Use a pipe to signal pending work for the iothread.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

Index: trunk/qemu-common.h
===================================================================
--- trunk.orig/qemu-common.h
+++ trunk/qemu-common.h
@@ -186,6 +186,8 @@ int cpu_load(QEMUFile *f, void *opaque, 
 /* Force QEMU to stop what it's doing and service IO */
 void qemu_service_io(void);
 
+void main_loop_break(void);
+
 /* Force QEMU to process pending events */
 void qemu_notify_event(void);
 
Index: trunk/vl.c
===================================================================
--- trunk.orig/vl.c
+++ trunk/vl.c
@@ -275,6 +275,8 @@ static QEMUTimer *nographic_timer;
 
 uint8_t qemu_uuid[16];
 
+static int io_thread_fd = -1;
+
 /***********************************************************/
 /* x86 ISA bus support */
 
@@ -3631,6 +3633,55 @@ void qemu_notify_event(void)
      }
 }
 
+void main_loop_break(void)
+{
+    uint64_t value = 1;
+    char buffer[8];
+    size_t offset = 0;
+
+    if (io_thread_fd == -1)
+        return;
+
+    memcpy(buffer, &value, sizeof(value));
+
+    while (offset < 8) {
+        ssize_t len;
+
+        len = write(io_thread_fd, buffer + offset, 8 - offset);
+        if (len == -1 && errno == EINTR)
+            continue;
+
+        if (len <= 0)
+            break;
+
+        offset += len;
+    }
+
+    if (offset != 8)
+        fprintf(stderr, "failed to notify io thread\n");
+}
+
+/* Used to break IO thread out of select */
+static void io_thread_wakeup(void *opaque)
+{
+    int fd = (unsigned long)opaque;
+    char buffer[8];
+    size_t offset = 0;
+
+    while (offset < 8) {
+        ssize_t len;
+
+        len = read(fd, buffer + offset, 8 - offset);
+        if (len == -1 && errno == EINTR)
+            continue;
+
+        if (len <= 0)
+            break;
+
+        offset += len;
+    }
+}
+
 #ifdef _WIN32
 static void host_main_loop_wait(int *timeout)
 {
@@ -3773,6 +3824,20 @@ void main_loop_wait(int timeout)
 
 }
 
+static void setup_iothread_fd(void)
+{
+    int fds[2];
+
+    if (pipe(fds) == -1) {
+        fprintf(stderr, "failed to create iothread pipe");
+        exit(0);
+    }
+
+    qemu_set_fd_handler2(fds[0], NULL, io_thread_wakeup, NULL,
+                         (void *)(unsigned long)fds[0]);
+    io_thread_fd = fds[1];
+}
+
 static int main_loop(void)
 {
     int ret, timeout;