Split out Xenstore access and delete the 'extensions' page

Signed-off-by: David Scott <[email protected]>

Author: David Scott

_data/navbar.yml

@@ -17,14 +17,14 @@
   - xen-api/overview.md
   - xen-api/usage.md
   - xen-api/http.md
-  - xen-api/extensions.md
   - xen-api/wire-protocol.md
   - xen-api/evolution.md
   - xen-api/vm-lifecycle.md
   - xen-api/snapshots.md
   - xen-api/consoles.md
   - xen-api/install-vms.md
   - xen-api/networking.md
+  - xen-api/guest-agents.md
   - xen-api/xencenter.md
   - xen-api/udhcp.md
   - xen-api/index.html

xen-api/extensions.md

@@ -0,0 +1,26 @@
+---
+title: Guest agents
+layout: default
+---
+
+"Guest agents" are special programs which run inside VMs which can be controlled
+via the XenAPI.
+
+One communication method between XenAPI clients is via Xenstore.
+
+Adding Xenstore entries to VMs
+------------------------------
+
+Developers may wish to install guest agents into VMs which take special action based on the type of the VM. In order to communicate this information into the guest, a special Xenstore name-space known as `vm-data` is available which is populated at VM creation time. It is populated from the `xenstore-data` map in the VM record.
+
+Set the `xenstore-data` parameter in the VM record:
+
+    xe vm-param-set uuid= xenstore-data:vm-data/foo=bar
+
+Start the VM.
+
+If it is a Linux-based VM, install the COMPANY\_TOOLS and use the `xenstore-read` to verify that the node exists in Xenstore.
+
+> **Note**
+>
+> Only prefixes beginning with `vm-data` are permitted, and anything not in this name-space will be silently ignored when starting the VM.