block/null.c

   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/module.h"
  18 #include "qemu/option.h"
  19 #include "block/block_int.h"
  20 #include "sysemu/replay.h"
  21
  22 #define NULL_OPT_LATENCY "latency-ns"
  23 #define NULL_OPT_ZEROES  "read-zeroes"
  24
  25 typedef struct {
  26     int64_t length;
  27     int64_t latency_ns;
  28     bool read_zeroes;
  29 } BDRVNullState;
  30
  31 static QemuOptsList runtime_opts = {
  32     .name = "null",
  33     .head = QTAILQ_HEAD_INITIALIZER(runtime_opts.head),
  34     .desc = {
  35         {
  36             .name = BLOCK_OPT_SIZE,
  37             .type = QEMU_OPT_SIZE,
  38             .help = "size of the null block",
  39         },
  40         {
  41             .name = NULL_OPT_LATENCY,
  42             .type = QEMU_OPT_NUMBER,
  43             .help = "nanoseconds (approximated) to wait "
  44                     "before completing request",
  45         },
  46         {
  47             .name = NULL_OPT_ZEROES,
  48             .type = QEMU_OPT_BOOL,
  49             .help = "return zeroes when read",
  50         },
  51         { /* end of list */ }
  52     },
  53 };
  54
  55 static void null_co_parse_filename(const char *filename, QDict *options,
  56                                    Error **errp)
  57 {
  58     /* This functions only exists so that a null-co:// filename is accepted
  59      * with the null-co driver. */
  60     if (strcmp(filename, "null-co://")) {
  61         error_setg(errp, "The only allowed filename for this driver is "
  62                          "'null-co://'");
  63         return;
  64     }
  65 }
  66
  67 static void null_aio_parse_filename(const char *filename, QDict *options,
  68                                     Error **errp)
  69 {
  70     /* This functions only exists so that a null-aio:// filename is accepted
  71      * with the null-aio driver. */
  72     if (strcmp(filename, "null-aio://")) {
  73         error_setg(errp, "The only allowed filename for this driver is "
  74                          "'null-aio://'");
  75         return;
  76     }
  77 }
  78
  79 static int null_file_open(BlockDriverState *bs, QDict *options, int flags,
  80                           Error **errp)
  81 {
  82     QemuOpts *opts;
  83     BDRVNullState *s = bs->opaque;
  84     int ret = 0;
  85
  86     opts = qemu_opts_create(&runtime_opts, NULL, 0, &error_abort);
  87     qemu_opts_absorb_qdict(opts, options, &error_abort);
  88     s->length =
  89         qemu_opt_get_size(opts, BLOCK_OPT_SIZE, 1 << 30);
  90     s->latency_ns =
  91         qemu_opt_get_number(opts, NULL_OPT_LATENCY, 0);
  92     if (s->latency_ns < 0) {
  93         error_setg(errp, "latency-ns is invalid");
  94         ret = -EINVAL;
  95     }
  96     s->read_zeroes = qemu_opt_get_bool(opts, NULL_OPT_ZEROES, false);
  97     qemu_opts_del(opts);
  98     bs->supported_write_flags = BDRV_REQ_FUA;
  99     return ret;
 100 }
 101
 102 static int64_t null_getlength(BlockDriverState *bs)
 103 {
 104     BDRVNullState *s = bs->opaque;
 105     return s->length;
 106 }
 107
 108 static coroutine_fn int null_co_common(BlockDriverState *bs)
 109 {
 110     BDRVNullState *s = bs->opaque;
 111
 112     if (s->latency_ns) {
 113         qemu_co_sleep_ns(QEMU_CLOCK_REALTIME, s->latency_ns);
 114     }
 115     return 0;
 116 }
 117
 118 static coroutine_fn int null_co_preadv(BlockDriverState *bs,
 119                                        uint64_t offset, uint64_t bytes,
 120                                        QEMUIOVector *qiov, int flags)
 121 {
 122     BDRVNullState *s = bs->opaque;
 123
 124     if (s->read_zeroes) {
 125         qemu_iovec_memset(qiov, 0, 0, bytes);
 126     }
 127
 128     return null_co_common(bs);
 129 }
 130
 131 static coroutine_fn int null_co_pwritev(BlockDriverState *bs,
 132                                         uint64_t offset, uint64_t bytes,
 133                                         QEMUIOVector *qiov, int flags)
 134 {
 135     return null_co_common(bs);
 136 }
 137
 138 static coroutine_fn int null_co_flush(BlockDriverState *bs)
 139 {
 140     return null_co_common(bs);
 141 }
 142
 143 typedef struct {
 144     BlockAIOCB common;
 145     QEMUTimer timer;
 146 } NullAIOCB;
 147
 148 static const AIOCBInfo null_aiocb_info = {
 149     .aiocb_size = sizeof(NullAIOCB),
 150 };
