Re: Xen Management API Draft, version 0.4

[Harry Butterworth <harry@hebutterworth.freeserve.co.uk>]

A site-wide emergency power outage happens during any of the use-cases.
The user wants the use-case to roll back to the start or proceed to
completion when power is restored.
User wants to run a text-only interactive application on a virtual
machine.
User wants to run a 2-D graphical interactive application on a virtual
machine.
User wants to run a 3-D graphical interactive application on a virtual
machine.
User wants to configure networking between virtual machines.
User wants to configure networking between virtual machines and the
outside world.
User wants to change storage provision allocated to a virtual machine.
User wants to connect a USB device to a virtual machine :-(
User wants to clone a virtual machine.
User wants to run synthesis on a cloned virtual machine (to make it
slightly different from the original) before connecting it to the
outside world.
User wants to replay virtual machine operation to analyse a security
breach or intermittent problem.
User wants to configure a fault-tolerant virtual machine for a high
availability application.
User wants to configure virtual machines to operate in lock-step to
evaluate whether a change to internal implementation has affected the
external interface (n-version programming).
User wants to single-step a consistent set of virtual machines in
virtual time to debug a cluster application.
User wants to restore a consistent set of virtual machines from a backup
(this one normally gets forgotten).
User wants to test an application designed for large SMP on cheaper
small SMP hardware.
User wants to repeatedly test an application against multiple versions
of a VM, resetting the VMs between each test run.

There must be lots of other use cases.  Yes, there's a bit of a gap
between the level of these use cases and the API proposal.  Which is why
it's important to have a sketch in the document about the software
that's going to be there to fill the gap, roughly how it's going to go
about doing it and how the low-level API operations are sequenced to
operate on the model to achieve these user-level use-cases.

People rarely comment on the notes I write.  I'm continually wondering
whether I'm managing to convey anything useful at all.

Harry.