RFC: erofs-utils:mkfs: add unprivileged container use-case support

[Naoto Yamaguchi]

Hi all.

I investigate each read only filesystem for linux at linux container
use-case.  The erofs is most interesting filesystem.
A each files of guest root filesystem need to shift uid/gid in case of
unprivileged container to use uid/gid namespace.  I work adding
uid/gid offsetting support to erofs-utils mkfs tool now.
Will be this patch accept in upstream community?

Thanks,
Naoto Yamaguchi,
a member of Automotive Grade Linux Instrument Cluster EG.