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Attach a path to the pathname space


#include <sys/iofunc.h>
#include <sys/dispatch.h>

int resmgr_attach (
       dispatch_t *dpp,
       resmgr_attr_t *attr,
       const char *path, 
       enum _file_type file_type,
       unsigned flags, 
       const resmgr_connect_funcs_t *connect_funcs,
       const resmgr_io_funcs_t *io_funcs,
       RESMGR_HANDLE_T *handle );


A dispatch handle created by dispatch_create().
A pointer to a resmgr_attr_t structure that defines attributes for the resource manager; see below.
NULL, or the path that you want to attach the resource manager to; see below.
The file type; one of the following (defined in <sys/ftype.h>):
Flags that control the pathname resolution:

For more information, see The flags argument,” below.

A pointer to the resmgr_connect_funcs_t structure that defines the POSIX-level connect functions.
A pointer to the resmgr_io_funcs_t structure that defines the POSIX-level I/O functions.
A pointer to an arbitrary structure that you want to associate with the pathname you're attaching. For most resource managers, this is an iofunc_attr_t structure.



Use the -l c option to qcc to link against this library. This library is usually included automatically.


The resmgr_attach() function puts the path into the general pathname space and binds requests on this path to the dispatch handle dpp.

Most of the above file types are used for special services that have their own open function associated with them. For example, the mqueue manager specifies file_type as _FTYPE_MQUEUE, and mq_open() requests a pathname match of the same type.

Specify _FTYPE_ANY for normal filesystems and simple devices, such as serial ports, that don't have their own special open type, or if your resource manager can handle the type of service or act as a redirection node to a manager that does. Most resource managers are of this type.

Your resource manager won't receive messages from an open of an inappropriate type. The following table shows the different open function types and the types of pathnames they'll match.

Function: file_type: Matches pathname of type:
open() _FTYPE_ANY All types
sem_open() _FTYPE_SEM _FTYPE_ANY or
shm_open() _FTYPE_SHMEM _FTYPE_ANY or

The generic open() can be used to open a pathname of any type.

If you want to use the POSIX functions, we've provided you with the POSIX layer; to fill your connect and I/O functions tables with the default handler functions supplied by the POSIX layer library, call iofunc_func_init(). You can then override the defaults placed in the structures with your own handlers.

Note: The resmgr_attach() function copies the pointers to the resmgr_connect_funcs_t and resmgr_io_funcs_t structures, not the structures themselves. You should allocate the structures, declare them to be static, or make them global variables. If your resource manager is for more than one device with different handlers, create separate structures that define the handlers.

In the most general case, the last argument, handle is an arbitrary structure that you wish to have associated with the pathname you're attaching. Practically, however, we recommend that it contain the POSIX layer's well defined attributes structure, iofunc_attr_t, because this lets you use the POSIX-layer default library. You can extend the data that's contained in the attributes structure to contain any device-specific data that you may require. This is commonly done, and is described in the Extending the POSIX-Layer Data Structures chapter of Writing a Resource Manager.

In order to use the POSIX layer default library, the attributes structure must be bound into the Open Control Block, and you must use the POSIX layer's iofunc_ocb_t OCB. This is described in the documentation for resmgr_open_bind(), as well as in the above reference.

resmgr_attr_t structure

You can specify attributes such as the maximum message size, number of parts (number of IOVs in context), and flags in the attr structure. The resmgr_attr_t structure looks like this:

typedef struct _resmgr_attr {
   unsigned      flags;
   unsigned      nparts_max;
   unsigned      msg_max_size;
   int           (*other_func)
                 ( resmgr_context_t *, void *msg );
} resmgr_attr_t;

The members include:

Flags that affect the behavior of the resource manager interface; 0, or a combination of the following bits (defined in <sys/dispatch.h>):

Note: Don't confuse these flags with the ones you pass in the flags argument to resmgr_attach(). The names of these flags don't start with an underscore (_).

The number of components to allocate for the IOV array. If you specify 0, the resource manager library bumps the value to the minimum usable by the library itself.
The minimum amount of room to reserve for receiving a message that's allocated in resmgr_context_alloc(). If the value is too low, or you specify it as 0, resmgr_attach() picks a value that's usable.
A pointer to a function that's called if the resource manager receives an I/O message that it didn't successfully handle. This function is attached only if RESMGR_FLAG_ATTACH_OTHERFUNC is set in the flags member of this structure.

The flags argument

The flags argument to resmgr_attach() specifies additional information to control the pathname resolution.

Note: Don't confuse these flags with the ones you set in the flags member of the resmgr_attr_t structure. The names of these flags start with an underscore (_).

