X-Git-Url: http://git.samba.org/samba.git/?a=blobdiff_plain;f=lib%2Ftevent%2Ftevent_standard.c;h=30e9b91a865161892b3fc2a16ea9d2c8e49ecde1;hb=c4ef0c8f3ecc4266fed3af8537ba2998730b3750;hp=762b834952c7e74cd69cceec9d1012bc607cce20;hpb=4f04b06ac2cfceddaabcbf661f9878ff69a6f01b;p=sfrench%2Fsamba-autobuild%2F.git

diff --git a/lib/tevent/tevent_standard.c b/lib/tevent/tevent_standard.c
index 762b834952c..30e9b91a865 100644
--- a/lib/tevent/tevent_standard.c
+++ b/lib/tevent/tevent_standard.c
@@ -1,609 +1,242 @@
 /* 
    Unix SMB/CIFS implementation.
    main select loop and event handling
-   Copyright (C) Andrew Tridgell	2003-2005
-   Copyright (C) Stefan Metzmacher	2005
-   
-   This program is free software; you can redistribute it and/or modify
-   it under the terms of the GNU General Public License as published by
-   the Free Software Foundation; either version 3 of the License, or
-   (at your option) any later version.
-   
-   This program is distributed in the hope that it will be useful,
+   Copyright (C) Stefan Metzmacher      2013
+   Copyright (C) Jeremy Allison         2013
+
+     ** 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 General Public License for more details.
-   
-   You should have received a copy of the GNU General Public License
-   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+   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()
+    otherwise we use poll()
   - if epoll is broken on the system or the kernel doesn't support it
-    at runtime we fallback to select()
+    at runtime we fallback to poll()
 */
 
 #include "replace.h"
-#include "system/filesys.h"
-#include "system/network.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;
-
-	/* list of filedescriptor events */
-	struct tevent_fd *fd_events;
-
-	/* the maximum file descriptor number in fd_events */
-	int maxfd;
-
-	/* information for exiting from the event loop */
-	int exit_code;
-
-	/* this is changed by the destructors for the fd event
-	   type. It is used to detect event destruction by event
-	   handlers, which means the code that is calling the event
-	   handler needs to assume that the linked list is no longer
-	   valid
-	*/
-	uint32_t destruction_count;
-
-	/* 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;
+struct std_event_glue {
+	const struct tevent_ops *epoll_ops;
+	const struct tevent_ops *poll_ops;
+	struct tevent_ops *glue_ops;
+	bool fallback_replay;
 };
 
-/* 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);
-}
+static int std_event_context_init(struct tevent_context *ev);
 
-/*
-  map from EVENT_FD_* to EPOLLIN/EPOLLOUT
-*/
-static uint32_t epoll_map_flags(uint16_t flags)
-{
-	uint32_t ret = 0;
-	if (flags & EVENT_FD_READ) ret |= (EPOLLIN | EPOLLERR | EPOLLHUP);
-	if (flags & EVENT_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;
-}
+static const struct tevent_ops std_event_ops = {
+	.context_init           = std_event_context_init,
+};
 
 /*
- init the epoll fd
+  If this function gets called. epoll failed at runtime.
+  Move us to using poll instead. If we return false here,
+  caller should abort().
 */
-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)
+#ifdef HAVE_EPOLL
+static bool std_fallback_to_poll(struct tevent_context *ev, bool replay)
 {
+	void *glue_ptr = talloc_parent(ev->ops);
+	struct std_event_glue *glue =
+		talloc_get_type_abort(glue_ptr,
+		struct std_event_glue);
+	int ret;
 	struct tevent_fd *fde;
+	struct tevent_fd *fde_next;
 
-	if (std_ev->pid == getpid()) {
-		return;
-	}
+	glue->fallback_replay = replay;
 
-	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->fd_events;fde;fde=fde->next) {
-		epoll_add_event(std_ev, fde);
-	}
-}
+	/* First switch all the ops to poll. */
+	glue->epoll_ops = NULL;
 
-#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)
+	/*
+	 * Set custom_ops the same as poll.
+	 */
+	*glue->glue_ops = *glue->poll_ops;
+	glue->glue_ops->context_init = std_event_context_init;
 
-/*
- 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");
+	/* Next initialize the poll backend. */
+	ret = glue->poll_ops->context_init(ev);
+	if (ret != 0) {
+		return false;
 	}
-	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 & EVENT_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;
+	/*
+	 * Now we have to change all the existing file descriptor
+	 * events from the epoll backend to the poll backend.
+	 */
+	for (fde = ev->fd_events; fde; fde = fde_next) {
+		/*
+		 * We must remove this fde off the ev->fd_events list.
+		 */
+		fde_next = fde->next;
 
-	fde->additional_flags &= ~EPOLL_ADDITIONAL_FD_FLAG_REPORT_ERROR;
+		/* Remove from the ev->fd_events list. */
+		DLIST_REMOVE(ev->fd_events, fde);
 
-	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");
+		/* Re-add this event as a poll backend event. */
+		tevent_poll_event_add_fd_internal(ev, fde);
 	}
 
