[libvirt] Documentation for synchronous hooks

Daniel Veillard veillard at redhat.com
Mon Apr 12 15:16:27 UTC 2010

Was still missing from main commits and would be needed for 0.8.0

Add documentation for synchronous hooks

* docs/sitemap.html.in: add in navigation under
* docs/hooks.html.in: new doc describing current support for 0.8.0

diff --git a/docs/hooks.html.in b/docs/hooks.html.in
new file mode 100644
index 0000000..4ebeec3
--- /dev/null
+++ b/docs/hooks.html.in
@@ -0,0 +1,71 @@
+<?xml version="1.0"?>
+  <body>
+    <h1>Hooks for specific system management</h1>
+    <p>Libvirt includes synchronous hooks starting from version 0.8.0,
+       this is a way to tie specific tailored system actions at specific
+       time. This is based on scripts being called on the Host where the
+       hypervisor is running, if the script is present when the libvirtd
+       daemon is doing some significant actions.</p>
+    <p>The scripts are expected to execute quickly, return a zero exit
+       status if all conditions are set for the daemon to continue the
+       action (non zero will be considered a failure which may
+       be ignored but in general will stops the ongoing operation).
+       The script also should not call back into libvirt as the daemon
+       is waiting for the script exit and deadlock is likely to occur
+       otherwise.</p>
+    <p>The scripts are stored in the directory <code>/etc/libvirt/hooks/</code>
+       when using a standard installation path
+       (<code>$SYSCONF_DIR/libvirt/hook/</code> in general).</p>
+    <p>The scripts gets arguments as parameter on their command line:</p>
+       <ul>
+         <li> the first argument is the name of the object involved in the
+              operation or '-' if there is none.
+         <li> the second argument is the name of the operation.
+         <li> the third argument is a suboperation indication like 'start'
+              'end' or '-' if there is none.
+         <li> the last argument is an extra argument string or '-' if there
+              is none.
+       </ul>
+    <p>There is currently scripts for 3 domains of operation:
+    <ul>
+      <li><p><code>/etc/libvirt/hooks/daemon</code> script if
+          present is called at 3 points in time:</p>
+          <p>at daemon startup, typically started with the following
+             arguments:</p>
+                <pre>/etc/libvirt/hooks/daemon - start - start</pre>
+            <p>at daemon shutdown when it is about to exit, with the following
+                arguments:</p>
+                <pre>/etc/libvirt/hooks/daemon - shutdown - shutdown</pre>
+            <p>When the daemon is asked to reload its driver state when
+                receiving the SIGHUP signal, arguments are:</p>
+                <pre>/etc/libvirt/hooks/daemon - reload begin SIGHUP</pre>
+          </li>
+      <li><p><code>/etc/libvirt/hooks/qemu</code> script and <br/>
+             <code>/etc/libvirt/hooks/lxc</code> to associate hooks for domain
+             operation on the respective QEmu/KVM and LXC drivers.</p>
+          <p> The domain related hooks also receive the full XML description
+              for the concerned domain on their stdin, which allows to get
+              all the informations from the domain, including UUID or storage
+              if that is needed for the script operation.</p>
+          <p> Currently only domain startup and domain end operations
+              involve the hook, the first one just before the domain gets
+              created.
+              For example if starting a QEmu domain named <code>test</code>
+              the following script will get called:</p>
+              <pre>/etc/libvirt/hooks/qemu test start begin -</pre>
+          <p> note that a non-zero return value from the script will abort the
+              domain startup operation, and if an error string is passed on
+              stderr by the hook script, it will be provided back to the user
+              at the libvirt API level.</p>
+          <p> For domain shutdown, the script will be called just after the
+              domain has finished execution, and the script will get:</p>
+              <pre>/etc/libvirt/hooks/qemu test stopped end -</pre>
+          <p> It is expected that other operation will be associated to hooks
+              but at the time of 0.8.0 only those 2 are associated to domains
+              lifecycle</p>
+          </li>
+    </ul>
+    <p></p>
+  </body>
diff --git a/docs/sitemap.html.in b/docs/sitemap.html.in
index 0c3f0c3..0117c8d 100644
--- a/docs/sitemap.html.in
+++ b/docs/sitemap.html.in
@@ -50,6 +50,10 @@
                 <a href="logging.html">Logging</a>
                 <span>The library and the daemon logging support</span>
+              <li>
+                <a href="hooks.html">Hooks</a>
+                <span>Hooks for system specific management</span>
+              </li>

Daniel Veillard      | libxml Gnome XML XSLT toolkit  http://xmlsoft.org/
daniel at veillard.com  | Rpmfind RPM search engine http://rpmfind.net/
http://veillard.com/ | virtualization library  http://libvirt.org/

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