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CS533 Concepts of Operating Systems
Class 6
Micro-kernels
Extensibility via Hardware or
Software Based Protection
Questions
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What is the structure of a pure emulation librarybased OS above a micro-kernel?
o
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What is the structure of a single-server based OS
above a micro-kernel?
o
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How are system calls handled?
How are system calls handled?
What is the structure of a multi-server based OS
above a micro-kernel?
o
How are system calls handled?
CS533 - Concepts of Operating Systems
2
Questions
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What are the main sources of overhead in microkernel based OSs compared to monolithic OSs?
How does L3 address these overheads?
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Do these optimizations completely solve the problem?
What minimal abstractions should a kernel provide?
CS533 - Concepts of Operating Systems
3
Questions
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What is the motivation for modular operating
systems?
o
o
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What is the motivation for using hardware
protection at module boundaries?
o
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Does this imply modules with hardware protection?
.. and what do I mean by hardware protection for modules?
Does this imply message passing across module boundaries?
… what other alternatives do you have?
What is the motivation for using message-passing
for inter-module communication?
CS533 - Concepts of Operating Systems
4
Questions
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What is extensibility and how does micro-kernelbased OS structure help?
o
What other approaches are there?
CS533 - Concepts of Operating Systems
5
Questions
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Why does Sandboxing slow down normal execution?
Why does it speed up inter-module communication
compared to Mach?
What is a jump-table and why is it needed?
On balance is Sandboxing a win or loss?
o
o
compared to Mach?
compared to L3/L4?
CS533 - Concepts of Operating Systems
6
Questions
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What exactly is a protection domain in SPIN?
How are module boundaries implemented in SPIN?
o
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What implications does this have for kernel extensions?
How does extension code invoke SPIN’s core
services, or code in other modules?
How do SPIN’s core services compare to those of
micro-kernels?
CS533 - Concepts of Operating Systems
7
Questions



Does the SPIN approach slow down normal
execution?
How does it speed up inter-module communication?
On balance is it a win or loss?
o
o
o
compared to Mach?
compared to L3/L4?
compared to Sandboxing?
CS533 - Concepts of Operating Systems
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