-	/* only if we want to read we want to tell the event handler about errors */
-	if (fde->flags & EVENT_FD_READ) {
-		fde->additional_flags |= EPOLL_ADDITIONAL_FD_FLAG_REPORT_ERROR;
-	}
+	return true;
 }
+#endif
 
-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 & EVENT_FD_READ);
-	bool want_write= (fde->flags & EVENT_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
+static int std_event_loop_once(struct tevent_context *ev, const char *location)
+{
+	void *glue_ptr = talloc_parent(ev->ops);
+	struct std_event_glue *glue =
+		talloc_get_type_abort(glue_ptr,
+		struct std_event_glue);
+	int ret;
+
+	ret = glue->epoll_ops->loop_once(ev, location);
+	/*
+	 * If the above hasn't panicked due to an epoll interface failure,
+	 * std_fallback_to_poll() wasn't called, and hasn't cleared epoll_ops to
+	 * signify fallback to poll_ops.
+	 */
+	if (glue->epoll_ops != NULL) {
+		/* No fallback */
+		return ret;
+	}
+
+	if (!glue->fallback_replay) {
+		/*
+		 * The problem happened while modifying an event.
+		 * An event handler was triggered in this case
+		 * and there is no need to call loop_once() again.
 		 */
-		epoll_del_event(std_ev, fde);
-		return;
+		return ret;
 	}
 
-	/* there's no epoll_event attached to the fde */
-	if (want_read || (want_write && !got_error)) {
-		epoll_add_event(std_ev, fde);
-		return;
-	}
+	return glue->poll_ops->loop_once(ev, location);
 }
 
-/*
-  event loop handling using epoll
-*/
-static int epoll_event_loop(struct std_event_context *std_ev, struct timeval *tvalp)
+static int std_event_loop_wait(struct tevent_context *ev, const char *location)
 {
-	int ret, i;
-#define MAXEVENTS 8
-	struct epoll_event events[MAXEVENTS];
-	uint32_t destruction_count = ++std_ev->destruction_count;
-	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);
-	}
+	void *glue_ptr = talloc_parent(ev->ops);
+	struct std_event_glue *glue =
+		talloc_get_type_abort(glue_ptr,
+		struct std_event_glue);
+	int ret;
 
-	if (std_ev->ev->num_signal_handlers && 
-	    tevent_common_check_signal(std_ev->ev)) {
-		return 0;
+	ret = glue->epoll_ops->loop_wait(ev, location);
+	/*
+	 * If the above hasn't panicked due to an epoll interface failure,
+	 * std_fallback_to_poll() wasn't called, and hasn't cleared epoll_ops to
+	 * signify fallback to poll_ops.
+	 */
+	if (glue->epoll_ops != NULL) {
+		/* No fallback */
+		return ret;
 	}
 
-	ret = epoll_wait(std_ev->epoll_fd, events, MAXEVENTS, timeout);
-
-	if (ret == -1 && errno == EINTR && std_ev->ev->num_signal_handlers) {
-		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 EVENT_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 |= EVENT_FD_READ;
-		}
-		if (events[i].events & EPOLLIN) flags |= EVENT_FD_READ;
-		if (events[i].events & EPOLLOUT) flags |= EVENT_FD_WRITE;
-		if (flags) {
-			fde->handler(std_ev->ev, fde, flags, fde->private_data);
-			if (destruction_count != std_ev->destruction_count) {
-				break;
-			}
-		}
-	}
-
-	return 0;
+	return glue->poll_ops->loop_wait(ev, location);
 }
-#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.
+  Initialize the epoll backend and allow it to call a
+  switch function if epoll fails at runtime.
 */
 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;
+	struct std_event_glue *glue;
+	int ret;
 
-	epoll_init_ctx(std_ev);
+	/*
+	 * If this is the first initialization
+	 * we need to set up the allocated ops
+	 * pointers.
+	 */
 
-	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->fd_events; fde; fde = fde->next) {
-		if (fde->fd > std_ev->maxfd) {
-			std_ev->maxfd = fde->fd;
+	if (ev->ops == &std_event_ops) {
+		glue = talloc_zero(ev, struct std_event_glue);
+		if (glue == NULL) {
+			return -1;
 		}
-	}
-}
-
-
-/* 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 = 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;
-	}
-
-	DLIST_REMOVE(std_ev->fd_events, fde);
-	std_ev->destruction_count++;
-
-	epoll_del_event(std_ev, fde);
-
-	if (fde->flags & EVENT_FD_AUTOCLOSE) {
-		close(fde->fd);
-		fde->fd = -1;
-	}
-
-	return 0;
-}
-
-/*
-  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 = talloc(mem_ctx?mem_ctx:ev, struct tevent_fd);
-	if (!fde) return NULL;
-
-	fde->event_ctx		= ev;
-	fde->fd			= fd;
-	fde->flags		= flags;
-	fde->handler		= handler;
-	fde->private_data	= private_data;
-	fde->additional_flags	= 0;
-	fde->additional_data	= NULL;
-
-	DLIST_ADD(std_ev->fd_events, fde);
-	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;
-}
-
-
-/*
-  return the fd event flags
-*/
-static uint16_t std_event_get_fd_flags(struct tevent_fd *fde)
-{
-	return fde->flags;
-}
-
-/*
-  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);
+		glue->epoll_ops = tevent_find_ops_byname("epoll");
 
