Re: [Qemu-devel] [PATCH RFC 8/8] virtio: add endian-ambivalent support to VirtIODevice

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Jun 12, 2014 at 11:43:20AM +0200, Alexander Graf wrote:
> 
> On 12.06.14 11:39, Paolo Bonzini wrote:
> >Il 12/06/2014 11:37, Michael S. Tsirkin ha scritto:
> >>Maybe just drop unnecessary stuff for new machine types?
> >>Then we won't need hacks to migrate it.
> >
> >For any machine type it's trivial to migrate it.  All machine types
> >including old ones can disregard the migrated values.
> 
> How about a patch like this before the actual LE awareness ones? With this
> we should make virtio-serial config space completely independent of live
> migration.
> 
> Also since QEMU versions that do read these swapped values during migration
> are not bi-endian aware, we can never get into a case where a cross-endian
> save needs to be considered ;).
> 
> 
> Alex
> 
> 
> diff --git a/hw/char/virtio-serial-bus.c b/hw/char/virtio-serial-bus.c
> index 2b647b6..73cb9b7 100644
> --- a/hw/char/virtio-serial-bus.c
> +++ b/hw/char/virtio-serial-bus.c
> @@ -670,6 +670,7 @@ static int virtio_serial_load(QEMUFile *f, void *opaque,
> int version_id)
>      uint32_t max_nr_ports, nr_active_ports, ports_map;
>      unsigned int i;
>      int ret;
> +    uint32_t tmp;
> 
>      if (version_id > 3) {
>          return -EINVAL;
> @@ -685,17 +686,12 @@ static int virtio_serial_load(QEMUFile *f, void
> *opaque, int version_id)
>          return 0;
>      }
> 
> -    /* The config space */
> -    qemu_get_be16s(f, &s->config.cols);
> -    qemu_get_be16s(f, &s->config.rows);
> -
> -    qemu_get_be32s(f, &max_nr_ports);
> -    tswap32s(&max_nr_ports);
> -    if (max_nr_ports > tswap32(s->config.max_nr_ports)) {
> -        /* Source could have had more ports than us. Fail migration. */
> -        return -EINVAL;
> -    }
> +    /* Unused */
> +    qemu_get_be16s(f, &tmp);
> +    qemu_get_be16s(f, &tmp);
> +    qemu_get_be32s(f, &tmp);
> 
> +    max_nr_ports = tswap32(s->config.max_nr_ports);
>      for (i = 0; i < (max_nr_ports + 31) / 32; i++) {
>          qemu_get_be32s(f, &ports_map);
>

Exactly.
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>