libevent
/
epoll.c

/*
 * Copyright 2000-2007 Niels Provos <provos@citi.umich.edu>
 * Copyright 2007-2012 Niels Provos, Nick Mathewson
 *
 * 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 "event2/event-config.h"
#include "evconfig-private.h"

#if defined EVENT__HAVE_EPOLL || defined EVENT__HAVE_WEPOLL

#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <limits.h>
#include <string.h>

#ifdef EVENT__HAVE_WEPOLL
#include "wepoll.h"
#define EPOLLET 0
#else
#include <sys/types.h>
#include <sys/resource.h>
#ifdef EVENT__HAVE_SYS_TIME_H
#include <sys/time.h>
#endif
#include <sys/queue.h>
#include <sys/epoll.h>
#include <signal.h>
#include <unistd.h>
#include <errno.h>
#ifdef EVENT__HAVE_FCNTL_H
#include <fcntl.h>
#endif
#ifdef EVENT__HAVE_SYS_TIMERFD_H
#include <sys/timerfd.h>
#endif
#endif

#include "event-internal.h"
#include "evsignal-internal.h"
#include "event2/thread.h"
#include "evthread-internal.h"
#include "log-internal.h"
#include "evmap-internal.h"
#include "changelist-internal.h"
#include "time-internal.h"

/* Since Linux 2.6.17, epoll is able to report about peer half-closed connection
   using special EPOLLRDHUP flag on a read event.
*/
#if !defined(EPOLLRDHUP)
#define EPOLLRDHUP 0
#define EARLY_CLOSE_IF_HAVE_RDHUP 0
#else
#define EARLY_CLOSE_IF_HAVE_RDHUP EV_FEATURE_EARLY_CLOSE
#endif

#include "epolltable-internal.h"

#if defined(EVENT__HAVE_SYS_TIMERFD_H) &&			  \
	defined(EVENT__HAVE_TIMERFD_CREATE) &&			  \
	defined(HAVE_POSIX_MONOTONIC) && defined(TFD_NONBLOCK) && \
	defined(TFD_CLOEXEC) && !defined(EVENT__HAVE_EPOLL_PWAIT2)
/* Note that we only use timerfd if TFD_NONBLOCK and TFD_CLOEXEC are available
   and working.  This means that we can't support it on 2.6.25 (where timerfd
   was introduced) or 2.6.26, since 2.6.27 introduced those flags. On recent
   enough systems (with 5.11 and never) and so epoll_pwait2() with nanosecond
   precision for timeouts, timerfd is not needed at all.
*/
#define USING_TIMERFD
#endif

#ifdef EVENT__HAVE_WEPOLL
typedef HANDLE epoll_handle;
#define INVALID_EPOLL_HANDLE NULL
static void close_epoll_handle(HANDLE h) { epoll_close(h); }
#else
typedef int epoll_handle;
#define INVALID_EPOLL_HANDLE -1
static void close_epoll_handle(int h) { close(h); }
#endif

struct epollop {
	struct epoll_event *events;
	int nevents;
	epoll_handle epfd;
#ifdef USING_TIMERFD
	int timerfd;
#endif
};

static void *epoll_init(struct event_base *);
static int epoll_dispatch(struct event_base *, struct timeval *);
static void epoll_dealloc(struct event_base *);

static const struct eventop epollops_changelist = {
	"epoll (with changelist)",
	epoll_init,
	event_changelist_add_,
	event_changelist_del_,
	epoll_dispatch,
	epoll_dealloc,
	1, /* need reinit */
	EV_FEATURE_ET|EV_FEATURE_O1| EARLY_CLOSE_IF_HAVE_RDHUP,
	EVENT_CHANGELIST_FDINFO_SIZE
};


static int epoll_nochangelist_add(struct event_base *base, evutil_socket_t fd,
    short old, short events, void *p);
static int epoll_nochangelist_del(struct event_base *base, evutil_socket_t fd,
    short old, short events, void *p);

