Re: [Qemu-devel] [PATCH 1/2] pcie: drop version_id field for live migration

[Michael S. Tsirkin]

On Fri, Aug 31, 2012 at 10:46:51AM -0400, Jason Baron wrote:
> On Fri, Aug 31, 2012 at 11:44:54AM +0300, Michael S. Tsirkin wrote:
> > On Thu, Aug 30, 2012 at 01:51:10PM -0400, Jason Baron wrote:
> > > While testing q35 live migration, I found that the migration would abort 
> > > with
> > > the following error: "Unknown savevm section type 76".
> > > 
> > > The error is due to this check failing in 'vmstate_load_state()':
> > > 
> > >     while(field->name) {
> > >         if ((field->field_exists &&
> > >              field->field_exists(opaque, version_id)) ||
> > >             (!field->field_exists &&
> > >              field->version_id <= version_id)) {
> > > 
> > > The VMSTATE_PCIE_DEVICE() currently has a 'version_id' set to 2. However,
> > > 'version_id' in the above check is 1. And thus we fail to load the pcie 
> > > device
> > > field. Further the code returns to 'qemu_loadvm_state()' which produces 
> > > the
> > > error that I saw.
> > > 
> > > I'm proposing to fix this by simply dropping the 'version_id' field from
> > > VMSTATE_PCIE_DEVICE(). VMSTATE_PCI_DEVICE() defines no such field and 
> > > further
> > > the vmstate_pcie_device that VMSTATE_PCI_DEVICE() refers to is already
> > > versioned. Thus, any versioning issues could be detected at the vmsd 
> > > level.
> > > 
> > > Taking a step back, I think that the 'field->version_id' should be 
> > > compared
> > > against a saved version number for the field not the 'version_id'. 
> > > Futhermore,
> > > once vmstate_load_state() is called recursively on another vmsd, the 
> > > check of:
> > > 
> > >     if (version_id > vmsd->version_id) {
> > >         return -EINVAL;
> > >     }
> > > 
> > > Will never fail since version_id is always equal to vmsd->version_id. So 
> > > I'm
> > > wondering why we aren't storing the vmsd version id of the source in the
> > > migration stream?
> > > 
> > > This patch also renames the 'name' field of vmstate_pcie_device from:
> > > PCIDevice -> PCIEDevice to differentiate it from vmstate_pci_device.
> > > 
> > > Signed-off-by: Jason Baron <address@hidden>
> > 
> > I have this queued to apply already - this is just a repost
> > or did I miss something?
> > 
> 
> just a repost...but now we have Juan's ack :)

Right. It is preferable to tag reposts explicitly but no big deal.