qemu: snapshot: Restructure control flow to detect errors sooner and work around...

Some compilers aren't happy when an automatically freed variable is used
just to free something (thus it's only assigned in the code):

When compiling qemuSnapshotDelete after recent commits they complain:

../src/qemu/qemu_snapshot.c:3153:61: error: variable 'delData' set but not used [-Werror,-Wunused-but-set-variable]
                g_autoslist(qemuSnapshotDeleteExternalData) delData = NULL;
                                                            ^

To work around the issue we can restructure the code which also has the
following semantic implications:
 - since qemuSnapshotDeleteExternalPrepare does validation we error out
   sooner than attempting to start the VM

 - we read the temporary variable at least in one code path

Fixes: 4a4d89a9252
Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Pavel Hrdina <phrdina@redhat.com>

diff --git a/src/qemu/qemu_snapshot.c b/src/qemu/qemu_snapshot.c
index 32f7011cbe5df1b15fac58ccee0a234de2ba6974..b8416808b32e4a3ee285706a1965ef4f988418b0 100644 (file)
--- a/src/qemu/qemu_snapshot.c
+++ b/src/qemu/qemu_snapshot.c
@@ -3146,12 +3146,13 @@ qemuSnapshotDelete(virDomainObj *vm,
         if (virDomainSnapshotIsExternal(snap) &&
             !(flags & (VIR_DOMAIN_SNAPSHOT_DELETE_CHILDREN |
                        VIR_DOMAIN_SNAPSHOT_DELETE_CHILDREN_ONLY))) {
+            g_autoslist(qemuSnapshotDeleteExternalData) tmpData = NULL;
 
-            externalData = qemuSnapshotDeleteExternalPrepare(vm, snap);
+            /* this also serves as validation whether the snapshot can be deleted */
+            if (!(tmpData = qemuSnapshotDeleteExternalPrepare(vm, snap)))
+                goto endjob;
 
             if (!virDomainObjIsActive(vm)) {
-                g_autoslist(qemuSnapshotDeleteExternalData) delData = NULL;
-
                 if (qemuProcessStart(NULL, driver, vm, NULL, VIR_ASYNC_JOB_SNAPSHOT,
                                      NULL, -1, NULL, NULL,
                                      VIR_NETDEV_VPORT_PROFILE_OP_CREATE,
@@ -3163,20 +3164,19 @@ qemuSnapshotDelete(virDomainObj *vm,
 
                 /* Call the prepare again as some data require that the VM is
                  * running to get everything we need. */
-                delData = g_steal_pointer(&externalData);
-                externalData = qemuSnapshotDeleteExternalPrepare(vm, snap);
+                if (!(externalData = qemuSnapshotDeleteExternalPrepare(vm, snap)))
+                    goto endjob;
             } else {
                 qemuDomainJobPrivate *jobPriv = vm->job->privateData;
 
+                externalData = g_steal_pointer(&tmpData);
+
                 /* If the VM is running we need to indicate that the async snapshot
                  * job is snapshot delete job. */
                 jobPriv->snapshotDelete = true;
 
                 qemuDomainSaveStatus(vm);
             }
-
-            if (!externalData)
-                goto endjob;
         }
     }