#ifdef EVENT__HAVE_WEPOLL
const struct eventop wepollops = {
	"wepoll",
	epoll_init,
	epoll_nochangelist_add,
	epoll_nochangelist_del,
	epoll_dispatch,
	epoll_dealloc,
	1, /* need reinit */
	EV_FEATURE_O1|EV_FEATURE_EARLY_CLOSE,
	0
};
#else
const struct eventop epollops = {
	"epoll",
	epoll_init,
	epoll_nochangelist_add,
	epoll_nochangelist_del,
	epoll_dispatch,
	epoll_dealloc,
	1, /* need reinit */
	EV_FEATURE_ET|EV_FEATURE_O1|EV_FEATURE_EARLY_CLOSE,
	0
};
#endif


#define INITIAL_NEVENT 32
#define MAX_NEVENT 4096

/* On Linux kernels at least up to 2.6.24.4, epoll can't handle timeout
 * values bigger than (LONG_MAX - 999ULL)/HZ.  HZ in the wild can be
 * as big as 1000, and LONG_MAX can be as small as (1<<31)-1, so the
 * largest number of msec we can support here is 2147482.  Let's
 * round that down by 47 seconds.
 */
#define MAX_EPOLL_TIMEOUT_MSEC (35*60*1000)

static void *
epoll_init(struct event_base *base)
{
	epoll_handle epfd = INVALID_EPOLL_HANDLE;
	struct epollop *epollop;

#ifdef EVENT__HAVE_EPOLL_CREATE1
	/* First, try the shiny new epoll_create1 interface, if we have it. */
	epfd = epoll_create1(EPOLL_CLOEXEC);
#endif
	if (epfd == INVALID_EPOLL_HANDLE) {
		/* Initialize the kernel queue using the old interface.  (The
		size field is ignored   since 2.6.8.) */
		if ((epfd = epoll_create(32000)) == INVALID_EPOLL_HANDLE) {
			if (errno != ENOSYS)
				event_warn("epoll_create");
			return (NULL);
		}
#ifndef EVENT__HAVE_WEPOLL
		evutil_make_socket_closeonexec(epfd);
#endif
	}

	if (!(epollop = mm_calloc(1, sizeof(struct epollop)))) {
		close_epoll_handle(epfd);
		return (NULL);
	}

	epollop->epfd = epfd;

	/* Initialize fields */
	epollop->events = mm_calloc(INITIAL_NEVENT, sizeof(struct epoll_event));
	if (epollop->events == NULL) {
		mm_free(epollop);
		close_epoll_handle(epfd);
		return (NULL);
	}
	epollop->nevents = INITIAL_NEVENT;

#ifndef EVENT__HAVE_WEPOLL
	if ((base->flags & EVENT_BASE_FLAG_EPOLL_USE_CHANGELIST) != 0 ||
	    ((base->flags & EVENT_BASE_FLAG_IGNORE_ENV) == 0 &&
		evutil_getenv_("EVENT_EPOLL_USE_CHANGELIST") != NULL)) {

		base->evsel = &epollops_changelist;
	}
#endif

#ifdef USING_TIMERFD
	/*
	  The epoll interface ordinarily gives us one-millisecond precision,
	  so on Linux it makes perfect sense to use the CLOCK_MONOTONIC_COARSE
	  timer.  But when the user has set the new PRECISE_TIMER flag for an
	  event_base, we can try to use timerfd to give them finer granularity.
	*/
	if ((base->flags & EVENT_BASE_FLAG_PRECISE_TIMER) &&
	    !(base->flags & EVENT_BASE_FLAG_EPOLL_DISALLOW_TIMERFD) &&
	    base->monotonic_timer.monotonic_clock == CLOCK_MONOTONIC) {
		int fd;
		fd = epollop->timerfd = timerfd_create(CLOCK_MONOTONIC, TFD_NONBLOCK|TFD_CLOEXEC);
		if (epollop->timerfd >= 0) {
			struct epoll_event epev;
			memset(&epev, 0, sizeof(epev));
			epev.data.fd = epollop->timerfd;
			epev.events = EPOLLIN;
			if (epoll_ctl(epollop->epfd, EPOLL_CTL_ADD, fd, &epev) < 0) {
				event_warn("epoll_ctl(timerfd)");
				close(fd);
				epollop->timerfd = -1;
			}
		} else {
			if (errno != EINVAL && errno != ENOSYS) {
				/* These errors probably mean that we were
				 * compiled with timerfd/TFD_* support, but
				 * we're running on a kernel that lacks those.
				 */
				event_warn("timerfd_create");
			}
			epollop->timerfd = -1;
		}
	} else {
		epollop->timerfd = -1;
	}
#endif

