[Openembedded-architecture] Switch sstate and other pieces of the project to xz?

[Richard Purdie]

Times change and xz is becoming the defacto compression format and
utility. It has better compression ratios than gz and similar
compression/decompression times. Its better than bzip2 decompression in
particular.

Given the bzip2 lack of performance, switching to xz for the SDK
appears to be an easy winning change.

Switching sstate over to xz may be a little more controversial and
invasive, not least that we'd need to update the docs to mention the xz
dependency.

Equally, I think I'm coming down strongly in favour of switching. DOes
anyone have any concerns about that?

There are no compatibility of sstate feed issues, objects just change
name at some point and the old and new can coexist side by side if
needed.

[NB: I know that some have proposed making sstate compression format
configurable. I still have mixed feelings about that, not least that it
encourages differences in a part of the system I'd prefer to try and
keep standardised and figure out the best selection. In this case, xz
does look like a clear winner over gzip]

Cheers,

Richard