dbwrap_cache: Check negative first

[Samba.git] / lib / tevent / tevent_signal.c

/*
   Unix SMB/CIFS implementation.

   common events code for signal events

   Copyright (C) Andrew Tridgell        2007

     ** NOTE! The following LGPL license applies to the tevent
     ** library. This does NOT imply that all of Samba is released
     ** under the LGPL

   This library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 3 of the License, or (at your option) any later version.

   This library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with this library; if not, see <http://www.gnu.org/licenses/>.
*/

#include "replace.h"
#include "system/filesys.h"
#include "system/wait.h"
#include "tevent.h"
#include "tevent_internal.h"
#include "tevent_util.h"

/* maximum number of SA_SIGINFO signals to hold in the queue.
  NB. This *MUST* be a power of 2, in order for the ring buffer
  wrap to work correctly. Thanks to Petr Vandrovec <petr@vandrovec.name>
  for this. */

#define TEVENT_SA_INFO_QUEUE_COUNT 256

size_t tevent_num_signals(void)
{
        return TEVENT_NUM_SIGNALS;
}

size_t tevent_sa_info_queue_count(void)
{
        return TEVENT_SA_INFO_QUEUE_COUNT;
}

struct tevent_sigcounter {
        uint32_t count;
        uint32_t seen;
};

#define TEVENT_SIG_INCREMENT(s) (s).count++
#define TEVENT_SIG_SEEN(s, n) (s).seen += (n)
#define TEVENT_SIG_PENDING(s) ((s).seen != (s).count)

struct tevent_common_signal_list {
        struct tevent_common_signal_list *prev, *next;
        struct tevent_signal *se;
};

/*
  the poor design of signals means that this table must be static global
*/
static struct tevent_sig_state {
        struct tevent_common_signal_list *sig_handlers[TEVENT_NUM_SIGNALS+1];
        struct sigaction *oldact[TEVENT_NUM_SIGNALS+1];
        struct tevent_sigcounter signal_count[TEVENT_NUM_SIGNALS+1];
        struct tevent_sigcounter got_signal;
#ifdef SA_SIGINFO
        /* with SA_SIGINFO we get quite a lot of info per signal */
        siginfo_t *sig_info[TEVENT_NUM_SIGNALS+1];
        struct tevent_sigcounter sig_blocked[TEVENT_NUM_SIGNALS+1];
#endif
} *sig_state;

/*
  return number of sigcounter events not processed yet
*/
static uint32_t tevent_sig_count(struct tevent_sigcounter s)
{
        return s.count - s.seen;
}

/*
  signal handler - redirects to registered signals
*/
static void tevent_common_signal_handler(int signum)
{
        char c = 0;
        struct tevent_common_signal_list *sl;
        struct tevent_context *ev = NULL;
        int saved_errno = errno;

        TEVENT_SIG_INCREMENT(sig_state->signal_count[signum]);
        TEVENT_SIG_INCREMENT(sig_state->got_signal);

        /* Write to each unique event context. */
        for (sl = sig_state->sig_handlers[signum]; sl; sl = sl->next) {
                if (sl->se->event_ctx && sl->se->event_ctx != ev) {
                        ev = sl->se->event_ctx;
                        /* doesn't matter if this pipe overflows */
                        (void) write(ev->pipe_fds[1], &c, 1);
                }
        }

        errno = saved_errno;
}

#ifdef SA_SIGINFO
/*
  signal handler with SA_SIGINFO - redirects to registered signals
*/
static void tevent_common_signal_handler_info(int signum, siginfo_t *info,
                                              void *uctx)
{
        uint32_t count = tevent_sig_count(sig_state->signal_count[signum]);
        /* sig_state->signal_count[signum].seen % TEVENT_SA_INFO_QUEUE_COUNT
         * is the base of the unprocessed signals in the ringbuffer. */
        uint32_t ofs = (sig_state->signal_count[signum].seen + count) %
                                TEVENT_SA_INFO_QUEUE_COUNT;
        sig_state->sig_info[signum][ofs] = *info;

        tevent_common_signal_handler(signum);

