
3. anbe42 commented on Jan 25, 2024

   

   anbe42

   on Jan 25, 2024

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   in the Linux git master as of today:

   $ grep -r -e --check=crc .
   ./Documentation/staging/xz.rst:--check=crc32.
   ./Documentation/staging/xz.rst: xz --check=crc32 --lzma2=dict=512KiB inputfile
   ./arch/powerpc/boot/wrapper:        xz --check=crc32 -f -6 "$vmz.$$"
   ./scripts/Makefile.modinst:      cmd_xz = $(XZ) --check=crc32 --lzma2=dict=1MiB -f $<
   ./scripts/Makefile.lib:      cmd_xzmisc = cat $(real-prereqs) | $(XZ) --check=crc32 --lzma2=dict=1MiB > $@
   ./scripts/xz_wrap.sh:exec $XZ --check=crc32 $BCJ --lzma2=$LZMA2OPTS,dict=32MiB
   
4. evelikov

   added a commit that references this issue on Jan 29, 2024

   dkms: use saner compression defaults

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   445c8a4
5. evelikov commented on Jan 29, 2024

   

   evelikov

   on Jan 29, 2024

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   Right - turns out both of our xz and zstd commands needed a tweak. The issue should be resolved with #390

   You are right though - ideally we'll be using the upstream modules_install. There' s task for that already #319, although I haven't checked if it'll have any caveats.

   For the short term, I think we can fix our cmdline args. If anyone want to pursue the modules_install please be my guest.
6. evelikov

   added a commit that references this issue on Jan 31, 2024

   dkms: use saner compression defaults

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   cda4025
7. evelikov

   closed this as completedin #390on Jan 31, 2024
8. evelikov

   added a commit that references this issue on Jan 31, 2024

   dkms: use saner compression defaults

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