[Qemu-devel] Re: [PATCH 33/41] virtio-net: port to vmstate

[Juan Quintela]

"Michael S. Tsirkin" <address@hidden> wrote:
> On Wed, Dec 02, 2009 at 01:04:31PM +0100, Juan Quintela wrote:
>> 
>> Signed-off-by: Juan Quintela <address@hidden>
>> ---
>>  hw/virtio-net.c |  148 
>> ++++++++++++++++++++++++-------------------------------
>>  1 files changed, 64 insertions(+), 84 deletions(-)
>> 
>> diff --git a/hw/virtio-net.c b/hw/virtio-net.c
>> index 4434827..3a59449 100644
>> --- a/hw/virtio-net.c
>> +++ b/hw/virtio-net.c
>> @@ -703,6 +703,38 @@ static void virtio_net_tx_timer(void *opaque)
>>      virtio_net_flush_tx(n, n->tx_vq);
>>  }
>> 
>> +/* Restore an uint8_t from an uint32_t
>> +   This is a Big hack, but it is how the old state did it.
>> + */
>> +
>> +static int get_uint8_from_uint32(QEMUFile *f, void *pv, size_t size)
>> +{
>> +    uint8_t *v = pv;
>> +    *v = qemu_get_be32(f);
>> +    return 0;
>> +}
>> +
>> +static void put_unused(QEMUFile *f, void *pv, size_t size)
>> +{
>> +    fprintf(stderr, "uint8_from_uint32 is used only for backwards 
>> compatibility.\n");
>
> line too long
>
>> +    fprintf(stderr, "Never should be used to write a new state.\n");
>> +    exit(0);
>
> I don't understand.  what is this dong?

it is used later.
current code is reading an uint32_t value into a int8_t value.  As you
can guess that don't fit (that is the HACK part of it).  That is only
needed for old versions that we are reading (get_* function has real
code).  But we are supposed to never write old versions (*).
Thet that shouldn't happen ever.



>  when
> is this called? Please supply a comment.
> Maybe call assert?
>

assert or exit is ok for me, what does people preffer?

Later, Juan.

(*): My next series will propose to change that and allow to write old
     versions, but that didn't exist when this code was written, and
     there are still no agreement about how/if doing it.