Method check_request

virtio-devices/src/block.rs:177–203

(
        features: u64,
        request: &Request,
        disable_sector0_writes: bool,
    )

impl BlockEpollHandler {
    fn check_request(
        features: u64,
        request: &Request,
        disable_sector0_writes: bool,
    ) -> result::Result<(), ExecuteError> {
        let request_type = request.request_type();
        if (has_feature(features, VIRTIO_BLK_F_RO.into()))
            && !(request_type == RequestType::In
                || request_type == RequestType::GetDeviceId
                || request_type == RequestType::Flush)
        {
            // For virtio spec compliance
            // "A device MUST set the status byte to VIRTIO_BLK_S_IOERR for a write request
            // if the VIRTIO_BLK_F_RO feature if offered, and MUST NOT write any data."
            warn!(
                "Rejecting block request {request_type:?}: device is read-only (VIRTIO_BLK_F_RO negotiated)"
            );
            return Err(ExecuteError::ReadOnly);
        }

        if request_type == RequestType::Out && disable_sector0_writes && request.sector() == 0 {
            warn!("Attempting to write to sector 0 on a disk without specifying image_type");
            return Err(ExecuteError::ReadOnly);
        }

        Ok(())
    }

    // A spec-compliant driver never reuses a virtqueue head_index while the
    // corresponding chain is still available (virtio 1.x §2.7.13.4).