main-loop.c - qemu - Git at Google

 /*
  * QEMU System Emulator
  *
  * Copyright (c) 2003-2008 Fabrice Bellard
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
  * in the Software without restriction, including without limitation the rights
  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  * copies of the Software, and to permit persons to whom the Software is
  * furnished to do so, subject to the following conditions:
  *
  * The above copyright notice and this permission notice shall be included in
  * all copies or substantial portions of the Software.
  *
  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  * THE SOFTWARE.
  */

 #include "qemu/osdep.h"
 #include "qemu-common.h"
 #include "qemu/timer.h"
 #include "qemu/sockets.h"	// struct in_addr needed for libslirp.h
 #include "sysemu/qtest.h"
 #include "slirp/libslirp.h"
 #include "qemu/main-loop.h"
 #include "block/aio.h"

 #ifndef _WIN32

 #include "qemu/compatfd.h"

 /* If we have signalfd, we mask out the signals we want to handle and then
  * use signalfd to listen for them.  We rely on whatever the current signal
  * handler is to dispatch the signals when we receive them.
  */
 static void sigfd_handler(void *opaque)
 {
     int fd = (intptr_t)opaque;
     struct qemu_signalfd_siginfo info;
     struct sigaction action;
     ssize_t len;

     while (1) {
         do {
             len = read(fd, &info, sizeof(info));
         } while (len == -1 && errno == EINTR);

         if (len == -1 && errno == EAGAIN) {
             break;
         }

         if (len != sizeof(info)) {
             printf("read from sigfd returned %zd: %m\n", len);
             return;
         }

         sigaction(info.ssi_signo, NULL, &action);
         if ((action.sa_flags & SA_SIGINFO) && action.sa_sigaction) {
             action.sa_sigaction(info.ssi_signo,
                                 (siginfo_t *)&info, NULL);
         } else if (action.sa_handler) {
             action.sa_handler(info.ssi_signo);
         }
     }
 }

 static int qemu_signal_init(void)
 {
     int sigfd;
     sigset_t set;

     /*
      * SIG_IPI must be blocked in the main thread and must not be caught
      * by sigwait() in the signal thread. Otherwise, the cpu thread will
      * not catch it reliably.
      */
     sigemptyset(&set);
     sigaddset(&set, SIG_IPI);
     sigaddset(&set, SIGIO);
     sigaddset(&set, SIGALRM);
     sigaddset(&set, SIGBUS);
     /* SIGINT cannot be handled via signalfd, so that ^C can be used
      * to interrupt QEMU when it is being run under gdb.  SIGHUP and
      * SIGTERM are also handled asynchronously, even though it is not
      * strictly necessary, because they use the same handler as SIGINT.
      */
     pthread_sigmask(SIG_BLOCK, &set, NULL);

     sigdelset(&set, SIG_IPI);
     sigfd = qemu_signalfd(&set);
     if (sigfd == -1) {
         fprintf(stderr, "failed to create signalfd\n");
         return -errno;
     }

     fcntl_setfl(sigfd, O_NONBLOCK);

     qemu_set_fd_handler(sigfd, sigfd_handler, NULL, (void *)(intptr_t)sigfd);

     return 0;
 }

 #else /* _WIN32 */

 static int qemu_signal_init(void)
 {
     return 0;
 }
 #endif

 static AioContext *qemu_aio_context;
 static QEMUBH *qemu_notify_bh;

 static void notify_event_cb(void *opaque)
 {
     /* No need to do anything; this bottom half is only used to
      * kick the kernel out of ppoll/poll/WaitForMultipleObjects.
      */
 }

