note the possibility of rebootless resizes

howto/ganeti.md

@@ -392,6 +392,9 @@ with resizes, because it's not possible to revert such a change:
 `grow-disk` does support shrinking disks. The only way to revert the
 change is by exporting / importing the instance.
 
+Note the reboot, above, will impose a downtime. See [upstream bug
+28](https://github.com/ganeti/ganeti/issues/28) about improving that.
+
 Then the filesystem needs to be resized inside the VM:
 
     ssh root@test1.torproject.org 
@@ -1393,6 +1396,26 @@ can consider reading the following:
  * [Tutorials](https://docs.openvswitch.org/en/latest/tutorials/index.html_)
  * [Debugging Open vSwitch slides](https://www.openvswitch.org/support/slides/OVS-Debugging-110414.pdf)
 
+## Accessing the QEMU control ports
+
+There is a magic warp zone on the node where an instance is running:
+
+```
+nc -U /var/run/ganeti/kvm-hypervisor/ctrl/$INSTANCE.monitor
+```
+
+This drops you in the [QEMU monitor](https://people.redhat.com/pbonzini/qemu-test-doc/_build/html/topics/pcsys_005fmonitor.html) which can do all sorts of
+things including adding/removing devices, save/restore the VM state,
+pause/resume the VM, do screenshots, etc.
+
+There are many sockets in the `ctrl` directory, including:
+
+ * `.serial`: the instance's serial port
+ * `.monitor`: the QEMU monitor control port
+ * `.qmp`: the same, but with a JSON interface that I can't figure out
+   (the `-qmp` argument to `qemu`)
+ * `.kvmd`: same as the above?
+
 ## Pager playbook
 
 ### I/O overload