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Re: [Xen-devel] Stubdom and blktap

To: "Yang, Xiaowei" <xiaowei.yang@xxxxxxxxx>
Subject: Re: [Xen-devel] Stubdom and blktap
From: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
Date: Mon, 29 Sep 2008 12:31:34 +0100
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Yang, Xiaowei wrote:

> Recently we had a try of stubdom, whose general status is good.
> One issue we found is with aio/sync blktap as backend, disk performance
> is obviously slower, and there are some IDE kernel error messages (like
> irq timeout) at boot time.

I'll try to reproduce the problem, thanks for reporting it.

> Another issue (not stubdom specific) comes from blktap's support for
> QCOW image which is based on a backing file. We never tried this
> configure before. The root cause is that in tdqcow_get_parent_id(), the
> backing file is hard-coded to be QCOW type and tdqcow_validate_parent()
> also presumes it, though the backing file is a raw image normally. With
> the image type set correctly and a good method for image validation,
> QCOW works.

I am not sure to understand what the issue is exactly: there is no image
format guessing using blktap, the user is supposed to specify correctly
the format in the VM configuration file.

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