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Subject: PCI cap for larger offsets/lengths
Hi, 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 */ #define VIRTIO_PCI_CAP_SHARED_MEMORY_CFG 8 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.: #define VIRTIO_MYDEV_PCI_SHMCAP_ID_CACHE 0 #define VIRTIO_MYDEV_PCI_SHMCAP_ID_JOURNAL 1 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 suggestions. Dave -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
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