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-common.h"
 #include "qemu-timer.h"
 #include "slirp/slirp.h"
 #include "main-loop.h"

 #ifndef _WIN32

 #include "compatfd.h"

 static int io_thread_fd = -1;

 void qemu_notify_event(void)
 {
     /* Write 8 bytes to be compatible with eventfd.  */
     static const uint64_t val = 1;
     ssize_t ret;

     if (io_thread_fd == -1) {
         return;
     }
     do {
         ret = write(io_thread_fd, &val, sizeof(val));
     } while (ret < 0 && errno == EINTR);

     /* EAGAIN is fine, a read must be pending.  */
     if (ret < 0 && errno != EAGAIN) {
         fprintf(stderr, "qemu_notify_event: write() failed: %s\n",
                 strerror(errno));
         exit(1);
     }
 }

 static void qemu_event_read(void *opaque)
 {
     int fd = (intptr_t)opaque;
     ssize_t len;
     char buffer[512];

     /* Drain the notify pipe.  For eventfd, only 8 bytes will be read.  */
     do {
         len = read(fd, buffer, sizeof(buffer));
     } while ((len == -1 && errno == EINTR) || len == sizeof(buffer));
 }

 static int qemu_event_init(void)
 {
     int err;
     int fds[2];

     err = qemu_eventfd(fds);
     if (err == -1) {
         return -errno;
     }
     err = fcntl_setfl(fds[0], O_NONBLOCK);
     if (err < 0) {
         goto fail;
     }
     err = fcntl_setfl(fds[1], O_NONBLOCK);
     if (err < 0) {
         goto fail;
     }
     qemu_set_fd_handler2(fds[0], NULL, qemu_event_read, NULL,
                          (void *)(intptr_t)fds[0]);

     io_thread_fd = fds[1];
     return 0;

 fail:
     close(fds[0]);
     close(fds[1]);
     return err;
 }

 /* 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);
     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_handler2(sigfd, NULL, sigfd_handler, NULL,
                          (void *)(intptr_t)sigfd);

     return 0;
 }

 #else /* _WIN32 */

 static HANDLE qemu_event_handle = NULL;

 static void dummy_event_handler(void *opaque)
 {
 }

 static int qemu_event_init(void)
 {
     qemu_event_handle = CreateEvent(NULL, FALSE, FALSE, NULL);
     if (!qemu_event_handle) {
         fprintf(stderr, "Failed CreateEvent: %ld\n", GetLastError());
         return -1;
     }
     qemu_add_wait_object(qemu_event_handle, dummy_event_handler, NULL);
     return 0;
 }

 void qemu_notify_event(void)
 {
     if (!qemu_event_handle) {
         return;
     }
     if (!SetEvent(qemu_event_handle)) {
         fprintf(stderr, "qemu_notify_event: SetEvent failed: %ld\n",
                 GetLastError());
         exit(1);
     }
 }

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

 int main_loop_init(void)
 {
     int ret;

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

     /* Note eventfd must be drained before signalfd handlers run */
     ret = qemu_event_init();
     if (ret) {
         return ret;
     }

     return 0;
 }

 static fd_set rfds, wfds, xfds;
 static int nfds;
 static GPollFD poll_fds[1024 * 2]; /* this is probably overkill */
 static int n_poll_fds;
 static int max_priority;

 #ifndef _WIN32
 static void glib_select_fill(int *max_fd, fd_set *rfds, fd_set *wfds,
                              fd_set *xfds, uint32_t *cur_timeout)
 {
     GMainContext *context = g_main_context_default();
     int i;
     int timeout = 0;

     g_main_context_prepare(context, &max_priority);

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

     for (i = 0; i < n_poll_fds; i++) {
         GPollFD *p = &poll_fds[i];

         if ((p->events & G_IO_IN)) {
             FD_SET(p->fd, rfds);
             *max_fd = MAX(*max_fd, p->fd);
         }
         if ((p->events & G_IO_OUT)) {
             FD_SET(p->fd, wfds);
             *max_fd = MAX(*max_fd, p->fd);
         }
         if ((p->events & G_IO_ERR)) {
             FD_SET(p->fd, xfds);
             *max_fd = MAX(*max_fd, p->fd);
         }
     }

     if (timeout >= 0 && timeout < *cur_timeout) {
         *cur_timeout = timeout;
     }
 }

 static void glib_select_poll(fd_set *rfds, fd_set *wfds, fd_set *xfds,
                              bool err)
 {
     GMainContext *context = g_main_context_default();

     if (!err) {
         int i;

         for (i = 0; i < n_poll_fds; i++) {
             GPollFD *p = &poll_fds[i];

