source: branches/samba-3.5.x/lib/tevent/tevent_standard.c

/* 
   Unix SMB/CIFS implementation.
   main select loop and event handling
   Copyright (C) Andrew Tridgell        2003-2005
   Copyright (C) Stefan Metzmacher      2005-2009

     ** 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/>.
*/

/*
  This is SAMBA's default event loop code

  - we try to use epoll if configure detected support for it
    otherwise we use select()
  - if epoll is broken on the system or the kernel doesn't support it
    at runtime we fallback to select()
*/

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

struct std_event_context {
        /* a pointer back to the generic event_context */
        struct tevent_context *ev;

        /* the maximum file descriptor number in fd_events */
        int maxfd;

        /* information for exiting from the event loop */
        int exit_code;

        /* when using epoll this is the handle from epoll_create */
        int epoll_fd;

        /* our pid at the time the epoll_fd was created */
        pid_t pid;
};

/* use epoll if it is available */
#if HAVE_EPOLL
/*
  called when a epoll call fails, and we should fallback
  to using select
*/
static void epoll_fallback_to_select(struct std_event_context *std_ev, const char *reason)
{
        tevent_debug(std_ev->ev, TEVENT_DEBUG_FATAL,
                     "%s (%s) - falling back to select()\n",
                     reason, strerror(errno));
        close(std_ev->epoll_fd);
        std_ev->epoll_fd = -1;
        talloc_set_destructor(std_ev, NULL);
}

/*
  map from TEVENT_FD_* to EPOLLIN/EPOLLOUT
*/
static uint32_t epoll_map_flags(uint16_t flags)
{
        uint32_t ret = 0;
        if (flags & TEVENT_FD_READ) ret |= (EPOLLIN | EPOLLERR | EPOLLHUP);
        if (flags & TEVENT_FD_WRITE) ret |= (EPOLLOUT | EPOLLERR | EPOLLHUP);
        return ret;
}

/*
 free the epoll fd
*/
static int epoll_ctx_destructor(struct std_event_context *std_ev)
{
        if (std_ev->epoll_fd != -1) {
                close(std_ev->epoll_fd);
        }
        std_ev->epoll_fd = -1;
        return 0;
}

/*
 init the epoll fd
*/
static void epoll_init_ctx(struct std_event_context *std_ev)
{
        std_ev->epoll_fd = epoll_create(64);
        std_ev->pid = getpid();
        talloc_set_destructor(std_ev, epoll_ctx_destructor);
}

static void epoll_add_event(struct std_event_context *std_ev, struct tevent_fd *fde);

/*
  reopen the epoll handle when our pid changes
  see http://junkcode.samba.org/ftp/unpacked/junkcode/epoll_fork.c for an 
  demonstration of why this is needed
 */
static void epoll_check_reopen(struct std_event_context *std_ev)
{
        struct tevent_fd *fde;

        if (std_ev->pid == getpid()) {
                return;
        }

        close(std_ev->epoll_fd);
        std_ev->epoll_fd = epoll_create(64);
        if (std_ev->epoll_fd == -1) {
                tevent_debug(std_ev->ev, TEVENT_DEBUG_FATAL,
                             "Failed to recreate epoll handle after fork\n");
                return;
        }
        std_ev->pid = getpid();
        for (fde=std_ev->ev->fd_events;fde;fde=fde->next) {
                epoll_add_event(std_ev, fde);
        }
}

#define EPOLL_ADDITIONAL_FD_FLAG_HAS_EVENT      (1<<0)
#define EPOLL_ADDITIONAL_FD_FLAG_REPORT_ERROR   (1<<1)
#define EPOLL_ADDITIONAL_FD_FLAG_GOT_ERROR      (1<<2)

/*
 add the epoll event to the given fd_event
*/
static void epoll_add_event(struct std_event_context *std_ev, struct tevent_fd *fde)
{
        struct epoll_event event;
        if (std_ev->epoll_fd == -1) return;

        fde->additional_flags &= ~EPOLL_ADDITIONAL_FD_FLAG_REPORT_ERROR;

        /* if we don't want events yet, don't add an epoll_event */
        if (fde->flags == 0) return;

        ZERO_STRUCT(event);
        event.events = epoll_map_flags(fde->flags);
        event.data.ptr = fde;
        if (epoll_ctl(std_ev->epoll_fd, EPOLL_CTL_ADD, fde->fd, &event) != 0) {
                epoll_fallback_to_select(std_ev, "EPOLL_CTL_ADD failed");
        }
        fde->additional_flags |= EPOLL_ADDITIONAL_FD_FLAG_HAS_EVENT;

