Section 2: System Calls
The Xinu operating system kernel consists of a set of run-time
procedures to implement operating system services on an LSI 11/2
microcomputer. The system supports multiple processes, I/O, syn-
chronization based on counting semaphores, preemptive scheduling,
and communication with other machines. Each page in this section
describes a system routine that can be called by a user process.
Each page describes one system call, giving the number and types
of arguments that must be passed to the procedure under the head-
ing "SYNOPSIS" (by giving their declaration in C syntax). The
heading "SEE ALSO" suggests the names of other system calls that
may be related to the described function. For example, the "SEE
ALSO" entry for system call _w_a_i_t suggests that the programmer may
want to look at the page for _s_i_g_n_a_l because both routines operate
on semaphores. In general, Xinu blocks processes when requested
services are not available. Unless the manual page suggests oth-
erwise, the programmer should assume that the process requesting
system services may be delayed until the request can be satis-
fied. For example, calling _r_e_a_d may cause an arbitrary delay un-
til data can be obtained from the device.