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 int64_t null_getlength(BlockDriverState *bs)
 101 {
 102     BDRVNullState *s = bs->opaque;
 103     return s->length;
 104 }
 105
 106 static coroutine_fn int null_co_common(BlockDriverState *bs)
 107 {
 108     BDRVNullState *s = bs->opaque;
 109
 110     if (s->latency_ns) {
 111         qemu_co_sleep_ns(QEMU_CLOCK_REALTIME, s->latency_ns);
 112     }
 113     return 0;
 114 }
 115
 116 static coroutine_fn int null_co_preadv(BlockDriverState *bs,
 117                                        uint64_t offset, uint64_t bytes,
 118                                        QEMUIOVector *qiov, int flags)
 119 {
 120     BDRVNullState *s = bs->opaque;
 121
 122     if (s->read_zeroes) {
 123         qemu_iovec_memset(qiov, 0, 0, bytes);
 124     }
 125
 126     return null_co_common(bs);
 127 }
 128
 129 static coroutine_fn int null_co_pwritev(BlockDriverState *bs,
 130                                         uint64_t offset, uint64_t bytes,
 131                                         QEMUIOVector *qiov, int flags)
 132 {
 133     return null_co_common(bs);
 134 }
 135
 136 static coroutine_fn int null_co_flush(BlockDriverState *bs)
 137 {
 138     return null_co_common(bs);
 139 }
 140
 141 typedef struct {
 142     BlockAIOCB common;
 143     QEMUTimer timer;
 144 } NullAIOCB;
 145
 146 static const AIOCBInfo null_aiocb_info = {
 147     .aiocb_size = sizeof(NullAIOCB),
 148 };
 149
 150 static void null_bh_cb(void *opaque)
 151 {
 152     NullAIOCB *acb = opaque;
 153     acb->common.cb(acb->common.opaque, 0);
 154     qemu_aio_unref(acb);
 155 }
 156
 157 static void null_timer_cb(void *opaque)
 158 {
 159     NullAIOCB *acb = opaque;
 160     acb->common.cb(acb->common.opaque, 0);
 161     timer_deinit(&acb->timer);
 162     qemu_aio_unref(acb);
 163 }
 164
 165 static inline BlockAIOCB *null_aio_common(BlockDriverState *bs,
 166                                           BlockCompletionFunc *cb,
 167                                           void *opaque)
 168 {
 169     NullAIOCB *acb;
 170     BDRVNullState *s = bs->opaque;
 171
 172     acb = qemu_aio_get(&null_aiocb_info, bs, cb, opaque);
 173     /* Only emulate latency after vcpu is running. */
 174     if (s->latency_ns) {
 175         aio_timer_init(bdrv_get_aio_context(bs), &acb->timer,
 176                        QEMU_CLOCK_REALTIME, SCALE_NS,
 177                        null_timer_cb, acb);
 178         timer_mod_ns(&acb->timer,
 179                      qemu_clock_get_ns(QEMU_CLOCK_REALTIME) + s->latency_ns);
 180     } else {
 181         aio_bh_schedule_oneshot(bdrv_get_aio_context(bs), null_bh_cb, acb);
 182     }
 183     return &acb->common;
 184 }
 185
 186 static BlockAIOCB *null_aio_preadv(BlockDriverState *bs,
 187                                    uint64_t offset, uint64_t bytes,
 188                                    QEMUIOVector *qiov, int flags,
 189                                    BlockCompletionFunc *cb,
 190                                    void *opaque)
 191 {
 192     BDRVNullState *s = bs->opaque;
 193
 194     if (s->read_zeroes) {
 195         qemu_iovec_memset(qiov, 0, 0, bytes);
 196     }
 197
 198     return null_aio_common(bs, cb, opaque);
 199 }
 200
 201 static BlockAIOCB *null_aio_pwritev(BlockDriverState *bs,
 202                                     uint64_t offset, uint64_t bytes,
 203                                     QEMUIOVector *qiov, int flags,
 204                                     BlockCompletionFunc *cb,