 AioContext *qemu_get_aio_context(void)
 {
     return qemu_aio_context;
 }

 void qemu_notify_event(void)
 {
     if (!qemu_aio_context) {
         return;
     }
     qemu_bh_schedule(qemu_notify_bh);
 }

 static GArray *gpollfds;

 int qemu_init_main_loop(Error **errp)
 {
     int ret;
     GSource *src;
     Error *local_error = NULL;

     init_clocks();

     ret = qemu_signal_init();
     if (ret) {
         return ret;
     }

     qemu_aio_context = aio_context_new(&local_error);
     qemu_notify_bh = qemu_bh_new(notify_event_cb, NULL);
     if (!qemu_aio_context) {
         error_propagate(errp, local_error);
         return -EMFILE;
     }
     gpollfds = g_array_new(FALSE, FALSE, sizeof(GPollFD));
     src = aio_get_g_source(qemu_aio_context);
     g_source_attach(src, NULL);
     g_source_unref(src);
     src = iohandler_get_g_source();
     g_source_attach(src, NULL);
     g_source_unref(src);
     return 0;
 }

 static int max_priority;

 #ifndef _WIN32
 static int glib_pollfds_idx;
 static int glib_n_poll_fds;

 static void glib_pollfds_fill(int64_t *cur_timeout)
 {
     GMainContext *context = g_main_context_default();
     int timeout = 0;
     int64_t timeout_ns;
     int n;

     g_main_context_prepare(context, &max_priority);

     glib_pollfds_idx = gpollfds->len;
     n = glib_n_poll_fds;
     do {
         GPollFD *pfds;
         glib_n_poll_fds = n;
         g_array_set_size(gpollfds, glib_pollfds_idx + glib_n_poll_fds);
         pfds = &g_array_index(gpollfds, GPollFD, glib_pollfds_idx);
         n = g_main_context_query(context, max_priority, &timeout, pfds,
                                  glib_n_poll_fds);
     } while (n != glib_n_poll_fds);

     if (timeout < 0) {
         timeout_ns = -1;
     } else {
         timeout_ns = (int64_t)timeout * (int64_t)SCALE_MS;
     }

     *cur_timeout = qemu_soonest_timeout(timeout_ns, *cur_timeout);
 }

 static void glib_pollfds_poll(void)
 {
     GMainContext *context = g_main_context_default();
     GPollFD *pfds = &g_array_index(gpollfds, GPollFD, glib_pollfds_idx);

     if (g_main_context_check(context, max_priority, pfds, glib_n_poll_fds)) {
         g_main_context_dispatch(context);
     }
 }

 #define MAX_MAIN_LOOP_SPIN (1000)

 static int os_host_main_loop_wait(int64_t timeout)
 {
     int ret;
     static int spin_counter;

     glib_pollfds_fill(&timeout);

     /* If the I/O thread is very busy or we are incorrectly busy waiting in
      * the I/O thread, this can lead to starvation of the BQL such that the
      * VCPU threads never run.  To make sure we can detect the later case,
      * print a message to the screen.  If we run into this condition, create
      * a fake timeout in order to give the VCPU threads a chance to run.
      */
     if (!timeout && (spin_counter > MAX_MAIN_LOOP_SPIN)) {
         static bool notified;

         if (!notified && !qtest_driver()) {
             fprintf(stderr,
                     "main-loop: WARNING: I/O thread spun for %d iterations\n",
                     MAX_MAIN_LOOP_SPIN);
             notified = true;
         }

         timeout = SCALE_MS;
     }

     if (timeout) {
         spin_counter = 0;
         qemu_mutex_unlock_iothread();
     } else {
         spin_counter++;
     }

     ret = qemu_poll_ns((GPollFD *)gpollfds->data, gpollfds->len, timeout);

     if (timeout) {
         qemu_mutex_lock_iothread();
     }

     glib_pollfds_poll();
     return ret;
 }
 #else
 /***********************************************************/
 /* Polling handling */

 typedef struct PollingEntry {
     PollingFunc *func;
     void *opaque;
     struct PollingEntry *next;
 } PollingEntry;

 static PollingEntry *first_polling_entry;

 int qemu_add_polling_cb(PollingFunc *func, void *opaque)
 {
     PollingEntry **ppe, *pe;
     pe = g_malloc0(sizeof(PollingEntry));
     pe->func = func;
     pe->opaque = opaque;
     for(ppe = &first_polling_entry; *ppe != NULL; ppe = &(*ppe)->next);
     *ppe = pe;
     return 0;
 }

 void qemu_del_polling_cb(PollingFunc *func, void *opaque)
 {
     PollingEntry **ppe, *pe;
     for(ppe = &first_polling_entry; *ppe != NULL; ppe = &(*ppe)->next) {
         pe = *ppe;
         if (pe->func == func && pe->opaque == opaque) {
             *ppe = pe->next;
             g_free(pe);
             break;
         }
     }
 }

