Re: [libvirt] [PATCH 1/3] conf: Reposition adding SCSI controller for SCSI hostdev hotplug
On 12/02/2015 01:16 AM, John Ferlan wrote:
On 11/30/2015 06:05 AM, Boris Fiuczynski wrote:
[...]
> diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c
> index cbfc41e..69cfd0f 100644
> --- a/src/conf/domain_conf.c
> +++ b/src/conf/domain_conf.c
> @@ -16285,6 +16285,9 @@ virDomainDefParseXML(xmlDocPtr xml,
> }
>
> def->hostdevs[def->nhostdevs++] = hostdev;
> +
> + if (virDomainDefMaybeAddHostdevSCSIcontroller(def) < 0)
> + goto error;
> }
> VIR_FREE(nodes);
>
>
After some more experimentation and making sure my debug environment was
"up to date" (e.g. had virtlogd started)...
Using top of tree I can hotplug a hostdev as long as it has a drive
address defined. Not sure why it was failing before, but at least things
are making more sense now. The reason why that path works with top of
tree is because virDomainDeviceDefPostParseInternal won't call
virDomainHostdevAssignAddress since hdev->info->type is not
VIR_DOMAIN_DEVICE_ADDRESS_TYPE_NONE. That means when the
qemuDomainFindOrCreateSCSIDiskController is called it will do the magic add.
The path for this patch handles the inactive domain definition. While
patch 2 handles the backend of the active domain path.
Patch 2 is also used in the
"inactive domain definition" case.
The important difference is that the controller is NOT created on the
device definition path so that the controller is added via hotplug by
qemuDomainFindOrCreateSCSIDiskController since device hotplug uses the
device definition path! That is why this patch reintroduces adding the
controller into domain definition that the hotplug code does not use.
When you have a running domain, then qemuDomainAttachDeviceFlags (e.g.
what virsh attach-device would use) calls virDomainDeviceDefParse which
is where the controller is added during virDomainDeviceDefPostParse. So
patch 2 where you're removing that PostParse callback is why the hotplug
will then work because no longer does post parse add the controller to
the domain def.
Correct.
The call to qemuDomainFindOrCreateSCSIDiskController called by
qemuDomainAttachSCSIDisk during qemuDomainAttachDeviceDiskLive in the
live path of qemuDomainAttachDeviceFlags would then automagically add
the controller. Since the active path wouldn't have added it during post
parse.
Correct.
While these patches would work for the active domain hostdev add, I
think perhaps a different mechanism should be used. Given the failure
from trying to add a disk in the same environment, I'm not sure either
patch solves the root problem that during hotplug we're relying on *not*
adding a controller device when a new one is deemed necessary (for both
hostdev and disk).
I think that the root problem was introduced by moving the
adding of the
controller from the DOMAIN definition parsing into the DEVICE definition
parsing.
Since the code at this point seems by its multiple usage patterns rather
complex and fragile to changes I choose for this fix to revert the code
rather than to reengineer the code and not potentially make things worse.
One thing that is of interest is that virDomainDefMaybeAddController has
3 return values -1 fail, 0 didn't add a controller, and 1 added a
controller. I'm wondering if that can somehow be used to ensure that if
we add a controller that we ensure it really gets plugged in. Instead of
relying on qemuDomainFindOrCreateSCSIDiskController to backdoor it in.
I must say
that calling vir > DomainDef < MaybeAddController from the
DEVICE parsing and not from the DOMAIN parsing feels rather strange to
me. In both cases domain parsing and hotplugging devices the controllers
are plugged in AFTER the device parsing is finished! I do not see any
backdoor on the hotplug path!
John
--
Mit freundlichen Grüßen/Kind regards
Boris Fiuczynski
IBM Deutschland Research & Development GmbH
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