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Subject: PCI cap for larger offsets/lengths

  We've got an experimental virtio device (using vhost-user) we're playing with
that would like to share multiple large mappings from the client back to qemu.

'virtio_pci_cap' only has 32bit offset and length fields and so
I've got a different capability to express larger regions:

/* Additional shared memory capability */

struct virtio_pci_shm_cap {
       struct virtio_pci_cap cap;
       le32 offset_hi;             /* Most sig 32 bits of offset */
       le32 length_hi;             /* Most sig 32 bits of length */
       u8   id;                    /* To distinguish shm chunks */

One oddity is that I'm allowing multiple instances of this capability
on one device, distinguished by their 'id' field which I've made device
type specific, e.g.:


Having more than one capability of the same type is a little different
from what the virtio-spec currently suggests; it currently talks
about 'order of preference suggested by the device' - i.e. two
capabilities where the user picks one; in this case I'm using
all of the instances for different things.

If this makes sense to people, I'd be happy to write this up into a more
formal change; if it doesn't I'd be interested to hear about alternative


Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK

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