Re: [Xen-devel] Network questions

[Mark Williamson <Mark.Williamson@xxxxxxxxxxxx>]

Are you using Xen 1.2 or unstable?  There have been big changes to networking 
in the unstable tree.  In my previous e-mail I was describing the current 
state of the unstable tree.

The old IO world: (as used by Xen 1.2 and as described in the SOSP paper)
* Device drivers for physical network devices are in Xen.
* All domains (including 0) use a "virtual" network driver, which talks to 
Xen.  Xen then routes packets between domains or out onto the physical network.
* VIRQ_NET is the IRQ associated with a virtual network device.  Xen uses it 
to signal a domain when it has been sent data by another domain or from the 
physical network.
* There's no "backend", just Xen.

The new IO world: (as used by the Unstable tree and the forthcoming 2.0 
release)
* Xen does not contain device drivers anymore.
* Instead, the device drivers for physical devices run in domains.  Usually, 
all the drivers for your hardware run in dom0.
* A domain that's controlling physical devices can export virtual devices to 
other domains.  The driver which exports a device to other domains is called 
the "backend".
* The driver which imports a virtual device from the backend is called the 
"frontend".  This driver runs in unprivileged domains to give them their 
virtual devices.  It's a lot like the old (1.2) virtual network interface 
driver except that it talks to another domain instead of to Xen.
* VIRQ_NET does not exist anymore.  Instead, the backend driver (in the domain 
that controls the hardware) can send an interrupt to the frontend driver (in 
the domain using the virtual devices) using the event channel mechanism I 
described in my last e-mail.

Does that make sense?

Mark



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