F #5516: Incremental backups not compatible with snapshots

- Qemu will terminate VMs with system snapshots and checkpoints, example:

libvirtd[7446]: internal error: qemu unexpectedly closed the monitor: 2022-12-07T16:06:59.603678Z qemu-kvm-one: Device has active dirty bitmaps.

- Also disk snapshots may render inconsistent bitmaps, example:

'virsh --connect qemu:///system checkpoint-delete 45d76e5f-25fa-416a-97fd-1624380d5e02 one-191-0':   error: Failed to delete checkpoint one-191-0 error: internal error: unable to execute QEMU command 'query-named-block-nodes': Bitmap '' doesn't satisfy the constraints Error preparing disk files

This commits prevents snapshot operations when increment backups are configured, and vice versa.

include/Backups.h

@@ -142,7 +142,7 @@ public:
      */
     bool configured()
     {
-        return config.empty();
+        return !config.empty();
     }
 
     /**

include/VirtualMachine.h

@@ -1602,6 +1602,11 @@ public:
     // ------------------------------------------------------------------------
     // System Snapshot related functions
     // ------------------------------------------------------------------------
+    /**
+     * @return true if VM has system snapshots defined
+     */
+    bool has_snapshots();
+
     /**
      * Creates a new Snapshot attribute, and sets it to ACTIVE=YES
      *

src/rm/RequestManagerVirtualMachine.cc

@@ -2307,6 +2307,17 @@ void VirtualMachineSnapshotCreate::request_execute(
             return;
         }
 
+        auto vm_bck = vm->backups();
+
+        if ( vm_bck.configured() && vm_bck.mode() == Backups::INCREMENT )
+        {
+            att.resp_msg = "Action \"snapshot-create\" is not compatible with "
+                "incremental backups";
+            failure_response(ACTION, att);
+
+            return;
+        }
+
         // get quota deltas
         snap = vm->new_snapshot(name, snap_id);
         snap = snap->clone();
@@ -3080,6 +3091,17 @@ void VirtualMachineDiskSnapshotCreate::request_execute(
             return;
         }
 
+        auto vm_bck = vm->backups();
+
+        if ( vm_bck.configured() && vm_bck.mode() == Backups::INCREMENT )
+        {
+            att.resp_msg = "Action \"disk-snapshot-create\" is not compatible with "
+                "incremental backups";
+            failure_response(ACTION, att);
+
+            return;
+        }
+
         disk = vm->get_disk(did);
 
         if (disk == nullptr)

src/vm/VirtualMachine.cc

@@ -3197,7 +3197,8 @@ int VirtualMachine::updateconf(VirtualMachineTemplate* tmpl, string &err,
     // -------------------------------------------------------------------------
     if ( lcm_state != BACKUP && lcm_state != BACKUP_POWEROFF)
     {
-        bool increment = disks.backup_increment(_backups.do_volatile());
+        bool increment = disks.backup_increment(_backups.do_volatile()) &&
+                            !has_snapshots();
 
         if ( _backups.parse(tmpl, increment, append, err) != 0 )
         {

src/vm/VirtualMachineDisk.cc

@@ -1579,7 +1579,7 @@ bool VirtualMachineDisks::backup_increment(bool do_volatile)
 
         one_util::toupper(format);
 
-        if (format != "QCOW2")
+        if (format != "QCOW2" || disk->has_snapshots())
         {
             return false;
         }

src/vm/VirtualMachineSystemSnapshot.cc

@@ -24,7 +24,17 @@ using namespace std;
 // System Snapshot Interface
 // -----------------------------------------------------------------------------
 // -----------------------------------------------------------------------------
-//
+
+bool VirtualMachine::has_snapshots()
+{
+    vector<VectorAttribute *> snaps;
+
+    return obj_template->get("SNAPSHOT", snaps) > 0;
+}
+
+// -----------------------------------------------------------------------------
+// -----------------------------------------------------------------------------
+
 VectorAttribute* VirtualMachine::new_snapshot(string& name, int& snap_id)
 {
     int num_snaps;