qemu_agent: Issue guest-sync prior to every command

If we issue guest command and GA is not running, the issuing thread
will block endlessly. We can check for GA presence by issuing
guest-sync with unique ID (timestamp). We don't want to issue real
command as even if GA is not running, once it is started, it process
all commands written to GA socket.

src/qemu/qemu_agent.c

@@ -39,6 +39,7 @@
 #include "virterror_internal.h"
 #include "json.h"
 #include "virfile.h"
+#include "virtime.h"
 
 #define VIR_FROM_THIS VIR_FROM_QEMU
 
@@ -316,6 +317,7 @@ qemuAgentIOProcessLine(qemuAgentPtr mon,
 {
     virJSONValuePtr obj = NULL;
     int ret = -1;
+    unsigned long long id;
 
     VIR_DEBUG("Line [%s]", line);
 
@@ -340,6 +342,20 @@ qemuAgentIOProcessLine(qemuAgentPtr mon,
             obj = NULL;
             ret = 0;
         } else {
+            /* If we've received something like:
+             *  {"return": 1234}
+             * it is likely that somebody started GA
+             * which is now processing our previous
+             * guest-sync commands. Check if this is
+             * the case and don't report an error but
+             * return silently.
+             */
+            if (virJSONValueObjectGetNumberUlong(obj, "return", &id) == 0) {
+                VIR_DEBUG("Ignoring delayed reply to guest-sync: %llu", id);
+                ret = 0;
+                goto cleanup;
+            }
+
             qemuReportError(VIR_ERR_INTERNAL_ERROR,
                             _("Unexpected JSON reply '%s'"), line);
         }
@@ -813,11 +829,28 @@ void qemuAgentClose(qemuAgentPtr mon)
         qemuAgentUnlock(mon);
 }
 
+#define QEMU_AGENT_WAIT_TIME (1000ull * 5)
 
+/**
+ * qemuAgentSend:
+ * @mon: Monitor
+ * @msg: Message
+ * @timeout: use timeout?
+ *
+ * Send @msg to agent @mon.
+ * Wait max QEMU_AGENT_WAIT_TIME for agent
+ * to reply.
+ *
+ * Returns: 0 on success,
+ *          -2 on timeout,
+ *          -1 otherwise
+ */
 static int qemuAgentSend(qemuAgentPtr mon,
-                         qemuAgentMessagePtr msg)
+                         qemuAgentMessagePtr msg,
+                         bool timeout)
 {
     int ret = -1;
+    unsigned long long now, then = 0;
 
     /* Check whether qemu quit unexpectedly */
     if (mon->lastError.code != VIR_ERR_OK) {
@@ -827,13 +860,26 @@ static int qemuAgentSend(qemuAgentPtr mon,
         return -1;
     }
 
+    if (timeout) {
+        if (virTimeMillisNow(&now) < 0)
+            return -1;
+        then = now + QEMU_AGENT_WAIT_TIME;
+    }
+
     mon->msg = msg;
     qemuAgentUpdateWatch(mon);
 
     while (!mon->msg->finished) {
-        if (virCondWait(&mon->notify, &mon->lock) < 0) {
+        if ((timeout && virCondWaitUntil(&mon->notify, &mon->lock, then) < 0) ||
+            (!timeout && virCondWait(&mon->notify, &mon->lock) < 0)) {
+            if (errno == ETIMEDOUT) {
+                qemuReportError(VIR_ERR_INTERNAL_ERROR, "%s",
+                                _("Guest agent not available for now"));
+                ret = -2;
+            } else {
                 qemuReportError(VIR_ERR_INTERNAL_ERROR, "%s",
                                 _("Unable to wait on monitor condition"));
+            }
             goto cleanup;
         }
     }
@@ -855,6 +901,78 @@ cleanup:
 }
 
 
+/**
+ * qemuAgentGuestSync:
+ * @mon: Monitor
+ *
+ * Send guest-sync with unique ID
+ * and wait for reply. If we get one, check if
+ * received ID is equal to given.
+ *
+ * Returns: 0 on success,
+ *          -1 otherwise
+ */
+static int
+qemuAgentGuestSync(qemuAgentPtr mon)
+{
+    int ret = -1;
+    int send_ret;
+    unsigned long long id, id_ret;
+    qemuAgentMessage sync_msg;
+
+    memset(&sync_msg, 0, sizeof(sync_msg));
+
+    if (virTimeMillisNow(&id) < 0)
+        return -1;
+
+    if (virAsprintf(&sync_msg.txBuffer,
+                    "{\"execute\":\"guest-sync\", "
+                    "\"arguments\":{\"id\":%llu}}", id) < 0) {
+        virReportOOMError();
+        return -1;
+    }
+
+    sync_msg.txLength = strlen(sync_msg.txBuffer);
+
+    VIR_DEBUG("Sending guest-sync command with ID: %llu", id);
+
+    send_ret = qemuAgentSend(mon, &sync_msg, true);
+
+    VIR_DEBUG("qemuAgentSend returned: %d", send_ret);
+
+    if (send_ret < 0) {
+        /* error reported */
+        goto cleanup;
+    }
+
+    if (!sync_msg.rxObject) {
+        qemuReportError(VIR_ERR_INTERNAL_ERROR, "%s",
+                        _("Missing monitor reply object"));
+        goto cleanup;
+    }
+
+    if (virJSONValueObjectGetNumberUlong(sync_msg.rxObject,
+                                         "return", &id_ret) < 0) {
+        qemuReportError(VIR_ERR_INTERNAL_ERROR, "%s",
+                        _("Malformed return value"));
+        goto cleanup;
+    }
+
+    VIR_DEBUG("Guest returned ID: %llu", id_ret);
+    if (id_ret != id) {
+        qemuReportError(VIR_ERR_INTERNAL_ERROR,
+                        _("Guest agent returned ID: %llu instead of %llu"),
+                        id_ret, id);
+        goto cleanup;
+    }
+    ret = 0;
+
+cleanup:
+    virJSONValueFree(sync_msg.rxObject);
+    VIR_FREE(sync_msg.txBuffer);
+    return ret;
+}
+
 static int
 qemuAgentCommand(qemuAgentPtr mon,
                  virJSONValuePtr cmd,
@@ -866,6 +984,11 @@ qemuAgentCommand(qemuAgentPtr mon,
 
     *reply = NULL;
 
+    if (qemuAgentGuestSync(mon) < 0) {
+        /* helper reported the error */
+        return -1;
+    }
+
     memset(&msg, 0, sizeof(msg));
 
     if (!(cmdstr = virJSONValueToString(cmd))) {
@@ -880,12 +1003,11 @@ qemuAgentCommand(qemuAgentPtr mon,
 
     VIR_DEBUG("Send command '%s' for write", cmdstr);
 
-    ret = qemuAgentSend(mon, &msg);
+    ret = qemuAgentSend(mon, &msg, false);
 
     VIR_DEBUG("Receive command reply ret=%d rxObject=%p",
               ret, msg.rxObject);
 
-
     if (ret == 0) {
         if (!msg.rxObject) {
             qemuReportError(VIR_ERR_INTERNAL_ERROR, "%s",