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 <stdint.h>
#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 <limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#ifdef _EVENT_HAVE_FCNTL_H
#include <fcntl.h>
#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"

struct epollop {
	struct epoll_event *events;
	int nevents;
	int epfd;
};

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,
	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);

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,
	0
};

#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)
{
	int epfd;
	struct epollop *epollop;

	/* Initialize the kernel queue.  (The size field is ignored since
	 * 2.6.8.) */
	if ((epfd = epoll_create(32000)) == -1) {
		if (errno != ENOSYS)
			event_warn("epoll_create");
		return (NULL);
	}

	evutil_make_socket_closeonexec(epfd);

	if (!(epollop = mm_calloc(1, sizeof(struct epollop)))) {
		close(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(epfd);
		return (NULL);
	}
	epollop->nevents = INITIAL_NEVENT;

	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;

	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":
	    "???";
}

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;

	if (1) {
		/* The logic here is a little tricky.  If we had no events set
		   on the fd before, we need to set op="ADD" and set
		   events=the events we want to add.  If we had any events set
		   on the fd before, and we want any events to remain on the
		   fd, we need to say op="MOD" and set events=the events we
		   want to remain.  But if we want to delete the last event,
		   we say op="DEL" and set events=the remaining events.  What
		   fun!
		*/

		/* TODO: Turn this into a switch or a table lookup. */

		if ((ch->read_change & EV_CHANGE_ADD) ||
		    (ch->write_change & EV_CHANGE_ADD)) {
			/* If we are adding anything at all, we'll want to do
			 * either an ADD or a MOD. */
			events = 0;
			op = EPOLL_CTL_ADD;
			if (ch->read_change & EV_CHANGE_ADD) {
				events |= EPOLLIN;
			} else if (ch->read_change & EV_CHANGE_DEL) {
				;
			} else if (ch->old_events & EV_READ) {
				events |= EPOLLIN;
			}
			if (ch->write_change & EV_CHANGE_ADD) {
				events |= EPOLLOUT;
			} else if (ch->write_change & EV_CHANGE_DEL) {
				;
			} else if (ch->old_events & EV_WRITE) {
				events |= EPOLLOUT;
			}
			if ((ch->read_change|ch->write_change) & EV_ET)
				events |= EPOLLET;

			if (ch->old_events) {
				/* If MOD fails, we retry as an ADD, and if
				 * ADD fails we will retry as a MOD.  So the
				 * only hard part here is to guess which one
				 * will work.  As a heuristic, we'll try
				 * MOD first if we think there were old
				 * events and ADD if we think there were none.
				 *
				 * We can be wrong about the MOD if the file
				 * has in fact been closed and re-opened.
				 *
				 * We can be wrong about the ADD if the
				 * the fd has been re-created with a dup()
				 * of the same file that it was before.
				 */
				op = EPOLL_CTL_MOD;
			}
		} else if ((ch->read_change & EV_CHANGE_DEL) ||
		    (ch->write_change & EV_CHANGE_DEL)) {
			/* If we're deleting anything, we'll want to do a MOD
			 * or a DEL. */
			op = EPOLL_CTL_DEL;

			if (ch->read_change & EV_CHANGE_DEL) {
				if (ch->write_change & EV_CHANGE_DEL) {
					events = EPOLLIN|EPOLLOUT;
				} else if (ch->old_events & EV_WRITE) {
					events = EPOLLOUT;
					op = EPOLL_CTL_MOD;
				} else {
					events = EPOLLIN;
				}
			} else if (ch->write_change & EV_CHANGE_DEL) {
				if (ch->old_events & EV_READ) {
					events = EPOLLIN;
					op = EPOLL_CTL_MOD;
				} else {
					events = EPOLLOUT;
				}
			}
		}

		if (!events)
			return 0;

		memset(&epev, 0, sizeof(epev));
		epev.data.fd = ch->fd;
		epev.events = events;
		if (epoll_ctl(epollop->epfd, op, ch->fd, &epev) == -1) {
			if (op == EPOLL_CTL_MOD && 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));
				}
			} else if (op == EPOLL_CTL_ADD && 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));
				}
			} else if (op == EPOLL_CTL_DEL &&
			    (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)));
			} else {
				event_warn("Epoll %s(%d) on fd %d failed.  Old events were %d; read change was %d (%s); write change was %d (%s)",
				    epoll_op_to_string(op),
				    (int)epev.events,
				    ch->fd,
				    ch->old_events,
				    ch->read_change,
				    change_to_string(ch->read_change),
				    ch->write_change,
				    change_to_string(ch->write_change));
				return -1;
			}
		} else {
			event_debug(("Epoll %s(%d) on fd %d okay. [old events were %d; read change was %d; write change was %d]",
				epoll_op_to_string(op),
				(int)epev.events,
				(int)ch->fd,
				ch->old_events,
				ch->read_change,
				ch->write_change));
		}
	}
	return 0;
}

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 = 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);

	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 = 0;
	if (events & EV_WRITE)
		ch.write_change = EV_CHANGE_DEL;
	if (events & EV_READ)
		ch.read_change = EV_CHANGE_DEL;

	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;
	long timeout = -1;

	if (tv != NULL) {
		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;
		}
	}

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

	EVBASE_RELEASE_LOCK(base, th_base_lock);

	res = epoll_wait(epollop->epfd, events, epollop->nevents, timeout);

	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;

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

		if (!ev)
			continue;

		evmap_io_active(base, events[i].data.fd, ev | EV_ET);
	}

	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 >= 0)
		close(epollop->epfd);

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