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Re: [Qemu-devel] [PATCH] blockdev: reset werror/rerror on drive_del
From: |
Eric Blake |
Subject: |
Re: [Qemu-devel] [PATCH] blockdev: reset werror/rerror on drive_del |
Date: |
Tue, 04 Jun 2013 13:32:48 -0600 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130514 Thunderbird/17.0.6 |
On 06/04/2013 01:24 PM, Markus Armbruster wrote:
> Paolo Bonzini <address@hidden> writes:
>
>> Il 04/06/2013 18:37, Markus Armbruster ha scritto:
>>> I figure the bit that can't be resolved now is letting the user switch
>>> off "stop on error" safely before a drive_del. Even if we had a command
>>> for that, there'd still be a window between that command's execution and
>>> drive_del's. Your patch solves the problem by having drive_del switch
>>> it off unconditionally. Oookay, but please document it, because it's
>>> not exactly obvious.
>>
>> It is not obvious, but it is not surprising either when you see it (i.e.
>> you won't really be surprised by the errors in the guest and won't need
>> to know that, under the hood, rerror has been changed from the value you
>> specified).
>>
> This is drive_add's documentation in hmp-commands.hx:
>
> Remove host block device. The result is that guest generated IO is
> no longer submitted against the host device underlying the disk.
> Once a drive has been deleted, the QEMU Block layer returns -EIO
> which results in IO errors in the guest for applications that are
> reading/writing to the device.
>
> Suggest to add:
>
> These errors are always reported to the guest, regardless of the
> drive's error actions (drive options rerror, werror).
>
> Independently, libvirt needs fixing.
Total agreement that libvirt needs to use a saner disk hot-unplug
sequence when it is known that qemu provides one. I've filed
https://bugzilla.redhat.com/show_bug.cgi?id=970761
to remind us to fix libvirt.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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Re: [Qemu-devel] [PATCH] blockdev: reset werror/rerror on drive_del, Fam Zheng, 2013/06/05