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

[Paolo Bonzini]

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.

Paolo