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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.
cdev.h
Support routines for virtual character devices
cdev_output_busy()
Check if a character device's output is busy

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
    - Definitions in cdev.h
      Preprocessor macro definitions for the cdev.h header file
    - cdev_control()
      Handle process-container character device operations
    - cdev_input_available()
      Read available data from the host device into the internal input buffer
    - cdev_input_num_available()
      Check how much space is available in a character device's input buffer
    - cdev_input_receive()
      Read available data from a host device into a provided buffer
    - cdev_output_busy()
      Check if a character device's output is busy
    - cdev_output_empty()
      Check if a character device's output buffer is empty
    - cdev_output_full()
      Check if a character device's output buffer is full
    - cdev_output_num_pending()
      Check how many characters are in a character device's output buffer
    - cdev_read()
      Read device data from the device's internal input buffer into a supplied buffer
    - cdev_setup()
      Complete the setup for a character device's state structure
    - cdev_state
      Callback state
    - cdev_write()
      Write data from a supplied buffer to a device
    - cdev_write_buffer()
      Write the contents of the internal buffer to a host device
  - 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
  - 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.

cdev_output_busy()

Check if a character device's output is busy

Synopsis:

#include <qvm/cdev.h>

static int cdev_output_busy(const struct cdev_state *const cds)

Arguments:

cds: A pointer to a structure with the character device state (see cdev_state).

Description:

This function checks if the specified character device's output is busy and hence, presently can't receive data. Calling this function makes sense only if you are using the internal buffers (i.e., you specified a non-zero buffer size when calling cdev_setup()).

Returns:

One (1) if the device's output is busy, or zero (0) if it's not.

Page updated: March 14, 2026