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[Xen-devel] Re: How is front driver get probed and loaded?

On Fri, Jun 24, 2011 at 9:32 PM, Stefano Stabellini
<stefano.stabellini@xxxxxxxxxxxxx> wrote:
> Xen frontend drivers probing and configuration is all done through
> xenstore. The toolstack writes the initial xenstore entries, then the
> frontend and the backend fill up the rest.
> There is a "state" node on xenstore that identifies in which state the
> frontend and the backend are, where 4 is "connected".

I understand. What I'm missing is that the key to connect frontend and
backend, how do they recognize each other?

For example, if I need VBD support, backend will first write "vbd"
protocol entries in xenstore. Then domU boots. It reads xenstore and
finds "vbd" entries, then it will automatically load xen-blkfront. Is
this right?

> I am not sure whether the existing xenstore protocol is going to help
> you, I would probably try to stay closer to the behaviour of the virtio
> pci protocol instead.

By design this transport layer's behavior resembles virtio pci
protocol. Things written to xenstore are only used to connect fe / be
transport layers. Lots of work is needed for QEMU backend.


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