Perhaps the minimum required to support zfs quotas (maximum volume sizes) at the filesystem level.
Have a VolumeSize object instead of a single integer
Note about what this branch will do.
Add VolumeSize and add a size to Volume.
Move testing helpers to testing helper module.  Fix names to follow naming convention.
Add `size` attribute to `IFilesystem` and teach `IStoragePool.create` to initialize it from `Volume.size`.
Did a couple of these things.  Also add a missing bit of docs.
Require that IStoragePool.enumerate implementations produce size information as well.

Move VolumeSize to a new module to eliminate a circular dependency.
Record the maximum size of the directory-based storage pool filesystems and produce it from `enumerate` results.
lint fixes
lint fixes
lint fix
lint fix
Add an exception type the interface can reference for the too-small-maximum-size case.
Oh dang.
Implemented this.  Also moved comment inline.
Let VolumeService.get initialize more parts of Volume.
Use new feature of VolumeService.get
Re-introduce the remainder of the design sketch for the user-facing feature.
Finish _DatasetInfo.