 /***********************************************************/
 /* Wait objects support */
 typedef struct WaitObjects {
     int num;
     int revents[MAXIMUM_WAIT_OBJECTS + 1];
     HANDLE events[MAXIMUM_WAIT_OBJECTS + 1];
     WaitObjectFunc *func[MAXIMUM_WAIT_OBJECTS + 1];
     void *opaque[MAXIMUM_WAIT_OBJECTS + 1];
 } WaitObjects;

 static WaitObjects wait_objects = {0};

 int qemu_add_wait_object(HANDLE handle, WaitObjectFunc *func, void *opaque)
 {
     WaitObjects *w = &wait_objects;
     if (w->num >= MAXIMUM_WAIT_OBJECTS) {
         return -1;
     }
     w->events[w->num] = handle;
     w->func[w->num] = func;
     w->opaque[w->num] = opaque;
     w->revents[w->num] = 0;
     w->num++;
     return 0;
 }

 void qemu_del_wait_object(HANDLE handle, WaitObjectFunc *func, void *opaque)
 {
     int i, found;
     WaitObjects *w = &wait_objects;

     found = 0;
     for (i = 0; i < w->num; i++) {
         if (w->events[i] == handle) {
             found = 1;
         }
         if (found) {
             w->events[i] = w->events[i + 1];
             w->func[i] = w->func[i + 1];
             w->opaque[i] = w->opaque[i + 1];
             w->revents[i] = w->revents[i + 1];
         }
     }
     if (found) {
         w->num--;
     }
 }

 void qemu_fd_register(int fd)
 {
     WSAEventSelect(fd, event_notifier_get_handle(&qemu_aio_context->notifier),
                    FD_READ | FD_ACCEPT | FD_CLOSE |
                    FD_CONNECT | FD_WRITE | FD_OOB);
 }

 static int pollfds_fill(GArray *pollfds, fd_set *rfds, fd_set *wfds,
                         fd_set *xfds)
 {
     int nfds = -1;
     int i;

     for (i = 0; i < pollfds->len; i++) {
         GPollFD *pfd = &g_array_index(pollfds, GPollFD, i);
         int fd = pfd->fd;
         int events = pfd->events;
         if (events & G_IO_IN) {
             FD_SET(fd, rfds);
             nfds = MAX(nfds, fd);
         }
         if (events & G_IO_OUT) {
             FD_SET(fd, wfds);
             nfds = MAX(nfds, fd);
         }
         if (events & G_IO_PRI) {
             FD_SET(fd, xfds);
             nfds = MAX(nfds, fd);
         }
     }
     return nfds;
 }

 static void pollfds_poll(GArray *pollfds, int nfds, fd_set *rfds,
                          fd_set *wfds, fd_set *xfds)
 {
     int i;

     for (i = 0; i < pollfds->len; i++) {
         GPollFD *pfd = &g_array_index(pollfds, GPollFD, i);
         int fd = pfd->fd;
         int revents = 0;

         if (FD_ISSET(fd, rfds)) {
             revents |= G_IO_IN;
         }
         if (FD_ISSET(fd, wfds)) {
             revents |= G_IO_OUT;
         }
         if (FD_ISSET(fd, xfds)) {
             revents |= G_IO_PRI;
         }
         pfd->revents = revents & pfd->events;
     }
 }

 static int os_host_main_loop_wait(int64_t timeout)
 {
     GMainContext *context = g_main_context_default();
     GPollFD poll_fds[1024 * 2]; /* this is probably overkill */
     int select_ret = 0;
     int g_poll_ret, ret, i, n_poll_fds;
     PollingEntry *pe;
     WaitObjects *w = &wait_objects;
     gint poll_timeout;
     int64_t poll_timeout_ns;
     static struct timeval tv0;
     fd_set rfds, wfds, xfds;
     int nfds;

