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/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     bs->supported_write_flags = BDRV_REQ_FUA;
  97     return ret;
  98 }
  99
 100 static void null_close(BlockDriverState *bs)
 101 {
 102 }
 103
 104 static int64_t null_getlength(BlockDriverState *bs)
 105 {
 106     BDRVNullState *s = bs->opaque;
 107     return s->length;
 108 }
 109
 110 static coroutine_fn int null_co_common(BlockDriverState *bs)
 111 {
 112     BDRVNullState *s = bs->opaque;
 113
 114     if (s->latency_ns) {
 115         qemu_co_sleep_ns(QEMU_CLOCK_REALTIME, s->latency_ns);
 116     }
 117     return 0;
 118 }
 119
 120 static coroutine_fn int null_co_preadv(BlockDriverState *bs,
 121                                        uint64_t offset, uint64_t bytes,
 122                                        QEMUIOVector *qiov, int flags)
 123 {
 124     BDRVNullState *s = bs->opaque;
 125
 126     if (s->read_zeroes) {
 127         qemu_iovec_memset(qiov, 0, 0, bytes);
 128     }
 129
 130     return null_co_common(bs);
 131 }
 132
 133 static coroutine_fn int null_co_pwritev(BlockDriverState *bs,
 134                                         uint64_t offset, uint64_t bytes,
 135                                         QEMUIOVector *qiov, int flags)
 136 {
 137     return null_co_common(bs);
 138 }
 139
 140 static coroutine_fn int null_co_flush(BlockDriverState *bs)
 141 {
 142     return null_co_common(bs);
 143 }
 144
 145 typedef struct {
 146     BlockAIOCB common;
 147     QEMUTimer timer;
 148 } NullAIOCB;
 149
 150 static const AIOCBInfo null_aiocb_info = {
 151     .aiocb_size = sizeof(NullAIOCB),
 152 };
 153
 154 static void null_bh_cb(void *opaque)
 155 {
 156     NullAIOCB *acb = opaque;
 157     acb->common.cb(acb->common.opaque, 0);
 158     qemu_aio_unref(acb);
 159 }
 160
 161 static void null_timer_cb(void *opaque)
 162 {
 163     NullAIOCB *acb = opaque;
 164     acb->common.cb(acb->common.opaque, 0);
 165     timer_deinit(&acb->timer);
 166     qemu_aio_unref(acb);
 167 }
 168
 169 static inline BlockAIOCB *null_aio_common(BlockDriverState *bs,
 170                                           BlockCompletionFunc *cb,
 171                                           void *opaque)
 172 {
 173     NullAIOCB *acb;
 174     BDRVNullState *s = bs->opaque;
 175
 176     acb = qemu_aio_get(&null_aiocb_info, bs, cb, opaque);
 177     /* Only emulate latency after vcpu is running. */
 178     if (s->latency_ns) {
 179         aio_timer_init(bdrv_get_aio_context(bs), &acb->timer,
 180                        QEMU_CLOCK_REALTIME, SCALE_NS,
 181                        null_timer_cb, acb);
 182         timer_mod_ns(&acb->timer,
 183                      qemu_clock_get_ns(QEMU_CLOCK_REALTIME) + s->latency_ns);
 184     } else {
 185         aio_bh_schedule_oneshot(bdrv_get_aio_context(bs), null_bh_cb, acb);
 186     }
 187     return &acb->common;
 188 }
 189
 190 static BlockAIOCB *null_aio_preadv(BlockDriverState *bs,
 191                                    uint64_t offset, uint64_t bytes,
 192                                    QEMUIOVector *qiov, int flags,
 193                                    BlockCompletionFunc *cb,
 194                                    void *opaque)
 195 {
 196     BDRVNullState *s = bs->opaque;
 197
 198     if (s->read_zeroes) {
 199         qemu_iovec_memset(qiov, 0, 0, bytes);
 200     }
 201
 202     return null_aio_common(bs, cb, opaque);
 203 }
 204
 205 static BlockAIOCB *null_aio_pwritev(BlockDriverState *bs,
 206                                     uint64_t offset, uint64_t bytes,
 207                                     QEMUIOVector *qiov, int flags,
 208                                     BlockCompletionFunc *cb,
 209                                     void *opaque)
 210 {
 211     return null_aio_common(bs, cb, opaque);
 212 }
 213
 214 static BlockAIOCB *null_aio_flush(BlockDriverState *bs,
 215                                   BlockCompletionFunc *cb,
 216                                   void *opaque)
 217 {
 218     return null_aio_common(bs, cb, opaque);
 219 }
 220
 221 static int null_reopen_prepare(BDRVReopenState *reopen_state,
 222                                BlockReopenQueue *queue, Error **errp)
 223 {
 224     return 0;
 225 }
 226
 227 static int coroutine_fn null_co_block_status(BlockDriverState *bs,
 228                                              bool want_zero, int64_t offset,
 229                                              int64_t bytes, int64_t *pnum,
 230                                              int64_t *map,
 231                                              BlockDriverState **file)
 232 {
 233     BDRVNullState *s = bs->opaque;
 234     int ret = BDRV_BLOCK_OFFSET_VALID;
 235
 236     *pnum = bytes;
 237     *map = offset;
 238     *file = bs;
 239
 240     if (s->read_zeroes) {
 241         ret |= BDRV_BLOCK_ZERO;
 242     }
 243     return ret;
 244 }
 245
 246 static void null_refresh_filename(BlockDriverState *bs, QDict *opts)
 247 {
 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 = qobject_ref(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_preadv         = null_co_preadv,
 270     .bdrv_co_pwritev        = null_co_pwritev,
 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_preadv        = null_aio_preadv,
 290     .bdrv_aio_pwritev       = null_aio_pwritev,
 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);