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

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

 static int os_host_main_loop_wait(uint32_t timeout)
 {
     struct timeval tv, *tvarg = NULL;
     int ret;

     glib_select_fill(&nfds, &rfds, &wfds, &xfds, &timeout);

     if (timeout < UINT32_MAX) {
         tvarg = &tv;
         tv.tv_sec = timeout / 1000;
         tv.tv_usec = (timeout % 1000) * 1000;
     }

     if (timeout > 0) {
         qemu_mutex_unlock_iothread();
     }

     ret = select(nfds + 1, &rfds, &wfds, &xfds, tvarg);

     if (timeout > 0) {
         qemu_mutex_lock_iothread();
     }

     glib_select_poll(&rfds, &wfds, &xfds, (ret < 0));
     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, qemu_event_handle, FD_READ | FD_ACCEPT | FD_CLOSE |
                    FD_CONNECT | FD_WRITE | FD_OOB);
 }

 static int os_host_main_loop_wait(uint32_t timeout)
 {
     GMainContext *context = g_main_context_default();
     int ret, i;
     PollingEntry *pe;
     WaitObjects *w = &wait_objects;
     gint poll_timeout;
     static struct timeval tv0;

     /* 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;
     }

     if (nfds >= 0) {
         ret = select(nfds + 1, &rfds, &wfds, &xfds, &tv0);
         if (ret != 0) {
             timeout = 0;
         }
     }

     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 || timeout < poll_timeout) {
         poll_timeout = timeout;
     }

     qemu_mutex_unlock_iothread();
     ret = g_poll(poll_fds, n_poll_fds + w->num, poll_timeout);
     qemu_mutex_lock_iothread();
     if (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);
     }

     /* If an edge-triggered socket event occurred, select will return a
      * positive result on the next iteration.  We do not need to do anything
      * here.
      */

     return ret;
 }
 #endif

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

     if (nonblocking) {
         timeout = 0;
     } else {
         qemu_bh_update_timeout(&timeout);
     }

     /* poll any events */
     /* XXX: separate device handlers from system ones */
     nfds = -1;
     FD_ZERO(&rfds);
     FD_ZERO(&wfds);
     FD_ZERO(&xfds);

 #ifdef CONFIG_SLIRP
     slirp_update_timeout(&timeout);
     slirp_select_fill(&nfds, &rfds, &wfds, &xfds);
 #endif
     qemu_iohandler_fill(&nfds, &rfds, &wfds, &xfds);
     ret = os_host_main_loop_wait(timeout);
     qemu_iohandler_poll(&rfds, &wfds, &xfds, ret);
 #ifdef CONFIG_SLIRP
     slirp_select_poll(&rfds, &wfds, &xfds, (ret < 0));
 #endif

     qemu_run_all_timers();

     /* Check bottom-halves last in case any of the earlier events triggered
        them.  */
     qemu_bh_poll();

     return ret;
 }
	/*
	* 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-common.h"
	#include "qemu-timer.h"
	#include "slirp/slirp.h"
	#include "main-loop.h"

	#ifndef _WIN32

	#include "compatfd.h"

	static int io_thread_fd = -1;

	void qemu_notify_event(void)
	{
	/* Write 8 bytes to be compatible with eventfd. */
	static const uint64_t val = 1;
	ssize_t ret;

	if (io_thread_fd == -1) {
	return;
	}
	do {
	ret = write(io_thread_fd, &val, sizeof(val));
	} while (ret < 0 && errno == EINTR);

	/* EAGAIN is fine, a read must be pending. */
	if (ret < 0 && errno != EAGAIN) {
	fprintf(stderr, "qemu_notify_event: write() failed: %s\n",
	strerror(errno));
	exit(1);
	}
	}

	static void qemu_event_read(void *opaque)
	{
	int fd = (intptr_t)opaque;
	ssize_t len;
	char buffer[512];

	/* Drain the notify pipe. For eventfd, only 8 bytes will be read. */
	do {
	len = read(fd, buffer, sizeof(buffer));
	} while ((len == -1 && errno == EINTR) \|\| len == sizeof(buffer));
	}

	static int qemu_event_init(void)
	{
	int err;
	int fds[2];

	err = qemu_eventfd(fds);
	if (err == -1) {
	return -errno;
	}
	err = fcntl_setfl(fds[0], O_NONBLOCK);
	if (err < 0) {
	goto fail;
	}
	err = fcntl_setfl(fds[1], O_NONBLOCK);
	if (err < 0) {
	goto fail;
	}
	qemu_set_fd_handler2(fds[0], NULL, qemu_event_read, NULL,
	(void *)(intptr_t)fds[0]);

	io_thread_fd = fds[1];
	return 0;

	fail:
	close(fds[0]);
	close(fds[1]);
	return err;
	}

	/* 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);
	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_handler2(sigfd, NULL, sigfd_handler, NULL,
	(void *)(intptr_t)sigfd);

	return 0;
	}

	#else /* _WIN32 */

	static HANDLE qemu_event_handle = NULL;

	static void dummy_event_handler(void *opaque)
	{
	}

	static int qemu_event_init(void)
	{
	qemu_event_handle = CreateEvent(NULL, FALSE, FALSE, NULL);
	if (!qemu_event_handle) {
	fprintf(stderr, "Failed CreateEvent: %ld\n", GetLastError());
	return -1;
	}
	qemu_add_wait_object(qemu_event_handle, dummy_event_handler, NULL);
	return 0;
	}

	void qemu_notify_event(void)
	{
	if (!qemu_event_handle) {
	return;
	}
	if (!SetEvent(qemu_event_handle)) {
	fprintf(stderr, "qemu_notify_event: SetEvent failed: %ld\n",
	GetLastError());
	exit(1);
	}
	}

