CS 3733 Operating Systems

Reading: Section 3.1 - 3.6 of PUP

An operating system manages resources --- processors, memory and I/O so that a process can execute. In the next two lectures, we'll go over the basics of I/O in Unix. We will then talk about I/O management more generally.

• What devices must an OS manage?

• Device independent I/O:
  Unix provides a uniform interface to devices through the following system calls:
  • open - set up the connection between the device and the process and return an integer handle to the process for future reference.
  • close - remove the association of the handle with the device.
  • read - read a block of data from the specified device.
  • write - write a block of data to the specified device.
  • ioctl - perform device-specific control.

  As a result of the device independent-interface, all devices look (more or less) like files.

• How does the open set up the connection? (PUP 3.3.1)
  • open prototype.
  • File handle as an index into the file descriptor table.
  • Meaning of the Posix values of the flags.
  • Nonblocking versus blocking I/O - a quick description.
  • Permissions.

• ANSI C standard I/O versus the Unix I/O library (PUP 3.3.2)

• Inheritance of file descriptors on fork (PUP 3.3.3)

• The read and write system calls: (PUP 3.6)
  • Prototypes.
  • Return values.
  • Difference between reading from a terminal and reading from a disk.

• File representation in Unix: (PUP 3.2)
  • Ordinary files (See Figure 3.3 of PUP).
  • Directories.
  • Special files (represent physical devices).

SKILL: Understand how to access files in Unix