Messages in this thread | | | From | Rusty Russell <> | Subject | Re: [PATCH] virtio config_ops refactoring | Date | Fri, 9 Nov 2007 22:54:07 +1100 |
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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).
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