     /* XXX: need to suppress polling by better using win32 events */
     ret = 0;
     for (pe = first_polling_entry; pe != NULL; pe = pe->next) {
         ret |= pe->func(pe->opaque);
     }
     if (ret != 0) {
         return ret;
     }

     FD_ZERO(&rfds);
     FD_ZERO(&wfds);
     FD_ZERO(&xfds);
     nfds = pollfds_fill(gpollfds, &rfds, &wfds, &xfds);
     if (nfds >= 0) {
         select_ret = select(nfds + 1, &rfds, &wfds, &xfds, &tv0);
         if (select_ret != 0) {
             timeout = 0;
         }
         if (select_ret > 0) {
             pollfds_poll(gpollfds, nfds, &rfds, &wfds, &xfds);
         }
     }

     g_main_context_prepare(context, &max_priority);
     n_poll_fds = g_main_context_query(context, max_priority, &poll_timeout,
                                       poll_fds, ARRAY_SIZE(poll_fds));
     g_assert(n_poll_fds <= ARRAY_SIZE(poll_fds));

     for (i = 0; i < w->num; i++) {
         poll_fds[n_poll_fds + i].fd = (DWORD_PTR)w->events[i];
         poll_fds[n_poll_fds + i].events = G_IO_IN;
     }

     if (poll_timeout < 0) {
         poll_timeout_ns = -1;
     } else {
         poll_timeout_ns = (int64_t)poll_timeout * (int64_t)SCALE_MS;
     }

     poll_timeout_ns = qemu_soonest_timeout(poll_timeout_ns, timeout);

     qemu_mutex_unlock_iothread();
     g_poll_ret = qemu_poll_ns(poll_fds, n_poll_fds + w->num, poll_timeout_ns);

     qemu_mutex_lock_iothread();
     if (g_poll_ret > 0) {
         for (i = 0; i < w->num; i++) {
             w->revents[i] = poll_fds[n_poll_fds + i].revents;
         }
         for (i = 0; i < w->num; i++) {
             if (w->revents[i] && w->func[i]) {
                 w->func[i](w->opaque[i]);
             }
         }
     }

     if (g_main_context_check(context, max_priority, poll_fds, n_poll_fds)) {
         g_main_context_dispatch(context);
     }

     return select_ret || g_poll_ret;
 }
 #endif

 int main_loop_wait(int nonblocking)
 {
     int ret;
     uint32_t timeout = UINT32_MAX;
     int64_t timeout_ns;

     if (nonblocking) {
         timeout = 0;
     }

     /* poll any events */
     g_array_set_size(gpollfds, 0); /* reset for new iteration */
     /* XXX: separate device handlers from system ones */
 #ifdef CONFIG_SLIRP
     slirp_pollfds_fill(gpollfds, &timeout);
 #endif

     if (timeout == UINT32_MAX) {
         timeout_ns = -1;
     } else {
         timeout_ns = (uint64_t)timeout * (int64_t)(SCALE_MS);
     }

     timeout_ns = qemu_soonest_timeout(timeout_ns,
                                       timerlistgroup_deadline_ns(
                                           &main_loop_tlg));

     ret = os_host_main_loop_wait(timeout_ns);
 #ifdef CONFIG_SLIRP
     slirp_pollfds_poll(gpollfds, (ret < 0));
 #endif

