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QNX Hypervisor
The QNX Hypervisor allows 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.
QNX Hypervisor for Safety Virtual Device Developer's API Reference
cdev.h
Functions to create virtual character devices for guests
cdev_output_busy()
Check if a character device's output is busy

QNX Momentics IDE User's Guide
This User's Guide describes version 7.1 of the Integrated Development Environment (IDE) that's part of the QNX Momentics 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 QNX Neutrino 7.1.
QNX Hypervisor
The QNX Hypervisor allows 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.
- QNX Hypervisor for Safety User's Guide
- QNX Hypervisor for Safety Virtual Device Developer's Guide
- QNX Hypervisor for Safety Virtual Device Developer's API Reference
  - Function Safety
    This section provides an overview of the restrictions that may apply when using the functions in this API.
  - aarch64/vmid.h
    Definitions to access a guest's VMID (ARM)
  - abi.h
    Application binary interface (ABI) version of the vdev API
  - cdev.h
    Functions to create virtual character devices for guests
    - 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 a host device write it 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 user-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 the character device's output buffer is full
    - cdev_output_num_pending()
      Check how many characters are in the output buffer
    - cdev_read()
      Transfer available data from the device's internal input buffer to a user-provided buffer
    - cdev_setup()
      Complete the setup for a character device's state structure
    - cdev_state
      Callback state
    - cdev_write()
      Write to the device in the hypervisor host
    - cdev_write_buffer()
      Write the contents of the internal buffer to the device
  - firmware.h
    Functions for working with the firmware components of the VM presented to the guest
  - gasp.h
    Functions for working in guest address spaces
  - guest.h
    Definitions for manipulating a guest system
  - hpci.h
    Host PCI interface for vdevs
  - hw_pci.h
    PCI support for vdevs
  - outpipe.h
    Definitions for the output pipe (outpipe)
  - types.h
    vdev API base types
  - utils.h
    Miscellaneous utility functions
  - vdev.h
    Source compatibility header file
  - vdev-core.h
    Definitions for vdevs
  - vio.h
    Definitions for VIRTIO vdevs
  - vpci.h
    Definitions for virtual PCI devices
  - wdog.h
    Definitions to support virtual watchdog devices
  - x86_64/apic.h
    Definitions for the virtual APIC bus (x86)
- QNX Hypervisor User's Guide
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 Advanced Virtualization Frameworks User's Guide
This User's Guide is aimed at all systems integrators and developers who want to design and build embedded systems using the QNX Advanced Virtualization Frameworks.
Typographical Conventions, Support, and Licensing
This section describes the typographical conventions used throughout the documentation and explains how to obtain technical support.

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 a 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:

An integer indicating whether the device output is busy (1) or not busy (0).

Page updated: March 12, 2026