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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.
utils.h
Miscellaneous utility functions
qvm_msgblock_start()
Set a maximum message timeout for a block of MsgSend() operations

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
    - Definitions in utils.h
      Preprocessor macro definitions for the utils.h header file
    - next_pow2()
      Round up to the next power of 2
    - qvm_block_string()
      Build a human-readable name for a state block
    - qvm_block_type_name()
      Return a string representation of a block type
    - qvm_callback
      The data structure to use for qvm callback functions
    - qvm_callback_func_t
      Prototype for generic qvm callback function
    - qvm_callback_pulse()
      Fill in a sigevent structure to call a function when the specified event gets delivered
    - qvm_channel()
      Return the qvm process channel ID
    - qvm_dcache_op_t
      Data type for storing data cache operation flags
    - qvm_dcache_operation()
      Perform data cache management
    - qvm_msgblock_oneshot()
      Set a maximum message timeout for just the next MsgSend() operation
    - qvm_msgblock_start()
      Set a maximum message timeout for a block of MsgSend() operations
    - qvm_msgblock_stop()
      Mark the end of a block of MsgSend() operations
    - qvm_overlap()
      Determine if two memory ranges overlap
    - qvm_parse_block()
      Parse a string to populate a structure that describes a data element
    - qvm_parse_num()
      Parse a number from a character string
    - qvm_parse_num_flags_t
      Data type for number-parsing operation flags
    - qvm_register_setvar()
      Add a new set variable to the list of available ones
    - qvm_setvar_context_t
      Possible set variable contexts
    - qvm_setvar_info_t
      Data type for storing set variable information
    - qvm_setvar_tristate_t
      Data type for storing tristate set variable values
    - qvm_setvar_type_t
      Set variable types
    - qvm_setvar_value_t
      Data type for storing variable information
    - qvm_slice()
      Given a starting offset and length, calculate the resulting slice array according to a descriptor array
    - qvm_slice_descriptor
      Structure that describes a specified range of offsets in a state structure
    - qvm_slice_result
      Structure that describes which descriptor is used for a specific slice, and the size of the slice
    - qvm_slice_sort()
      Sort the data of a slice descriptor array
    - qvm_slice_store()
      Given a slice descriptor, store some of its state data
    - qvm_unique()
      Obtain a system-wide unique number
  - 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.

qvm_msgblock_start()

Set a maximum message timeout for a block of MsgSend() operations

Synopsis:

#include <qvm/utils.h>

void qvm_msgblock_start(const vdev_t *vdp,
                        unsigned mult)

Arguments:

vdp: A pointer to a virtual device (vdev), or NULL for all vdevs in this VM.
mult: The multiplier of the configured timeout.

Description:

Use this function when you are communicating with an untrusted server and you don't know how many MsgSend() operations there will be. Wrap your messages with qvm_msgblock_start() and qvm_msgblock_stop() calls to make sure that you don't block if a server doesn't reply within the prescribed time.

To set the maximum message time for a single MsgSend() operation, call qvm_msgblock_oneshot().

To configure timeouts, use the qvm set option's message-block-timeout and vdev-message-block-timeout variables. For details, see the set section in the "VM Configuration Reference" chapter in the QNX hypervisor User's Guide.

Page updated: March 14, 2026