Re: [Qemu-devel] [PATCH] virtio-balloon: don't hardcode config size value

[Luiz Capitulino <lcapitulino@redhat.com>]

On Tue, 14 Jan 2014 21:05:31 +0400
Michael Tokarev <mjt@tls.msk.ru> wrote:

> 09.01.2014 18:58, Luiz Capitulino wrote:
> > Use sizeof(strucy virtio_balloon_config) instead.
> > 
> > --- a/hw/virtio/virtio-balloon.c
> > +++ b/hw/virtio/virtio-balloon.c
> > @@ -263,7 +263,7 @@ static void virtio_balloon_get_config(VirtIODevice *vdev, uint8_t *config_data)
> >      config.num_pages = cpu_to_le32(dev->num_pages);
> >      config.actual = cpu_to_le32(dev->actual);
> >  
> > -    memcpy(config_data, &config, 8);
> > +    memcpy(config_data, &config, sizeof(struct virtio_balloon_config));
> 
> I'm not sure any of those is better than another.

No duplication, no risk of changing virtio_balloon_config and
forgetting about changing all the memcpys out there (which is
exactly what happened to me). This is also what the other
devices do.

> This is a published guest <=> host interface, the config _must_ be 8 bytes
> long and must contain 2 4-byte words in it.

That's not changed by this patch.

> We may use assert(sizeof(struct virtio_balloon_config) == 8) somewhere,
> but to my taste it is a bit overkill.  No?
> 
> Thanks,
> 
> /mjt
>