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Session 23 - April 07, 2003
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AGENDA:
0 Admin
1 Homework #5
2 Ch 5.6: overview of the MINIX file system

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0 - ADMIN
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Startout Q: What is an inode?

Due today
* HM #5

Due Wednesday
* RI #8: Ch 5.6-7

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1 - HM #5
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Discuss homework.

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2 - CH 5.6: OVERVIEW OF THE MINIX FILE SYSTEM
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MINIX file system is a network file server that is on
  same machine as caller.
FS can be modified, experimented with, etc. with
  almost no modifications for rest of O/S.
Very easy to turn into remote file server.

MESSAGES
39 messages
* fig 5-27 p. 455
* most regard system calls
* basic algorithm similar to MM

FILE SYSTEM LAYOUT
A MINIX file system is self-contained
* it is not hardware dependent
* fig 5-28 p. 456

Boot block
* contains executable code that read at startup
* starts loading O/S
* not all storage devices can be used for booting,
  but to keep structure uniform, every block device has
  a block reserved
* magic number in specific location prevents trying to
  boot unbootable device. No magic => don't boot.
Super-block
* fig 5-29 p. 457
* Why both number of nodes and number of i-node bitmap
  blocks? Same for zones.
* Zones are similar to clusters
- Track Log2 (block/zone) => quick conversion from
  zones to blocks.
- Track only data blocks with zones
* super-block acts partially as cache of calculable
  info about file system
* super-block in memory

BIT MAPS
* track i-nodes and zones

I-NODES
* fig 5-30 p. 461

BLOC CACHE
* fig 5-31 p. 462

DIRECTORIES & PATHS
* 16 bytes, 2 for I-node + 14 for name
* fig 5-32 p. 464

FILE DESCRIPTORS
* fig 5-33 p. 466
* where does file pointer go?
  - not in i-node
  - must have shared pointer between parent and child
  -> separate table

FILE LOCKING
* MINIX supports advisory file locking

PIPES & SPECIAL FILES
* suspend a process if tries reading from a pipe
  and no data is available
* suspend it and restart syscall when data available
COS 421 - Lecture Notes #25		SPRING 2003	
COS421-lect-2003-04-07.doc	Page 1	Printed 07.04.03