Portals in 4.4BSD

Portals were added to 4.4BSD as an experimental feature and are in the publicly available 4.4BSD-Lite distribution. Portals provide access to alternate file types or devices using names in the normal filesystem that a process just opens. For example, an open of /p/tcp/foo.com/smtp returns a TCP socket descriptor to the calling process that is connected to the SMTP server on the specified host. By providing access through the normal filesystem, the calling process need not be aware of the special functions necessary to create a TCP socket and establish a TCP connection. This makes TCP connections, for example, available to programs such as Awk, Tcl, and shell scripts.

This paper describes the implementation of portals in 4.4BSD as another type of filesystem and provides some examples.