fusd/examples/helloworld.c

   1 /*
   2  *
   3  * Copyright (c) 2003 The Regents of the University of California.  All
   4  * rights reserved.
   5  *
   6  * Redistribution and use in source and binary forms, with or without
   7  * modification, are permitted provided that the following conditions
   8  * are met:
   9  *
  10  * - Redistributions of source code must retain the above copyright
  11  *   notice, this list of conditions and the following disclaimer.
  12  *
  13  * - Neither the name of the University nor the names of its
  14  *   contributors may be used to endorse or promote products derived
  15  *   from this software without specific prior written permission.
  16  *
  17  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS''
  18  * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
  19  * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
  20  * PARTICULAR  PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR
  21  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  22  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  23  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  24  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
  25  * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  26  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  27  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  28  *
  29  */
  30
  31
  32 /*
  33  * FUSD - The Framework for UserSpace Devices - Example program
  34  *
  35  * Jeremy Elson <jelson@circlemud.org>
  36  *
  37  * hello-world: Simply creates a device called /dev/hello-world, which
  38  * greets you when you try to get it.
  39  *
  40  * $Id$
  41  */
  42
  43 /* EXAMPLE START helloworld.c */
  44 #include <stdio.h>
  45 #include <string.h>
  46 #include <errno.h>
  47 #include "fusd.h"
  48
  49 #define GREETING "Hello, world!\n"
  50
  51 int do_open_or_close(struct fusd_file_info *file)
  52 {
  53   return 0; /* attempts to open and close this file always succeed */
  54 }
  55
  56 ssize_t do_read(struct fusd_file_info *file, char *user_buffer,
  57             size_t user_length, loff_t *offset)
  58 {
  59   int retval = 0;
  60
  61   /* The first read to the device returns a greeting.  The second read
  62    * returns EOF. */
  63   if (*offset == 0) {
  64     if (user_length < strlen(GREETING))
  65       retval = -EINVAL;  /* the user must supply a big enough buffer! */
  66     else {
  67       memcpy(user_buffer, GREETING, strlen(GREETING)); /* greet user */
  68       retval = strlen(GREETING); /* retval = number of bytes returned */
  69       *offset += retval; /* advance user's file pointer */
  70     }
  71   }
  72
  73   return retval;
  74 }
  75
  76 int main(int argc, char *argv[])
  77 {
  78   struct fusd_file_operations fops = {
  79     open: do_open_or_close,
  80     read: do_read,
  81     close: do_open_or_close };
  82
  83   if (fusd_register("/dev/hello-world", "test", "hello-world", 0666, NULL, &fops) < 0)
  84     perror("Unable to register device");
  85   else {
  86     printf("/dev/hello-world should now exist - calling fusd_run...\n");
  87     fusd_run();
  88   }
  89   return 0;
  90 }
  91 /* EXAMPLE STOP helloworld.c */