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[Qemu-devel] Re: QCOW2 bugs releated to qcow2_aio_cancel()
From: |
Kevin Wolf |
Subject: |
[Qemu-devel] Re: QCOW2 bugs releated to qcow2_aio_cancel() |
Date: |
Thu, 03 Feb 2011 18:44:28 +0100 |
User-agent: |
Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.15) Gecko/20101027 Fedora/3.0.10-1.fc12 Thunderbird/3.0.10 |
Am 03.02.2011 18:21, schrieb Chunqiang Tang:
> Hi Kevin,
>
> Fast Virtual Disk (FVD) has an automated testing tool (see
> http://wiki.qemu.org/Features/FVD/Engineering). For a long time, I knew
> that QCOW2 could not pass the automated tests. Today I finally sit down to
> look into those bugs. I already submitted multiple patches for different
> bugs, but there is one case that I am not certain how to handle. Instead
> of creating a potentially broken patch, I though you might be able to
> handle it better than me. Bugs showed up when the testing tool injected
> aio cancel.
We have discussed this before and yes, aio_cancel is a problem. It is
very hard to do this correctly, and so most block drivers just wait for
completion instead of actually cancelling anything.
Given that a cancel shouldn't happen too often, I think it would be
reasonable to take the same approach for qcow2. I don't think adding a
lot of complexity for getting this right is justified.
Stefan, what do you think? Maybe we could even have a default
implementation in generic block code?
Kevin