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

From: John Snow
Subject: Re: [Qemu-devel] [PATCH v3 0/2] block: allow flush on devices with open tray
Date: Thu, 15 Sep 2016 20:09:20 -0400
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.2.0

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.

 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?

I can follow up with that if Max and Kevin agree to what I've already posted.


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