`unsquashfs` can use multiple CPU cores during image extraction, significantly reducing boot time.
For example the whole boot time from PXE to shell on a 8-core VM, from approximately 45 seconds to 20 seconds.
This PR adds `squashfs-tools` as a dependency. Since the package is smaller than 1 MB, the additional image size is justified by the performance improvement.
For backward compatibility, the existing `cp`-based extraction method is used when `unsquashfs` is unavailable, such as with images built before this change.
The extraction logic has also been moved into the common functions and is now shared between EL9, EL10, and Ubuntu.
Both untethered `squashfs` images and `confluent_multisquash` images are supported.
Images must be rebuilt to include `unsquashfs` and benefit from the faster extraction path.
By default, the squashfs file was being cached as well as the contents after extraction.
This is superfluous pressure on the cache of the OS.
However, it does help keep the image afloat through 'confignet', so
leave it on until onboot completes, then reclaim cache and disable further caching.
Markus Hilger
Jarrod Johnson