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Date: Tue, 14 Jan 2014 22:05:35 +0200
From: "Michael S. Tsirkin" <mst@redhat.com>
Message-ID: <20140114200535.GA31642@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] virtio-balloon: don't hardcode config size
 value
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To: Michael Tokarev <mjt@tls.msk.ru>
Cc: qemu-trivial <qemu-trivial@nongnu.org>, Peter Crosthwaite <peter.crosthwaite@xilinx.com>, qemu-devel <qemu-devel@nongnu.org>, Luiz Capitulino <lcapitulino@redhat.com>

On Tue, Jan 14, 2014 at 09:05:31PM +0400, Michael Tokarev 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.
> 
> This is a published guest <=> host interface, the config _must_ be 8 bytes
> long and must contain 2 4-byte words in it.

no, config can be extended in the future.
and hard coded constants are evil.

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

I agree assert like this would be overkill.

> Thanks,
> 
> /mjt
-- 
MST