     /* CPU thread can infinitely wait for event after
        missing the warp */
     qemu_start_warp_timer();
     qemu_clock_run_all_timers();

     return ret;
 }

 /* Functions to operate on the main QEMU AioContext.  */

 QEMUBH *qemu_bh_new(QEMUBHFunc *cb, void *opaque)
 {
     return aio_bh_new(qemu_aio_context, cb, opaque);
 }
	/*
	* QEMU System Emulator
	*
	* Copyright (c) 2003-2008 Fabrice Bellard
	*
	* Permission is hereby granted, free of charge, to any person obtaining a copy
	* of this software and associated documentation files (the "Software"), to deal
	* in the Software without restriction, including without limitation the rights
	* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
	* copies of the Software, and to permit persons to whom the Software is
	* furnished to do so, subject to the following conditions:
	*
	* The above copyright notice and this permission notice shall be included in
	* all copies or substantial portions of the Software.
	*
	* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
	* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
	* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
	* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
	* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
	* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
	* THE SOFTWARE.
	*/

	#include "qemu/osdep.h"
	#include "qemu-common.h"
	#include "qemu/timer.h"
	#include "qemu/sockets.h" // struct in_addr needed for libslirp.h
	#include "sysemu/qtest.h"
	#include "slirp/libslirp.h"
	#include "qemu/main-loop.h"
	#include "block/aio.h"

	#ifndef _WIN32

	#include "qemu/compatfd.h"

	/* If we have signalfd, we mask out the signals we want to handle and then
	* use signalfd to listen for them. We rely on whatever the current signal
	* handler is to dispatch the signals when we receive them.
	*/
	static void sigfd_handler(void *opaque)
	{
	int fd = (intptr_t)opaque;
	struct qemu_signalfd_siginfo info;
	struct sigaction action;
	ssize_t len;

	while (1) {
	do {
	len = read(fd, &info, sizeof(info));
	} while (len == -1 && errno == EINTR);

	if (len == -1 && errno == EAGAIN) {
	break;
	}

	if (len != sizeof(info)) {
	printf("read from sigfd returned %zd: %m\n", len);
	return;
	}

	sigaction(info.ssi_signo, NULL, &action);
	if ((action.sa_flags & SA_SIGINFO) && action.sa_sigaction) {
	action.sa_sigaction(info.ssi_signo,
	(siginfo_t *)&info, NULL);
	} else if (action.sa_handler) {
	action.sa_handler(info.ssi_signo);
	}
	}
	}

	static int qemu_signal_init(void)
	{
	int sigfd;
	sigset_t set;

	/*
	* SIG_IPI must be blocked in the main thread and must not be caught
	* by sigwait() in the signal thread. Otherwise, the cpu thread will
	* not catch it reliably.
	*/
	sigemptyset(&set);
	sigaddset(&set, SIG_IPI);
	sigaddset(&set, SIGIO);
	sigaddset(&set, SIGALRM);
	sigaddset(&set, SIGBUS);
	/* SIGINT cannot be handled via signalfd, so that ^C can be used
	* to interrupt QEMU when it is being run under gdb. SIGHUP and
	* SIGTERM are also handled asynchronously, even though it is not
	* strictly necessary, because they use the same handler as SIGINT.
	*/
	pthread_sigmask(SIG_BLOCK, &set, NULL);

	sigdelset(&set, SIG_IPI);
	sigfd = qemu_signalfd(&set);
	if (sigfd == -1) {
	fprintf(stderr, "failed to create signalfd\n");
	return -errno;
	}

	fcntl_setfl(sigfd, O_NONBLOCK);

	qemu_set_fd_handler(sigfd, sigfd_handler, NULL, (void *)(intptr_t)sigfd);

	return 0;
	}

	#else /* _WIN32 */

	static int qemu_signal_init(void)
	{
	return 0;
	}
	#endif

	static AioContext *qemu_aio_context;
	static QEMUBH *qemu_notify_bh;

	static void notify_event_cb(void *opaque)
	{
	/* No need to do anything; this bottom half is only used to
	* kick the kernel out of ppoll/poll/WaitForMultipleObjects.
	*/
	}