-	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;
-	uint32_t destruction_count = ++std_ev->destruction_count;
-
-	/* 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->fd_events; fde; fde = fde->next) {
-		if (fde->flags & EVENT_FD_READ) {
-			FD_SET(fde->fd, &r_fds);
-		}
-		if (fde->flags & EVENT_FD_WRITE) {
-			FD_SET(fde->fd, &w_fds);
+		glue->poll_ops = tevent_find_ops_byname("poll");
+		if (glue->poll_ops == NULL) {
+			return -1;
 		}
-	}
-
-	if (std_ev->ev->num_signal_handlers && 
-	    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->num_signal_handlers) {
-		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->fd_events; fde; fde = fde->next) {
-			uint16_t flags = 0;
-
-			if (FD_ISSET(fde->fd, &r_fds)) flags |= EVENT_FD_READ;
-			if (FD_ISSET(fde->fd, &w_fds)) flags |= EVENT_FD_WRITE;
-			if (flags) {
-				fde->handler(std_ev->ev, fde, flags, fde->private_data);
-				if (destruction_count != std_ev->destruction_count) {
-					break;
-				}
-			}
+		/*
+		 * Allocate space for our custom ops.
+		 * Allocate as a child of our epoll_ops pointer
+		 * so we can easily get to it using talloc_parent.
+		 */
+		glue->glue_ops = talloc_zero(glue, struct tevent_ops);
+		if (glue->glue_ops == NULL) {
+			talloc_free(glue);
+			return -1;
 		}
-	}
-
-	return 0;
-}		
 
-/*
-  do a single event loop using the events defined in ev 
-*/
-static int std_event_loop_once(struct tevent_context *ev)
-{
-	struct std_event_context *std_ev = talloc_get_type(ev->additional_data,
-		 					   struct std_event_context);
-	struct timeval tval;
-
-	tval = tevent_common_loop_timer_delay(ev);
-	if (ev_timeval_is_zero(&tval)) {
-		return 0;
+		ev->ops = glue->glue_ops;
+	} else {
+		void *glue_ptr = talloc_parent(ev->ops);
+		glue = talloc_get_type_abort(glue_ptr, struct std_event_glue);
 	}
 
-	epoll_check_reopen(std_ev);
+	if (glue->epoll_ops != NULL) {
+		/*
+		 * Set custom_ops the same as epoll,
+		 * except re-init using std_event_context_init()
+		 * and use std_event_loop_once() to add the
+		 * ability to fallback to a poll backend on
+		 * epoll runtime error.
+		 */
+		*glue->glue_ops = *glue->epoll_ops;
+		glue->glue_ops->context_init = std_event_context_init;
+		glue->glue_ops->loop_once = std_event_loop_once;
+		glue->glue_ops->loop_wait = std_event_loop_wait;
+
+		ret = glue->epoll_ops->context_init(ev);
+		if (ret == -1) {
+			goto fallback;
+		}
+#ifdef HAVE_EPOLL
+		tevent_epoll_set_panic_fallback(ev, std_fallback_to_poll);
+#endif
 
-	if (epoll_event_loop(std_ev, &tval) == 0) {
-		return 0;
+		return ret;
 	}
 
-	return std_event_loop_select(std_ev, &tval);
-}
-
-/*
-  return on failure or (with 0) if all fd events are removed
-*/
-static int std_event_loop_wait(struct tevent_context *ev)
-{
-	struct std_event_context *std_ev = talloc_get_type(ev->additional_data,
-							   struct std_event_context);
-	std_ev->exit_code = 0;
+fallback:
+	glue->epoll_ops = NULL;
 
-	while (std_ev->fd_events && std_ev->exit_code == 0) {
-		if (std_event_loop_once(ev) != 0) {
-			break;
-		}
-	}
+	/*
+	 * Set custom_ops the same as poll.
+	 */
+	*glue->glue_ops = *glue->poll_ops;
+	glue->glue_ops->context_init = std_event_context_init;
 
-	return std_ev->exit_code;
+	return glue->poll_ops->context_init(ev);
 }
 
-static const struct tevent_ops std_event_ops = {
-	.context_init	= std_event_context_init,
-	.add_fd		= std_event_add_fd,
-	.get_fd_flags	= std_event_get_fd_flags,
-	.set_fd_flags	= std_event_set_fd_flags,
-	.add_timer	= tevent_common_add_timer,
-	.add_signal	= tevent_common_add_signal,
-	.loop_once	= std_event_loop_once,
-	.loop_wait	= std_event_loop_wait,
-};
-
-
-bool tevent_standard_init(void)
+_PRIVATE_ bool tevent_standard_init(void)
 {
 	return tevent_register_backend("standard", &std_event_ops);
 }
-