/*      $OpenBSD: signal.c,v 1.25 2015/01/06 11:42:37 bluhm Exp $       */

/*
 * Copyright 2000-2002 Niels Provos <provos@citi.umich.edu>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <sys/types.h>
#include <sys/time.h>
#include <sys/queue.h>
#include <sys/socket.h>

#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <fcntl.h>
#include <assert.h>

#include "event.h"
#include "event-internal.h"
#include "evsignal.h"
#include "log.h"

struct event_base *evsignal_base = NULL;

static void evsignal_handler(int sig);

/* Callback for when the signal handler write a byte to our signaling socket */
static void
evsignal_cb(int fd, short what, void *arg)
{
        static char signals[1];
        ssize_t n;

        n = recv(fd, signals, sizeof(signals), 0);
        if (n == -1) {
                if (errno != EAGAIN)
                        event_err(1, "%s: read", __func__);
        }
}

int
evsignal_init(struct event_base *base)
{
        int i;

        /*
         * Our signal handler is going to write to one end of the socket
         * pair to wake up our event loop.  The event loop then scans for
         * signals that got delivered.
         */
        if (socketpair(AF_UNIX, SOCK_STREAM | SOCK_CLOEXEC | SOCK_NONBLOCK,
            0, base->sig.ev_signal_pair) == -1) {
                event_err(1, "%s: socketpair", __func__);
                return -1;
        }

        base->sig.sh_old = NULL;
        base->sig.sh_old_max = 0;
        base->sig.evsignal_caught = 0;
        memset(&base->sig.evsigcaught, 0, sizeof(sig_atomic_t)*NSIG);
        /* initialize the queues for all events */
        for (i = 0; i < NSIG; ++i)
                TAILQ_INIT(&base->sig.evsigevents[i]);

        event_set(&base->sig.ev_signal, base->sig.ev_signal_pair[1],
                EV_READ | EV_PERSIST, evsignal_cb, &base->sig.ev_signal);
        base->sig.ev_signal.ev_base = base;
        base->sig.ev_signal.ev_flags |= EVLIST_INTERNAL;

        return 0;
}

/* Helper: set the signal handler for evsignal to handler in base, so that
 * we can restore the original handler when we clear the current one. */
int
_evsignal_set_handler(struct event_base *base,
                      int evsignal, void (*handler)(int))
{
        struct sigaction sa;
        struct evsignal_info *sig = &base->sig;
        void *p;

        /*
         * resize saved signal handler array up to the highest signal number.
         * a dynamic array is used to keep footprint on the low side.
         */
        if (evsignal >= sig->sh_old_max) {
                int new_max = evsignal + 1;
                event_debug(("%s: evsignal (%d) >= sh_old_max (%d), resizing",
                            __func__, evsignal, sig->sh_old_max));
                p = reallocarray(sig->sh_old, new_max, sizeof(*sig->sh_old));
                if (p == NULL) {
                        event_warn("realloc");
                        return (-1);
                }

                memset((char *)p + sig->sh_old_max * sizeof(*sig->sh_old),
                    0, (new_max - sig->sh_old_max) * sizeof(*sig->sh_old));

                sig->sh_old_max = new_max;
                sig->sh_old = p;
        }

        /* allocate space for previous handler out of dynamic array */
        sig->sh_old[evsignal] = malloc(sizeof *sig->sh_old[evsignal]);
        if (sig->sh_old[evsignal] == NULL) {
                event_warn("malloc");
                return (-1);
        }

        /* save previous handler and setup new handler */
        memset(&sa, 0, sizeof(sa));
        sa.sa_handler = handler;
        sa.sa_flags |= SA_RESTART;
        sigfillset(&sa.sa_mask);

        if (sigaction(evsignal, &sa, sig->sh_old[evsignal]) == -1) {
                event_warn("sigaction");
                free(sig->sh_old[evsignal]);
                sig->sh_old[evsignal] = NULL;
                return (-1);
        }

        return (0);
}

int
evsignal_add(struct event *ev)
{
        int evsignal;
        struct event_base *base = ev->ev_base;
        struct evsignal_info *sig = &ev->ev_base->sig;

        if (ev->ev_events & (EV_READ|EV_WRITE))
                event_errx(1, "%s: EV_SIGNAL incompatible use", __func__);
        evsignal = EVENT_SIGNAL(ev);
        assert(evsignal >= 0 && evsignal < NSIG);
        if (TAILQ_EMPTY(&sig->evsigevents[evsignal])) {
                event_debug(("%s: %p: changing signal handler", __func__, ev));
                if (_evsignal_set_handler(
                            base, evsignal, evsignal_handler) == -1)
                        return (-1);

