[feature request]: mksquashfs: Add `--no-compression` flag to disable all compression

[nh2]

I'm generating squashfs images to make seekable archives that are then fed into deduplicating backup programs (bup, bupstash, kopia, etc). These programs do not perform well when there are billions of small files, so making a single-file archives helps.

These programs work by chunking the input byte stream using a rolling hash. Rolling hashes deduplicating backup programs work best on uncrompessed inputs.

Would it be possible to add a flag to mksquashfs that disables all compression?

The problem with the existing -noI -noD -noF -noX flags is that when automating backups, one needs to constantly monitor whether a new mksquashfs-tools is released that adds another one (and this happens in practice, for example -noX was added, and the man page section on disabling compression does mention it).

The key idea of a --no-compressoin flag is that it would provide the guarantee that it would disable also the compression of new things added to mksquashfs in the future, thus making it easier to script for no-compression use cases.