Re: [Xen-devel] Is the hotplug/udev stuff worth the troubles?

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 4 Dec 2005, at 13:57, Michael Holzt wrote:

> There is nothing
> changing in my setup during this, so why do i need hotplug? Now, i 
> don't
> know why you have opted to use hotplug in Xen 3. Maybe it has big
> advantages which i fail to see. Maybe someone who knows can explain
> why hotplug is needed.
Main reason is for dynamic creation of virtual devices. The best 
example is that every guest network interface needs a 'backend' virtual 
interface to be created in domain0, and that needs to be configured 
after creation. The callback for userspace to do that setup (e.g., 
attach to a bridge) is via hotplug. In 2.0 the config (attach to bridge 
xen-br0) was hardcoded in the kernel. Which is a nice simple solution 
but hardly flexible.
For simple setups that really don't want to be running full 
hotplug/udev scripts perhaps a solution is to hijack the hotplug 
callback utility -- e.g., install a very simple script or even C 
program, point /proc/sys/kernel/hotplug at it, and implement fairly 
'dumb' setup policies in there. It's probably less effort to just get 
hotplug running though. :-)
 -- Keir


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