	AioContext *qemu_get_aio_context(void)
	{
	return qemu_aio_context;
	}

	void qemu_notify_event(void)
	{
	if (!qemu_aio_context) {
	return;
	}
	qemu_bh_schedule(qemu_notify_bh);
	}

	static GArray *gpollfds;

	int qemu_init_main_loop(Error **errp)
	{
	int ret;
	GSource *src;
	Error *local_error = NULL;

	init_clocks();

	ret = qemu_signal_init();
	if (ret) {
	return ret;
	}

	qemu_aio_context = aio_context_new(&local_error);
	qemu_notify_bh = qemu_bh_new(notify_event_cb, NULL);
	if (!qemu_aio_context) {
	error_propagate(errp, local_error);
	return -EMFILE;
	}
	gpollfds = g_array_new(FALSE, FALSE, sizeof(GPollFD));
	src = aio_get_g_source(qemu_aio_context);
	g_source_attach(src, NULL);
	g_source_unref(src);
	src = iohandler_get_g_source();
	g_source_attach(src, NULL);
	g_source_unref(src);
	return 0;
	}

	static int max_priority;

	#ifndef _WIN32
	static int glib_pollfds_idx;
	static int glib_n_poll_fds;

	static void glib_pollfds_fill(int64_t *cur_timeout)
	{
	GMainContext *context = g_main_context_default();
	int timeout = 0;
	int64_t timeout_ns;
	int n;

	g_main_context_prepare(context, &max_priority);

	glib_pollfds_idx = gpollfds->len;
	n = glib_n_poll_fds;
	do {
	GPollFD *pfds;
	glib_n_poll_fds = n;
	g_array_set_size(gpollfds, glib_pollfds_idx + glib_n_poll_fds);
	pfds = &g_array_index(gpollfds, GPollFD, glib_pollfds_idx);
	n = g_main_context_query(context, max_priority, &timeout, pfds,
	glib_n_poll_fds);
	} while (n != glib_n_poll_fds);

	if (timeout < 0) {
	timeout_ns = -1;
	} else {
	timeout_ns = (int64_t)timeout * (int64_t)SCALE_MS;
	}

	cur_timeout = qemu_soonest_timeout(timeout_ns, cur_timeout);
	}

	static void glib_pollfds_poll(void)
	{
	GMainContext *context = g_main_context_default();
	GPollFD *pfds = &g_array_index(gpollfds, GPollFD, glib_pollfds_idx);

	if (g_main_context_check(context, max_priority, pfds, glib_n_poll_fds)) {
	g_main_context_dispatch(context);
	}
	}

	#define MAX_MAIN_LOOP_SPIN (1000)

	static int os_host_main_loop_wait(int64_t timeout)
	{
	int ret;
	static int spin_counter;

	glib_pollfds_fill(&timeout);

	/* If the I/O thread is very busy or we are incorrectly busy waiting in
	* the I/O thread, this can lead to starvation of the BQL such that the
	* VCPU threads never run. To make sure we can detect the later case,
	* print a message to the screen. If we run into this condition, create
	* a fake timeout in order to give the VCPU threads a chance to run.
	*/
	if (!timeout && (spin_counter > MAX_MAIN_LOOP_SPIN)) {
	static bool notified;

	if (!notified && !qtest_driver()) {
	fprintf(stderr,
	"main-loop: WARNING: I/O thread spun for %d iterations\n",
	MAX_MAIN_LOOP_SPIN);
	notified = true;
	}

	timeout = SCALE_MS;
	}

	if (timeout) {
	spin_counter = 0;
	qemu_mutex_unlock_iothread();
	} else {
	spin_counter++;
	}

	ret = qemu_poll_ns((GPollFD *)gpollfds->data, gpollfds->len, timeout);

	if (timeout) {
	qemu_mutex_lock_iothread();
	}

	glib_pollfds_poll();
	return ret;
	}
	#else
	/***********************************************************/
	/* Polling handling */

	typedef struct PollingEntry {
	PollingFunc *func;
	void *opaque;
	struct PollingEntry *next;
	} PollingEntry;

	static PollingEntry *first_polling_entry;

	int qemu_add_polling_cb(PollingFunc func, void opaque)
	{
	PollingEntry *ppe, pe;
	pe = g_malloc0(sizeof(PollingEntry));
	pe->func = func;
	pe->opaque = opaque;
	for(ppe = &first_polling_entry; ppe != NULL; ppe = &(ppe)->next);
	*ppe = pe;
	return 0;
	}

	void qemu_del_polling_cb(PollingFunc func, void opaque)
	{
	PollingEntry *ppe, pe;
	for(ppe = &first_polling_entry; ppe != NULL; ppe = &(ppe)->next) {
	pe = *ppe;
	if (pe->func == func && pe->opaque == opaque) {
	*ppe = pe->next;
	g_free(pe);
	break;
	}
	}
	}

