Lecture 7: filesystems
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What is a file?
  key->value pair
  key: hierarchical filename (pathname)
  value: arbitrary number of bytes

In principle, you can use files to store very small values
 - most filesystems have a minimum file size of at least 1K, often 4K or more.
 - one byte of data wastes a lot of space

A set of files "stored" together, sharing a common hierarchical root, is a filesystem

 - no storage for virtual filesystems such as /proc and /sys

When you first start a UNIX system, you start with the "root" filesystem
  - but other filesystems can be put on top by "mount"-ing them.

traditional filesystems are stored in block devices
 - but a filesystem can be anything that provides a filesystem interface

block size issues
 - larger blocks, less overhead (fixed overhead for each block access)
 - smaller blocks, more efficient space usage
   (fewer files smaller than one block)

file interface basics:
 - open, read, write, seek, close
 - open directory, read/write directory, close directory

filesystem interface basics:
 - mount, unmount

filesystem blocksize is a multiple of disk blocksize

How do you structure a filesystem?

First, you have to understand inodes

One other file API: mmap