The flags (defined in <sys/resmgr.h>) include at least the following bits:

Force the path to be resolved after others with the same pathname at the same mountpoint.
Force the path to be resolved before others with the same pathname at the same mountpoint.
Treat the pathname as a directory and allow the resolving of longer pathnames. The _IO_CONNECT message contains the pathname passed to the client open() with the matching prefix stripped off. Without this flag, the pathname is treated as a simple file requiring an exact match.
Attached path Opened path _RESMGR_FLAG_DIR set _RESMGR_FLAG_DIR clear
/a/b /a/b Match "" Match ""
/a/b /a/b/c Match c No match
/a/b /a/b/c/d Match c/d No match
/a/b /a/bc No match No match

You can't attach a directory pathname that contains, as a subset, an existing file pathname. Likewise, you can't attach a file pathname that's a subset of an existing directory pathname.

Existing path New path New path allowed?
Directory /a/b Directory /a Yes
Directory /a/b Directory /a/b/c Yes
File /a/b Directory /a Yes
File /a/b Directory /a/b/c No; the directory is beneath a file
Directory /a/b File /a No; the directory is beneath a file
Directory /a/b File /a/b/c Yes
File /a/b File /a Yes
File /a/b File /a/b/c Yes
Handle requests for all file types. You must specify a registration file type of FTYPE_ALL.
Handle only requests for the specific filetype indicated. The pathname must be NULL.
Don't resolve paths to mountpoints on a path shorter than this (i.e. find the longest match against all pathnames attached).
Allow requests to resolve back to this server; in other words, allow the resource manager to open a path to itself.

Caution: Be very careful if you set _RESMGR_FLAG_SELF because it's possible for a deadlock to occur. For more information, see Robust implementations with Send/Receive/Reply in the Interprocess Communication (IPC) chapter of the System Architecture guide.


A unique link ID associated with this attach, or -1 on failure (errno is set).

The returned ID is needed to detach the pathname at a later time using resmgr_detach(). The ID is also passed back in the resmgr_handler() function in ctp->id.


There isn't enough free memory to complete the operation.
A component of the pathname wasn't a directory entry.


Here's an example of a simple single-threaded resource manager:

#include <stdio.h>
#include <stddef.h>
#include <stdlib.h>
#include <sys/iofunc.h>
#include <sys/dispatch.h>

static resmgr_connect_funcs_t    connect_funcs;
static resmgr_io_funcs_t         io_funcs;
static iofunc_attr_t             attr;

int main(int argc, char **argv)
    dispatch_t           *dpp;
    resmgr_attr_t        resmgr_attr;
    resmgr_context_t     *ctp;
    int                  id;

    /* initialize dispatch interface */
    if ( (dpp = dispatch_create()) == NULL ) {
       fprintf( stderr, "%s: Unable to allocate \
                dispatch handle.\n", argv[0] );
       return EXIT_FAILURE;

    /* initialize resource manager attributes */
    memset( &resmgr_attr, 0, sizeof resmgr_attr );
    resmgr_attr.nparts_max = 1;
    resmgr_attr.msg_max_size = 2048;

    /* initialize functions for handling messages */
    iofunc_func_init( _RESMGR_CONNECT_NFUNCS, &connect_funcs,
                      _RESMGR_IO_NFUNCS, &io_funcs );

    /* initialize attribute structure */
    iofunc_attr_init( &attr, S_IFNAM | 0666, 0, 0 );

    /* attach our device name (passing in the POSIX defaults 
       from the iofunc_func_init and iofunc_attr_init functions) 
    if ( (id = resmgr_attach
          ( dpp, &resmgr_attr, "/dev/mynull", _FTYPE_ANY, 0,
          &connect_funcs, &io_funcs, &attr)) == -1 ) {
        fprintf( stderr, "%s: Unable to attach name.\n", \
                 argv[0] );
        return EXIT_FAILURE;

    /* allocate a context structure */
    ctp = resmgr_context_alloc( dpp );

    /* start the resource manager message loop */
    while (1) {
        if ( (ctp = resmgr_block( ctp )) == NULL ) {
           fprintf(stderr, "block error\n");
           return EXIT_FAILURE;

For more examples using the dispatch interface, see dispatch_create(), message_attach(), and thread_pool_create(). For more information on writing a resource manager, see Writing a Resource Manager


QNX Neutrino

Cancellation point Yes
Interrupt handler No
Signal handler No
Thread Yes


If your application calls this function, it must run as root.

See also:

dispatch_create(), iofunc_attr_init(), iofunc_attr_t, iofunc_func_init(), iofunc_ocb_t, resmgr_block(), resmgr_connect_funcs_t, resmgr_context_alloc(), resmgr_context_free(), resmgr_detach(), resmgr_handler(), resmgr_io_funcs_t

Writing a Resource Manager

Resource Managers chapter of Getting Started with QNX Neutrino