Locking of the qemuMonitorPtr object

In preparation of the monitor I/O process becoming fully asynchronous,
it is neccessary to ensure all access to internals of the qemuMonitorPtr
object is protected by a mutex lock.

* src/qemu/qemu_monitor.c, src/qemu/qemu_monitor.h: Add mutex for locking
  monitor.
* src/qemu/qemu_driver.c: Add locking around all monitor commands

src/qemu/qemu_monitor.c

@@ -39,6 +39,8 @@
 #define VIR_FROM_THIS VIR_FROM_QEMU
 
 struct _qemuMonitor {
+    virMutex lock;
+
     int fd;
     int watch;
     int hasSendFD;
@@ -49,6 +51,16 @@ struct _qemuMonitor {
     qemuMonitorDiskSecretLookup secretCB;
 };
 
+void qemuMonitorLock(qemuMonitorPtr mon)
+{
+    virMutexLock(&mon->lock);
+}
+
+void qemuMonitorUnlock(qemuMonitorPtr mon)
+{
+    virMutexUnlock(&mon->lock);
+}
+
 /* Return -1 for error, 1 to continue reading and 0 for success */
 typedef int qemuMonitorHandleOutput(virDomainObjPtr vm,
                                     const char *output);
@@ -292,6 +304,12 @@ qemuMonitorOpen(virDomainObjPtr vm,
         return NULL;
     }
 
+    if (virMutexInit(&mon->lock) < 0) {
+        qemudReportError(NULL, NULL, NULL, VIR_ERR_INTERNAL_ERROR, "%s",
+                         _("cannot initialize monitor mutex"));
+        VIR_FREE(mon);
+        return NULL;
+    }
     mon->fd = -1;
     mon->vm = vm;
     mon->eofCB = eofCB;
@@ -343,6 +361,7 @@ void qemuMonitorClose(qemuMonitorPtr mon)
 
     if (mon->fd != -1)
         close(mon->fd);
+    virMutexDestroy(&mon->lock);
     VIR_FREE(mon);
 }
 

src/qemu/qemu_monitor.h

@@ -54,6 +54,9 @@ qemuMonitorPtr qemuMonitorOpen(virDomainObjPtr vm,
 
 void qemuMonitorClose(qemuMonitorPtr mon);
 
+void qemuMonitorLock(qemuMonitorPtr mon);
+void qemuMonitorUnlock(qemuMonitorPtr mon);
+
 void qemuMonitorRegisterDiskSecretLookup(qemuMonitorPtr mon,
                                          qemuMonitorDiskSecretLookup secretCB);