Add a vhost-user frontend for virtio-gpu using the current vhost-user
protocol (GET_SHMEM_CONFIG=44, SHMEM_MAP/UNMAP=9/10, SHMEM=0x0020_0000).
The GPU device queries the backend for shared memory regions via
get_shmem_config(), allocates a PCI BAR for the shmem region, and
implements a BackendReqHandler that handles SHMEM_MAP/UNMAP requests
by mmapping file descriptors from the backend into the shared memory
region.
To support non-contiguous shared memory region IDs (needed for
VIRTIO_GPU_SHM_ID_HOST_VISIBLE=1), VirtioSharedMemoryList.region_list
is changed from Vec<VirtioSharedMemory> to BTreeMap<u8, VirtioSharedMemory>,
and the PCI BAR code uses the map key as the PCI capability shmid.
Includes full VMM plumbing: GpuConfig, --gpu CLI, API, device_manager,
seccomp rules, and hotplug support.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Davíð Steinn Geirsson
c22c15b963