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savevm: Ignore minimum_version_id_old if there is no load_state_old 

At the moment we require vmstate definitions to set minimum_version_id_old
to the same value as minimum_version_id if they do not provide a
load_state_old handler. Since the load_state_old functionality is
required only for a handful of devices that need to retain migration
compatibility with a pre-vmstate implementation, this means the bulk
of devices have pointless boilerplate. Relax the definition so that
minimum_version_id_old is ignored if there is no load_state_old handler.

Note that under the old scheme we would segfault if the vmstate
specified a minimum_version_id_old that was less than minimum_version_id
but did not provide a load_state_old function, and the incoming state
specified a version number between minimum_version_id_old and
minimum_version_id. Under the new scheme this will just result in
our failing the migration.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
This commit is contained in:
Peter Maydell 2014-04-03 19:52:28 +03:00 committed by Juan Quintela
parent 9f8e9895c5
commit 767adce2d9
2 changed files with 10 additions and 11 deletions
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12
docs/migration.txt
View File

@ -139,7 +139,6 @@ static const VMStateDescription vmstate_kbd = {
.name = "pckbd",
.version_id = 3,
.minimum_version_id = 3,
.minimum_version_id_old = 3,
.fields = (VMStateField []) {
VMSTATE_UINT8(write_cmd, KBDState),
VMSTATE_UINT8(status, KBDState),
@ -168,12 +167,13 @@ You can see that there are several version fields:
- minimum_version_id: the minimum version_id that VMState is able to understand
for that device.
- minimum_version_id_old: For devices that were not able to port to vmstate, we can
assign a function that knows how to read this old state.
assign a function that knows how to read this old state. This field is
ignored if there is no load_state_old handler.
So, VMState is able to read versions from minimum_version_id to
version_id. And the function load_state_old() is able to load state
from minimum_version_id_old to minimum_version_id. This function is
deprecated and will be removed when no more users are left.
version_id. And the function load_state_old() (if present) is able to
load state from minimum_version_id_old to minimum_version_id. This
function is deprecated and will be removed when no more users are left.
=== Massaging functions ===
@ -255,7 +255,6 @@ const VMStateDescription vmstate_ide_drive_pio_state = {
.name = "ide_drive/pio_state",
.version_id = 1,
.minimum_version_id = 1,
.minimum_version_id_old = 1,
.pre_save = ide_drive_pio_pre_save,
.post_load = ide_drive_pio_post_load,
.fields = (VMStateField []) {
@ -275,7 +274,6 @@ const VMStateDescription vmstate_ide_drive = {
.name = "ide_drive",
.version_id = 3,
.minimum_version_id = 0,
.minimum_version_id_old = 0,
.post_load = ide_drive_post_load,
.fields = (VMStateField []) {
.... several fields ....

9
vmstate.c
View File

@ -63,11 +63,12 @@ int vmstate_load_state(QEMUFile *f, const VMStateDescription *vmsd,
if (version_id > vmsd->version_id) {
return -EINVAL;
}
if (version_id < vmsd->minimum_version_id_old) {
return -EINVAL;
}
if (version_id < vmsd->minimum_version_id) {
return vmsd->load_state_old(f, opaque, version_id);
if (vmsd->load_state_old &&
version_id >= vmsd->minimum_version_id_old) {
return vmsd->load_state_old(f, opaque, version_id);
}
return -EINVAL;
}
if (vmsd->pre_load) {
int ret = vmsd->pre_load(opaque);