 151
 152 static void null_bh_cb(void *opaque)
 153 {
 154     NullAIOCB *acb = opaque;
 155     acb->common.cb(acb->common.opaque, 0);
 156     qemu_aio_unref(acb);
 157 }
 158
 159 static void null_timer_cb(void *opaque)
 160 {
 161     NullAIOCB *acb = opaque;
 162     acb->common.cb(acb->common.opaque, 0);
 163     timer_deinit(&acb->timer);
 164     qemu_aio_unref(acb);
 165 }
 166
 167 static inline BlockAIOCB *null_aio_common(BlockDriverState *bs,
 168                                           BlockCompletionFunc *cb,
 169                                           void *opaque)
 170 {
 171     NullAIOCB *acb;
 172     BDRVNullState *s = bs->opaque;
 173
 174     acb = qemu_aio_get(&null_aiocb_info, bs, cb, opaque);
 175     /* Only emulate latency after vcpu is running. */
 176     if (s->latency_ns) {
 177         aio_timer_init(bdrv_get_aio_context(bs), &acb->timer,
 178                        QEMU_CLOCK_REALTIME, SCALE_NS,
 179                        null_timer_cb, acb);
 180         timer_mod_ns(&acb->timer,
 181                      qemu_clock_get_ns(QEMU_CLOCK_REALTIME) + s->latency_ns);
 182     } else {
 183         replay_bh_schedule_oneshot_event(bdrv_get_aio_context(bs),
 184                                          null_bh_cb, acb);
 185     }
 186     return &acb->common;
 187 }
 188
 189 static BlockAIOCB *null_aio_preadv(BlockDriverState *bs,
 190                                    uint64_t offset, uint64_t bytes,
 191                                    QEMUIOVector *qiov, int flags,
 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, bytes);
 199     }
 200
 201     return null_aio_common(bs, cb, opaque);
 202 }
 203
 204 static BlockAIOCB *null_aio_pwritev(BlockDriverState *bs,
 205                                     uint64_t offset, uint64_t bytes,
 206                                     QEMUIOVector *qiov, int flags,
 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)
 246 {
 247     const QDictEntry *e;
 248
 249     for (e = qdict_first(bs->full_open_options); e;
 250          e = qdict_next(bs->full_open_options, e))
 251     {
 252         /* These options can be ignored */
 253         if (strcmp(qdict_entry_key(e), "filename") &&
 254             strcmp(qdict_entry_key(e), "driver") &&
 255             strcmp(qdict_entry_key(e), NULL_OPT_LATENCY))
 256         {
 257             return;
 258         }
 259     }
 260
 261     snprintf(bs->exact_filename, sizeof(bs->exact_filename), "%s://",
 262              bs->drv->format_name);
 263 }
 264
 265 static const char *const null_strong_runtime_opts[] = {
 266     BLOCK_OPT_SIZE,
 267     NULL_OPT_ZEROES,
 268
 269     NULL
 270 };
 271
 272 static BlockDriver bdrv_null_co = {
 273     .format_name            = "null-co",
 274     .protocol_name          = "null-co",
 275     .instance_size          = sizeof(BDRVNullState),
 276
 277     .bdrv_file_open         = null_file_open,
 278     .bdrv_parse_filename    = null_co_parse_filename,
 279     .bdrv_getlength         = null_getlength,
 280
 281     .bdrv_co_preadv         = null_co_preadv,
 282     .bdrv_co_pwritev        = null_co_pwritev,
 283     .bdrv_co_flush_to_disk  = null_co_flush,
 284     .bdrv_reopen_prepare    = null_reopen_prepare,
 285
 286     .bdrv_co_block_status   = null_co_block_status,
 287
 288     .bdrv_refresh_filename  = null_refresh_filename,
 289     .strong_runtime_opts    = null_strong_runtime_opts,
 290 };
 291
 292 static BlockDriver bdrv_null_aio = {
 293     .format_name            = "null-aio",
 294     .protocol_name          = "null-aio",
 295     .instance_size          = sizeof(BDRVNullState),
 296
 297     .bdrv_file_open         = null_file_open,
 298     .bdrv_parse_filename    = null_aio_parse_filename,
 299     .bdrv_getlength         = null_getlength,
 300
 301     .bdrv_aio_preadv        = null_aio_preadv,
 302     .bdrv_aio_pwritev       = null_aio_pwritev,
 303     .bdrv_aio_flush         = null_aio_flush,
 304     .bdrv_reopen_prepare    = null_reopen_prepare,
 305
 306     .bdrv_co_block_status   = null_co_block_status,
 307
 308     .bdrv_refresh_filename  = null_refresh_filename,
 309     .strong_runtime_opts    = null_strong_runtime_opts,
 310 };
 311
 312 static void bdrv_null_init(void)
 313 {
 314     bdrv_register(&bdrv_null_co);
 315     bdrv_register(&bdrv_null_aio);
 316 }
 317
 318 block_init(bdrv_null_init);