/*

 * libev epoll fd activity backend

 *

 * Copyright (c) 2007,2008,2009,2010,2011 Marc Alexander Lehmann <libev@schmorp.de>

 * All rights reserved.

 *

 * Redistribution and use in source and binary forms, with or without modifica-

 * tion, 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.

 *

 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED

 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MER-

 * CHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO

 * EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPE-

 * CIAL, 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 OTH-

 * ERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED

 * OF THE POSSIBILITY OF SUCH DAMAGE.

 *

 * Alternatively, the contents of this file may be used under the terms of

 * the GNU General Public License ("GPL") version 2 or any later version,

 * in which case the provisions of the GPL are applicable instead of

 * the above. If you wish to allow the use of your version of this file

 * only under the terms of the GPL and not to allow others to use your

 * version of this file under the BSD license, indicate your decision

 * by deleting the provisions above and replace them with the notice

 * and other provisions required by the GPL. If you do not delete the

 * provisions above, a recipient may use your version of this file under

 * either the BSD or the GPL.

 */

/*

 * general notes about epoll:

 *

 * a) epoll silently removes fds from the fd set. as nothing tells us

 *    that an fd has been removed otherwise, we have to continually

 *    "rearm" fds that we suspect *might* have changed (same

 *    problem with kqueue, but much less costly there).

 * b) the fact that ADD != MOD creates a lot of extra syscalls due to a)

 *    and seems not to have any advantage.

 * c) the inability to handle fork or file descriptors (think dup)

 *    limits the applicability over poll, so this is not a generic

 *    poll replacement.

 * d) epoll doesn't work the same as select with many file descriptors

 *    (such as files). while not critical, no other advanced interface

 *    seems to share this (rather non-unixy) limitation.

 * e) epoll claims to be embeddable, but in practise you never get

 *    a ready event for the epoll fd (broken: <=2.6.26, working: >=2.6.32).

 * f) epoll_ctl returning EPERM means the fd is always ready.

 *

 * lots of "weird code" and complication handling in this file is due

 * to these design problems with epoll, as we try very hard to avoid

 * epoll_ctl syscalls for common usage patterns and handle the breakage

 * ensuing from receiving events for closed and otherwise long gone

 * file descriptors.

 */

#include <sys/epoll.h>

#define EV_EMASK_EPERM 0x80

static void

epoll_modify (EV_P_ int fd, int oev, int nev)

{

  struct epoll_event ev;

  unsigned char oldmask;

  /*

   * we handle EPOLL_CTL_DEL by ignoring it here

   * on the assumption that the fd is gone anyways

   * if that is wrong, we have to handle the spurious

   * event in epoll_poll.

   * if the fd is added again, we try to ADD it, and, if that

   * fails, we assume it still has the same eventmask.

   */

  if (!nev)

    return;

  oldmask = anfds [fd].emask;

  anfds [fd].emask = nev;

  /* store the generation counter in the upper 32 bits, the fd in the lower 32 bits */

  ev.data.u64 = (uint64_t)(uint32_t)fd

              | ((uint64_t)(uint32_t)++anfds [fd].egen << 32);

  ev.events   = (nev & EV_READ  ? EPOLLIN  : 0)

              | (nev & EV_WRITE ? EPOLLOUT : 0);

  if (expect_true (!epoll_ctl (backend_fd, oev && oldmask != nev ? EPOLL_CTL_MOD : EPOLL_CTL_ADD, fd, &ev)))

    return;

  if (expect_true (errno == ENOENT))

    {

      /* if ENOENT then the fd went away, so try to do the right thing */

      if (!nev)

        goto dec_egen;

      if (!epoll_ctl (backend_fd, EPOLL_CTL_ADD, fd, &ev))

        return;

    }

  else if (expect_true (errno == EEXIST))

    {

      /* EEXIST means we ignored a previous DEL, but the fd is still active */

      /* if the kernel mask is the same as the new mask, we assume it hasn't changed */

      if (oldmask == nev)

        goto dec_egen;

      if (!epoll_ctl (backend_fd, EPOLL_CTL_MOD, fd, &ev))

        return;

    }

  else if (expect_true (errno == EPERM))

    {

      /* EPERM means the fd is always ready, but epoll is too snobbish */

      /* to handle it, unlike select or poll. */

      anfds [fd].emask = EV_EMASK_EPERM;

      /* add fd to epoll_eperms, if not already inside */

      if (!(oldmask & EV_EMASK_EPERM))

        {

          array_needsize (int, epoll_eperms, epoll_epermmax, epoll_epermcnt + 1, EMPTY2);

          epoll_eperms [epoll_epermcnt++] = fd;

        }

      return;

    }

  fd_kill (EV_A_ fd);

dec_egen:

  /* we didn't successfully call epoll_ctl, so decrement the generation counter again */

  --anfds [fd].egen;

