Re: [Xen-devel] tap interfce in xen

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> frnds,  i am confuse regarding the role of tap interface and its handling
> within Xen from developer perspective. Can anyboyd useful insights or
> usefuill links about it.

I'm not sure which interface you mean, so I'll cover both possibilities:

There's the Linux tun / tap network interface.  This allows a userspace 
process to create a virtual network device.  This is used by the Qemu-based 
device model in order to supply emulated network services for HVM virtual 
machines.

There's also the blktap interface.  This is used to provide some forms of 
virtual disk storage for domains: currently supported are file-based storage 
and the QCow copy-on-write format.  This should work for HVM or paravirt 
domains (although I've heard conflicting reports about how well it works for 
HVM at the moment).  Blktap is implemented by allowing a userspace process to 
satisfy the virtual IO requests from the guests; the userspace blocktap 
process is then able to issue the appropriate IOs on the guest's behalf.

There's also a device mapper plugin called dm-userspace that offers some 
similar functionality to blktap.  I'm not sure what the status of this is 
right now, though.

Hope that helps you some,
Cheers,
Mark

-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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