related: #348 squashfs becomes supported and preferred image distribution method Exporting container images through Charliecloud produces a compressed tar file. The squashfs workflow piggy backs off most of the existing scripts to convert from tar to squashfs, but this has some overhead. example: `ch-docker2tar` `ch-tar2sqfs` to produce a squashfs via `ch-docker2sqfs` - export to tar - compress tar - extract and uncompress tar - compress directory to squashfs There are two ways I thought of to avoid the extra compression step for exporting from docker. 1. add an optional flag to not compress when exporting to tar to existing scripts 2. don't use the existing scripts, copy code from them and modify to skip compression This would make the new workflow for squashfs: - export to uncompressed tar - extract tar - compress directory to squashfs Using option 1 the squashfs scripts would call the tar scripts with the optional no compression flag. `ch-docker2tar -nocompress IMAGE OUTDIR` `ch-tar2sqfs` Option 2 would just put all the work that `ch-docker2tar` performs in the `ch-docker2sqfs` script, and avoid calling `ch-docker2tar` in `ch-docker2sqfs`.