main() and declarations

The first section of code presented is the main() function and some of the declarations. There's a convenience macro, ALIGN(), that's used for alignment by the dirent_fill() and dirent_size() functions.

The atoz_attrs array contains the attributes structures used for the "files" in this example. We declare NUM_ENTS array members, because we have NUM_ENTS (26) files "a" through "z." The attributes structure used for the directory itself (i.e., the /dev/atoz directory) is declared within main() and is called simply attr. Notice the differences in the way the two types of attributes structures are filled:

file attribute structure
Marked as a regular file (the S_IFREG constant) with an access mode of 0444 (meaning everyone has read access, no one has write access). The size is "1"—the file contains only one byte, namely, the uppercase letter corresponding to the filename. The inodes for these individual files are numbered "1" through "26" inclusive (it would have been more convenient to number them "0" through "25," but "0" is reserved).
directory attribute structure
Marked as a directory file (the S_IFDIR constant) with an access mode of 0555 (meaning that everyone has read and seek access, no one has write access). The size is "26"—this is simply a number picked based on the number of entries in the directory. The inode is "27"—a number known not to be in use by any of the other attributes structures.

Notice how we've overridden only the open member of the connect_func structure and the read member of the io_func structure. We've left all the others to use the POSIX defaults.

Finally, notice how we created the name /dev/atoz using resmgr_attach(). Most importantly, we used the flag _RESMGR_FLAG_DIR, which tells the process manager that it can resolve requests at and below this mountpoint.

 *  atoz.c
 *  /dev/atoz using the resource manager library

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

#define ALIGN(x) (((x) + 3) & ~3)
#define NUM_ENTS            26

static  iofunc_attr_t   atoz_attrs [NUM_ENTS];

main (int argc, char **argv)
    dispatch_t              *dpp;
    resmgr_attr_t           resmgr_attr;
    dispatch_context_t      *ctp;
    resmgr_connect_funcs_t  connect_func;
    resmgr_io_funcs_t       io_func;
    iofunc_attr_t           attr;
    int                     i;

    // create the dispatch structure
    if ((dpp = dispatch_create ()) == NULL) {
        perror ("Unable to dispatch_create");
        exit (EXIT_FAILURE);

    // initialize the various data structures
    memset (&resmgr_attr, 0, sizeof (resmgr_attr));
    resmgr_attr.nparts_max = 1;
    resmgr_attr.msg_max_size = 2048;

    // bind default functions into the outcall tables
    iofunc_func_init (_RESMGR_CONNECT_NFUNCS, &connect_func,
                      _RESMGR_IO_NFUNCS, &io_func);

    // create and initialize the attributes structure
    // for the directory.  Inodes 1-26 are reserved for the 
    // files 'a' through 'z'.  The number of bytes is 26 
    // because that's how many entries there are.
    iofunc_attr_init (&attr, S_IFDIR | 0555, 0, 0);
    attr.inode = NUM_ENTS + 1;
    attr.nbytes = NUM_ENTS;

    // and for the "a" through "z" names
    for (i = 0; i < NUM_ENTS; i++) {
        iofunc_attr_init (&atoz_attrs [i], 
                          S_IFREG | 0444, 0, 0);
        atoz_attrs [i].inode = i + 1;
        atoz_attrs [i].nbytes = 1;

    // add our functions; we're interested only in
    // io_open and io_read = my_open; = my_read;

    // establish a name in the pathname space
    if (resmgr_attach (dpp, &resmgr_attr, "/dev/atoz", 
                       _FTYPE_ANY, _RESMGR_FLAG_DIR, 
                       &connect_func, &io_func, 
                       &attr) == -1) {
        perror ("Unable to resmgr_attach");
        exit (EXIT_FAILURE);

    // allocate a context
    ctp = dispatch_context_alloc (dpp);

    // wait here forever, handling messages
    while (1) {
        if ((ctp = dispatch_block (ctp)) == NULL) {
            perror ("Unable to dispatch_block");
            exit (EXIT_FAILURE);
        dispatch_handler (ctp);

    // you'll never get here
    return (EXIT_SUCCESS);