1 /* nbdkit
2 * Copyright (C) 2017-2020 Red Hat Inc.
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions are
6 * met:
7 *
8 * * Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 *
11 * * Redistributions in binary form must reproduce the above copyright
12 * notice, this list of conditions and the following disclaimer in the
13 * documentation and/or other materials provided with the distribution.
14 *
15 * * Neither the name of Red Hat nor the names of its contributors may be
16 * used to endorse or promote products derived from this software without
17 * specific prior written permission.
18 *
19 * THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND
20 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
21 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
22 * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR
23 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
24 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
25 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
26 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
27 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
28 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
29 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
30 * SUCH DAMAGE.
31 */
32
33 #include <config.h>
34
35 #include <stdio.h>
36 #include <stdlib.h>
37 #include <stdint.h>
38 #include <string.h>
39 #include <errno.h>
40
41 #define NBDKIT_API_VERSION 2
42
43 #include <nbdkit-plugin.h>
44
45 /* The size of disk in bytes (initialized by size=<SIZE> parameter). */
46 static int64_t size = 0;
47
48 static int
null_config(const char * key,const char * value)49 null_config (const char *key, const char *value)
50 {
51 int64_t r;
52
53 if (strcmp (key, "size") == 0) {
54 r = nbdkit_parse_size (value);
55 if (r == -1)
56 return -1;
57 size = r;
58 }
59 else {
60 nbdkit_error ("unknown parameter '%s'", key);
61 return -1;
62 }
63
64 return 0;
65 }
66
67 #define null_config_help \
68 "size=<SIZE> Size of the backing disk"
69
70 /* Create the per-connection handle. */
71 static void *
null_open(int readonly)72 null_open (int readonly)
73 {
74 return NBDKIT_HANDLE_NOT_NEEDED;
75 }
76
77 #define THREAD_MODEL NBDKIT_THREAD_MODEL_PARALLEL
78
79 /* Get the disk size. */
80 static int64_t
null_get_size(void * handle)81 null_get_size (void *handle)
82 {
83 return size;
84 }
85
86 /* Serves the same data over multiple connections. */
87 static int
null_can_multi_conn(void * handle)88 null_can_multi_conn (void *handle)
89 {
90 return 1;
91 }
92
93 /* Cache. */
94 static int
null_can_cache(void * handle)95 null_can_cache (void *handle)
96 {
97 /* Everything is already in memory, returning this without
98 * implementing .cache lets nbdkit do the correct no-op.
99 */
100 return NBDKIT_CACHE_NATIVE;
101 }
102
103 /* Fast zero. */
104 static int
null_can_fast_zero(void * handle)105 null_can_fast_zero (void *handle)
106 {
107 return 1;
108 }
109
110 /* Read data. */
111 static int
null_pread(void * handle,void * buf,uint32_t count,uint64_t offset,uint32_t flags)112 null_pread (void *handle, void *buf, uint32_t count, uint64_t offset,
113 uint32_t flags)
114 {
115 memset (buf, 0, count);
116 return 0;
117 }
118
119 /* Write data. */
120 static int
null_pwrite(void * handle,const void * buf,uint32_t count,uint64_t offset,uint32_t flags)121 null_pwrite (void *handle, const void *buf, uint32_t count, uint64_t offset,
122 uint32_t flags)
123 {
124 /* nothing */
125 return 0;
126 }
127
128 /* Write zeroes. */
129 static int
null_zero(void * handle,uint32_t count,uint64_t offset,uint32_t flags)130 null_zero (void *handle, uint32_t count, uint64_t offset, uint32_t flags)
131 {
132 /* nothing */
133 return 0;
134 }
135
136 /* Flush is a no-op, so advertise native FUA support */
137 static int
null_can_fua(void * handle)138 null_can_fua (void *handle)
139 {
140 return NBDKIT_FUA_NATIVE;
141 }
142
143 /* Trim. */
144 static int
null_trim(void * handle,uint32_t count,uint64_t offset,uint32_t flags)145 null_trim (void *handle, uint32_t count, uint64_t offset, uint32_t flags)
146 {
147 /* nothing */
148 return 0;
149 }
150
151 /* Nothing is persistent, so flush is trivially supported */
152 static int
null_flush(void * handle,uint32_t flags)153 null_flush (void *handle, uint32_t flags)
154 {
155 return 0;
156 }
157
158 /* Extents. */
159 static int
null_extents(void * handle,uint32_t count,uint64_t offset,uint32_t flags,struct nbdkit_extents * extents)160 null_extents (void *handle, uint32_t count, uint64_t offset, uint32_t flags,
161 struct nbdkit_extents *extents)
162 {
163 return nbdkit_add_extent (extents, 0, size,
164 NBDKIT_EXTENT_HOLE | NBDKIT_EXTENT_ZERO);
165 }
166
167 static struct nbdkit_plugin plugin = {
168 .name = "null",
169 .version = PACKAGE_VERSION,
170 .config = null_config,
171 .config_help = null_config_help,
172 .magic_config_key = "size",
173 .open = null_open,
174 .get_size = null_get_size,
175 .can_multi_conn = null_can_multi_conn,
176 .can_cache = null_can_cache,
177 .can_fast_zero = null_can_fast_zero,
178 .pread = null_pread,
179 .pwrite = null_pwrite,
180 .zero = null_zero,
181 .trim = null_trim,
182 .can_fua = null_can_fua,
183 .flush = null_flush,
184 .extents = null_extents,
185 /* In this plugin, errno is preserved properly along error return
186 * paths from failed system calls.
187 */
188 .errno_is_preserved = 1,
189 };
190
191 NBDKIT_REGISTER_PLUGIN(plugin)
192