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Re: [libvirt] Documentation for synchronous hooks



On 04/12/2010 11:16 AM, Daniel Veillard wrote:
> 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
>   Documentation/Deployment/Hooks
> * 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"?>
> +<html>
> +  <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
          ^^^^
          which

> +       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>

This last sentence is probably better worded as something like:

"If these scripts are present on the host where the hypervisor is running,
then they are called when the libvirt daemon is doing some significant action."

> +    <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).
                                         ^^^^^
                                         stop

> +       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>
          ^^^^^^^^^
          s/otherwise//

> +    <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:
                ^^
                are

> +    <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
                                                    ^^
                                                    s/to//

> +             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
                                                                      ^
                                                                      them

> +              all the informations from the domain, including UUID or storage
                         ^^^^^^^^^^^^
                         information

> +              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
                                           ^^^^^^^^^
                                           operations


-- 
Chris Lalancette


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