Unformatted text preview: sing a cost benefit policy Systems
Be clever at high utilization!
Bulk operations work better than large number of smaller ones
Indirection, indirection, …. LFS
Improves performance significantly for writes to small files
- influenced journalling
Cute idea but … never put in production file systems
compatibility issues with existing FSs
reads may be slower (for fragmented files) – cache is never big
read bandwidth may be poor for large files -> want contiguity
latency improvements are on the horizon
- SSDs, PCM, RamCloud (Stanford) Break
Chap 9 Protection
What are we protecting?
files, CPU, memory, peripherals, etc
Think of these as objects
Rights: what can be done to w/r an object
Domain: object, rights pairs
Subject: “who or what” is doing the accessing Protection Domains
How are domains established and by whom? A process runs in a domain – set of objects it can access Protection Domains
A protection matrix: maintained in the OS Protection Domains A protection matrix with domains as objects
How this can be done in Unix? Access Control Lists Vertical slice
of matrix Capabilities
Horizontal slice of matrix When capabilities are used, each process has a capability list
In kernel -> Hydra OS Capabilities check known to server Client held capabilities – if in possession of one, have its rights
Extends nicely to distributed systems
A cryptographically protected capability – why?
What doesn’t this protect against? Capabilities
Object specific rights: read, append, draw...
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