xref: /qemu/block/null.c (revision 05c33f10) 
1 /*
2  * Null block driver
3  *
4  * Authors:
5  *  Fam Zheng <famz@redhat.com>
6  *
7  * Copyright (C) 2014 Red Hat, Inc.
8  *
9  * This work is licensed under the terms of the GNU GPL, version 2 or later.
10  * See the COPYING file in the top-level directory.
11  */
12 
13 #include "qemu/osdep.h"
14 #include "qapi/error.h"
15 #include "qapi/qmp/qdict.h"
16 #include "qapi/qmp/qstring.h"
17 #include "qemu/option.h"
18 #include "block/block_int.h"
19 
20 #define NULL_OPT_LATENCY "latency-ns"
21 #define NULL_OPT_ZEROES  "read-zeroes"
22 
23 typedef struct {
24     int64_t length;
25     int64_t latency_ns;
26     bool read_zeroes;
27 } BDRVNullState;
28 
29 static QemuOptsList runtime_opts = {
30     .name = "null",
31     .head = QTAILQ_HEAD_INITIALIZER(runtime_opts.head),
32     .desc = {
33         {
34             .name = BLOCK_OPT_SIZE,
35             .type = QEMU_OPT_SIZE,
36             .help = "size of the null block",
37         },
38         {
39             .name = NULL_OPT_LATENCY,
40             .type = QEMU_OPT_NUMBER,
41             .help = "nanoseconds (approximated) to wait "
42                     "before completing request",
43         },
44         {
45             .name = NULL_OPT_ZEROES,
46             .type = QEMU_OPT_BOOL,
47             .help = "return zeroes when read",
48         },
49         { /* end of list */ }
50     },
51 };
52 
53 static void null_co_parse_filename(const char *filename, QDict *options,
54                                    Error **errp)
55 {
56     /* This functions only exists so that a null-co:// filename is accepted
57      * with the null-co driver. */
58     if (strcmp(filename, "null-co://")) {
59         error_setg(errp, "The only allowed filename for this driver is "
60                          "'null-co://'");
61         return;
62     }
63 }
64 
65 static void null_aio_parse_filename(const char *filename, QDict *options,
66                                     Error **errp)
67 {
68     /* This functions only exists so that a null-aio:// filename is accepted
69      * with the null-aio driver. */
70     if (strcmp(filename, "null-aio://")) {
71         error_setg(errp, "The only allowed filename for this driver is "
72                          "'null-aio://'");
73         return;
74     }
75 }
76 
77 static int null_file_open(BlockDriverState *bs, QDict *options, int flags,
78                           Error **errp)
79 {
80     QemuOpts *opts;
81     BDRVNullState *s = bs->opaque;
82     int ret = 0;
83 
84     opts = qemu_opts_create(&runtime_opts, NULL, 0, &error_abort);
85     qemu_opts_absorb_qdict(opts, options, &error_abort);
86     s->length =
87         qemu_opt_get_size(opts, BLOCK_OPT_SIZE, 1 << 30);
88     s->latency_ns =
89         qemu_opt_get_number(opts, NULL_OPT_LATENCY, 0);
90     if (s->latency_ns < 0) {
91         error_setg(errp, "latency-ns is invalid");
92         ret = -EINVAL;
93     }
94     s->read_zeroes = qemu_opt_get_bool(opts, NULL_OPT_ZEROES, false);
95     qemu_opts_del(opts);
96     return ret;
97 }
98 
99 static void null_close(BlockDriverState *bs)
100 {
101 }
102 
103 static int64_t null_getlength(BlockDriverState *bs)
104 {
105     BDRVNullState *s = bs->opaque;
106     return s->length;
107 }
108 
109 static coroutine_fn int null_co_common(BlockDriverState *bs)
110 {
111     BDRVNullState *s = bs->opaque;
112 
113     if (s->latency_ns) {
114         qemu_co_sleep_ns(QEMU_CLOCK_REALTIME, s->latency_ns);
115     }
116     return 0;
117 }
118 
119 static coroutine_fn int null_co_readv(BlockDriverState *bs,
120                                       int64_t sector_num, int nb_sectors,
121                                       QEMUIOVector *qiov)
122 {
123     BDRVNullState *s = bs->opaque;
124 
125     if (s->read_zeroes) {
126         qemu_iovec_memset(qiov, 0, 0, nb_sectors * BDRV_SECTOR_SIZE);
127     }
128 
129     return null_co_common(bs);
130 }
131 
132 static coroutine_fn int null_co_writev(BlockDriverState *bs,
133                                        int64_t sector_num, int nb_sectors,
134                                        QEMUIOVector *qiov)
135 {
136     return null_co_common(bs);
137 }
138 
139 static coroutine_fn int null_co_flush(BlockDriverState *bs)
140 {
141     return null_co_common(bs);
142 }
143 
144 typedef struct {
145     BlockAIOCB common;
146     QEMUTimer timer;
147 } NullAIOCB;
148 
149 static const AIOCBInfo null_aiocb_info = {
150     .aiocb_size = sizeof(NullAIOCB),
151 };
152 
153 static void null_bh_cb(void *opaque)
154 {
155     NullAIOCB *acb = opaque;
156     acb->common.cb(acb->common.opaque, 0);
157     qemu_aio_unref(acb);
158 }
159 
160 static void null_timer_cb(void *opaque)
161 {
162     NullAIOCB *acb = opaque;
163     acb->common.cb(acb->common.opaque, 0);
164     timer_deinit(&acb->timer);
165     qemu_aio_unref(acb);
166 }