        /* only if we want to read we want to tell the event handler about errors */
        if (fde->flags & TEVENT_FD_READ) {
                fde->additional_flags |= EPOLL_ADDITIONAL_FD_FLAG_REPORT_ERROR;
        }
}

/*
 delete the epoll event for given fd_event
*/
static void epoll_del_event(struct std_event_context *std_ev, struct tevent_fd *fde)
{
        struct epoll_event event;
        if (std_ev->epoll_fd == -1) return;

        fde->additional_flags &= ~EPOLL_ADDITIONAL_FD_FLAG_REPORT_ERROR;

        /* if there's no epoll_event, we don't need to delete it */
        if (!(fde->additional_flags & EPOLL_ADDITIONAL_FD_FLAG_HAS_EVENT)) return;

        ZERO_STRUCT(event);
        event.events = epoll_map_flags(fde->flags);
        event.data.ptr = fde;
        epoll_ctl(std_ev->epoll_fd, EPOLL_CTL_DEL, fde->fd, &event);
        fde->additional_flags &= ~EPOLL_ADDITIONAL_FD_FLAG_HAS_EVENT;
}

/*
 change the epoll event to the given fd_event
*/
static void epoll_mod_event(struct std_event_context *std_ev, struct tevent_fd *fde)
{
        struct epoll_event event;
        if (std_ev->epoll_fd == -1) return;

        fde->additional_flags &= ~EPOLL_ADDITIONAL_FD_FLAG_REPORT_ERROR;

        ZERO_STRUCT(event);
        event.events = epoll_map_flags(fde->flags);
        event.data.ptr = fde;
        if (epoll_ctl(std_ev->epoll_fd, EPOLL_CTL_MOD, fde->fd, &event) != 0) {
                epoll_fallback_to_select(std_ev, "EPOLL_CTL_MOD failed");
        }

        /* only if we want to read we want to tell the event handler about errors */
        if (fde->flags & TEVENT_FD_READ) {
                fde->additional_flags |= EPOLL_ADDITIONAL_FD_FLAG_REPORT_ERROR;
        }
}

static void epoll_change_event(struct std_event_context *std_ev, struct tevent_fd *fde)
{
        bool got_error = (fde->additional_flags & EPOLL_ADDITIONAL_FD_FLAG_GOT_ERROR);
        bool want_read = (fde->flags & TEVENT_FD_READ);
        bool want_write= (fde->flags & TEVENT_FD_WRITE);

        if (std_ev->epoll_fd == -1) return;

        fde->additional_flags &= ~EPOLL_ADDITIONAL_FD_FLAG_REPORT_ERROR;

        /* there's already an event */
        if (fde->additional_flags & EPOLL_ADDITIONAL_FD_FLAG_HAS_EVENT) {
                if (want_read || (want_write && !got_error)) {
                        epoll_mod_event(std_ev, fde);
                        return;
                }
                /* 
                 * if we want to match the select behavior, we need to remove the epoll_event
                 * when the caller isn't interested in events.
                 *
                 * this is because epoll reports EPOLLERR and EPOLLHUP, even without asking for them
                 */
                epoll_del_event(std_ev, fde);
                return;
        }

        /* there's no epoll_event attached to the fde */
        if (want_read || (want_write && !got_error)) {
                epoll_add_event(std_ev, fde);
                return;
        }
}

/*
  event loop handling using epoll
*/
static int epoll_event_loop(struct std_event_context *std_ev, struct timeval *tvalp)
{
        int ret, i;
#define MAXEVENTS 1
        struct epoll_event events[MAXEVENTS];
        int timeout = -1;

        if (std_ev->epoll_fd == -1) return -1;

        if (tvalp) {
                /* it's better to trigger timed events a bit later than to early */
                timeout = ((tvalp->tv_usec+999) / 1000) + (tvalp->tv_sec*1000);
        }

        if (std_ev->ev->signal_events &&
            tevent_common_check_signal(std_ev->ev)) {
                return 0;
        }

        ret = epoll_wait(std_ev->epoll_fd, events, MAXEVENTS, timeout);

        if (ret == -1 && errno == EINTR && std_ev->ev->signal_events) {
                if (tevent_common_check_signal(std_ev->ev)) {
                        return 0;
                }
        }

        if (ret == -1 && errno != EINTR) {
                epoll_fallback_to_select(std_ev, "epoll_wait() failed");
                return -1;
        }

