[CFR][DEVFS] Add "ruleset" mount option

[Jaakko Heinonen]

On 2012-02-06, Martin Matuska wrote:
> It is not displayed in mount -v / -p and is not used anywhere on
> existing mounts, devfs_mount() doesn't support MNT_UPDATE.

True. There has been some suggestions to add an interface to query
string mount options.

> If we would add update support than we still wouldn't rely on this
> option as it would be read from devfs.

If there is no use for the value after initial mount, IMO it shouldn't
be stored.

This again demonstrates the fragility of nmount.

-- 
Jaakko