	/***********************************************************/
	/* Wait objects support */
	typedef struct WaitObjects {
	int num;
	int revents[MAXIMUM_WAIT_OBJECTS + 1];
	HANDLE events[MAXIMUM_WAIT_OBJECTS + 1];
	WaitObjectFunc *func[MAXIMUM_WAIT_OBJECTS + 1];
	void *opaque[MAXIMUM_WAIT_OBJECTS + 1];
	} WaitObjects;

	static WaitObjects wait_objects = {0};

	int qemu_add_wait_object(HANDLE handle, WaitObjectFunc func, void opaque)
	{
	WaitObjects *w = &wait_objects;
	if (w->num >= MAXIMUM_WAIT_OBJECTS) {
	return -1;
	}
	w->events[w->num] = handle;
	w->func[w->num] = func;
	w->opaque[w->num] = opaque;
	w->revents[w->num] = 0;
	w->num++;
	return 0;
	}

	void qemu_del_wait_object(HANDLE handle, WaitObjectFunc func, void opaque)
	{
	int i, found;
	WaitObjects *w = &wait_objects;

	found = 0;
	for (i = 0; i < w->num; i++) {
	if (w->events[i] == handle) {
	found = 1;
	}
	if (found) {
	w->events[i] = w->events[i + 1];
	w->func[i] = w->func[i + 1];
	w->opaque[i] = w->opaque[i + 1];
	w->revents[i] = w->revents[i + 1];
	}
	}
	if (found) {
	w->num--;
	}
	}

	void qemu_fd_register(int fd)
	{
	WSAEventSelect(fd, event_notifier_get_handle(&qemu_aio_context->notifier),
	FD_READ \| FD_ACCEPT \| FD_CLOSE \|
	FD_CONNECT \| FD_WRITE \| FD_OOB);
	}

	static int pollfds_fill(GArray pollfds, fd_set rfds, fd_set *wfds,
	fd_set *xfds)
	{
	int nfds = -1;
	int i;

	for (i = 0; i < pollfds->len; i++) {
	GPollFD *pfd = &g_array_index(pollfds, GPollFD, i);
	int fd = pfd->fd;
	int events = pfd->events;
	if (events & G_IO_IN) {
	FD_SET(fd, rfds);
	nfds = MAX(nfds, fd);
	}
	if (events & G_IO_OUT) {
	FD_SET(fd, wfds);
	nfds = MAX(nfds, fd);
	}
	if (events & G_IO_PRI) {
	FD_SET(fd, xfds);
	nfds = MAX(nfds, fd);
	}
	}
	return nfds;
	}

	static void pollfds_poll(GArray pollfds, int nfds, fd_set rfds,
	fd_set wfds, fd_set xfds)
	{
	int i;

	for (i = 0; i < pollfds->len; i++) {
	GPollFD *pfd = &g_array_index(pollfds, GPollFD, i);
	int fd = pfd->fd;
	int revents = 0;

	if (FD_ISSET(fd, rfds)) {
	revents \|= G_IO_IN;
	}
	if (FD_ISSET(fd, wfds)) {
	revents \|= G_IO_OUT;
	}
	if (FD_ISSET(fd, xfds)) {
	revents \|= G_IO_PRI;
	}
	pfd->revents = revents & pfd->events;
	}
	}

	static int os_host_main_loop_wait(int64_t timeout)
	{
	GMainContext *context = g_main_context_default();
	GPollFD poll_fds[1024 * 2]; /* this is probably overkill */
	int select_ret = 0;
	int g_poll_ret, ret, i, n_poll_fds;
	PollingEntry *pe;
	WaitObjects *w = &wait_objects;
	gint poll_timeout;
	int64_t poll_timeout_ns;
	static struct timeval tv0;
	fd_set rfds, wfds, xfds;
	int nfds;