                /* catch signals if they happen quickly */
                evsignal_base = base;

                if (!sig->ev_signal_added) {
                        if (event_add(&sig->ev_signal, NULL))
                                return (-1);
                        sig->ev_signal_added = 1;
                }
        }

        /* multiple events may listen to the same signal */
        TAILQ_INSERT_TAIL(&sig->evsigevents[evsignal], ev, ev_signal_next);

        return (0);
}

int
_evsignal_restore_handler(struct event_base *base, int evsignal)
{
        int ret = 0;
        struct evsignal_info *sig = &base->sig;
        struct sigaction *sh;

        /* restore previous handler */
        sh = sig->sh_old[evsignal];
        sig->sh_old[evsignal] = NULL;
        if (sigaction(evsignal, sh, NULL) == -1) {
                event_warn("sigaction");
                ret = -1;
        }
        free(sh);

        return ret;
}

int
evsignal_del(struct event *ev)
{
        struct event_base *base = ev->ev_base;
        struct evsignal_info *sig = &base->sig;
        int evsignal = EVENT_SIGNAL(ev);

        assert(evsignal >= 0 && evsignal < NSIG);

        /* multiple events may listen to the same signal */
        TAILQ_REMOVE(&sig->evsigevents[evsignal], ev, ev_signal_next);

        if (!TAILQ_EMPTY(&sig->evsigevents[evsignal]))
                return (0);

        event_debug(("%s: %p: restoring signal handler", __func__, ev));

        return (_evsignal_restore_handler(ev->ev_base, EVENT_SIGNAL(ev)));
}

static void
evsignal_handler(int sig)
{
        int save_errno = errno;

        if (evsignal_base == NULL) {
                event_warn(
                        "%s: received signal %d, but have no base configured",
                        __func__, sig);
                return;
        }

        evsignal_base->sig.evsigcaught[sig]++;
        evsignal_base->sig.evsignal_caught = 1;

        /* Wake up our notification mechanism */
        send(evsignal_base->sig.ev_signal_pair[0], "a", 1, 0);
        errno = save_errno;
}

void
evsignal_process(struct event_base *base)
{
        struct evsignal_info *sig = &base->sig;
        struct event *ev, *next_ev;
        sig_atomic_t ncalls;
        int i;

        base->sig.evsignal_caught = 0;
        for (i = 1; i < NSIG; ++i) {
                ncalls = sig->evsigcaught[i];
                if (ncalls == 0)
                        continue;
                sig->evsigcaught[i] -= ncalls;

                for (ev = TAILQ_FIRST(&sig->evsigevents[i]);
                    ev != NULL; ev = next_ev) {
                        next_ev = TAILQ_NEXT(ev, ev_signal_next);
                        if (!(ev->ev_events & EV_PERSIST))
                                event_del(ev);
                        event_active(ev, EV_SIGNAL, ncalls);
                }

        }
}

void
evsignal_dealloc(struct event_base *base)
{
        int i = 0;
        if (base->sig.ev_signal_added) {
                event_del(&base->sig.ev_signal);
                base->sig.ev_signal_added = 0;
        }
        for (i = 0; i < NSIG; ++i) {
                if (i < base->sig.sh_old_max && base->sig.sh_old[i] != NULL)
                        _evsignal_restore_handler(base, i);
        }

        if (base->sig.ev_signal_pair[0] != -1) {
                close(base->sig.ev_signal_pair[0]);
                base->sig.ev_signal_pair[0] = -1;
        }
        if (base->sig.ev_signal_pair[1] != -1) {
                close(base->sig.ev_signal_pair[1]);
                base->sig.ev_signal_pair[1] = -1;
        }
        base->sig.sh_old_max = 0;

        /* per index frees are handled in evsignal_del() */
        if (base->sig.sh_old) {
                free(base->sig.sh_old);
                base->sig.sh_old = NULL;
        }
}