Master Resource Manager in QNX (2026)

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By Raj Kumar
On: May 1, 2025

In QNX, a Resource Manager is a core component of the QNX Neutrino RTOS responsible for handling I/O requests from applications for a particular device or virtual resource. It acts like a server that manages access to a resource, similar to how device drivers work in other operating systems — but with more flexibility and user-space implementation options.

Key Concepts of Resource Manager in QNX:

1. Abstraction of Resources:

  • Every resource (device, file, network socket, etc.) is represented as a file path in the namespace (e.g., /dev/ser1).
  • A resource manager associates this path with handling logic.

2. Handles Client Requests:

  • It handles requests like:
    • open(), read(), write(), ioctl(), close()
  • These come from user applications via message passing.

3. Message Passing Mechanism:

  • QNX is a microkernel OS, and most services are built on interprocess communication (IPC).
  • Applications send messages to resource managers, which process and respond to them.

4. User-space Drivers:

  • Unlike monolithic kernels, in QNX, many drivers (resource managers) can be run in user space.
  • This improves stability and debuggability.

5. Based on iofunc Library:

  • QNX provides iofunc_* functions and data structures to simplify resource manager development, handling common POSIX operations.

Structure of a Resource Manager:

A typical resource manager:

  1. Registers a path (like /dev/mydevice) using resmgr_attach().
  2. Initializes attributes and function tables (e.g., io_read, io_write).
  3. Enters a dispatch loop to receive and process client messages.

Benefits:

  • Modular design – easy to write, update, and test drivers/services.
  • Secure – isolation between services via IPC.
  • Real-time friendly – built on QNX’s predictable scheduling and messaging.

Example Use Cases:

  • Writing a driver for a custom hardware device
  • Creating a virtual device (e.g., /dev/random)
  • Handling a network protocol stack
  • Simulating a filesystem interface

Simple QNX resource manager example in C

Creates a virtual device (e.g., /dev/mydevice) and supports basic read() and write() operations.

Goal:

Create a resource manager for a virtual device /dev/mydevice, where:

  • read() returns a fixed message.
  • write() accepts input but doesn’t store it.

Main Components:

  1. Initialization (dispatch, iofunc)
  2. Attaching to /dev/mydevice
  3. Handling read and write
  4. Dispatch loop

Code: Basic Resource Manager

#include 
#include 
#include 
#include 
#include 
#include 
#include 

// Global dispatch handle
static resmgr_connect_funcs_t connect_funcs;
static resmgr_io_funcs_t io_funcs;
static iofunc_attr_t attr;

// Data to be returned on read
const char* msg = "Hello from /dev/mydevice!\n";

int io_read(resmgr_context_t* ctp, io_read_t* msg_hdr, iofunc_ocb_t* ocb) {
    int nbytes;
    int msg_len = strlen(msg);

    if (ocb->offset >= msg_len)
        return 0;  // EOF

    nbytes = min(msg_len - ocb->offset, msg_hdr->i.nbytes);
    _IO_SET_READ_NBYTES(ctp, nbytes);

    memcpy(_RESMGR_PTR(ctp, msg_hdr), msg + ocb->offset, nbytes);
    ocb->offset += nbytes;

    return _RESMGR_NPARTS(0);
}

int io_write(resmgr_context_t* ctp, io_write_t* msg_hdr, iofunc_ocb_t* ocb) {
    char buf[1024] = {0};
    int nbytes = msg_hdr->i.nbytes;

    if (nbytes > sizeof(buf) - 1)
        nbytes = sizeof(buf) - 1;

    resmgr_msgread(ctp, buf, nbytes, sizeof(io_write_t));
    buf[nbytes] = '\0';

    printf("Received from client: %s\n", buf);

    _IO_SET_WRITE_NBYTES(ctp, nbytes);
    return EOK;
}

int main(int argc, char** argv) {
    resmgr_attr_t resmgr_attr;
    dispatch_t* dpp;
    dispatch_context_t* ctp;

    dpp = dispatch_create();
    if (!dpp) {
        perror("dispatch_create");
        exit(EXIT_FAILURE);
    }

    memset(&resmgr_attr, 0, sizeof(resmgr_attr));
    resmgr_attr.nparts_max = 1;
    resmgr_attr.msg_max_size = 2048;

    iofunc_func_init(_RESMGR_CONNECT_NFUNCS, &connect_funcs,
                     _RESMGR_IO_NFUNCS, &io_funcs);

    io_funcs.read = io_read;
    io_funcs.write = io_write;

    iofunc_attr_init(&attr, S_IFCHR | 0666, NULL, NULL);

    if (resmgr_attach(dpp, &resmgr_attr, "/dev/mydevice", _FTYPE_ANY, 0,
                      &connect_funcs, &io_funcs, &attr) == -1) {
        perror("resmgr_attach");
        exit(EXIT_FAILURE);
    }

    ctp = dispatch_context_alloc(dpp);

    printf("Resource manager running. Access /dev/mydevice\n");
    while (1) {
        if ((ctp = dispatch_block(ctp)) != NULL)
            dispatch_handler(ctp);
    }

    return 0;
}

Build & Run:

qcc -o myresmgr myresmgr.c
./myresmgr &

Then:

cat /dev/mydevice     # Should print "Hello from /dev/mydevice!"
echo "test" > /dev/mydevice  # Should show output in your terminal

Code Breakdown

1. Headers and Globals

#include 
#include
  • These are QNX-specific headers for resource manager and IPC functions.
  • iofunc.h helps handle POSIX-style operations like open, read, write.
  • dispatch.h enables message handling between client and resource manager.

2. Resource Manager Function Tables

static resmgr_connect_funcs_t connect_funcs;
static resmgr_io_funcs_t io_funcs;
static iofunc_attr_t attr;
  • These hold the function pointers for handling open, read, write, etc.
  • iofunc_attr_t keeps metadata (file permissions, type, etc.) for the resource.

3. Read Handler

int io_read(...) {
    ...
}
  • This function runs when a client calls read() on /dev/mydevice.
  • ocb->offset keeps track of where reading left off.
  • _RESMGR_PTR(ctp, msg_hdr) gives the buffer to write into.
  • _IO_SET_READ_NBYTES() tells how many bytes are read.

4. Write Handler

int io_write(...) {
    ...
}
  • Called when a client does write() to /dev/mydevice.
  • resmgr_msgread() reads data from the message sent by the client.
  • We just print it, but you could instead send it to hardware.

5. Initialization

dpp = dispatch_create();
  • This sets up the dispatch loop, which listens for client messages.
resmgr_attr.nparts_max = 1;
resmgr_attr.msg_max_size = 2048;
  • Set the resource manager’s capabilities.
iofunc_func_init(...)
  • Initializes the function tables with defaults (open, close, etc.).
io_funcs.read = io_read;
io_funcs.write = io_write;
  • Override only the functions you want to customize.

6. Attach to /dev/mydevice

resmgr_attach(..., "/dev/mydevice", ...);
  • Registers the path so it’s visible in the /dev namespace.
  • Now applications can open(), read(), and write() on /dev/mydevice.

7. Main Loop

while (1) {
    if ((ctp = dispatch_block(ctp)) != NULL)
        dispatch_handler(ctp);
}
  • This is the event loop where the resource manager waits for and handles requests.

Real Hardware Device Example?

To extend this to real hardware:

  • Replace io_read/io_write with actual memory-mapped I/O or driver logic.
  • Use mmap_device_io() or mmap_device_memory() to talk to hardware registers.
  • You can also handle ioctl() to support custom control operations.
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