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Re: [PATCH 3/3] spapr: Migrate SpaprDrc::unplug_requested
From: |
David Gibson |
Subject: |
Re: [PATCH 3/3] spapr: Migrate SpaprDrc::unplug_requested |
Date: |
Fri, 14 Feb 2020 13:29:00 +1100 |
On Mon, Feb 03, 2020 at 11:36:22PM +0100, Greg Kurz wrote:
> Hot unplugging a device is an asynchronous operation. If the guest is
> migrated after the event was sent but before it could release the
> device with RTAS, the destination QEMU doesn't know about the pending
> unplug operation and doesn't actually remove the device when the guest
> finally releases it. The device
>
> Migrate SpaprDrc::unplug_requested to fix the inconsistency. This is
> done with a subsection that is only sent if an unplug request is
> pending. This allows to preserve migration with older guests in the
> case of a pending hotplug request. This will cause migration to fail
> if the destination can't handle the subsection, but this is better
> than ending with an inconsistency.
>
> Signed-off-by: Greg Kurz <address@hidden>
> ---
> hw/ppc/spapr_drc.c | 27 +++++++++++++++++++++++++--
> 1 file changed, 25 insertions(+), 2 deletions(-)
>
> diff --git a/hw/ppc/spapr_drc.c b/hw/ppc/spapr_drc.c
> index d512ac6e1e7f..6f5cab70fc6b 100644
> --- a/hw/ppc/spapr_drc.c
> +++ b/hw/ppc/spapr_drc.c
> @@ -455,6 +455,22 @@ void spapr_drc_reset(SpaprDrc *drc)
> }
> }
>
> +static bool spapr_drc_unplug_requested_needed(void *opaque)
> +{
> + return spapr_drc_unplug_requested(opaque);
> +}
> +
> +static const VMStateDescription vmstate_spapr_drc_unplug_requested = {
> + .name = "spapr_drc/unplug_requested",
> + .version_id = 1,
> + .minimum_version_id = 1,
> + .needed = spapr_drc_unplug_requested_needed,
> + .fields = (VMStateField []) {
> + VMSTATE_BOOL(unplug_requested, SpaprDrc),
> + VMSTATE_END_OF_LIST()
> + }
> +};
> +
> static bool spapr_drc_needed(void *opaque)
> {
> SpaprDrc *drc = (SpaprDrc *)opaque;
> @@ -467,8 +483,11 @@ static bool spapr_drc_needed(void *opaque)
> /*
> * We need to migrate the state if it's not equal to the expected
> * long-term state, which is the same as the coldplugged initial
> - * state */
> - return !spapr_drc_device_ready(drc);
> + * state, or if an unplug request is pending.
> + */
> + return
> + spapr_drc_unplug_requested_needed(drc) ||
> + !spapr_drc_device_ready(drc);
Hrm. You start the series by splitting spapr_drc_device_ready() from
spapr_drc_needed(). But at this point, I'm pretty sure you've now got
all the callers of spapr_drc_device_ready() doing equivalent logic
about them, so they might as well be one function again. That seems
pretty roundabout.
I don't think the rationale for not using the drc_ready function from
the CAS path really makes sense. It's not just an accident that those
use the same logic - in both cases what we're testing is "Is the DRC
in a state other than that of a default cold-plugged device?".
Changing the name might be sensible, but I still think we want a
common function for the two cases.
> }
>
> static const VMStateDescription vmstate_spapr_drc = {
> @@ -479,6 +498,10 @@ static const VMStateDescription vmstate_spapr_drc = {
> .fields = (VMStateField []) {
> VMSTATE_UINT32(state, SpaprDrc),
> VMSTATE_END_OF_LIST()
> + },
> + .subsections = (const VMStateDescription * []) {
> + &vmstate_spapr_drc_unplug_requested,
> + NULL
> }
> };
>
>
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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