[Bug 1933491] Re: kmod add zstd support

[Dimitri John Ledkov]

@sil2100

--disable-test-modules \

 override_dh_auto_test:
+	dh_auto_test --builddir=build-deb

are needed together to enable building and running unittests during
build.

Note previously focal builds did not run unittests at all.

The autoconf help text for the option says "disable building test
modules during make check: cached modules will be used". What it means
use the prebuilt kernel modules from the orig tarball for unittests,
which works in launchpad builders. Without this option an attempt is
made to rebuild test modules for the currently running kernel which is
not possible or useful in launchpad. Installing linux-generic-headers
and forcing the build for the current kernel in a given series is
another alternative, but also not too sure if that is useful given
prebuilt known/working modules for unittests are available.

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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
Status in kmod package in Debian:
  New

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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