qemu: Defer support checks for external active snapshots to blockdev code or qemu

Remove libvirt's support check for the target of an external snapshot to
the blockdev code or qemu. This will potentially require a more complex
cleanup but removes a level of hardcoded feature checks.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>

src/qemu/qemu_driver.c

@@ -14917,7 +14917,8 @@ qemuDomainSnapshotPrepareDiskExternalInactive(virDomainSnapshotDiskDefPtr snapdi
 
 static int
 qemuDomainSnapshotPrepareDiskExternalActive(virDomainSnapshotDiskDefPtr snapdisk,
-                                            virDomainDiskDefPtr domdisk)
+                                            virDomainDiskDefPtr domdisk,
+                                            bool blockdev)
 {
     int actualType = virStorageSourceGetActualType(snapdisk->src);
 
@@ -14934,6 +14935,10 @@ qemuDomainSnapshotPrepareDiskExternalActive(virDomainSnapshotDiskDefPtr snapdisk
         break;
 
     case VIR_STORAGE_TYPE_NETWORK:
+        /* defer all of the checking to either qemu or libvirt's blockdev code */
+        if (blockdev)
+            break;
+
         switch ((virStorageNetProtocol) snapdisk->src->protocol) {
         case VIR_STORAGE_NET_PROTOCOL_GLUSTER:
             break;
@@ -14981,7 +14986,8 @@ static int
 qemuDomainSnapshotPrepareDiskExternal(virDomainDiskDefPtr disk,
                                       virDomainSnapshotDiskDefPtr snapdisk,
                                       bool active,
-                                      bool reuse)
+                                      bool reuse,
+                                      bool blockdev)
 {
     struct stat st;
     int err;
@@ -15004,7 +15010,7 @@ qemuDomainSnapshotPrepareDiskExternal(virDomainDiskDefPtr disk,
         if (qemuDomainSnapshotPrepareDiskExternalInactive(snapdisk, disk) < 0)
             return -1;
     } else {
-        if (qemuDomainSnapshotPrepareDiskExternalActive(snapdisk, disk) < 0)
+        if (qemuDomainSnapshotPrepareDiskExternalActive(snapdisk, disk, blockdev) < 0)
             return -1;
     }
 
@@ -15105,6 +15111,8 @@ qemuDomainSnapshotPrepare(virDomainObjPtr vm,
                           virDomainSnapshotDefPtr def,
                           unsigned int *flags)
 {
+    qemuDomainObjPrivatePtr priv = vm->privateData;
+    bool blockdev = virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_BLOCKDEV);
     int ret = -1;
     size_t i;
     bool active = virDomainObjIsActive(vm);
@@ -15163,7 +15171,7 @@ qemuDomainSnapshotPrepare(virDomainObjPtr vm,
             }
 
             if (qemuDomainSnapshotPrepareDiskExternal(dom_disk, disk,
-                                                      active, reuse) < 0)
+                                                      active, reuse, blockdev) < 0)
                 goto cleanup;
 
             external++;