[Bug 1933491] Re: kmod add zstd support

[Dimitri John Ledkov]

** Description changed:

- kmod add zstd support
+ [Impact]
  
- * v27+ needs patches cherrypicked from v28
+  * To safe diskspace, upcoming devel series / hwe kernels may turn on
+ zstd kernel module compression. Kmod since impish support zstd support.
+ But in order to keep hwe kernels at parity, or allow inspecting jammy
+ modules from focal host, it would be beneficial for kmod in focal to
+ support zstd compressed modules.
  
- * v28+ needs new build-time deps adjusted
+ [Test Plan]
+ 
+  * Pick any kernel module
+ 
+  * Compress it with zstd: $ zstd *.ko
+ 
+  * Check that modinfo can read it: $ modinfo *.ko.zst
+ 
+ [Where problems could occur]
+ 
+  * kmod will gain a new dependecy on libzstd1, however it should already
+ be present, because dpkg in focal depends on libzstd1 already.
+ 
+  * initramfs-tools already supports compressed modules, but in focal at
+ the moment it does so in an inefficient manner (regresses bootspeed),
+ this has been improved in
+ https://launchpad.net/ubuntu/+source/initramfs-tools/0.140ubuntu8 and is
+ yet to be SRUed into Focal.

** Also affects: kmod (Ubuntu Impish)
   Importance: Undecided
       Status: New

** Also affects: kmod (Ubuntu Jammy)
   Importance: Undecided
       Status: Fix Released

** Also affects: kmod (Ubuntu Focal)
   Importance: Undecided
       Status: New

** Changed in: kmod (Ubuntu Impish)
       Status: New => Fix Released

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https://bugs.launchpad.net/bugs/1933491

Title:
  kmod add zstd support

Status in kmod package in Ubuntu:
  Fix Released
Status in kmod source package in Focal:
  New
Status in kmod source package in Impish:
  Fix Released
Status in kmod source package in Jammy:
  Fix Released

Bug description:
  [Impact]

   * To safe diskspace, upcoming devel series / hwe kernels may turn on
  zstd kernel module compression. Kmod since impish support zstd
  support. But in order to keep hwe kernels at parity, or allow
  inspecting jammy modules from focal host, it would be beneficial for
  kmod in focal to support zstd compressed modules.

  [Test Plan]

   * Pick any kernel module

   * Compress it with zstd: $ zstd *.ko

   * Check that modinfo can read it: $ modinfo *.ko.zst

  [Where problems could occur]

   * kmod will gain a new dependecy on libzstd1, however it should
  already be present, because dpkg in focal depends on libzstd1 already.

   * initramfs-tools already supports compressed modules, but in focal
  at the moment it does so in an inefficient manner (regresses
  bootspeed), this has been improved in
  https://launchpad.net/ubuntu/+source/initramfs-tools/0.140ubuntu8 and
  is yet to be SRUed into Focal.

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