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

[Greg Kurz]

On Thu, 12 Jun 2014 11:43:20 +0200
Alexander Graf <address@hidden> 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);
> 
> 

For the moment, we have 0 < max_nr_ports < 32 so the source
machine only stores a single 32 bit value... If this limit
gets raised, we can end up sending more than that... and
only the source machine max_nr_ports value can give the
information...

-- 
Gregory Kurz                                     address@hidden
                                                 address@hidden
Software Engineer @ IBM/Meiosys                  http://www.ibm.com
Tel +33 (0)562 165 496

"Anarchy is about taking complete responsibility for yourself."
        Alan Moore.