/dev/hda is the Xen Virtual Block Device Driver that talks to the idealised IO interface exported by Xen. It doesn't implement the HDIO ioctls because they're not really relevant (it's not an IDE hard disk). The communication is via shared memory, so is high performance.

As to whether Xen is using DMA with your hardware, you'll need to take a look at the boot messages as Xen comes up. One of the items on our todo list is to make those messages available from domain0 after boot, but for now, they only flash by on the VGA console unless you've attached a serial line.

Best, Ian

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