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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.
Programming
Writing a Resource Manager
Handling Read and Write Messages
A resource manager must define routines or handlers to process requests by the client to receive data (read) or send data to the underlying device (write). Here, we give detailed examples of such handlers.
Updating the time for reads and writes

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.
- Quickstart Guide
- System Architecture
  The System Architecture guide accompanies the QNX OS and is intended for both application developers and end-users.
- OS Components & Operations
- Graphics
- Programming
  - Getting Started with the QNX OS
    Getting Started with the QNX OS: A Guide for Realtime Programmers is intended to introduce you to the QNX OS and help you develop applications and resource managers for it.
  - Programmer's Guide
    The QNX OS Programmer's Guide covers a variety of topics that might interest developers who are building applications that will run under the QNX OS.
  - Writing a Resource Manager
    - What Is a Resource Manager?
      In general terms, a resource manager is a process that registers a pathname in the filesystem namespace. Other processes use that pathname to communicate with the resource manager.
    - The Bones of a Resource Manager
      Let's start with the overall structure of a resource manager. First we'll look at what happens under the covers on both the client side and the server side. After that, we'll go into the layers in a resource manager and then look at some examples.
    - Fleshing Out the Skeleton
      It's time now to start adding some flesh to the basic bones of the resource manager. We'll look at the types of messages you might have to handle, how to set the resource manager's attributes, how to add functionality, and some security issues you should consider.
    - POSIX-Layer Data Structures
      The resource manager library defines (in <sys/iofunc.h>) several key structures that are related to the POSIX-layer support routines.
    - Handling Read and Write Messages
      A resource manager must define routines or handlers to process requests by the client to receive data (read) or send data to the underlying device (write). Here, we give detailed examples of such handlers.
      - Handling the _IO_READ message
      - Handling the _IO_WRITE message
      - Methods of returning and replying
      - Handling other read/write details
        You may want to define read and write handler functions with specialized behavior depending on the function the client calls or the type of the underlying device.
      - Updating the time for reads and writes
    - Resource Managers that Handle Multiple Devices
      Resource managers can easily be adapted to handle multiple devices.
    - Combine Messages
      To conserve bandwidth and to support atomic operations, combine messages are supported. A combine message is constructed by the client's C library and consists of multiple I/O and/or connect messages packaged together into one.
    - Using the Receive Buffer as a Reply Buffer
      When building a response to a client request, you often need a temporary buffer in which to build this response.
    - Handling Other Messages
      Your resource manager will likely need to handle messages for operations other than read and write. Here, we explain and demonstrate how to handle other common message types.
    - Unblocking Clients and Handling Interrupts
      Your resource manager needs to avoid leaving clients blocked indefinitely, and it might need to handle interrupts.
    - Multithreaded Resource Managers
      When you create a multithreaded resource manager, you should design it so that there's always at least one RECEIVE-blocked thread.
    - Filesystem Resource Managers
      Some resource managers need to implement filesystems by responding to access requests for any pathname within a directory structure.
    - Glossary
- System Security Guide
  The QNX System Security Guide is intended for both system integrators who are responsible for the security of a QNX OS system and developers who want to create a QNX OS resource manager free from vulnerabilities.
- Utilities & Libraries
- Migrating to QNX OS 8.0
QNX Software in the Cloud
QNX Software in the Cloud enables developers to use the QNX OS in the Amazon cloud environment.
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 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).
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.

Updating the time for reads and writes

QNX SDP8.0Writing a Resource ManagerDeveloper

In the read sample above we did:

if (msg->i.nbytes > 0)
    ocb->attr->flags |= IOFUNC_ATTR_ATIME;

According to POSIX, if the read succeeds and the reader had asked for more than zero bytes, then the access time must be marked for update. But POSIX doesn't say that it must be updated right away. If you're doing many reads, you may not want to read the time from the kernel for every read. In the code above, we mark the time only as needing to be updated. When the next _IO_STAT or _IO_CLOSE_OCB message is processed, the resource manager library will see that the time needs to be updated and will get it from the kernel then. This of course has the disadvantage that the time is not the time of the read.

Similarly for the write sample above, we did:

if (msg->i.nbytes > 0)
    ocb->attr->flags |= IOFUNC_ATTR_MTIME | IOFUNC_ATTR_CTIME;

so the same thing will happen.

If you do want to have the times represent the read or write times, then after setting the flags you need only call the iofunc_time_update() helper function. So the read lines become:

if (msg->i.nbytes > 0) {
    ocb->attr->flags |= IOFUNC_ATTR_ATIME;
    iofunc_time_update(ocb->attr);
}

and the write lines become:

if (msg->i.nbytes > 0) {
    ocb->attr->flags |= IOFUNC_ATTR_MTIME | IOFUNC_ATTR_CTIME;
    iofunc_time_update(ocb->attr);
}

You should call iofunc_time_update() before you flush out any cached attributes. As a result of changing the time fields, the attribute structure will have the IOFUNC_ATTR_DIRTY_TIME bit set in the flags field, indicating that this field of the attribute must be updated when the attribute is flushed from the cache.

Page updated: March 05, 2025