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Re: [Qemu-devel] [PATCH v3 0/2] block: allow flush on devices with open

From: Paolo Bonzini
Subject: Re: [Qemu-devel] [PATCH v3 0/2] block: allow flush on devices with open tray
Date: Fri, 16 Sep 2016 02:10:16 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.2.0

On 16/09/2016 02:09, John Snow wrote:
> On 09/15/2016 08:06 PM, Paolo Bonzini wrote:
>> On 16/09/2016 01:42, John Snow wrote:
>>> One more try.
>>> The move to blk_flush altered the behavior of migration and flushing
>>> nodes that are not reachable via the guest, but are still reachable
>>> via QEMU and may or may not need to be flushed.
>>> This is likely the simplest solution for now until we nail down our
>>> policy a bit more.
>>> This is intended for 2.6.2 and/or 2.7.1, to fix problems with libvirt
>>> et al being unable to migrate QEMU when the CDROM tray is open.
>>> v3:
>>>  Trying to take a hint from Kevin, reinstating bdrv_flush_all.
>>>  If it's not what we want, we can try moving back to v2,
>>>  acknowledging that a nicer solution in the future:
>>>  (A) Can skip flushing on devices that just don't need it, and
>>>  (B) Optionally institutes some sort of flush-on-eject policy.
>> If you move flushing from platform_fixed_ioport_writew's blk_flush_all
>> to blk_flush calls in pci_piix3_xen_ide_unplug, you can get rid of
>> blk_flush_all completely.
> I assume you mean in addition to re-adding bdrv_flush_all for the sake
> of vm_stop, we can also get rid of blk_flush_all from xen and avoid the
> duplication?

Yep.  Devices really should not use the *_all() variants.


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