        if (ret == 0 && tvalp) {
                /* we don't care about a possible delay here */
                tevent_common_loop_timer_delay(std_ev->ev);
                return 0;
        }

        for (i=0;i<ret;i++) {
                struct tevent_fd *fde = talloc_get_type(events[i].data.ptr, 
                                                       struct tevent_fd);
                uint16_t flags = 0;

                if (fde == NULL) {
                        epoll_fallback_to_select(std_ev, "epoll_wait() gave bad data");
                        return -1;
                }
                if (events[i].events & (EPOLLHUP|EPOLLERR)) {
                        fde->additional_flags |= EPOLL_ADDITIONAL_FD_FLAG_GOT_ERROR;
                        /*
                         * if we only wait for TEVENT_FD_WRITE, we should not tell the
                         * event handler about it, and remove the epoll_event,
                         * as we only report errors when waiting for read events,
                         * to match the select() behavior
                         */
                        if (!(fde->additional_flags & EPOLL_ADDITIONAL_FD_FLAG_REPORT_ERROR)) {
                                epoll_del_event(std_ev, fde);
                                continue;
                        }
                        flags |= TEVENT_FD_READ;
                }
                if (events[i].events & EPOLLIN) flags |= TEVENT_FD_READ;
                if (events[i].events & EPOLLOUT) flags |= TEVENT_FD_WRITE;
                if (flags) {
                        fde->handler(std_ev->ev, fde, flags, fde->private_data);
                        break;
                }
        }

        return 0;
}
#else
#define epoll_init_ctx(std_ev) 
#define epoll_add_event(std_ev,fde)
#define epoll_del_event(std_ev,fde)
#define epoll_change_event(std_ev,fde)
#define epoll_event_loop(std_ev,tvalp) (-1)
#define epoll_check_reopen(std_ev)
#endif

/*
  create a std_event_context structure.
*/
static int std_event_context_init(struct tevent_context *ev)
{
        struct std_event_context *std_ev;

        std_ev = talloc_zero(ev, struct std_event_context);
        if (!std_ev) return -1;
        std_ev->ev = ev;
        std_ev->epoll_fd = -1;

        epoll_init_ctx(std_ev);

        ev->additional_data = std_ev;
        return 0;
}

/*
  recalculate the maxfd
*/
static void calc_maxfd(struct std_event_context *std_ev)
{
        struct tevent_fd *fde;

        std_ev->maxfd = 0;
        for (fde = std_ev->ev->fd_events; fde; fde = fde->next) {
                if (fde->fd > std_ev->maxfd) {
                        std_ev->maxfd = fde->fd;
                }
        }
}


/* to mark the ev->maxfd invalid
 * this means we need to recalculate it
 */
#define EVENT_INVALID_MAXFD (-1)

/*
  destroy an fd_event
*/
static int std_event_fd_destructor(struct tevent_fd *fde)
{
        struct tevent_context *ev = fde->event_ctx;
        struct std_event_context *std_ev = NULL;

        if (ev) {
                std_ev = talloc_get_type(ev->additional_data,
                                         struct std_event_context);

                epoll_check_reopen(std_ev);

                if (std_ev->maxfd == fde->fd) {
                        std_ev->maxfd = EVENT_INVALID_MAXFD;
                }

                epoll_del_event(std_ev, fde);
        }

        return tevent_common_fd_destructor(fde);
}

/*
  add a fd based event
  return NULL on failure (memory allocation error)
*/
static struct tevent_fd *std_event_add_fd(struct tevent_context *ev, TALLOC_CTX *mem_ctx,
                                          int fd, uint16_t flags,
                                          tevent_fd_handler_t handler,
                                          void *private_data,
                                          const char *handler_name,
                                          const char *location)
{
        struct std_event_context *std_ev = talloc_get_type(ev->additional_data,
                                                           struct std_event_context);
        struct tevent_fd *fde;

        epoll_check_reopen(std_ev);

        fde = tevent_common_add_fd(ev, mem_ctx, fd, flags,
                                   handler, private_data,
                                   handler_name, location);
        if (!fde) return NULL;

        if ((std_ev->maxfd != EVENT_INVALID_MAXFD)
            && (fde->fd > std_ev->maxfd)) {
                std_ev->maxfd = fde->fd;
        }
        talloc_set_destructor(fde, std_event_fd_destructor);

        epoll_add_event(std_ev, fde);

        return fde;
}

/*
  set the fd event flags
*/
static void std_event_set_fd_flags(struct tevent_fd *fde, uint16_t flags)
{
        struct tevent_context *ev;
        struct std_event_context *std_ev;

        if (fde->flags == flags) return;

        ev = fde->event_ctx;
        std_ev = talloc_get_type(ev->additional_data, struct std_event_context);

        fde->flags = flags;

        epoll_check_reopen(std_ev);

        epoll_change_event(std_ev, fde);
}

/*
  event loop handling using select()
*/
static int std_event_loop_select(struct std_event_context *std_ev, struct timeval *tvalp)
{
        fd_set r_fds, w_fds;
        struct tevent_fd *fde;
        int selrtn;

