On Friday 09 November 2007 09:33:04 Anthony Liguori wrote:
> I really want to make sure that if a guest tries
> to read a 4-byte PCI config field, that it does so using an "outl"
> instruction so that in my QEMU backend
So you want to enforce PCI requirements onto virtio config accesses. This
doesn't seem very nice: the fact that PCI accesses use different namespaces
for different sizes makes sense from a primitive hardware point of view, but
sucks for software. Fortunately, if you insist on byte-at-a-time they're the
same.
> switch (addr) {
> case VIRTIO_BLK_CONFIG_MAX_SEG:
> return vdev->max_seg & 0xFF;
> case VIRTIO_BLK_CONFIG_MAX_SEG + 1:
> return (vdev->max_seg >> 8) & 0xFF;
> case VIRTIO_BLK_CONFIG_MAX_SEG + 2:
> return (vdev->max_seg >> 16) & 0xFF;
> case VIRTIO_BLK_CONFIG_MAX_SEG + 3:
> return (vdev->max_seg >> 24) & 0xFF;
> case VIRTIO_BLK_CONFIG_MAX_SIZE:
> return vdev->max_size & 0xFF;
> case VIRTIO_BLK_CONFIG_MAX_SIZE + 1:
> return (vdev->max_size >> 8) & 0xFF;
> case VIRTIO_BLK_CONFIG_MAX_SIZE + 2:
> return (vdev->max_size >> 16) & 0xFF;
> case VIRTIO_BLK_CONFIG_MAX_SIZE + 3:
> return (vdev->max_size >> 24) & 0xFF;
> ...
struct virtio_blk_config
{
uint32_t max_seg, max_size;
};
...
struct virtio_blk_config conf = { vdev->max_seg, vdev->max_size };
return ((unsigned char *)&conf)[addr];
(Which strongly implies our headers should expose that nominal struct, rather
than numerical constants).
Rusty.
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