sigvec



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
     signal that caused their invocation blocked, but other signals may yet
     occur.  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
     sigblock(3) or sigsetmask(3) call, or when a signal is delivered to the
     process.

     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
     handler is invoked.  The call to the handler is arranged so that if the
     signal 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(3)
     or sigsetmask(3) 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 associated 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
     defaults are process termination, possibly with core dump; no action;
     stopping 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 sigaltstack(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
     requested, or the call may be forced to terminate with the error EINTR.
     Interrupting 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.


EXAMPLES

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


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.


SEE ALSO

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


HISTORY

     A sigvec() system call first appeared in 4.2BSD.  It was reimplemented as
     a wrapper around sigaction(2) in 4.3BSD-Reno.  The old system call was
     kept for compatibility until OpenBSD 4.9.

OpenBSD 5.4                      July 17, 2013                     OpenBSD 5.4

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