Message ID | 1396283826-7100-1-git-send-email-peter.maydell@linaro.org |
---|---|
State | New |
Headers | show |
On Mon, Mar 31, 2014 at 05:37:06PM +0100, Peter Maydell wrote: > 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> > --- > There's obviously scope for subsequent cleanup to delete all the > now-redundant setting of minimum_version_id_old in vmstates; in this > patch I only changed the occurrences in the documentation. > > docs/migration.txt | 12 +++++------- > vmstate.c | 9 +++++---- > 2 files changed, 10 insertions(+), 11 deletions(-) > > diff --git a/docs/migration.txt b/docs/migration.txt > index 0e0a1d4..fe1f2bb 100644 > --- a/docs/migration.txt > +++ b/docs/migration.txt > @@ -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 .... > diff --git a/vmstate.c b/vmstate.c > index b689f2f..bfa34cc 100644 > --- a/vmstate.c > +++ b/vmstate.c > @@ -19,11 +19,12 @@ 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); > -- > 1.9.0
diff --git a/docs/migration.txt b/docs/migration.txt index 0e0a1d4..fe1f2bb 100644 --- a/docs/migration.txt +++ b/docs/migration.txt @@ -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 .... diff --git a/vmstate.c b/vmstate.c index b689f2f..bfa34cc 100644 --- a/vmstate.c +++ b/vmstate.c @@ -19,11 +19,12 @@ 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);
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> --- There's obviously scope for subsequent cleanup to delete all the now-redundant setting of minimum_version_id_old in vmstates; in this patch I only changed the occurrences in the documentation. docs/migration.txt | 12 +++++------- vmstate.c | 9 +++++---- 2 files changed, 10 insertions(+), 11 deletions(-)