	if (sigfd_init_(base) < 0)
		evsig_init_(base);

	return (epollop);
}

static const char *
change_to_string(int change)
{
	change &= (EV_CHANGE_ADD|EV_CHANGE_DEL);
	if (change == EV_CHANGE_ADD) {
		return "add";
	} else if (change == EV_CHANGE_DEL) {
		return "del";
	} else if (change == 0) {
		return "none";
	} else {
		return "???";
	}
}

static const char *
epoll_op_to_string(int op)
{
	return op == EPOLL_CTL_ADD?"ADD":
	    op == EPOLL_CTL_DEL?"DEL":
	    op == EPOLL_CTL_MOD?"MOD":
	    "???";
}

#define PRINT_CHANGES(op, events, ch, status)  \
	"Epoll %s(%d) on fd %d " status ". "       \
	"Old events were %d; "                     \
	"read change was %d (%s); "                \
	"write change was %d (%s); "               \
	"close change was %d (%s)",                \
	epoll_op_to_string(op),                    \
	events,                                    \
	ch->fd,                                    \
	ch->old_events,                            \
	ch->read_change,                           \
	change_to_string(ch->read_change),         \
	ch->write_change,                          \
	change_to_string(ch->write_change),        \
	ch->close_change,                          \
	change_to_string(ch->close_change)

static int
epoll_apply_one_change(struct event_base *base,
    struct epollop *epollop,
    const struct event_change *ch)
{
	struct epoll_event epev;
	int op, events = 0;
	int idx;

	idx = EPOLL_OP_TABLE_INDEX(ch);
	op = epoll_op_table[idx].op;
	events = epoll_op_table[idx].events;

	if (!events) {
		EVUTIL_ASSERT(op == 0);
		return 0;
	}

	if ((ch->read_change|ch->write_change|ch->close_change) & EV_CHANGE_ET)
		events |= EPOLLET;

	memset(&epev, 0, sizeof(epev));
#ifdef EVENT__HAVE_WEPOLL
	epev.data.sock = ch->fd;
#else
	epev.data.fd = ch->fd;
#endif
	epev.events = events;
	if (epoll_ctl(epollop->epfd, op, ch->fd, &epev) == 0) {
		event_debug((PRINT_CHANGES(op, epev.events, ch, "okay")));
		return 0;
	}

	switch (op) {
	case EPOLL_CTL_MOD:
		if (errno == ENOENT) {
			/* If a MOD operation fails with ENOENT, the
			 * fd was probably closed and re-opened.  We
			 * should retry the operation as an ADD.
			 */
			if (epoll_ctl(epollop->epfd, EPOLL_CTL_ADD, ch->fd, &epev) == -1) {
				event_warn("Epoll MOD(%d) on %d retried as ADD; that failed too",
				    (int)epev.events, ch->fd);
				return -1;
			} else {
				event_debug(("Epoll MOD(%d) on %d retried as ADD; succeeded.",
					(int)epev.events,
					ch->fd));
				return 0;
			}
		}
		break;
	case EPOLL_CTL_ADD:
		if (errno == EEXIST) {
			/* If an ADD operation fails with EEXIST,
			 * either the operation was redundant (as with a
			 * precautionary add), or we ran into a fun
			 * kernel bug where using dup*() to duplicate the
			 * same file into the same fd gives you the same epitem
			 * rather than a fresh one.  For the second case,
			 * we must retry with MOD. */
			if (epoll_ctl(epollop->epfd, EPOLL_CTL_MOD, ch->fd, &epev) == -1) {
				event_warn("Epoll ADD(%d) on %d retried as MOD; that failed too",
				    (int)epev.events, ch->fd);
				return -1;
			} else {
				event_debug(("Epoll ADD(%d) on %d retried as MOD; succeeded.",
					(int)epev.events,
					ch->fd));
				return 0;
			}
		}
		break;
	case EPOLL_CTL_DEL:
		if (errno == ENOENT || errno == EBADF || errno == EPERM) {
			/* If a delete fails with one of these errors,
			 * that's fine too: we closed the fd before we
			 * got around to calling epoll_dispatch. */
			event_debug(("Epoll DEL(%d) on fd %d gave %s: DEL was unnecessary.",
				(int)epev.events,
				ch->fd,
				strerror(errno)));
			return 0;
		}
		break;
	default:
		break;
	}

