Commit 3753b5fd ("modules: let tar automatically determine decompression program") introduced a regression for not gzip compatible compressors, which is sad.
Let's allow user to explicitly configure decompression programm if required, and pick decompression programm automatically otherwise.
New option: --decompressprog (default is empty) New variable: DECOMPRESSPROG: default is empty, let tar automatically determine decompression program
For example, pigz decompression is about 30% faster than gzip, but personaly I prefer zstd (https://github.com/facebook/zstd) which support smp and has very fast decompression speed.
Comparison: $ time pbuilder --execute --configfile pbuilderrc-gz /bin/true > /dev/null 2>&1 real 0m2.339s
$ time pbuilder --execute --configfile pbuilderrc-gz --decompressprog pigz /bin/true > /dev/null 2>&1 real 0m1.576s
pbuilderrc-zst
COMPRESSPROG=zstdmt
DECOMPRESSPROG=zstdmt
BASETGZ=base.tar.zst
$ time pbuilder --execute --configfile pbuilderrc-zst /bin/true > /dev/null 2>&1 real 0m1.060s