qemu: Add possibility to prepare top image only for attachment via blockdev

qemuBuildStorageSourceChainAttachPrepareBlockdev prepares the full
backing chain for attachment via blockdev. For snapshots we'll need to
prepare one image only as it needs to be plugged on top of the existing
chain.

This patch introduces qemuBuildStorageSourceChainAttachPrepareBlockdevTop
which prepares only @top similarly to the original function by splitting
out the functionality into an internal function so that the API does not
change.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>

src/qemu/qemu_command.c

@@ -11159,16 +11159,10 @@ qemuBuildStorageSourceChainAttachPrepareDrive(virDomainDiskDefPtr disk,
 }
 
 
-/**
- * qemuBuildStorageSourceChainAttachPrepareBlockdev:
- * @top: storage source chain
- * @qemuCaps: qemu capabilities object
- *
- * Prepares qemuBlockStorageSourceChainDataPtr for attaching @top via -blockdev.
- */
-qemuBlockStorageSourceChainDataPtr
-qemuBuildStorageSourceChainAttachPrepareBlockdev(virStorageSourcePtr top,
-                                                 virQEMUCapsPtr qemuCaps)
+static qemuBlockStorageSourceChainDataPtr
+qemuBuildStorageSourceChainAttachPrepareBlockdevInternal(virStorageSourcePtr top,
+                                                         virQEMUCapsPtr qemuCaps,
+                                                         bool onlyTop)
 {
     VIR_AUTOPTR(qemuBlockStorageSourceAttachData) elem = NULL;
     VIR_AUTOPTR(qemuBlockStorageSourceChainData) data = NULL;
@@ -11186,7 +11180,44 @@ qemuBuildStorageSourceChainAttachPrepareBlockdev(virStorageSourcePtr top,
 
         if (VIR_APPEND_ELEMENT(data->srcdata, data->nsrcdata, elem) < 0)
             return NULL;
+
+        if (onlyTop)
+            break;
     }
 
     VIR_RETURN_PTR(data);
 }
+
+
+/**
+ * qemuBuildStorageSourceChainAttachPrepareBlockdev:
+ * @top: storage source chain
+ * @qemuCaps: qemu capabilities object
+ *
+ * Prepares qemuBlockStorageSourceChainDataPtr for attaching the chain of images
+ * starting at @top via -blockdev.
+ */
+qemuBlockStorageSourceChainDataPtr
+qemuBuildStorageSourceChainAttachPrepareBlockdev(virStorageSourcePtr top,
+                                                 virQEMUCapsPtr qemuCaps)
+{
+    return qemuBuildStorageSourceChainAttachPrepareBlockdevInternal(top, qemuCaps,
+                                                                    false);
+}
+
+
+/**
+ * qemuBuildStorageSourceChainAttachPrepareBlockdevTop:
+ * @top: storage source chain
+ * @qemuCaps: qemu capabilities object
+ *
+ * Prepares qemuBlockStorageSourceChainDataPtr for attaching of @top image only
+ * via -blockdev.
+ */
+qemuBlockStorageSourceChainDataPtr
+qemuBuildStorageSourceChainAttachPrepareBlockdevTop(virStorageSourcePtr top,
+                                                    virQEMUCapsPtr qemuCaps)
+{
+    return qemuBuildStorageSourceChainAttachPrepareBlockdevInternal(top, qemuCaps,
+                                                                    true);
+}

src/qemu/qemu_command.h

@@ -117,6 +117,9 @@ qemuBlockStorageSourceChainDataPtr
 qemuBuildStorageSourceChainAttachPrepareBlockdev(virStorageSourcePtr top,
                                                  virQEMUCapsPtr qemuCaps);
 
+qemuBlockStorageSourceChainDataPtr
+qemuBuildStorageSourceChainAttachPrepareBlockdevTop(virStorageSourcePtr top,
+                                                    virQEMUCapsPtr qemuCaps);
 
 char
 *qemuBuildDiskDeviceStr(const virDomainDef *def,