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[Xen-devel] Direct IO or dom0 kernel cache

In some mail which was sent to someone else,  you wrote:
file: uses dom0 kernel page cache, and thus might give better performance than phy: or tap:aio:, but it's also more insecure because of the caching.
tap:aio: uses direct IO, so it bypasses dom0 kernel caches, and works like phy: in that sense.

Thus here I come to refer to you.I have two questions:
1.What is difference between tap:qcow2 and tap2:tapdisk:qcow2?
2.Does tap:qcow2: and tap2:tapdisk:qcow2 use direct IO and bypass dom0 kernel caches?
3.If a qcow2 format image is based on a raw format image and this qcow2 format image is configured with "tap:qcow2" or "tap2:tapdisk:qcow2" , Does the VM created by this qcow2 format image use direct IO and bypass dom0 kernel caches?
Thank you for any response~

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