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

	int main_loop_init(void)
	{
	int ret;

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

	/* Note eventfd must be drained before signalfd handlers run */
	ret = qemu_event_init();
	if (ret) {
	return ret;
	}

	return 0;
	}

	static fd_set rfds, wfds, xfds;
	static int nfds;
	static GPollFD poll_fds[1024 * 2]; /* this is probably overkill */
	static int n_poll_fds;
	static int max_priority;

	#ifndef _WIN32
	static void glib_select_fill(int max_fd, fd_set rfds, fd_set *wfds,
	fd_set xfds, uint32_t cur_timeout)
	{
	GMainContext *context = g_main_context_default();
	int i;
	int timeout = 0;

	g_main_context_prepare(context, &max_priority);

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

	for (i = 0; i < n_poll_fds; i++) {
	GPollFD *p = &poll_fds[i];

	if ((p->events & G_IO_IN)) {
	FD_SET(p->fd, rfds);
	max_fd = MAX(max_fd, p->fd);
	}
	if ((p->events & G_IO_OUT)) {
	FD_SET(p->fd, wfds);
	max_fd = MAX(max_fd, p->fd);
	}
	if ((p->events & G_IO_ERR)) {
	FD_SET(p->fd, xfds);
	max_fd = MAX(max_fd, p->fd);
	}
	}

	if (timeout >= 0 && timeout < *cur_timeout) {
	*cur_timeout = timeout;
	}
	}

	static void glib_select_poll(fd_set rfds, fd_set wfds, fd_set *xfds,
	bool err)
	{
	GMainContext *context = g_main_context_default();

	if (!err) {
	int i;

	for (i = 0; i < n_poll_fds; i++) {
	GPollFD *p = &poll_fds[i];

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

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

	static int os_host_main_loop_wait(uint32_t timeout)
	{
	struct timeval tv, *tvarg = NULL;
	int ret;

	glib_select_fill(&nfds, &rfds, &wfds, &xfds, &timeout);

	if (timeout < UINT32_MAX) {
	tvarg = &tv;
	tv.tv_sec = timeout / 1000;
	tv.tv_usec = (timeout % 1000) * 1000;
	}

	if (timeout > 0) {
	qemu_mutex_unlock_iothread();
	}

	ret = select(nfds + 1, &rfds, &wfds, &xfds, tvarg);

	if (timeout > 0) {
	qemu_mutex_lock_iothread();
	}

	glib_select_poll(&rfds, &wfds, &xfds, (ret < 0));
	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, qemu_event_handle, FD_READ \| FD_ACCEPT \| FD_CLOSE \|
	FD_CONNECT \| FD_WRITE \| FD_OOB);
	}

	static int os_host_main_loop_wait(uint32_t timeout)
	{
	GMainContext *context = g_main_context_default();
	int ret, i;
	PollingEntry *pe;
	WaitObjects *w = &wait_objects;
	gint poll_timeout;
	static struct timeval tv0;

	/* 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;
	}

	if (nfds >= 0) {
	ret = select(nfds + 1, &rfds, &wfds, &xfds, &tv0);
	if (ret != 0) {
	timeout = 0;
	}
	}

	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 \|\| timeout < poll_timeout) {
	poll_timeout = timeout;
	}

	qemu_mutex_unlock_iothread();
	ret = g_poll(poll_fds, n_poll_fds + w->num, poll_timeout);
	qemu_mutex_lock_iothread();
	if (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);
	}

	/* If an edge-triggered socket event occurred, select will return a
	* positive result on the next iteration. We do not need to do anything
	* here.
	*/

	return ret;
	}
	#endif

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

	if (nonblocking) {
	timeout = 0;
	} else {
	qemu_bh_update_timeout(&timeout);
	}

	/* poll any events */
	/* XXX: separate device handlers from system ones */
	nfds = -1;
	FD_ZERO(&rfds);
	FD_ZERO(&wfds);
	FD_ZERO(&xfds);

	#ifdef CONFIG_SLIRP
	slirp_update_timeout(&timeout);
	slirp_select_fill(&nfds, &rfds, &wfds, &xfds);
	#endif
	qemu_iohandler_fill(&nfds, &rfds, &wfds, &xfds);
	ret = os_host_main_loop_wait(timeout);
	qemu_iohandler_poll(&rfds, &wfds, &xfds, ret);
	#ifdef CONFIG_SLIRP
	slirp_select_poll(&rfds, &wfds, &xfds, (ret < 0));
	#endif

	qemu_run_all_timers();

	/* Check bottom-halves last in case any of the earlier events triggered
	them. */
	qemu_bh_poll();

	return ret;
	}