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From: Juan Quintela <quintela@redhat.com>
In-Reply-To: <20091202134153.GC18193@redhat.com> (Michael S. Tsirkin's message
	of "Wed, 2 Dec 2009 15:41:53 +0200")
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Date: Wed, 02 Dec 2009 19:19:17 +0100
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Subject: [Qemu-devel] Re: [PATCH 06/41] virtio: Use DO_UPCAST instead of a
	cast
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To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: qemu-devel@nongnu.org

"Michael S. Tsirkin" <mst@redhat.com> 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 <quintela@redhat.com>
>
> 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.

Later, Juan.