In my_read_dir() is where the fun begins. From a high level perspective, we allocate a buffer that's going to hold the result of this operation (called reply_msg). We then use dp to "walk" along the output buffer, stuffing struct dirent entries as we go along. The helper routine dirent_size() is used to determine if we have sufficient room in the output buffer to stuff the next entry; the helper routine dirent_fill() is used to perform the stuffing. (Note that these routines are not part of the resource manager library; they're discussed and documented below.)

On first glance this code may look inefficient; we're using sprintf() to create a two-byte filename (the filename character and a NUL terminator) into a buffer that's _POSIX_PATH_MAX (256) bytes long. This was done to keep the code as generic as possible.

Finally, notice that we use the OCB's offset member to indicate to us which particular filename we're generating the struct dirent for at any given time. This means that we also have to update the offset field whenever we return data.

The return of data to the client is accomplished in the "usual" way, via MsgReply(). Note that the status field of MsgReply() is used to indicate the number of bytes that were sent to the client.

static int
my_read_dir (resmgr_context_t *ctp, io_read_t *msg,
             iofunc_ocb_t *ocb)
    int     nbytes;
    int     nleft;
    struct  dirent *dp;
    char    *reply_msg;
    char    fname [_POSIX_PATH_MAX];

    // allocate a buffer for the reply
    reply_msg = calloc (1, msg -> i.nbytes);
    if (reply_msg == NULL) {
        return (ENOMEM);

    // assign output buffer
    dp = (struct dirent *) reply_msg;

    // we have "nleft" bytes left
    nleft = msg -> i.nbytes;
    while (ocb -> offset < NUM_ENTS) {

        // create the filename
        sprintf (fname, "%c", ocb -> offset + 'a');

        // see how big the result is
        nbytes = dirent_size (fname);

        // do we have room for it?
        if (nleft - nbytes >= 0) {

            // fill the dirent, and advance the dirent pointer
            dp = dirent_fill (dp, ocb -> offset + 1,
                              ocb -> offset, fname);

            // move the OCB offset
            ocb -> offset++;

            // account for the bytes we just used up
            nleft -= nbytes;
        } else {

            // don't have any more room, stop

    // return info back to the client
    MsgReply (ctp -> rcvid, (char *) dp - reply_msg,
              reply_msg, (char *) dp - reply_msg);

    // release our buffer
    free (reply_msg);

    // tell resource manager library we already did the reply
    return (_RESMGR_NOREPLY);