plugins/example2/example2.c

   1 /* nbdkit
   2  * Copyright (C) 2013 Red Hat Inc.
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions are
   7  * met:
   8  *
   9  * * Redistributions of source code must retain the above copyright
  10  * notice, this list of conditions and the following disclaimer.
  11  *
  12  * * Redistributions in binary form must reproduce the above copyright
  13  * notice, this list of conditions and the following disclaimer in the
  14  * documentation and/or other materials provided with the distribution.
  15  *
  16  * * Neither the name of Red Hat nor the names of its contributors may be
  17  * used to endorse or promote products derived from this software without
  18  * specific prior written permission.
  19  *
  20  * THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND
  21  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
  22  * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
  23  * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR
  24  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  25  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  26  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
  27  * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
  28  * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
  29  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
  30  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  31  * SUCH DAMAGE.
  32  */
  33
  34 /* example2:
  35  *
  36  * A simple but more realistic read-only file server.
  37  */
  38
  39 #include <config.h>
  40
  41 #include <stdio.h>
  42 #include <stdlib.h>
  43 #include <string.h>
  44 #include <fcntl.h>
  45 #include <unistd.h>
  46
  47 #include <nbdkit-plugin.h>
  48
  49 static const char *filename = NULL;
  50
  51 /* Called for each key=value passed on the command line.  This plugin
  52  * only accepts file=<filename>, which is required.
  53  */
  54 static int
  55 example2_config (const char *key, const char *value)
  56 {
  57   if (strcmp (key, "file") == 0) {
  58     filename = value;
  59   }
  60   else {
  61     nbdkit_error ("unknown parameter '%s'", key);
  62     return -1;
  63   }
  64
  65   return 0;
  66 }
  67
  68 /* Check the user did pass a file=<FILENAME> parameter. */
  69 static int
  70 example2_config_complete (void)
  71 {
  72   if (filename == NULL) {
  73     nbdkit_error ("you must supply the file=<FILENAME> parameter after the plugin name on the command line");
  74     return -1;
  75   }
  76
  77   return 0;
  78 }
  79
  80 #define example2_config_help \
  81   "file=<FILENAME>     (required) The filename to serve."
  82
  83 /* The per-connection handle. */
  84 struct example2_handle {
  85   int fd;
  86 };
  87
  88 /* Create the per-connection handle. */
  89 static void *
  90 example2_open (void)
  91 {
  92   struct example2_handle *h;
  93
  94   h = malloc (sizeof *h);
  95   if (h == NULL) {
  96     nbdkit_error ("malloc: %m");
  97     return NULL;
  98   }
  99
 100   h->fd = open (filename, O_RDONLY|O_CLOEXEC);
 101   if (h->fd == -1) {
 102     nbdkit_error ("open: %s: %m", filename);
 103     free (h);
 104     return NULL;
 105   }
 106
 107   return h;
 108 }
 109
 110 /* Free up the per-connection handle. */
 111 static void
 112 example2_close (void *handle)
 113 {
 114   struct example2_handle *h = handle;
 115
 116   close (h->fd);
 117   free (h);
 118 }
 119
 120 /* In fact NBDKIT_THREAD_MODEL_SERIALIZE_REQUESTS would work here.
 121  * However for the benefit of people who blindly cut and paste code
 122  * without bothering to read any documentation, leave this at a safe
 123  * default.
 124  */
 125 #define THREAD_MODEL NBDKIT_THREAD_MODEL_SERIALIZE_ALL_REQUESTS
 126
 127 /* Read data from the file. */
 128 static int
 129 example2_pread (void *handle, void *buf, size_t count, off_t offset)
 130 {
 131   struct example2_handle *h = handle;
 132
 133   while (count > 0) {
 134     ssize_t r = read (h->fd, buf, count);
 135     if (r == -1) {
 136       nbdkit_error ("read error: %m");
 137       return -1;
 138     }
 139     if (r == 0) {
 140       nbdkit_error ("unexpected end of file");
 141       return -1;
 142     }
 143     buf += r;
 144     count -= r;
 145   }
 146
 147   return 0;
 148 }
 149
 150 static struct nbdkit_plugin plugin = {
 151   .name              = "example2",
 152   .config            = example2_config,
 153   .config_complete   = example2_config_complete,
 154   .config_help       = example2_config_help,
 155   .open              = example2_open,
 156   .close             = example2_close,
 157   .pread             = example2_pread,
 158 };
 159
 160 NBDKIT_REGISTER_PLUGIN(plugin)