rpm5 use lrzip as new compression function

Probably could be some interest for rpm5 to adopt in future lrzip as a compression program.

Description

The lrzip result are very impressive so there is no doubt on the choice. At the time of writing is missing a library implementation, but Kolivas, well-known kernel hackers known for its branch-ck and the , is developing it.

OTHO, for those compression formats that have only an executable, no libraries, there's a need for a pipe based "external helper" RPMIO layer. There are issues with helpers and signals and error handling: external helpers cannot be easily mapped onto informative errno's precisely.
But a pipe I/O layer in which helpers can be "plugged" as needed solves the issues(s) generally, not case-by-case.

It is also easier to just add whatever compression might be desired to RPMIO id there is a library available in order to avoid the inevitable feature request discussion. All that is needed is open/close/read/write/seek methods, usually very not hard to construct from any library. The harder issues have to do with multi-threading and --rsyncable etc, and it takes a fair
amount of time and thought and try-and-see to get "reliable" in place.

Reference

- The Kolivas blog http://ck-hack.blogspot.com/2011/06/lrzip-tarball-of-all-40-linux-26.html

- The announcement of the creation of a library for lzrip

    http://freshmeat.net/projects/lrzip/releases/329841