	event_warn(PRINT_CHANGES(op, epev.events, ch, "failed"));
	return -1;
}

static int
epoll_apply_changes(struct event_base *base)
{
	struct event_changelist *changelist = &base->changelist;
	struct epollop *epollop = base->evbase;
	struct event_change *ch;

	int r = 0;
	int i;

	for (i = 0; i < changelist->n_changes; ++i) {
		ch = &changelist->changes[i];
		if (epoll_apply_one_change(base, epollop, ch) < 0)
			r = -1;
	}

	return (r);
}

static int
epoll_nochangelist_add(struct event_base *base, evutil_socket_t fd,
    short old, short events, void *p)
{
	struct event_change ch;
	ch.fd = fd;
	ch.old_events = old;
	ch.read_change = ch.write_change = ch.close_change = 0;
	if (events & EV_WRITE)
		ch.write_change = EV_CHANGE_ADD |
		    (events & EV_ET);
	if (events & EV_READ)
		ch.read_change = EV_CHANGE_ADD |
		    (events & EV_ET);
	if (events & EV_CLOSED)
		ch.close_change = EV_CHANGE_ADD |
		    (events & EV_ET);

	return epoll_apply_one_change(base, base->evbase, &ch);
}

static int
epoll_nochangelist_del(struct event_base *base, evutil_socket_t fd,
    short old, short events, void *p)
{
	struct event_change ch;
	ch.fd = fd;
	ch.old_events = old;
	ch.read_change = ch.write_change = ch.close_change = 0;
	if (events & EV_WRITE)
		ch.write_change = EV_CHANGE_DEL |
		    (events & EV_ET);
	if (events & EV_READ)
		ch.read_change = EV_CHANGE_DEL |
		    (events & EV_ET);
	if (events & EV_CLOSED)
		ch.close_change = EV_CHANGE_DEL |
		    (events & EV_ET);

	return epoll_apply_one_change(base, base->evbase, &ch);
}

static int
epoll_dispatch(struct event_base *base, struct timeval *tv)
{
	struct epollop *epollop = base->evbase;
	struct epoll_event *events = epollop->events;
	int i, res;
#if defined(EVENT__HAVE_EPOLL_PWAIT2)
	struct timespec ts = { 0, 0 };
#else /* no epoll_pwait2() */
	long timeout = -1;
#endif /* EVENT__HAVE_EPOLL_PWAIT2 */

