siginterrupt - allow signals to interrupt system calls

siginterrupt(sig, flag);
int sig, flag;

Siginterrupt is used to change the system call restart behavior
when a system call is interrupted by the specified signal. If the
flag is false (0), then system calls will be restarted if they are
interrupted by the specified signal and no data has been
transferred yet. System call restart is the default behavior on
4.2 BSD.

If the flag is true (1), then restarting of system calls is
disabled. If a system call is interrupted by the specified signal
and no data has been transferred, the system call will return -1
with errno set to EINTR. Interrupted system calls that have
started transferring data will return the amount of data actually
transferred. System call interrupt is the signal behavior found on
4.1 BSD and AT&T System V UNIX systems.

Note that the new 4.2 BSD signal handling semantics are not altered
in any other way. Most notably, signal handlers always remain
installed until explicitly changed by a subsequent sigvec(2) call,
and the signal mask operates as documented in sigvec(2). Programs
may switch between restartable and interruptible system call
operation as often as desired in the execution of a program.

Issuing a siginterrupt(3) call during the execution of a signal
handler will cause the new action to take place on the next signal
to be caught.

This library routine uses an extension of the sigvec(2) system call
that is not available in 4.2BSD, hence it should not be used if
backward compatibility is needed.

A 0 value indicates that the call succeeded. A -1 value indicates
that an invalid signal number has been supplied.

sigvec(2), sigblock(2), sigpause(2), sigsetmask(2).