        /* handle SA_SIGINFO */
        if (count+1 == TEVENT_SA_INFO_QUEUE_COUNT) {
                /* we've filled the info array - block this signal until
                   these ones are delivered */
#ifdef HAVE_UCONTEXT_T
                /*
                 * This is the only way for this to work.
                 * By default signum is blocked inside this
                 * signal handler using a temporary mask,
                 * but what we really need to do now is
                 * block it in the callers mask, so it
                 * stays blocked when the temporary signal
                 * handler mask is replaced when we return
                 * from here. The callers mask can be found
                 * in the ucontext_t passed in as the
                 * void *uctx argument.
                 */
                ucontext_t *ucp = (ucontext_t *)uctx;
                sigaddset(&ucp->uc_sigmask, signum);
#else
                /*
                 * WARNING !!! WARNING !!!!
                 *
                 * This code doesn't work.
                 * By default signum is blocked inside this
                 * signal handler, but calling sigprocmask
                 * modifies the temporary signal mask being
                 * used *inside* this handler, which will be
                 * replaced by the callers signal mask once
                 * we return from here. See Samba
                 * bug #9550 for details.
                 */
                sigset_t set;
                sigemptyset(&set);
                sigaddset(&set, signum);
                sigprocmask(SIG_BLOCK, &set, NULL);
#endif
                TEVENT_SIG_INCREMENT(sig_state->sig_blocked[signum]);
        }
}
#endif

static int tevent_common_signal_list_destructor(struct tevent_common_signal_list *sl)
{
        if (sig_state->sig_handlers[sl->se->signum]) {
                DLIST_REMOVE(sig_state->sig_handlers[sl->se->signum], sl);
        }
        return 0;
}

/*
  destroy a signal event
*/
static int tevent_signal_destructor(struct tevent_signal *se)
{
        struct tevent_common_signal_list *sl =
                talloc_get_type_abort(se->additional_data,
                struct tevent_common_signal_list);

        if (se->event_ctx) {
                struct tevent_context *ev = se->event_ctx;

                DLIST_REMOVE(ev->signal_events, se);

                if (ev->signal_events == NULL && ev->pipe_fde != NULL) {
                        /*
                         * This was the last signal. Destroy the pipe.
                         */
                        TALLOC_FREE(ev->pipe_fde);

                        close(ev->pipe_fds[0]);
                        close(ev->pipe_fds[1]);
                }
        }

        talloc_free(sl);

        if (sig_state->sig_handlers[se->signum] == NULL) {
                /* restore old handler, if any */
                if (sig_state->oldact[se->signum]) {
                        sigaction(se->signum, sig_state->oldact[se->signum], NULL);
                        sig_state->oldact[se->signum] = NULL;
                }
#ifdef SA_SIGINFO
                if (se->sa_flags & SA_SIGINFO) {
                        if (sig_state->sig_info[se->signum]) {
                                talloc_free(sig_state->sig_info[se->signum]);
                                sig_state->sig_info[se->signum] = NULL;
                        }
                }
#endif
        }

        return 0;
}

/*
  this is part of the pipe hack needed to avoid the signal race condition
*/
static void signal_pipe_handler(struct tevent_context *ev, struct tevent_fd *fde, 
                                uint16_t flags, void *_private)
{
        char c[16];
        /* its non-blocking, doesn't matter if we read too much */
        (void) read(fde->fd, c, sizeof(c));
}

/*
  add a signal event
  return NULL on failure (memory allocation error)
*/
struct tevent_signal *tevent_common_add_signal(struct tevent_context *ev,
                                               TALLOC_CTX *mem_ctx,
                                               int signum,
                                               int sa_flags,
                                               tevent_signal_handler_t handler,
                                               void *private_data,
                                               const char *handler_name,
                                               const char *location)
{
        struct tevent_signal *se;
        struct tevent_common_signal_list *sl;
        sigset_t set, oldset;

        if (signum >= TEVENT_NUM_SIGNALS) {
                errno = EINVAL;
                return NULL;
        }

