Add pigz for parallel decompression by containerd

[ohkinozomu]

Issue number:

Closes #2886

Description of changes:

Let containerd use pigz (or more precisely, unpigz).
pigz doesn't have a LICENSE file (madler/pigz#89) and I decided to use README...

If there is no pigz, and the log level of containerd is set to debug, the following log will be output at the time of pull.

Mar 14 09:30:08 10.0.2.15 containerd[1175]: time="2023-03-14T09:30:08.609765577Z" level=debug msg="unpigz not found, falling back to go gzip" error="exec: \"unpigz\": executable file not found in $PATH"

I have confirmed that with this change that log disappears (i.e. containerd uses unpigz).

Here is a quick benchmark.

machine spec:
Google Compute Engine c3-highcpu-22 Ubuntu 22.04.2 (enable nested virtualization)

Command to execute:

ctr image pull docker.io/library/mysql:8.0.32

without pigz(commit b1ac8ef)

6.139457575s
7.236172524s
7.730825494s

with pigz(this commit)

5.842488681s
6.319545383s
5.777997267s

Testing done: yes

Terms of contribution:

By submitting this pull request, I agree that this contribution is dual-licensed under the terms of both the Apache License, version 2.0, and the MIT license.

[bcressey]

Thanks so much for picking this up!

Overall looks good, but needs a few fixes for some subtle cross-compiling and software licensing issues.

[ohkinozomu]

Thanks for your review, I have fixed.

[stmcginnis]

Thanks for working on this!

[cbgbt]

Thanks so much for working on this! It looks good to me, just a minor nit.

[ohkinozomu]

Thanks to all reviewers!
Fix completed.

[bcressey]

Nice work. Thanks for doing this, @ohkinozomu!

[stmcginnis]

All comments addressed - looks great!