qemu_monitor_json: add support to search QOM device path by device alias

Commit ce745914 introduced detection of actual video ram sizes to fix migration
if QEMU decide to modify the values provided by libvirt.  This works perfectly
for domains with number of video devices up to two.

If there are more than two video devices in the guest all the secondary devices
in the XML will have the same memory values.  This is because our current code
search for QOM device path only by the device type name and all the secondary
video devices has the same name "qxl".

This patch introduces a new search function that will try to search a QOM device
path using also device's alias if the alias is available. After that it will
fallback to the old recursive code if the alias search found no results.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1358728Signed-off-by: NPavel Hrdina <phrdina@redhat.com>

src/qemu/qemu_monitor.c

@@ -1084,10 +1084,11 @@ qemuMonitorInitBalloonObjectPath(qemuMonitorPtr mon)
     }
     mon->ballooninit = true;
 
-    flp_ret = qemuMonitorJSONFindLinkPath(mon, "virtio-balloon-pci", &path);
+    flp_ret = qemuMonitorJSONFindLinkPath(mon, "virtio-balloon-pci", NULL, &path);
     if (flp_ret == -2) {
         /* pci object was not found retry search for ccw object */
-        if (qemuMonitorJSONFindLinkPath(mon, "virtio-balloon-ccw", &path) < 0)
+        if (qemuMonitorJSONFindLinkPath(mon, "virtio-balloon-ccw",
+                                        NULL, &path) < 0)
             return;
     } else if (flp_ret < 0) {
         return;
@@ -1138,7 +1139,8 @@ qemuMonitorUpdateVideoMemorySize(qemuMonitorPtr mon,
     QEMU_CHECK_MONITOR(mon);
 
     if (mon->json) {
-        ret = qemuMonitorJSONFindLinkPath(mon, videoName, &path);
+        ret = qemuMonitorJSONFindLinkPath(mon, videoName,
+                                          video->info.alias, &path);
         if (ret < 0) {
             if (ret == -2)
                 virReportError(VIR_ERR_INTERNAL_ERROR,
@@ -1173,7 +1175,8 @@ qemuMonitorUpdateVideoVram64Size(qemuMonitorPtr mon,
     QEMU_CHECK_MONITOR(mon);
 
     if (mon->json) {
-        ret = qemuMonitorJSONFindLinkPath(mon, videoName, &path);
+        ret = qemuMonitorJSONFindLinkPath(mon, videoName,
+                                          video->info.alias, &path);
         if (ret < 0) {
             if (ret == -2)
                 virReportError(VIR_ERR_INTERNAL_ERROR,

src/qemu/qemu_monitor_json.c

@@ -6810,7 +6810,58 @@ qemuMonitorJSONGetMemoryDeviceInfo(qemuMonitorPtr mon,
 
 
 /**
- * Recursively search for a QOM object link.
+ * Search for a QOM object link by alias and name.
+ *
+ * For @alias and @name, this function tries to find QOM object named @name
+ * with id @alias in /machine/peripheral.
+ *
+ * Returns:
+ *   0  - Found
+ *  -1  - Error - bail out
+ *  -2  - Not found
+ */
+static int
+qemuMonitorJSONFindObjectPathByAlias(qemuMonitorPtr mon,
+                                     const char *name,
+                                     const char *alias,
+                                     char **path)
+{
+    qemuMonitorJSONListPathPtr *paths = NULL;
+    char *child = NULL;
+    int npaths;
+    int ret = -1;
+    size_t i;
+
+    npaths = qemuMonitorJSONGetObjectListPaths(mon, "/machine/peripheral", &paths);
+    if (npaths < 0)
+        return -1;
+
+    if (virAsprintf(&child, "child<%s>", name) < 0)
+        goto cleanup;
+
+    for (i = 0; i < npaths; i++) {
+        if (STREQ(paths[i]->name, alias) && STREQ(paths[i]->type, child)) {
+            if (virAsprintf(path, "/machine/peripheral/%s", alias) < 0)
+                goto cleanup;
+
+            ret = 0;
+            goto cleanup;
+        }
+    }
+
+    ret = -2;
+
+ cleanup:
+    for (i = 0; i < npaths; i++)
+        qemuMonitorJSONListPathFree(paths[i]);
+    VIR_FREE(paths);
+    VIR_FREE(child);
+    return ret;
+}
+
+
+/**
+ * Recursively search for a QOM object link only by name.
  *
  * For @name, this function finds the first QOM object
  * named @name, recursively going through all the "child<>"
@@ -6822,10 +6873,10 @@ qemuMonitorJSONGetMemoryDeviceInfo(qemuMonitorPtr mon,
  *  -2  - Not found
  */
 static int
-qemuMonitorJSONFindObjectPath(qemuMonitorPtr mon,
-                              const char *curpath,
-                              const char *name,
-                              char **path)
+qemuMonitorJSONFindObjectPathByName(qemuMonitorPtr mon,
+                                    const char *curpath,
+                                    const char *name,
+                                    char **path)
 {
     ssize_t i, npaths = 0;
     int ret = -2;
@@ -6859,7 +6910,7 @@ qemuMonitorJSONFindObjectPath(qemuMonitorPtr mon,
                 goto cleanup;
             }
 
-            ret = qemuMonitorJSONFindObjectPath(mon, nextpath, name, path);
+            ret = qemuMonitorJSONFindObjectPathByName(mon, nextpath, name, path);
             VIR_FREE(nextpath);
         }
     }
@@ -6876,8 +6927,9 @@ qemuMonitorJSONFindObjectPath(qemuMonitorPtr mon,
 /**
  * Recursively search for a QOM object link.
  *
- * For @name, this function finds the first QOM object
- * pointed to by a link in the form of 'link<@name>'
+ * For @name and @alias, this function finds the first QOM object.
+ * The search is done at first by @alias and @name and if nothing was found
+ * it continues recursively only with @name.
  *
  * Returns:
  *   0  - Found
@@ -6887,15 +6939,22 @@ qemuMonitorJSONFindObjectPath(qemuMonitorPtr mon,
 int
 qemuMonitorJSONFindLinkPath(qemuMonitorPtr mon,
                             const char *name,
+                            const char *alias,
                             char **path)
 {
     char *linkname = NULL;
     int ret = -1;
 
+    if (alias) {
+        ret = qemuMonitorJSONFindObjectPathByAlias(mon, name, alias, path);
+        if (ret == -1 || ret == 0)
+            return ret;
+    }
+
     if (virAsprintf(&linkname, "link<%s>", name) < 0)
         return -1;
 
-    ret = qemuMonitorJSONFindObjectPath(mon, "/", linkname, path);
+    ret = qemuMonitorJSONFindObjectPathByName(mon, "/", linkname, path);
     VIR_FREE(linkname);
     return ret;
 }

src/qemu/qemu_monitor_json.h

@@ -477,8 +477,9 @@ int qemuMonitorJSONGetMemoryDeviceInfo(qemuMonitorPtr mon,
 
 int qemuMonitorJSONFindLinkPath(qemuMonitorPtr mon,
                                 const char *name,
+                                const char *alias,
                                 char **path)
-    ATTRIBUTE_NONNULL(1) ATTRIBUTE_NONNULL(2) ATTRIBUTE_NONNULL(3);
+    ATTRIBUTE_NONNULL(1) ATTRIBUTE_NONNULL(2) ATTRIBUTE_NONNULL(4);
 
 int qemuMonitorJSONMigrateIncoming(qemuMonitorPtr mon,
                                    const char *uri)