fusd/examples/echo.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  * echo.c: Example of how to use both the 'read' and 'write' callbacks.
  38  *
  39  * This example creates a single device, /dev/echo.  If you write
  40  * something to /dev/echo (e.g., "echo HI THERE > /dev/echo"), it gets
  41  * stored.  Then, when you read (e.g. "cat /dev/echo"), you get back
  42  * whatever you wrote most recently.
  43  *
  44  * $Id$
  45  */
  46
  47 #include <stdio.h>
  48 #include <stdlib.h>
  49 #include <string.h>
  50 #include <errno.h>
  51 #include <unistd.h>
  52
  53 #include "fusd.h"
  54
  55 #define MIN(x, y) ((x) < (y) ? (x) : (y))
  56
  57 /* EXAMPLE START echo.c */
  58 char *data = NULL;
  59 int data_length = 0;
  60
  61 ssize_t echo_read(struct fusd_file_info *file, char *user_buffer,
  62               size_t user_length, loff_t *offset)
  63 {
  64   /* if the user has read past the end of the data, return EOF */
  65   if (*offset >= data_length)
  66     return 0;
  67
  68   /* only return as much data as we have */
  69   user_length = MIN(user_length, data_length - *offset);
  70
  71   /* copy data to user starting from the first byte they haven't seen */
  72   memcpy(user_buffer, data + *offset, user_length);
  73   *offset += user_length;
  74
  75   /* tell them how much data they got */
  76   return user_length;
  77 }
  78
  79 ssize_t echo_write(struct fusd_file_info *file, const char *user_buffer,
  80                    size_t user_length, loff_t *offset)
  81 {
  82   /* free the old data, if any */
  83   if (data != NULL) {
  84     free(data);
  85     data = NULL;
  86     data_length = 0;
  87   }
  88
  89   /* allocate space for new data; return error if that fails */
  90   if ((data = malloc(user_length)) == NULL)
  91     return -ENOMEM;
  92
  93   /* make a copy of user's data; tell the user we copied everything */
  94   memcpy(data, user_buffer, user_length);
  95   data_length = user_length;
  96   return user_length;
  97 }
  98 /* EXAMPLE STOP */
  99
 100 int do_open_or_close(struct fusd_file_info *file)
 101 {
 102   return 0; /* opens and closes always succeed */
 103 }
 104
 105
 106 struct fusd_file_operations echo_fops = {
 107   open: do_open_or_close,
 108   read: echo_read,
 109   write: echo_write,
 110   close: do_open_or_close
 111 };
 112
 113
 114 int main(int argc, char *argv[])
 115 {
 116   if (fusd_register("/dev/echo", "misc", "echo", 0666, NULL, &echo_fops) < 0) {
 117     perror("register of /dev/echo failed");
 118     exit(1);
 119   }
 120
 121   fprintf(stderr, "calling fusd_run...\n");
 122   fusd_run();
 123   return 0;
 124 }