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

[Jason Baron <jbaron@redhat.com>]

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>
---
 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