        /* the sig_state needs to be on a global context as it can last across
           multiple event contexts */
        if (sig_state == NULL) {
                sig_state = talloc_zero(NULL, struct tevent_sig_state);
                if (sig_state == NULL) {
                        return NULL;
                }
        }

        se = talloc(mem_ctx?mem_ctx:ev, struct tevent_signal);
        if (se == NULL) return NULL;

        se->event_ctx           = ev;
        se->signum              = signum;
        se->sa_flags            = sa_flags;
        se->handler             = handler;
        se->private_data        = private_data;
        se->handler_name        = handler_name;
        se->location            = location;
        se->additional_data     = NULL;

        sl = talloc(se, struct tevent_common_signal_list);
        if (!sl) {
                talloc_free(se);
                return NULL;
        }
        sl->se = se;
        se->additional_data     = sl;

        /* Ensure, no matter the destruction order, that we always have a handle on the global sig_state */
        if (!talloc_reference(se, sig_state)) {
                talloc_free(se);
                return NULL;
        }

        /* we need to setup the pipe hack handler if not already
           setup */
        if (ev->pipe_fde == NULL) {
                if (pipe(ev->pipe_fds) == -1) {
                        talloc_free(se);
                        return NULL;
                }
                ev_set_blocking(ev->pipe_fds[0], false);
                ev_set_blocking(ev->pipe_fds[1], false);
                ev->pipe_fde = tevent_add_fd(ev, ev, ev->pipe_fds[0],
                                             TEVENT_FD_READ,
                                             signal_pipe_handler, NULL);
                if (!ev->pipe_fde) {
                        close(ev->pipe_fds[0]);
                        close(ev->pipe_fds[1]);
                        talloc_free(se);
                        return NULL;
                }
        }

        /* only install a signal handler if not already installed */
        if (sig_state->sig_handlers[signum] == NULL) {
                struct sigaction act;
                ZERO_STRUCT(act);
                act.sa_handler = tevent_common_signal_handler;
                act.sa_flags = sa_flags;
#ifdef SA_SIGINFO
                if (sa_flags & SA_SIGINFO) {
                        act.sa_handler   = NULL;
                        act.sa_sigaction = tevent_common_signal_handler_info;
                        if (sig_state->sig_info[signum] == NULL) {
                                sig_state->sig_info[signum] =
                                        talloc_zero_array(sig_state, siginfo_t,
                                                          TEVENT_SA_INFO_QUEUE_COUNT);
                                if (sig_state->sig_info[signum] == NULL) {
                                        talloc_free(se);
                                        return NULL;
                                }
                        }
                }
#endif
                sig_state->oldact[signum] = talloc(sig_state, struct sigaction);
                if (sig_state->oldact[signum] == NULL) {
                        talloc_free(se);
                        return NULL;
                }
                if (sigaction(signum, &act, sig_state->oldact[signum]) == -1) {
                        talloc_free(se);
                        return NULL;
                }
        }

        DLIST_ADD(se->event_ctx->signal_events, se);

        /* Make sure the signal doesn't come in while we're mangling list. */
        sigemptyset(&set);
        sigaddset(&set, signum);
        sigprocmask(SIG_BLOCK, &set, &oldset);
        DLIST_ADD(sig_state->sig_handlers[signum], sl);
        sigprocmask(SIG_SETMASK, &oldset, NULL);

        talloc_set_destructor(se, tevent_signal_destructor);
        talloc_set_destructor(sl, tevent_common_signal_list_destructor);

        return se;
}

struct tevent_se_exists {
        struct tevent_se_exists **myself;
};

static int tevent_se_exists_destructor(struct tevent_se_exists *s)
{
        *s->myself = NULL;
        return 0;
}

/*
  check if a signal is pending
  return != 0 if a signal was pending
*/
int tevent_common_check_signal(struct tevent_context *ev)
{
        int i;

        if (!sig_state || !TEVENT_SIG_PENDING(sig_state->got_signal)) {
                return 0;
        }

        for (i=0;i<TEVENT_NUM_SIGNALS+1;i++) {
                struct tevent_common_signal_list *sl, *next;
                struct tevent_sigcounter counter = sig_state->signal_count[i];
                uint32_t count = tevent_sig_count(counter);
#ifdef SA_SIGINFO
                /* Ensure we null out any stored siginfo_t entries
                 * after processing for debugging purposes. */
                bool clear_processed_siginfo = false;
#endif

                if (count == 0) {
                        continue;
                }
                for (sl=sig_state->sig_handlers[i];sl;sl=next) {
                        struct tevent_signal *se = sl->se;
                        struct tevent_se_exists *exists;

