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BSD Facilities

The facilities that are available to a user process are logically divided into two parts: kernel facilities and system facilities implemented by or in cooperation with a server process.

The facilities implemented in the kernel define the virtual machine in which each process runs. Like many real machines, this virtual machine has memory management, an interrupt facility, timers, and counters.

The virtual machine also allows access to files and other objects through a set of descriptors. Each descriptor resembles a device controller and supports a set of operations. Like devices on real machines, some of which are internal to the machine and some of which are external, parts of the descriptor machinery are built into the operating system, while other parts are often implemented in server processes.

The BSD component provides the following kernel facilities:

• processes and protection

  • host and process identifiers

  • process creation and termination

  • user and group IDs

  • process groups

• memory management

  • text, data, stack, and dynamic shared libraries

  • mapping pages

  • page protection control

• POSIX synchronization primitives

• POSIX shared memory

• signals

  • signal types

  • signal handlers

  • sending signals

• timing and statistics

  • real time

  • interval time

• descriptors

  • files

  • pipes

  • sockets

• resource controls

  • process priorities

  • resource utilization and resource limits

  • quotas

• system operation support

  • bootstrap operations

  • shut-down operations

  • accounting

BSD system facilities (facilities that may interact with user space) include

• generic input/output operations such as read and write, nonblocking, and asynchronous operations

• file-system operations

• interprocess communication

• handling of terminals and other devices

• process control

• networking operations

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