Problem

How can we refactor a commerical OS to follow libOS architecture and achieve a better performance than VMM approach?

Background

• Three categories of services in OS implementations:

• Why does a guest OS need a kernel? Because the host interface is virtual hardware

System Design

• Goals:

  • Compatibility: Runs applications you use
  • Lightweight: <1% of Windows library code
  • Performance: 10x to 20x lower overheads than a VM
  • Security: Secure isolation comparable to VM
  • Mobility: Migrate running applications
  • Generality: Independent evolution of host OS
  • Manageability: Smaller "servicing" area

• Hypothesis: it's possible to design a software ABI with the same properties as hardware ABI:

  • Clearly specified, clean separation of concerns (No undocumented dependencies)

  • Minimally stateful:

    • Registers, etc. are visible to guest OS/application
    • State can be programmatically recreated
    • Analogous to a stateless network protocol

• Guest/Host ABI:

  • Private virtual memory
  • Threads, synchronization
  • I/O streams
  • Thread/process exit
  • Time, random bits, handle reference management, checkpoint/restore

• Refactoring the Desktop:

  • Host OS manages hardware
  • Application services in library

  • Desktop manager

    • Trusted host process
    • Remote Desktop protocol
    • Stateless
    • Shell can be remote

• Drawbridge Architecture:

• Limitations:

  • Incomplete port of windows API

    • Printer support
    • Accelerated graphics

  • Support for multi-process applications (e.g., Outlook with Word as an editor, sharing state through windows subsystem)

  • Administrative tools will not work by design

    • Need more low-level system access

• End results:

  • Refactored Windows 7 as a Library OS (80MB)

  • Functional benefits of VMs:

    • Robust to changes in host system software
    • Security isolation
    • Migration

  • Drastically better scalability

  • Run rich desktop applications