	/* XXX: need to suppress polling by better using win32 events */
	ret = 0;
	for (pe = first_polling_entry; pe != NULL; pe = pe->next) {
	ret \|= pe->func(pe->opaque);
	}
	if (ret != 0) {
	return ret;
	}

	FD_ZERO(&rfds);
	FD_ZERO(&wfds);
	FD_ZERO(&xfds);
	nfds = pollfds_fill(gpollfds, &rfds, &wfds, &xfds);
	if (nfds >= 0) {
	select_ret = select(nfds + 1, &rfds, &wfds, &xfds, &tv0);
	if (select_ret != 0) {
	timeout = 0;
	}
	if (select_ret > 0) {
	pollfds_poll(gpollfds, nfds, &rfds, &wfds, &xfds);
	}
	}

	g_main_context_prepare(context, &max_priority);
	n_poll_fds = g_main_context_query(context, max_priority, &poll_timeout,
	poll_fds, ARRAY_SIZE(poll_fds));
	g_assert(n_poll_fds <= ARRAY_SIZE(poll_fds));

	for (i = 0; i < w->num; i++) {
	poll_fds[n_poll_fds + i].fd = (DWORD_PTR)w->events[i];
	poll_fds[n_poll_fds + i].events = G_IO_IN;
	}

	if (poll_timeout < 0) {
	poll_timeout_ns = -1;
	} else {
	poll_timeout_ns = (int64_t)poll_timeout * (int64_t)SCALE_MS;
	}

	poll_timeout_ns = qemu_soonest_timeout(poll_timeout_ns, timeout);

	qemu_mutex_unlock_iothread();
	g_poll_ret = qemu_poll_ns(poll_fds, n_poll_fds + w->num, poll_timeout_ns);

	qemu_mutex_lock_iothread();
	if (g_poll_ret > 0) {
	for (i = 0; i < w->num; i++) {
	w->revents[i] = poll_fds[n_poll_fds + i].revents;
	}
	for (i = 0; i < w->num; i++) {
	if (w->revents[i] && w->func[i]) {
	w->func[i](w->opaque[i]);
	}
	}
	}

	if (g_main_context_check(context, max_priority, poll_fds, n_poll_fds)) {
	g_main_context_dispatch(context);
	}

	return select_ret \|\| g_poll_ret;
	}
	#endif

	int main_loop_wait(int nonblocking)
	{
	int ret;
	uint32_t timeout = UINT32_MAX;
	int64_t timeout_ns;

	if (nonblocking) {
	timeout = 0;
	}

	/* poll any events */
	g_array_set_size(gpollfds, 0); /* reset for new iteration */
	/* XXX: separate device handlers from system ones */
	#ifdef CONFIG_SLIRP
	slirp_pollfds_fill(gpollfds, &timeout);
	#endif

	if (timeout == UINT32_MAX) {
	timeout_ns = -1;
	} else {
	timeout_ns = (uint64_t)timeout * (int64_t)(SCALE_MS);
	}

	timeout_ns = qemu_soonest_timeout(timeout_ns,
	timerlistgroup_deadline_ns(
	&main_loop_tlg));

	ret = os_host_main_loop_wait(timeout_ns);
	#ifdef CONFIG_SLIRP
	slirp_pollfds_poll(gpollfds, (ret < 0));
	#endif

	/* CPU thread can infinitely wait for event after
	missing the warp */
	qemu_start_warp_timer();
	qemu_clock_run_all_timers();

	return ret;
	}

	/* Functions to operate on the main QEMU AioContext. */

	QEMUBH qemu_bh_new(QEMUBHFunc cb, void *opaque)
	{
	return aio_bh_new(qemu_aio_context, cb, opaque);
	}