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

["Michael S. Tsirkin" <mst@redhat.com>]

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 <jbaron@redhat.com>

I have this queued to apply already - this is just a repost
or did I miss something?

I have no idea about the larger issues - Juan?

> ---
>  hw/pci.c  |    2 +-
>  hw/pcie.h |    1 -
>  2 files changed, 1 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/pci.c b/hw/pci.c
> index 3727afa..5386a4f 100644
> --- a/hw/pci.c
> +++ b/hw/pci.c
> @@ -439,7 +439,7 @@ const VMStateDescription vmstate_pci_device = {
>  };
>  
>  const VMStateDescription vmstate_pcie_device = {
> -    .name = "PCIDevice",
> +    .name = "PCIEDevice",
>      .version_id = 2,
>      .minimum_version_id = 1,
>      .minimum_version_id_old = 1,
> diff --git a/hw/pcie.h b/hw/pcie.h
> index b8ab0c7..4889194 100644
> --- a/hw/pcie.h
> +++ b/hw/pcie.h
> @@ -133,7 +133,6 @@ extern const VMStateDescription vmstate_pcie_device;
>  
>  #define VMSTATE_PCIE_DEVICE(_field, _state) {                        \
>      .name       = (stringify(_field)),                               \
> -    .version_id = 2,                                                 \
>      .size       = sizeof(PCIDevice),                                 \
>      .vmsd       = &vmstate_pcie_device,                              \
>      .flags      = VMS_STRUCT,                                        \
> -- 
> 1.7.1