qemuDomainChangeDiskLive: rework slightly

Firstly, our coding guidelines suggest using 'cleanup' label
instead of 'end'. Then, @ret should be set to value representing
success as the last statement before the 'cleanup' label.
And while I am at this function, lets enumerate all the possible
enum items (virDomainDiskDevice) and avoid using 'default' in
switch(). Pooh. Also, nothing bad happens if we look up the disk
to change in the domain upfront. In fact, it's going to be
helpful later when we want to keep some old values for performing
a rollback.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

src/qemu/qemu_driver.c

@@ -7907,48 +7907,54 @@ qemuDomainChangeDiskLive(virConnectPtr conn,
     int ret = -1;
 
     if (virStorageTranslateDiskSourcePool(conn, disk) < 0)
-        goto end;
+        goto cleanup;
 
     if (qemuDomainDetermineDiskChain(driver, vm, disk, false, true) < 0)
-        goto end;
+        goto cleanup;
 
-    switch (disk->device) {
+    if (!(orig_disk = virDomainDiskFindByBusAndDst(vm->def,
+                                                   disk->bus, disk->dst))) {
+        virReportError(VIR_ERR_INTERNAL_ERROR,
+                       _("No device with bus '%s' and target '%s'"),
+                       virDomainDiskBusTypeToString(disk->bus),
+                       disk->dst);
+        goto cleanup;
+    }
+
+    switch ((virDomainDiskDevice) disk->device) {
     case VIR_DOMAIN_DISK_DEVICE_CDROM:
     case VIR_DOMAIN_DISK_DEVICE_FLOPPY:
-        if (!(orig_disk = virDomainDiskFindByBusAndDst(vm->def,
-                                                       disk->bus, disk->dst))) {
-            virReportError(VIR_ERR_INTERNAL_ERROR,
-                           _("No device with bus '%s' and target '%s'"),
-                           virDomainDiskBusTypeToString(disk->bus),
-                           disk->dst);
-            goto end;
-        }
-
         if (!virDomainDiskDiffersSourceOnly(disk, orig_disk))
-            goto end;
+            goto cleanup;
 
         /* Add the new disk src into shared disk hash table */
         if (qemuAddSharedDevice(driver, dev, vm->def->name) < 0)
-            goto end;
+            goto cleanup;
 
         if (qemuDomainChangeEjectableMedia(driver, conn, vm,
-                                           orig_disk, dev->data.disk->src, force) < 0) {
-            ignore_value(qemuRemoveSharedDisk(driver, dev->data.disk, vm->def->name));
-            goto end;
+                                           orig_disk, disk->src, force) < 0) {
+            ignore_value(qemuRemoveSharedDisk(driver, disk, vm->def->name));
+            goto cleanup;
         }
 
-        dev->data.disk->src = NULL;
-        ret = 0;
+        disk->src = NULL;
         break;
 
-    default:
+    case VIR_DOMAIN_DISK_DEVICE_DISK:
+    case VIR_DOMAIN_DISK_DEVICE_LUN:
         virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
                        _("disk bus '%s' cannot be updated."),
                        virDomainDiskBusTypeToString(disk->bus));
+        goto cleanup;
+        break;
+
+    case VIR_DOMAIN_DISK_DEVICE_LAST:
+        /* nada */
         break;
     }
 
- end:
+    ret = 0;
+ cleanup:
     return ret;
 }