Gerd Hoffmann <kra...@redhat.com> wrote:
> On Di, 2014-04-22 at 08:16 +0000, Gonglei (Arei) wrote:
>> >
>> > > diff --git a/hw/input/ps2.c b/hw/input/ps2.c
>> > > index 3412079..a754fef 100644
>> > > --- a/hw/input/ps2.c
>> > > +++ b/hw/input/ps2.c
>> > > @@ -71,7 +71,7 @@
>> > > #define MOUSE_STATUS_ENABLED 0x20
>> > > #define MOUSE_STATUS_SCALE21 0x10
>> > >
>> > > -#define PS2_QUEUE_SIZE 256
>> > > +#define PS2_QUEUE_SIZE 16 /* Keyboard output buffer size */
>> > >
>> > > typedef struct {
>> > > uint8_t data[PS2_QUEUE_SIZE];
>> >
>> > This changes ps2 vmstate and breaks live migration.
>> >
>> Good catch, Gerd.
>> I got the information in the destination of live migration:
>> Unknown savevm section type 24
>> load of migration failed
>>
>> I'm not familiar with the situation of cross-version live migration,
>> could you give me
>> some guide ? Thanks.
>
> Keep the data array 256 bytes long, best with a comment that
> compatibility with older qemu versions requires this.
>
> Also the post_load function must handle the case that rptr, wptr & count
> variables have values which used to be valid for the older qemu versions
> but are not valid any more with the smaller queue. In the (unlikely)
> case that count is larger than 16 the best you can do is probably simply
> throw away the queue. 16 and less queue elements you can move to the
> start of the data array (so they are within the 16 bytes still used
> after your patch is merged) and adjust rptr+wptr accordingly.
>
> Cc'ing Juan for additional insights.
>
> HTH,
> Gerd
static int ps2_common_post_load(void *opaque, int version_id)
{
PS2State *s = opaque;
/* Here goes the code that resets rptr/wptr/count if it is bigger
than p16
Gerd said that dropping the queue is a good idea.
*/
return 0;
}
static const VMStateDescription vmstate_ps2_common = {
.name = "PS2 Common State",
.version_id = 3,
.minimum_version_id = 2,
.minimum_version_id_old = 2,
.post_load = ps2_common_post_load,
.fields = (VMStateField[]) {
VMSTATE_INT32(write_cmd, PS2State),
VMSTATE_INT32(queue.rptr, PS2State),
VMSTATE_INT32(queue.wptr, PS2State),
VMSTATE_INT32(queue.count, PS2State),
VMSTATE_BUFFER(queue.data, PS2State),
/* A coment here explaining why we changed the queue from 256 to
16 could be a good idea */
VMSTATE_UNUSED_BUFFER(256-16 );
VMSTATE_END_OF_LIST()
}
};
Hope it helps.
Later, Juan.
