Method parse

virtio-devices/src/iommu.rs:351–805

Parse the available vring buffer. Based on the hashmap table of external mappings required from various devices such as VFIO or vhost-user ones, this function might update the hashmap table of external mappings per domain. Basically, the VMM knows about the device_id <=> mapping relationship before running the VM, but at runtime, a new domain <=> mapping hashmap is created based on the information

(
        desc_chain: &mut DescriptorChain<GuestMemoryLoadGuard<GuestMemoryMmap>>,
        mapping: &Arc<IommuMapping>,
        ext_mapping: &BTreeMap<u32, Arc<dyn ExternalDmaMapping>>,
        msi_io

    // is created based on the information provided from the guest driver for
    // virtio-iommu (giving the link device_id <=> domain).
    fn parse(
        desc_chain: &mut DescriptorChain<GuestMemoryLoadGuard<GuestMemoryMmap>>,
        mapping: &Arc<IommuMapping>,
        ext_mapping: &BTreeMap<u32, Arc<dyn ExternalDmaMapping>>,
        msi_iova_space: (u64, u64),
        input_range: Option<(u64, u64)>,
    ) -> result::Result<usize, Error> {
        let desc = desc_chain
            .next()
            .ok_or(Error::DescriptorChainTooShort)
            .inspect_err(|_| {
                error!("Missing head descriptor");
            })?;

        // The descriptor contains the request type which MUST be readable.
        if desc.is_write_only() {
            return Err(Error::UnexpectedWriteOnlyDescriptor);
        }

        if (desc.len() as usize) < size_of::<VirtioIommuReqHead>() {
            return Err(Error::InvalidRequest);
        }

        let req_head: VirtioIommuReqHead = desc_chain
            .memory()
            .read_obj(desc.addr())
            .map_err(Error::GuestMemory)?;
        let req_offset = size_of::<VirtioIommuReqHead>();
        let desc_size_left = (desc.len() as usize) - req_offset;
        let req_addr = if let Some(addr) = desc.addr().checked_add(req_offset as u64) {
            addr
        } else {
            return Err(Error::InvalidRequest);
        };

        let (msi_iova_start, msi_iova_end) = msi_iova_space;

        // Create the reply
        let mut reply: Vec<u8> = Vec::new();
        let mut status = VIRTIO_IOMMU_S_OK;
        let mut hdr_len = 0;
        let mut unrecognised_type = false;

        let result = (|| {
            match req_head.type_ {
                VIRTIO_IOMMU_T_ATTACH => {
                    if desc_size_left != size_of::<VirtioIommuReqAttach>() {
                        status = VIRTIO_IOMMU_S_INVAL;
                        return Err(Error::InvalidAttachRequest);
                    }

                    let req: VirtioIommuReqAttach = desc_chain
                        .memory()
                        .read_obj(req_addr as GuestAddress)
                        .map_err(Error::GuestMemory)?;
                    debug!("Attach request 0x{req:x?}");

                    if req.reserved.iter().any(|&b| b != 0)