167 
168 static inline BlockAIOCB *null_aio_common(BlockDriverState *bs,
169                                           BlockCompletionFunc *cb,
170                                           void *opaque)
171 {
172     NullAIOCB *acb;
173     BDRVNullState *s = bs->opaque;
174 
175     acb = qemu_aio_get(&null_aiocb_info, bs, cb, opaque);
176     /* Only emulate latency after vcpu is running. */
177     if (s->latency_ns) {
178         aio_timer_init(bdrv_get_aio_context(bs), &acb->timer,
179                        QEMU_CLOCK_REALTIME, SCALE_NS,
180                        null_timer_cb, acb);
181         timer_mod_ns(&acb->timer,
182                      qemu_clock_get_ns(QEMU_CLOCK_REALTIME) + s->latency_ns);
183     } else {
184         aio_bh_schedule_oneshot(bdrv_get_aio_context(bs), null_bh_cb, acb);
185     }
186     return &acb->common;
187 }
188 
189 static BlockAIOCB *null_aio_readv(BlockDriverState *bs,
190                                   int64_t sector_num, QEMUIOVector *qiov,
191                                   int nb_sectors,
192                                   BlockCompletionFunc *cb,
193                                   void *opaque)
194 {
195     BDRVNullState *s = bs->opaque;
196 
197     if (s->read_zeroes) {
198         qemu_iovec_memset(qiov, 0, 0, nb_sectors * BDRV_SECTOR_SIZE);
199     }
200 
201     return null_aio_common(bs, cb, opaque);
202 }
203 
204 static BlockAIOCB *null_aio_writev(BlockDriverState *bs,
205                                    int64_t sector_num, QEMUIOVector *qiov,
206                                    int nb_sectors,
207                                    BlockCompletionFunc *cb,
208                                    void *opaque)
209 {
210     return null_aio_common(bs, cb, opaque);
211 }
212 
213 static BlockAIOCB *null_aio_flush(BlockDriverState *bs,
214                                   BlockCompletionFunc *cb,
215                                   void *opaque)
216 {
217     return null_aio_common(bs, cb, opaque);
218 }
219 
220 static int null_reopen_prepare(BDRVReopenState *reopen_state,
221                                BlockReopenQueue *queue, Error **errp)
222 {
223     return 0;
224 }
225 
226 static int coroutine_fn null_co_block_status(BlockDriverState *bs,
227                                              bool want_zero, int64_t offset,
228                                              int64_t bytes, int64_t *pnum,
229                                              int64_t *map,
230                                              BlockDriverState **file)
231 {
232     BDRVNullState *s = bs->opaque;
233     int ret = BDRV_BLOCK_OFFSET_VALID;
234 
235     *pnum = bytes;
236     *map = offset;
237     *file = bs;
238 
239     if (s->read_zeroes) {
240         ret |= BDRV_BLOCK_ZERO;
241     }
242     return ret;
243 }
244 
245 static void null_refresh_filename(BlockDriverState *bs, QDict *opts)
246 {
247     QINCREF(opts);
248     qdict_del(opts, "filename");
249 
250     if (!qdict_size(opts)) {
251         snprintf(bs->exact_filename, sizeof(bs->exact_filename), "%s://",
252                  bs->drv->format_name);
253     }
254 
255     qdict_put_str(opts, "driver", bs->drv->format_name);
256     bs->full_open_options = opts;
257 }
258 
259 static BlockDriver bdrv_null_co = {
260     .format_name            = "null-co",
261     .protocol_name          = "null-co",
262     .instance_size          = sizeof(BDRVNullState),
263 
264     .bdrv_file_open         = null_file_open,
265     .bdrv_parse_filename    = null_co_parse_filename,
266     .bdrv_close             = null_close,
267     .bdrv_getlength         = null_getlength,
268 
269     .bdrv_co_readv          = null_co_readv,
270     .bdrv_co_writev         = null_co_writev,
271     .bdrv_co_flush_to_disk  = null_co_flush,
272     .bdrv_reopen_prepare    = null_reopen_prepare,
273 
274     .bdrv_co_block_status   = null_co_block_status,
275 
276     .bdrv_refresh_filename  = null_refresh_filename,
277 };
278 
279 static BlockDriver bdrv_null_aio = {
280     .format_name            = "null-aio",
281     .protocol_name          = "null-aio",
282     .instance_size          = sizeof(BDRVNullState),
283 
284     .bdrv_file_open         = null_file_open,
285     .bdrv_parse_filename    = null_aio_parse_filename,
286     .bdrv_close             = null_close,
287     .bdrv_getlength         = null_getlength,
288 
289     .bdrv_aio_readv         = null_aio_readv,
290     .bdrv_aio_writev        = null_aio_writev,
291     .bdrv_aio_flush         = null_aio_flush,
292     .bdrv_reopen_prepare    = null_reopen_prepare,
293 
294     .bdrv_co_block_status   = null_co_block_status,
295 
296     .bdrv_refresh_filename  = null_refresh_filename,
297 };
298 
299 static void bdrv_null_init(void)
300 {
301     bdrv_register(&bdrv_null_co);
302     bdrv_register(&bdrv_null_aio);
303 }
304 
305 block_init(bdrv_null_init);
306