                        next = sl->next;

                        /*
                         * We have to be careful to not touch "se"
                         * after it was deleted in its handler. Thus
                         * we allocate a child whose destructor will
                         * tell by nulling out itself that its parent
                         * is gone.
                         */
                        exists = talloc(se, struct tevent_se_exists);
                        if (exists == NULL) {
                                continue;
                        }
                        exists->myself = &exists;
                        talloc_set_destructor(
                                exists, tevent_se_exists_destructor);

#ifdef SA_SIGINFO
                        if (se->sa_flags & SA_SIGINFO) {
                                uint32_t j;

                                clear_processed_siginfo = true;

                                for (j=0;j<count;j++) {
                                        /* sig_state->signal_count[i].seen
                                         * % TEVENT_SA_INFO_QUEUE_COUNT is
                                         * the base position of the unprocessed
                                         * signals in the ringbuffer. */
                                        uint32_t ofs = (counter.seen + j)
                                                % TEVENT_SA_INFO_QUEUE_COUNT;
                                        se->handler(ev, se, i, 1,
                                                    (void*)&sig_state->sig_info[i][ofs],
                                                    se->private_data);
                                        if (!exists) {
                                                break;
                                        }
                                }
#ifdef SA_RESETHAND
                                if (exists && (se->sa_flags & SA_RESETHAND)) {
                                        talloc_free(se);
                                }
#endif
                                talloc_free(exists);
                                continue;
                        }
#endif
                        se->handler(ev, se, i, count, NULL, se->private_data);
#ifdef SA_RESETHAND
                        if (exists && (se->sa_flags & SA_RESETHAND)) {
                                talloc_free(se);
                        }
#endif
                        talloc_free(exists);
                }

#ifdef SA_SIGINFO
                if (clear_processed_siginfo) {
                        uint32_t j;
                        for (j=0;j<count;j++) {
                                uint32_t ofs = (counter.seen + j)
                                        % TEVENT_SA_INFO_QUEUE_COUNT;
                                memset((void*)&sig_state->sig_info[i][ofs],
                                        '\0',
                                        sizeof(siginfo_t));
                        }
                }
#endif

                TEVENT_SIG_SEEN(sig_state->signal_count[i], count);
                TEVENT_SIG_SEEN(sig_state->got_signal, count);

#ifdef SA_SIGINFO
                if (TEVENT_SIG_PENDING(sig_state->sig_blocked[i])) {
                        /* We'd filled the queue, unblock the
                           signal now the queue is empty again.
                           Note we MUST do this after the
                           TEVENT_SIG_SEEN(sig_state->signal_count[i], count)
                           call to prevent a new signal running
                           out of room in the sig_state->sig_info[i][]
                           ring buffer. */
                        sigset_t set;
                        sigemptyset(&set);
                        sigaddset(&set, i);
                        TEVENT_SIG_SEEN(sig_state->sig_blocked[i],
                                 tevent_sig_count(sig_state->sig_blocked[i]));
                        sigprocmask(SIG_UNBLOCK, &set, NULL);
                }
#endif
        }

        return 1;
}

void tevent_cleanup_pending_signal_handlers(struct tevent_signal *se)
{
        struct tevent_common_signal_list *sl =
                talloc_get_type_abort(se->additional_data,
                struct tevent_common_signal_list);

        tevent_common_signal_list_destructor(sl);

        if (sig_state->sig_handlers[se->signum] == NULL) {
                if (sig_state->oldact[se->signum]) {
                        sigaction(se->signum, sig_state->oldact[se->signum], NULL);
                        sig_state->oldact[se->signum] = NULL;
                }
        }
        return;
}