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Directory Structure
===================
tools/vtpm_manager/crypto    -> crypto files
tools/vtpm_manager/TCS       -> TCS implementation
tools/vtpm_manager/util      -> Utility Library. Include disk-io and buffers.
tools/vtpm_manager/manager   -> VTPM Manager

Compile Flags
===================
LOGGING_MODULES              -> How extensive logging happens
                                see util/log.h for more info

VTPM_MULTI_VM                -> Defined: VTPMs run in their own VMs
                                Not Defined (default): VTPMs are processes

# Debugging flags that may disappear without notice in the future

DUMMY_BACKEND                -> vtpm_manager listens on /tmp/in.fifo and 
                                /tmp/out.fifo rather than backend

MANUAL_DM_LAUNCH             -> Must manually launch & kill VTPMs

WELL_KNOWN_OWNER_AUTH        -> Rather than randomly generating the password for the owner,
                                use a well known value. This is useful for debugging and for
                                poor bios which do not support clearing TPM if OwnerAuth is
                                lost. However this has no protection from malicious app
                                issuing a TPM_OwnerClear to wipe the TPM 

Requirements
============
- xen-unstable 
- vtpm frontend/backend driver patch
- OpenSSL Library

Single-VM Flow
============================
- Launch the VTPM manager (vtpm_managerd) which which begins listening to the BE with one thread
  and listens to a named fifo that is shared by the vtpms to commuincate with the manager.
- VTPM Manager listens to TPM BE.
- When xend launches a tpm frontend equipped VM it contacts the manager over the vtpm backend. 
- When the manager receives the open message from the BE, it launches a vtpm
- Xend allows the VM to continue booting. 
- When a TPM request is issued to the front end, the front end transmits the TPM request to the backend.
- The manager receives the TPM requests and uses a named fifo to forward the request to the vtpm.
- The fifo listener begins listening for the reply from vtpm for the request.
- Vtpm processes request and replies to manager over shared named fifo.
- If needed, the vtpm may send a request to the vtpm_manager at any time to save it's secrets to disk.
- Manager receives response from vtpm and passes it back to backend for forwarding to guest.

NOTES:
* SaveService SHOULD seal it's table before saving it to disk. However,
  the current Xen infrastructure does not provide a mechanism for this to be
  unsealed later. Specifically, the auth and wrapped key must be available ONLY
  to the service, or it's not even worth encrypting

  In the future the vtpm manager will be protected by an early boot mechanism
  that will allow for better protection of it's data.

TODO:
- Timeout on crashed vtpms
- create lock for shared fifo for talking to vtpms.