qemu: hotplug: Prepare for multiple backing chain member hotplug

Similarly to how we've intergrated data belonging to a single
virStorageSource for purposes of attaching it to a qemu instance we will
need to agregate data relevant for the whole disk. With blockdev there
will be some disk-wide backing chain members such as the copy-on-read
handler.

Introduce qemuHotplugDiskSourceData which agregates the backing chain
and other data relevant for the disk and functions which generate it
and apply and rollback it.

In addition to disk hotplug this will also be reused for media changing
where we need to exchange the full disk backend.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>

src/qemu/qemu_hotplug.c

@@ -350,6 +350,110 @@ qemuDomainDiskAttachManagedPR(virDomainObjPtr vm,
 }
 
 
+struct _qemuHotplugDiskSourceData {
+    qemuBlockStorageSourceAttachDataPtr *backends;
+    size_t nbackends;
+};
+typedef struct _qemuHotplugDiskSourceData qemuHotplugDiskSourceData;
+typedef qemuHotplugDiskSourceData *qemuHotplugDiskSourceDataPtr;
+
+
+static void
+qemuHotplugDiskSourceDataFree(qemuHotplugDiskSourceDataPtr data)
+{
+    size_t i;
+
+    if (!data)
+        return;
+
+    for (i = 0; i < data->nbackends; i++)
+        qemuBlockStorageSourceAttachDataFree(data->backends[i]);
+
+    VIR_FREE(data);
+}
+
+
+/**
+ * qemuHotplugDiskSourceAttachPrepare:
+ * @disk: disk to generate attachment data for
+ * @qemuCaps: capabilities of the qemu process
+ *
+ * Prepares and returns qemuHotplugDiskSourceData structure filled with all data
+ * which will fully attach the source backend of the disk to a given VM.
+ */
+static qemuHotplugDiskSourceDataPtr
+qemuHotplugDiskSourceAttachPrepare(virDomainDiskDefPtr disk,
+                                   virQEMUCapsPtr qemuCaps)
+{
+    qemuBlockStorageSourceAttachDataPtr backend;
+    qemuHotplugDiskSourceDataPtr data;
+    qemuHotplugDiskSourceDataPtr ret = NULL;
+
+    if (VIR_ALLOC(data) < 0)
+        return NULL;
+
+    if (!(backend = qemuBuildStorageSourceAttachPrepareDrive(disk, qemuCaps, false)))
+        goto cleanup;
+
+    if (qemuBuildStorageSourceAttachPrepareCommon(disk->src, backend, qemuCaps) < 0)
+        goto cleanup;
+
+    if (VIR_APPEND_ELEMENT(data->backends, data->nbackends, backend) < 0)
+        goto cleanup;
+
+    VIR_STEAL_PTR(ret, data);
+
+ cleanup:
+    qemuBlockStorageSourceAttachDataFree(backend);
+    qemuHotplugDiskSourceDataFree(data);
+    return ret;
+}
+
+
+/**
+ * qemuHotplugDiskSourceAttach:
+ * @mon: monitor object
+ * @data: disk backend data object describing what to remove
+ *
+ * Attach a disk source backend with all relevant pieces. Caller must enter the
+ * monitor context for @mon.
+ */
+static int
+qemuHotplugDiskSourceAttach(qemuMonitorPtr mon,
+                            qemuHotplugDiskSourceDataPtr data)
+{
+    size_t i;
+
+    for (i = data->nbackends; i > 0; i--) {
+        if (qemuBlockStorageSourceAttachApply(mon, data->backends[i - 1]) < 0)
+            return -1;
+    }
+
+    return 0;
+}
+
+
+/**
+ * qemuHotplugDiskSourceRemove:
+ * @mon: monitor object
+ * @data: disk backend data object describing what to remove
+ *
+ * Remove a disk source backend with all relevant pieces. This function
+ * preserves the error which was set prior to calling it. Caller must enter the
+ * monitor context for @mon.
+ */
+static void
+qemuHotplugDiskSourceRemove(qemuMonitorPtr mon,
+                            qemuHotplugDiskSourceDataPtr data)
+
+{
+    size_t i;
+
+    for (i = 0; i < data->nbackends; i++)
+        qemuBlockStorageSourceAttachRollback(mon, data->backends[i]);
+}
+
+
 /**
  * qemuDomainAttachDiskGeneric:
  *
@@ -362,7 +466,7 @@ qemuDomainAttachDiskGeneric(virQEMUDriverPtr driver,
 {
     int ret = -1;
     qemuDomainObjPrivatePtr priv = vm->privateData;
-    qemuBlockStorageSourceAttachDataPtr data = NULL;
+    qemuHotplugDiskSourceDataPtr diskdata = NULL;
     virErrorPtr orig_err;
     char *devstr = NULL;
     char *managedPrmgrAlias = NULL;
@@ -381,11 +485,7 @@ qemuDomainAttachDiskGeneric(virQEMUDriverPtr driver,
     if (qemuDomainDiskAttachManagedPR(vm, disk, &managedPrmgrProps) < 0)
         goto error;
 
-    if (!(data = qemuBuildStorageSourceAttachPrepareDrive(disk, priv->qemuCaps,
-                                                          false)))
-        goto error;
-
-    if (qemuBuildStorageSourceAttachPrepareCommon(disk->src, data, priv->qemuCaps) < 0)
+    if (!(diskdata = qemuHotplugDiskSourceAttachPrepare(disk, priv->qemuCaps)))
         goto error;
 
     if (!(devstr = qemuBuildDiskDeviceStr(vm->def, disk, 0, priv->qemuCaps)))
@@ -400,7 +500,7 @@ qemuDomainAttachDiskGeneric(virQEMUDriverPtr driver,
         qemuMonitorAddObject(priv->mon, &managedPrmgrProps, &managedPrmgrAlias) < 0)
         goto exit_monitor;
 
-    if (qemuBlockStorageSourceAttachApply(priv->mon, data) < 0)
+    if (qemuHotplugDiskSourceAttach(priv->mon, diskdata) < 0)
         goto exit_monitor;
 
     if (qemuMonitorAddDevice(priv->mon, devstr) < 0)
@@ -417,7 +517,7 @@ qemuDomainAttachDiskGeneric(virQEMUDriverPtr driver,
     ret = 0;
 
  cleanup:
-    qemuBlockStorageSourceAttachDataFree(data);
+    qemuHotplugDiskSourceDataFree(diskdata);
     virJSONValueFree(managedPrmgrProps);
     qemuDomainSecretDiskDestroy(disk);
     VIR_FREE(managedPrmgrAlias);
@@ -426,7 +526,7 @@ qemuDomainAttachDiskGeneric(virQEMUDriverPtr driver,
     return ret;
 
  exit_monitor:
-    qemuBlockStorageSourceAttachRollback(priv->mon, data);
+    qemuHotplugDiskSourceRemove(priv->mon, diskdata);
 
     virErrorPreserveLast(&orig_err);
     if (managedPrmgrAlias)