Operating System Reliability - Operating System - Lecture Slides, Slides of Computer Science

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Operating System Reliability

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What issues need to be tackled by

an operating system that

emphasizes reliability?

• Fault tolerance-- e.g., hardware faults
• Minimizing number of system crashes
  • E.g., not having to restart the system
• Recovery
• Independent failure: when one component

fails, entire system should not crash

• Verifiability-- e.g., verify that write succeeded,

atomic writes, journaling

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p. 27Docsity.com

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EROS Kernel Structure

• EROS provides low-level facilities
  • Application code implements most of the system functions, even “trusted” functions
  • Components: reusable parts built on O/S primitives
  • Separate process implements each component instance
  • High-performance IPC (Inter-Process Communication)
• Example
  • Kernel directly provides pages of disk storage, but not a file system
  • File abstractions entirely at application level
  • Principle: separation of policy from mechanism
  • File application
    • Stores file content in an address space, growing the address space as needed to hold the file
    • Implements operations such as read & write on files

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EROS: Safe Restart

“EROS resolves both issues by using a

transacted checkpointing system. The system

periodically takes an efficient, asynchronous

snapshot of the entire state of

the machine , performs a consistency check

on this state, and then writes it [to disk as a

single] transaction. Because the system

is transacted as a whole, no possibility of

global inconsistency exists. On restart, the

system simply reloads the last completed

transaction. System installation consists of

writing (by hand) an initial system image;

the processes of this system image have no

unusual authority.” (p. 28, color, underline, & italics added)Docsity.com

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Principle: No Kernel Allocation

• EROS has a stateless kernel
  • System’s execution state resides in user-allocated storage
  • Kernel cache’s this state
• Applications must explicitly allocate all of the

pieces that comprise the memory map

structure

• EROS data-- large space of protected objects
  • In application memory space

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Application Structure

• Protected, capability-connected

components

• Each component has limited access to

resources

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