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QNX Hypervisor and QNX Hypervisor for Safety
The QNX Hypervisor and QNX Hypervisor for Safety products allow you to run multiple OSs on a target system so you can separate critical and non-critical functions, support a wide variety of applications, and reduce hardware costs.
Virtual Device Developer's API Reference
The Virtual Device Developer's API Reference presents the QNX hypervisor public virtual device (vdev) API. It is intended for use by developers writing virtual devices (vdevs) in a QNX hypervisor system.
vio.h
Definitions and functions for working with VIRTIO vdevs
vio_read()
Handle a read reference for a vdev

QNX Momentics IDE User's Guide
This User's Guide describes version 8.0 of the Integrated Development Environment (IDE) that's part of the QNX Tool Suite.
QNX Software Development Platform
QNX SDP is a cross-compiling and debugging environment, including an IDE and command-line tools, for building binary images and programs for target boards running the QNX OS 8.0.
QNX Software in the Cloud
QNX Software in the Cloud enables developers to use the QNX software in Amazon Web Services (AWS) and Microsoft Azure (Azure).
QNX Toolkit for Visual Studio Code
This User's Guide describes the QNX^® Toolkit for Visual Studio Code. The guide introduces you to the QNX Toolkit by explaining the QNX development environment and how to build, run, and debug your QNX^® Operating System (OS) applications and systems.
QNX Hypervisor and QNX Hypervisor for Safety
The QNX Hypervisor and QNX Hypervisor for Safety products allow you to run multiple OSs on a target system so you can separate critical and non-critical functions, support a wide variety of applications, and reduce hardware costs.
- User's Guide
  This User's Guide explains the QNX hypervisor architecture and provides instructions for installing and running a QNX hypervisor system, changing system components and configuration, and using hypervisor features such as virtual devices (vdevs).
- Virtual Device Developer's Guide
  The Virtual Device Developer's Guide is intended for use by developers writing virtual devices (vdevs) in a QNX hypervisor system.
- Virtual Device Developer's API Reference
  The Virtual Device Developer's API Reference presents the QNX hypervisor public virtual device (vdev) API. It is intended for use by developers writing virtual devices (vdevs) in a QNX hypervisor system.
  - Function Safety
    This section provides an overview of the restrictions that may apply when using the functions in this API.
  - aarch64/vmid.h
    Functions to access a guest's VMID (ARM)
  - abi.h
    Application binary interface (ABI) information
  - cdev.h
    Support routines for virtual character devices
  - firmware.h
    Functions for working with the firmware components of the VM presented to the guest
  - gasp.h
    Definitions and functions for working in guest address spaces
  - guest.h
    Controls for manipulating a guest system
  - hpci.h
    Host PCI interface for vdevs
  - hw_pci.h
    PCI support for vdevs
  - log.h
    Controls for logging messages
  - types.h
    vdev API base types
  - utils.h
    Miscellaneous utility functions
  - vdev-core.h
    Definitions and functions that support vdev control functions and callbacks
  - vio.h
    Definitions and functions for working with VIRTIO vdevs
    - Definitions in vio.h
      Preprocessor macro definitions for the vio.h header file
    - iov_postmap_elem_t
      Data type for vi_is_postmap field in vio_iov structure
    - vio_append_iov()
      Extend an iov array to cover an additional VIRTIO descriptor
    - vio_config_update()
      Inform the guest driver that the host device has modified its configuration
    - vio_control_status()
      Function called by the control function to output the vdev's status information
    - vio_ctrl_gen_fdt()
      Generate an FDT node for VIRTIO devices
    - vio_ctrl_pci_bars()
      Function to be called from a vdev's VDEV_CTRL_PCI_BARS callback
    - vio_description
      Information describing the VIRTIO device being created
    - vio_device_status()
      Update the VIRTIO status register for the device
    - vio_get_iov()
      Convert a VIRTIO descriptor request into an iov array
    - vio_has_vendor_feature()
      Check if the bit for a vendor-specific feature is set
    - vio_init()
      Initialize the vdev's state
    - vio_init_qinfo()
      Initialize the queue-dependent vdev state
    - vio_init_queue()
      Initialize one virtqueue in the device
    - vio_iov
      Structure for converting a virtqueue descriptor list into an iov_t array
    - vio_iov_flags_t
      Data type for vi_flags field in vio_iov structure
    - vio_iov_set_flags()
      Handle setting or clearing flags in a vio_iov structure
    - vio_parse_vendor_features()
      Update the statuses of the vendor-specific features to advertise to guest drivers
    - vio_prepare_iov()
      Set the required fields for one logical sequence of calls to vio_append_iov()
    - vio_put_iov()
      Finish handling a VIRTIO request
    - vio_queue_info
      Information for one virtqueue on the device
    - vio_read()
      Handle a read reference for a vdev
    - vio_reset()
      Reset device state fields to their initial values
    - vio_set_vendor_feature()
      Set the bit for a vendor-specific feature
    - vio_setup_queues()
      Get host-virtual addresses for the virtqueue rings
    - vio_state
      State of a VIRTIO device
    - vio_vendor_feature
      Information about vendor-specific features that can be advertised at unused bits
    - vio_version
      Version of the VIRTIO standard the device is implementing
    - vio_write()
      Handle a write reference for a vdev
  - vpci.h
    Controls for virtual PCI (vPCI) devices
  - wdog.h
    Constants, data types, and functions to support virtual watchdog devices
  - x86_64/apic.h
    Definitions for the virtual APIC bus (x86)
Typographical Conventions, Support, and Licensing
This section describes the typographical conventions used throughout the documentation, explains how to obtain technical support, and provides some information about licensing.

vio_read()

Handle a read reference for a vdev

Synopsis:

#include <qvm/vio.h>

unsigned vio_read(struct vio_state *vsp,
                  unsigned cookie,
                  const struct qvm_state_block *vopnd,
                  const struct qvm_state_block *oopnd,
                  struct guest_cpu *gcp)

Arguments:

vsp: A pointer to the vdev's state structure.
cookie: A region cookie.
vopnd: A pointer to the vdev operand.
oopnd: A pointer to the other operand.
gcp: A pointer to the guest system's vCPU that is making the reference.

Description:

This function handles a read reference for a vdev; it must be called by the vdev's vread() function, passing the parameters through.

Returns:

A VIOREF_CLASS_* value indicating any further action that the reference requires the vdev to take.

Page updated: March 14, 2026