Spin

Summary

• What are we searching for?
• Approaches to Extensibility
  • Logical Protection Domains
  • Spin Mechanisms for Protection Domains
• Customized OS with SPIN
  • SPIN Mechanisms for Events
  • Default Core Services in SPIN

What are we searching for?

• thin
  • Like a microkernel
  • only mechanisms, not policies
• access to resources without border crossing
• flexible
  • resource management should be able to be changed to suit particular applications

Approaches to Extensibility

Capability based [Hydra OS]

• kernel mechanisms for resource allocation
• capability based resource access
• resource manager as coarse-grained objects to reduce border crossing overhead

Microkernel-based [Mach from CMU in 90’s]

• focused on extensibility and portability

Spin

• colocation of kernel + extensions
  • avoid border crossing
• compiler enforced modularity
• Logical protection domains
  • not hardware address spaces
• Dynamic call binding
  • flexibility

Logical Protection Domains

Modula-3 safety + encapsulation mechanisms

• type safety
• auto storage management
• objects
• threads
• exception
• generic interfaces

Fine grained protection via capabilities

• hardware resources (e.g. page frame)
• interfaces (e.g. page allocation module)
• collection of interfaces (e.g. entire vm)

Capabilities as language supported pointers

Spin Mechanisms for Protection Domains

Create

• init with object file contents + export names

Resolve

• names between source + target domains
  • once resolved, resources sharing at memory speeds

Combine

• to create an aggregate domain

Customized OS with SPIN

Multiple extensions can live concurrently on the same core, and include (or exclude) submodules at will

SPIN Mechanisms for Events

Services can register event handlers on specified envets

Default Core Services in SPIN

SPIN provides interfraces for core services while allowing extensions to dictate implementation

• Memory Management
  • Physical address
    • allocate
    • deallocate
    • reclaim
  • Virtual address
    • allocate
    • deallocate
  • Translation
    • create/destroy as
    • add/remove mapping
  • Event Handler
    • page fault
    • access fault
    • bad address
• CPU Scheduling
  • SPIN Abstraction:
    • strand
      • unit of schedule
    • semantics defined by extension
  • event handler
    • block
    • unblock
    • checkpoint
    • resume
  • SPIN global scheduler
    • interacts with application threads package