echo.c 3.6 KB

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  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. * FUSD - The Framework for UserSpace Devices - Example program
  32. *
  33. * Jeremy Elson <jelson@circlemud.org>
  34. *
  35. * echo.c: Example of how to use both the 'read' and 'write' callbacks.
  36. *
  37. * This example creates a single device, /dev/echo. If you write
  38. * something to /dev/echo (e.g., "echo HI THERE > /dev/echo"), it gets
  39. * stored. Then, when you read (e.g. "cat /dev/echo"), you get back
  40. * whatever you wrote most recently.
  41. *
  42. * $Id$
  43. */
  44. #include <stdio.h>
  45. #include <stdlib.h>
  46. #include <string.h>
  47. #include <errno.h>
  48. #include <unistd.h>
  49. #include "fusd.h"
  50. #define MIN(x, y) ((x) < (y) ? (x) : (y))
  51. /* EXAMPLE START echo.c */
  52. char *data = NULL;
  53. int data_length = 0;
  54. ssize_t echo_read(struct fusd_file_info *file, char *user_buffer,
  55. size_t user_length, loff_t *offset)
  56. {
  57. /* if the user has read past the end of the data, return EOF */
  58. if (*offset >= data_length)
  59. return 0;
  60. /* only return as much data as we have */
  61. user_length = MIN(user_length, data_length - *offset);
  62. /* copy data to user starting from the first byte they haven't seen */
  63. memcpy(user_buffer, data + *offset, user_length);
  64. *offset += user_length;
  65. /* tell them how much data they got */
  66. return user_length;
  67. }
  68. ssize_t echo_write(struct fusd_file_info *file, const char *user_buffer,
  69. size_t user_length, loff_t *offset)
  70. {
  71. /* free the old data, if any */
  72. if (data != NULL) {
  73. free(data);
  74. data = NULL;
  75. data_length = 0;
  76. }
  77. /* allocate space for new data; return error if that fails */
  78. if ((data = malloc(user_length)) == NULL)
  79. return -ENOMEM;
  80. /* make a copy of user's data; tell the user we copied everything */
  81. memcpy(data, user_buffer, user_length);
  82. data_length = user_length;
  83. return user_length;
  84. }
  85. /* EXAMPLE STOP */
  86. int do_open_or_close(struct fusd_file_info *file)
  87. {
  88. return 0; /* opens and closes always succeed */
  89. }
  90. struct fusd_file_operations echo_fops = {
  91. open: do_open_or_close,
  92. read: echo_read,
  93. write: echo_write,
  94. close: do_open_or_close
  95. };
  96. int main(int argc, char *argv[])
  97. {
  98. if (fusd_register("/dev/echo", "misc", "echo", 0666, NULL, &echo_fops) < 0) {
  99. perror("register of /dev/echo failed");
  100. exit(1);
  101. }
  102. fprintf(stderr, "calling fusd_run...\n");
  103. fusd_run();
  104. return 0;
  105. }