support os.Root

[sean9999]

go 1.24 defines a new type os.Root:

https://go.dev/doc/go1.24#directory-limited-filesystem-access

implement it. document it.

[sean9999]

I would like to try my hand at this

[cedws]

Maybe the BasePathFs type could be retrofitted to use this. The way afero currently implements this is not ideal, os.Root should be more secure.

[sagikazarmark]

There is an IOFS driver: https://pkg.go.dev/github.com/spf13/afero#FromIOFS

Would that work?

[sean9999]

At first glance, not entirely. Because writeability should be supported. Will investigate

[sean9999]

Wrapping BasePathFs worked well and I submitted a PR.

But do you think it would be smarter to remove it and replace it with something that behaves exactly as os.Root does? I say this because @cedws mentions that *BasePathFs implementation has rough edges. I didn't notice any huge smells.

[cedws]

BasePathFs doesn't use the same syscall-based strategies as os.Root to prevent traversal - it uses path sanitisation only.

https://go.dev/blog/osroot

[sean9999]

oh, for sure. The "real" back-end simply wraps os.Root.

But for the other back-ends such as MemMapFs, syscalls are not possible.