[Qemu-devel] Re: [PATCH 06/41] virtio: Use DO_UPCAST instead of a cast

[Michael S. Tsirkin]

On Wed, Dec 02, 2009 at 07:19:17PM +0100, Juan Quintela wrote:
> "Michael S. Tsirkin" <address@hidden> wrote:
> > On Wed, Dec 02, 2009 at 01:04:04PM +0100, Juan Quintela wrote:
> >> virtio_common_init() creates a struct with the right size, DO_UPCAST
> >> is the appropiate thing here
> >> 
> >> Signed-off-by: Juan Quintela <address@hidden>
> >
> > BTW why not container_of? That one does not require
> > field to be at the beginning of structure.
> 
> VirtIO devices (and PCIDevices) are declared in this way:
> 
> typedef struct VirtIOBalloon
> {
>     VirtIODevice vdev;
>     VirtQueue *ivq, *dvq;
>     uint32_t num_pages;
>     uint32_t actual;
> } VirtIOBalloon;
> 
> 
> I.e. the virtioDevice is always the 1st element, otherwise things don't
> work.  There are code that requires it to be the 1st element.

I know. But I think we should slowly fix these assumptions, and not
introduce more of them. IOW: don't use DO_UPCAST.

> 
> Later, Juan.