[Bug 1942260] Re: compress firmware in /lib/firmware

[Dimitri John Ledkov]

** Changed in: linux-firmware (Ubuntu)
    Milestone: None => ubuntu-23.10-beta

** Changed in: linux-firmware-raspi2 (Ubuntu)
    Milestone: None => ubuntu-23.10

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https://bugs.launchpad.net/bugs/1942260

Title:
  compress firmware in /lib/firmware

Status in initramfs-tools package in Ubuntu:
  Fix Released
Status in linux-firmware package in Ubuntu:
  Confirmed
Status in linux-firmware-raspi2 package in Ubuntu:
  Confirmed

Bug description:
  -- initramfs-tools

  [Impact]

   * linux supports xz compressed linux-firmware which saves disk space.
  In focal, initramfs-tools only knows how to included uncompressed
  firmware files (even when kernel supports loading compressed ones).
  Newer releases of linux-firmware may use compressed firmware files
  only, in such cases it would be nice for focal's initramfs-tools to
  support compressed firmware files in case of partial or incomplete
  upgrades (i.e. linux-firmware force installed or upgraded, without
  newer initramfs-tools). The proposed changes to initramfs-tools are
  backwards and forwards compatible, they prefer to include uncompressed
  firmware files; and if missing, include compressed firmware files in
  their uncompressed form. Thus maintaining compatibility with any
  kernels, irrespective of compressed/uncompressed firmware inputs.

  [Test Plan]

   * Compress all files shipped by linux-firmware with xz

   * Rebuild initrd

   * Check that all the same firmware files are still included in the
  initramfs, in their uncompressed form as before

  [Where problems could occur]

   * This SRU is precautionary to prevent accidental installation of
  compressed linux-firmware from generating incorrect initramfs. It
  should be noted that whilst initramfs-tools would create a compatible
  initramfs with any kernels, pre-v5.3 kernels do not support xz
  compressed firmware files at runtime. Mixing this new initramfs with
  compressed firmwares and pre 5.3 kernels may lead to expectations of
  supporting compressed firmware files with them only working at initrd
  stage and not at runtime.

  [Other Info]
  Original bug report

  Some facts:
   - The linux kernel has supported loading xz compressed firmware since 5.3
   - The size of /lib/firmware in impish is ~650Mb (and growing)
   - The compressed size of firmware could be ~230Mb

  It would be nice to install compressed firmware to save space.

  Here are the plans from the Fedora project:
  https://fedoraproject.org/wiki/Changes/CompressKernelFirmware

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