        /* we maybe need to recalculate the maxfd */
        if (std_ev->maxfd == EVENT_INVALID_MAXFD) {
                calc_maxfd(std_ev);
        }

        FD_ZERO(&r_fds);
        FD_ZERO(&w_fds);

        /* setup any fd events */
        for (fde = std_ev->ev->fd_events; fde; fde = fde->next) {
                if (fde->fd < 0 || fde->fd >= FD_SETSIZE) {
                        std_ev->exit_code = EBADF;
                        return -1;
                }

                if (fde->flags & TEVENT_FD_READ) {
                        FD_SET(fde->fd, &r_fds);
                }
                if (fde->flags & TEVENT_FD_WRITE) {
                        FD_SET(fde->fd, &w_fds);
                }
        }

        if (std_ev->ev->signal_events &&
            tevent_common_check_signal(std_ev->ev)) {
                return 0;
        }

        selrtn = select(std_ev->maxfd+1, &r_fds, &w_fds, NULL, tvalp);

        if (selrtn == -1 && errno == EINTR && 
            std_ev->ev->signal_events) {
                tevent_common_check_signal(std_ev->ev);
                return 0;
        }

        if (selrtn == -1 && errno == EBADF) {
                /* the socket is dead! this should never
                   happen as the socket should have first been
                   made readable and that should have removed
                   the event, so this must be a bug. This is a
                   fatal error. */
                tevent_debug(std_ev->ev, TEVENT_DEBUG_FATAL,
                             "ERROR: EBADF on std_event_loop_once\n");
                std_ev->exit_code = EBADF;
                return -1;
        }

        if (selrtn == 0 && tvalp) {
                /* we don't care about a possible delay here */
                tevent_common_loop_timer_delay(std_ev->ev);
                return 0;
        }

        if (selrtn > 0) {
                /* at least one file descriptor is ready - check
                   which ones and call the handler, being careful to allow
                   the handler to remove itself when called */
                for (fde = std_ev->ev->fd_events; fde; fde = fde->next) {
                        uint16_t flags = 0;

                        if (FD_ISSET(fde->fd, &r_fds)) flags |= TEVENT_FD_READ;
                        if (FD_ISSET(fde->fd, &w_fds)) flags |= TEVENT_FD_WRITE;
                        if (flags) {
                                fde->handler(std_ev->ev, fde, flags, fde->private_data);
                                break;
                        }
                }
        }

        return 0;
}               

/*
  do a single event loop using the events defined in ev 
*/
static int std_event_loop_once(struct tevent_context *ev, const char *location)
{
        struct std_event_context *std_ev = talloc_get_type(ev->additional_data,
                                                           struct std_event_context);
        struct timeval tval;

        if (ev->signal_events &&
            tevent_common_check_signal(ev)) {
                return 0;
        }

        if (ev->immediate_events &&
            tevent_common_loop_immediate(ev)) {
                return 0;
        }

        tval = tevent_common_loop_timer_delay(ev);
        if (tevent_timeval_is_zero(&tval)) {
                return 0;
        }

        epoll_check_reopen(std_ev);

        if (epoll_event_loop(std_ev, &tval) == 0) {
                return 0;
        }

        return std_event_loop_select(std_ev, &tval);
}

static const struct tevent_ops std_event_ops = {
        .context_init           = std_event_context_init,
        .add_fd                 = std_event_add_fd,
        .set_fd_close_fn        = tevent_common_fd_set_close_fn,
        .get_fd_flags           = tevent_common_fd_get_flags,
        .set_fd_flags           = std_event_set_fd_flags,
        .add_timer              = tevent_common_add_timer,
        .schedule_immediate     = tevent_common_schedule_immediate,
        .add_signal             = tevent_common_add_signal,
        .loop_once              = std_event_loop_once,
        .loop_wait              = tevent_common_loop_wait,
};


bool tevent_standard_init(void)
{
        return tevent_register_backend("standard", &std_event_ops);
}