non-UTF8 filename support

[cgwalters]

Since its creation ostree (current bootc backend) intentionally didn't support non-UTF8 filenames. In theory, we could lift that restriction as we look towards a direct composefs backend.

I personally think it's almost always going to be a mistake to ship non-UTF8 filenames in containers, but just filing this so we have a tracker.

Also, it'd probably be good to add this to container lint.

[allisonkarlitskaya]

composefs-rs is pretty agnostic about filename encoding. It processes filenames either as Path, OsString, or [u8], all of which should be fine. It never tries to stringify anything except for output/debugging purposes...

[cgwalters]

Yeah, the UTF-8 restriction was an intentional choice many years ago for ostree. Another two example opinionated choices:

• Not having modification times at all
• No support for device files

The mtime thing is still a huge overall issue...and devices are basically always a bad idea (even the overlayfs whiteout nesting one is as discussed better done another way)

But of course since OCI didn't add these restrictions we need to be compatible and yes, composefs will help with that.

It's actually really nice that with composefs specifically the non-UTF8 filenames don't leak onto the physical filesystem and only impact the container using them.