qemu: block: Extract logic decision when to use a separate 'raw' layer for slice

Introduce qemuBlockStorageSourceNeedsStorageSliceLayer which will hold
the decision logic and fix all places that open-code it.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>

src/qemu/qemu_block.c

@@ -1446,8 +1446,7 @@ qemuBlockStorageSourceGetBlockdevProps(virStorageSourcePtr src,
     g_autoptr(virJSONValue) props = NULL;
     const char *storagenode = src->nodestorage;
 
-    if (src->sliceStorage &&
-        src->format != VIR_STORAGE_FILE_RAW)
+    if (qemuBlockStorageSourceNeedsStorageSliceLayer(src))
         storagenode = src->sliceStorage->nodename;
 
     if (!(props = qemuBlockStorageSourceGetBlockdevFormatProps(src)))
@@ -1568,7 +1567,7 @@ qemuBlockStorageSourceAttachPrepareBlockdev(virStorageSourcePtr src,
     data->storageNodeName = src->nodestorage;
     data->formatNodeName = src->nodeformat;
 
-    if (src->sliceStorage && src->format != VIR_STORAGE_FILE_RAW) {
+    if (qemuBlockStorageSourceNeedsStorageSliceLayer(src)) {
         if (!(data->storageSliceProps = qemuBlockStorageSourceGetBlockdevStorageSliceProps(src)))
             return NULL;
 
@@ -3308,3 +3307,22 @@ qemuBlockReopenReadOnly(virDomainObjPtr vm,
 
     return 0;
 }
+
+/**
+ * qemuBlockStorageSourceNeedSliceLayer:
+ * @src: source to inspect
+ *
+ * Returns true if @src requires an extra 'raw' layer for handling of the storage
+ * slice.
+ */
+bool
+qemuBlockStorageSourceNeedsStorageSliceLayer(const virStorageSource *src)
+{
+    if (!src->sliceStorage)
+        return false;
+
+    if (src->format != VIR_STORAGE_FILE_RAW)
+        return true;
+
+    return false;
+}

src/qemu/qemu_block.h

@@ -254,3 +254,6 @@ int
 qemuBlockReopenReadOnly(virDomainObjPtr vm,
                         virStorageSourcePtr src,
                         qemuDomainAsyncJob asyncJob);
+
+bool
+qemuBlockStorageSourceNeedsStorageSliceLayer(const virStorageSource *src);

src/qemu/qemu_domain.c

@@ -16591,8 +16591,7 @@ qemuDomainPrepareStorageSourceBlockdev(virDomainDiskDefPtr disk,
     src->nodestorage = g_strdup_printf("libvirt-%u-storage", src->id);
     src->nodeformat = g_strdup_printf("libvirt-%u-format", src->id);
 
-    if (src->sliceStorage &&
-        src->format != VIR_STORAGE_FILE_RAW)
+    if (qemuBlockStorageSourceNeedsStorageSliceLayer(src))
         src->sliceStorage->nodename = g_strdup_printf("libvirt-%u-slice-sto", src->id);
 
     if (qemuDomainValidateStorageSource(src, priv->qemuCaps) < 0)