SIGVEC(3)                 OpenBSD Programmer's Manual                SIGVEC(3)

NAME
     sigvec - software signal facilities



SYNOPSIS
     #include <signal.h>

     struct sigvec {
             void     (*sv_handler)();
             int      sv_mask;
             int      sv_flags;
     };

     int
     sigvec(int sig, struct sigvec *vec, struct sigvec *ovec);

DESCRIPTION
     This interface is made obsolete by sigaction(2).

     The system defines a set of signals that may be delivered to a process.
     Signal delivery resembles the occurrence of a hardware interrupt: the
     signal is blocked from further occurrence, the current process context is
     saved, and a new one is built.  A process may specify a handler to which
     a signal is delivered, or specify that a signal is to be blocked or
     ignored. A process may also specify that a default action is to be taken
     by the system when a signal occurs.  A signal may also be blocked, in
     which case its delivery is postponed until it is unblocked. The action to
     be taken on delivery is determined at the time of delivery.  Normally,
     signal handlers execute on the current stack of the process.  This may be
     changed, on a per-handler basis, so that signals are taken on a special
     signal stack.

     All signals have the same priority. Signal routines execute with the sig-
     nal that caused their invocation blocked, but other signals may yet oc-
     cur.  A global signal mask defines the set of signals currently blocked
     from delivery to a process.  The signal mask for a process is initialized
     from that of its parent (normally 0).  It may be changed with a sig-
     block(3) or sigsetmask(3) call, or when a signal is delivered to the pro-
     cess.

     When a signal condition arises for a process, the signal is added to a
     set of signals pending for the process.  If the signal is not currently
     blocked by the process then it is delivered to the process.  When a
     caught signal is delivered, the current state of the process is saved, a
     new signal mask is calculated (as described below), and the signal han-
     dler is invoked.  The call to the handler is arranged so that if the sig-
     nal handling routine returns normally the process will resume execution
     in the context from before the signal's delivery.  If the process wishes
     to resume in a different context, then it must arrange to restore the
     previous context itself.

     When a signal is delivered to a process a new signal mask is installed
     for the duration of the process' signal handler (or until a sigblock or
     sigsetmask call is made).  This mask is formed by taking the union of the
     current signal mask, the signal to be delivered, and the signal mask as-
     sociated with the handler to be invoked.

     sigvec() assigns a handler for a specific signal.  If vec is non-zero, it
     specifies an action (SIG_DFL, SIG_IGN, or a handler routine) and mask to
     be used when delivering the specified signal.  If ovec is non-zero, the
     previous handling information for the signal is returned to the user.

     Once a signal handler is installed, it remains installed until another
     sigvec() call is made, or an execve(2) is performed.  A signal-specific
     default action may be reset by setting sv_handler to SIG_DFL. The de-
     faults are process termination, possibly with core dump; no action; stop-
     ping the process; or continuing the process.  See the signal list below
     for each signal's default action.  If sv_handler is set to SIG_IGN, the
     default action for the signal is to discard the signal, and if a signal
     is pending, the pending signal is discarded even if the signal is masked.
     If sv_handler is set to SIG_IGN, current and pending instances of the
     signal are ignored and discarded.

     Options may be specified by setting sv_flags. If the SV_ONSTACK bit is
     set in sv_flags, the system will deliver the signal to the process on a
     signal stack, specified with sigstack(2).

     If a signal is caught during the system calls listed below, the call may
     be restarted, the call may return with a data transfer shorter than re-
     quested, or the call may forced to terminate with the error EINTR. Inter-
     rupting of pending calls is requested by setting the SV_INTERRUPT bit in
     sv_flags. The affected system calls include open(2),  read(2),  write(2),
      sendto(2),  recvfrom(2),  sendmsg(2) and recvmsg(2) on a communications
     channel or a slow device (such as a terminal, but not a regular file) and
     during a wait(2) or ioctl(2).  However, calls that have already committed
     are not restarted, but instead return a partial success (for example, a
     short read count).

     After a fork(2) or vfork(2) all signals, the signal mask, the signal
     stack, and the interrupt/restart flags are inherited by the child.

     execve(2) reinstates the default action for all signals which were caught
     and resets all signals to be caught on the user stack.  Ignored signals
     remain ignored; the signal mask remains the same; signals that interrupt
     pending system calls continue to do so.

     The following is a list of all signals with names as in the include file
     <signal.h>:

     NAME            Default Action          Description
     SIGHUP          terminate process       terminal line hangup
     SIGINT          terminate process       interrupt program
     SIGQUIT         create core image       quit program
     SIGILL          create core image       illegal instruction
     SIGTRAP         create core image       trace trap
     SIGABRT         create core image       abort(3) call (formerly SIGIOT)
     SIGEMT          create core image       emulate instruction executed
     SIGFPE          create core image       floating-point exception
     SIGKILL         terminate process       kill program (cannot be caught or
                                             ignored)
     SIGBUS          create core image       bus error
     SIGSEGV         create core image       segmentation violation
     SIGSYS          create core image       system call given invalid
                                             argument
     SIGPIPE         terminate process       write on a pipe with no reader
     SIGALRM         terminate process       real-time timer expired
     SIGTERM         terminate process       software termination signal
     SIGURG          discard signal          urgent condition present on
                                             socket
     SIGSTOP         stop process            stop (cannot be caught or
                                             ignored)
     SIGTSTP         stop process            stop signal generated from
                                             keyboard
     SIGCONT         discard signal          continue after stop
     SIGCHLD         discard signal          child status has changed
     SIGTTIN         stop process            background read attempted from
                                             control terminal
     SIGTTOU         stop process            background write attempted to


                                             control terminal
     SIGIO           discard signal          I/O is possible on a descriptor
                                             (see fcntl(2))
     SIGXCPU         terminate process       cpu time limit exceeded (see
                                             setrlimit(2))
     SIGXFSZ         terminate process       file size limit exceeded (see
                                             setrlimit(2))
     SIGVTALRM       terminate process       virtual time alarm (see
                                             setitimer(2))
     SIGPROF         terminate process       profiling timer alarm (see
                                             setitimer(2))
     SIGWINCH        discard signal          window size change
     SIGINFO         discard signal          status request from keyboard
     SIGUSR1         terminate process       user-defined signal 1
     SIGUSR2         terminate process       user-defined signal 2

NOTES
     The mask specified in vec is not allowed to block SIGKILL or SIGSTOP.
     This is enforced silently by the system.

     The SV_INTERRUPT flag is not available in 4.2BSD, hence it should not be
     used if backward compatibility is needed.

RETURN VALUES
     A 0 value indicated that the call succeeded.  A -1 return value indicates
     an error occurred and errno is set to indicated the reason.

ERRORS
     sigvec() will fail and no new signal handler will be installed if one of
     the following occurs:

     [EFAULT]      Either vec or ovec points to memory that is not a valid
                   part of the process address space.

     [EINVAL]      sig is not a valid signal number.

     [EINVAL]      An attempt is made to ignore or supply a handler for
                   SIGKILL or SIGSTOP.

EXAMPLE
     For an example of signal handler declarations, see sigaction(2).

SEE ALSO
     kill(1),  kill(2),  ptrace(2),  sigaction(2),  sigaltstack(2),
     sigpause(2),  sigprocmask(2),  sigstack(2),  sigsuspend(2),  setjmp(3),
     sigblock(3),  siginterrupt(3),  sigsetmask(3),  sigsetops(3),  sigvec(3),
      tty(4)

OpenBSD 2.6                     April 29, 1991                               3