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Date: Fri, 1 Apr 2016 19:49:53 +0200
From: Olaf Hering <olaf@aepfle.de>
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Subject: Re: [Qemu-devel] [Qemu-block] [PATCH] block: split large discard
 requests from block frontend
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To: Max Reitz <mreitz@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Stefan Hajnoczi <stefanha@redhat.com>, qemu-devel@nongnu.org, qemu-block@nongnu.org

On Fri, Apr 01, Max Reitz wrote:

> In any case, do you have a test case where a guest was able to submit a
> request that led to the overflow error you described in the commit message?

mkfs -t ext4 /dev/sdb1 in a xen guest with qcow2 as backing device.
When I added discard support to libxl I worked with raw images, so I did
not notice this. Not sure why it happens to work in kvm guests. I assume
the frontend driver just works around the qemu bug by limiting its
request size.

Olaf