}

static void

epoll_poll (EV_P_ ev_tstamp timeout)

{

  int i;

  int eventcnt;

  if (expect_false (epoll_epermcnt))

    timeout = 0.;

  /* epoll wait times cannot be larger than (LONG_MAX - 999UL) / HZ msecs, which is below */

  /* the default libev max wait time, however. */

  EV_RELEASE_CB;

  eventcnt = epoll_wait (backend_fd, epoll_events, epoll_eventmax, timeout * 1e3);

  EV_ACQUIRE_CB;

  if (expect_false (eventcnt < 0))

    {

      if (errno != EINTR)

        ev_syserr ("(libev) epoll_wait");

      return;

    }

  for (i = 0; i < eventcnt; ++i)

    {

      struct epoll_event *ev = epoll_events + i;

      int fd = (uint32_t)ev->data.u64; /* mask out the lower 32 bits */

      int want = anfds [fd].events;

      int got  = (ev->events & (EPOLLOUT | EPOLLERR | EPOLLHUP) ? EV_WRITE : 0)

               | (ev->events & (EPOLLIN  | EPOLLERR | EPOLLHUP) ? EV_READ  : 0);

      /*

       * check for spurious notification.

       * this only finds spurious notifications on egen updates

       * other spurious notifications will be found by epoll_ctl, below

       * we assume that fd is always in range, as we never shrink the anfds array

       */

      if (expect_false ((uint32_t)anfds [fd].egen != (uint32_t)(ev->data.u64 >> 32)))

        {

          /* recreate kernel state */

          postfork |= 2;

          continue;

        }

      if (expect_false (got & ~want))

        {

          anfds [fd].emask = want;

          /*

           * we received an event but are not interested in it, try mod or del

           * this often happens because we optimistically do not unregister fds

           * when we are no longer interested in them, but also when we get spurious

           * notifications for fds from another process. this is partially handled

           * above with the gencounter check (== our fd is not the event fd), and

           * partially here, when epoll_ctl returns an error (== a child has the fd

           * but we closed it).

           */

          ev->events = (want & EV_READ  ? EPOLLIN  : 0)

                     | (want & EV_WRITE ? EPOLLOUT : 0);

          /* pre-2.6.9 kernels require a non-null pointer with EPOLL_CTL_DEL, */

          /* which is fortunately easy to do for us. */

          if (epoll_ctl (backend_fd, want ? EPOLL_CTL_MOD : EPOLL_CTL_DEL, fd, ev))

            {

              postfork |= 2; /* an error occurred, recreate kernel state */

              continue;

            }

        }

      fd_event (EV_A_ fd, got);

    }

  /* if the receive array was full, increase its size */

  if (expect_false (eventcnt == epoll_eventmax))

    {

      ev_free (epoll_events);

      epoll_eventmax = array_nextsize (sizeof (struct epoll_event), epoll_eventmax, epoll_eventmax + 1);

      epoll_events = (struct epoll_event *)ev_malloc (sizeof (struct epoll_event) * epoll_eventmax);

    }

  /* now synthesize events for all fds where epoll fails, while select works... */

  for (i = epoll_epermcnt; i--; )

    {

      int fd = epoll_eperms [i];

      unsigned char events = anfds [fd].events & (EV_READ | EV_WRITE);

      if (anfds [fd].emask & EV_EMASK_EPERM && events)

        fd_event (EV_A_ fd, events);

      else

        {

          epoll_eperms [i] = epoll_eperms [--epoll_epermcnt];

          anfds [fd].emask = 0;

        }

    }

}

inline_size

int

epoll_init (EV_P_ int flags)

{

#ifdef EPOLL_CLOEXEC

  backend_fd = epoll_create1 (EPOLL_CLOEXEC);

  if (backend_fd < 0 && (errno == EINVAL || errno == ENOSYS))

#endif

    backend_fd = epoll_create (256);

  if (backend_fd < 0)

    return 0;

  fcntl (backend_fd, F_SETFD, FD_CLOEXEC);

  backend_mintime = 1e-3; /* epoll does sometimes return early, this is just to avoid the worst */

  backend_modify  = epoll_modify;

  backend_poll    = epoll_poll;

  epoll_eventmax = 64; /* initial number of events receivable per poll */

  epoll_events = (struct epoll_event *)ev_malloc (sizeof (struct epoll_event) * epoll_eventmax);

  return EVBACKEND_EPOLL;

}

inline_size

void

epoll_destroy (EV_P)

{

  ev_free (epoll_events);

  array_free (epoll_eperm, EMPTY);

}

inline_size

void

epoll_fork (EV_P)

{

  close (backend_fd);

  while ((backend_fd = epoll_create (256)) < 0)

    ev_syserr ("(libev) epoll_create");

  fcntl (backend_fd, F_SETFD, FD_CLOEXEC);

  fd_rearm_all (EV_A);

}