#ifdef USING_TIMERFD
	if (epollop->timerfd >= 0) {
		struct itimerspec is;
		is.it_interval.tv_sec = 0;
		is.it_interval.tv_nsec = 0;
		if (tv == NULL) {
			/* No timeout; disarm the timer. */
			is.it_value.tv_sec = 0;
			is.it_value.tv_nsec = 0;
		} else {
			if (tv->tv_sec == 0 && tv->tv_usec == 0) {
				/* we need to exit immediately; timerfd can't
				 * do that. */
				timeout = 0;
			}
			is.it_value.tv_sec = tv->tv_sec;
			is.it_value.tv_nsec = tv->tv_usec * 1000;
		}
		/* TODO: we could avoid unnecessary syscalls here by only
		   calling timerfd_settime when the top timeout changes, or
		   when we're called with a different timeval.
		*/
		if (timerfd_settime(epollop->timerfd, 0, &is, NULL) < 0) {
			event_warn("timerfd_settime");
		}
	} else
#endif
	if (tv != NULL) {
#if defined(EVENT__HAVE_EPOLL_PWAIT2)
		TIMEVAL_TO_TIMESPEC(tv, &ts);
#else /* no epoll_pwait2() */
		timeout = evutil_tv_to_msec_(tv);
		if (timeout < 0 || timeout > MAX_EPOLL_TIMEOUT_MSEC) {
			/* Linux kernels can wait forever if the timeout is
			 * too big; see comment on MAX_EPOLL_TIMEOUT_MSEC. */
			timeout = MAX_EPOLL_TIMEOUT_MSEC;
		}
#endif /* EVENT__HAVE_EPOLL_PWAIT2 */
	}

	epoll_apply_changes(base);
	event_changelist_remove_all_(&base->changelist, base);

	EVBASE_RELEASE_LOCK(base, th_base_lock);

#if defined(EVENT__HAVE_EPOLL_PWAIT2)
	res = epoll_pwait2(epollop->epfd, events, epollop->nevents, tv ? &ts : NULL, NULL);
#else /* no epoll_pwait2() */
	res = epoll_wait(epollop->epfd, events, epollop->nevents, timeout);
#endif /* EVENT__HAVE_EPOLL_PWAIT2 */

	EVBASE_ACQUIRE_LOCK(base, th_base_lock);

	if (res == -1) {
		if (errno != EINTR) {
			event_warn("epoll_wait");
			return (-1);
		}

		return (0);
	}

	event_debug(("%s: epoll_wait reports %d", __func__, res));
	EVUTIL_ASSERT(res <= epollop->nevents);

	for (i = 0; i < res; i++) {
		int what = events[i].events;
		short ev = 0;
#ifdef USING_TIMERFD
		if (events[i].data.fd == epollop->timerfd)
			continue;
#endif

		if (what & EPOLLERR) {
			ev = EV_READ | EV_WRITE;
		} else if ((what & EPOLLHUP) && !(what & EPOLLRDHUP)) {
			ev = EV_READ | EV_WRITE;
		} else {
			if (what & EPOLLIN)
				ev |= EV_READ;
			if (what & EPOLLOUT)
				ev |= EV_WRITE;
			if (what & EPOLLRDHUP)
				ev |= EV_CLOSED;
		}

		if (!ev)
			continue;

#ifdef EVENT__HAVE_WEPOLL
		evmap_io_active_(base, events[i].data.sock, ev);
#else
		evmap_io_active_(base, events[i].data.fd, ev | EV_ET);
#endif
	}

	if (res == epollop->nevents && epollop->nevents < MAX_NEVENT) {
		/* We used all of the event space this time.  We should
		   be ready for more events next time. */
		int new_nevents = epollop->nevents * 2;
		struct epoll_event *new_events;

		new_events = mm_realloc(epollop->events,
		    new_nevents * sizeof(struct epoll_event));
		if (new_events) {
			epollop->events = new_events;
			epollop->nevents = new_nevents;
		}
	}

	return (0);
}


static void
epoll_dealloc(struct event_base *base)
{
	struct epollop *epollop = base->evbase;

	evsig_dealloc_(base);
	if (epollop->events)
		mm_free(epollop->events);
	if (epollop->epfd != INVALID_EPOLL_HANDLE)
		close_epoll_handle(epollop->epfd);
#ifdef USING_TIMERFD
	if (epollop->timerfd >= 0)
		close(epollop->timerfd);
#endif

	memset(epollop, 0, sizeof(struct epollop));
	mm_free(epollop);
}

#endif /* defined EVENT__HAVE_EPOLL || defined EVENT__HAVE_WEPOLL */