[LSF/MM TOPIC] Filesystem namespaces and uid/gid/lsm remapping

[Andy Lutomirski <luto@amacapital.net>]

This should hopefully be a short topic, and it's possible that it'll
be settled by the time LSF/MM comes around, but:

There's a fair amount of interest from different directions for
allowing filesystems with a backing store to be mounted (in the
mount-from-scratch sense, not the bind-mount sense) in a user
namespace.  For example, Seth has patches to allow unprivileged FUSE
mounts.  There are a few issues here, for example:

 - What happens to device nodes in those filesystems?

 - If a FUSE backend is in a user namespace, how should UIDs be
translated to/from that backend?

 - How should LSM security labels be translated?

 - Should a struct super_block be associated with a user namespace?
(Answer: probably, I think.)  If so, what should the semantics be?

There are also some remapping cases that aren't directly user
namespace-related.  For example, I'd like to be able to insert
removable media and create files owned by uid 0 (or any other uid)
without actually being root.

--Andy