Re: [Xen-devel] Problem creating a new device type

[Ewan Mellor <ewan@xxxxxxxxxxxxx>]

On Sat, Nov 12, 2005 at 02:53:10PM -0500, John L Griffin wrote:

> Howdy xen folks,
> 
> I am having trouble creating a new device type (e.g., vif, vbd, vtpm).  I 
> call this new device type "meter".
> 
> I'm using an up-to-date xen-unstable tree.  When I start a guest domain 
> (with a "meter" domain configuration option), the startup process hangs 
> for two minutes and produces a "Error: Device 0 (meter) could not be 
> connected. Hotplug scripts not working" message.  The guest domain is then 
> stuck in the "paused" state until I kill it.
> 
> During this, the xenbus successfully probes the backend, and the correct 
> "frontend" and "frontend-id" are available to the backend on the xenbus.
> 
> I've included the "xm log" error and a summary of the files I've modified 
> below.
> 
> My questions are:
> 
> 1. Have I left out modifying a necessary file when creating a new device 
> type?
> 
> 2. Any ideas as to what could be going on that's preventing my new guest 
> domain from starting?

It looks like your driver doesn't use any hotplug scripts.  The code in
DevController expects all drivers to be using hotplug, and to write a node
backend/<deviceClass>/<deviceID>/hotplug-status = connected when the
hotplugging is complete.

If you are not going to use hotplug, then the easiest way to work around this
is to write this node yourself by adding it to the backend dictionary returned
from MeterifController.getDeviceDetails.  This will mean that you have no
check that your device is working, but that sounds like exactly what you want
at the moment.

This check will be changing soon (though not in any major way) so we ought to
be able to accommodate non-hotplug drivers more neatly.

> 3. Once it's working with dom0 as the backend, will it be possible to 
> start my backend in a non-dom0 domain, or is the code not to that point 
> yet?

You lost me completely.  What is it you want to do?

Ewan.

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