 205                                     void *opaque)
 206 {
 207     return null_aio_common(bs, cb, opaque);
 208 }
 209
 210 static BlockAIOCB *null_aio_flush(BlockDriverState *bs,
 211                                   BlockCompletionFunc *cb,
 212                                   void *opaque)
 213 {
 214     return null_aio_common(bs, cb, opaque);
 215 }
 216
 217 static int null_reopen_prepare(BDRVReopenState *reopen_state,
 218                                BlockReopenQueue *queue, Error **errp)
 219 {
 220     return 0;
 221 }
 222
 223 static int coroutine_fn null_co_block_status(BlockDriverState *bs,
 224                                              bool want_zero, int64_t offset,
 225                                              int64_t bytes, int64_t *pnum,
 226                                              int64_t *map,
 227                                              BlockDriverState **file)
 228 {
 229     BDRVNullState *s = bs->opaque;
 230     int ret = BDRV_BLOCK_OFFSET_VALID;
 231
 232     *pnum = bytes;
 233     *map = offset;
 234     *file = bs;
 235
 236     if (s->read_zeroes) {
 237         ret |= BDRV_BLOCK_ZERO;
 238     }
 239     return ret;
 240 }
 241
 242 static void null_refresh_filename(BlockDriverState *bs)
 243 {
 244     const QDictEntry *e;
 245
 246     for (e = qdict_first(bs->full_open_options); e;
 247          e = qdict_next(bs->full_open_options, e))
 248     {
 249         /* These options can be ignored */
 250         if (strcmp(qdict_entry_key(e), "filename") &&
 251             strcmp(qdict_entry_key(e), "driver") &&
 252             strcmp(qdict_entry_key(e), NULL_OPT_LATENCY))
 253         {
 254             return;
 255         }
 256     }
 257
 258     snprintf(bs->exact_filename, sizeof(bs->exact_filename), "%s://",
 259              bs->drv->format_name);
 260 }
 261
 262 static const char *const null_strong_runtime_opts[] = {
 263     BLOCK_OPT_SIZE,
 264     NULL_OPT_ZEROES,
 265
 266     NULL
 267 };
 268
 269 static BlockDriver bdrv_null_co = {
 270     .format_name            = "null-co",
 271     .protocol_name          = "null-co",
 272     .instance_size          = sizeof(BDRVNullState),
 273
 274     .bdrv_file_open         = null_file_open,
 275     .bdrv_parse_filename    = null_co_parse_filename,
 276     .bdrv_getlength         = null_getlength,
 277
 278     .bdrv_co_preadv         = null_co_preadv,
 279     .bdrv_co_pwritev        = null_co_pwritev,
 280     .bdrv_co_flush_to_disk  = null_co_flush,
 281     .bdrv_reopen_prepare    = null_reopen_prepare,
 282
 283     .bdrv_co_block_status   = null_co_block_status,
 284
 285     .bdrv_refresh_filename  = null_refresh_filename,
 286     .strong_runtime_opts    = null_strong_runtime_opts,
 287 };
 288
 289 static BlockDriver bdrv_null_aio = {
 290     .format_name            = "null-aio",
 291     .protocol_name          = "null-aio",
 292     .instance_size          = sizeof(BDRVNullState),
 293
 294     .bdrv_file_open         = null_file_open,
 295     .bdrv_parse_filename    = null_aio_parse_filename,
 296     .bdrv_getlength         = null_getlength,
 297
 298     .bdrv_aio_preadv        = null_aio_preadv,
 299     .bdrv_aio_pwritev       = null_aio_pwritev,
 300     .bdrv_aio_flush         = null_aio_flush,
 301     .bdrv_reopen_prepare    = null_reopen_prepare,
 302
 303     .bdrv_co_block_status   = null_co_block_status,
 304
 305     .bdrv_refresh_filename  = null_refresh_filename,
 306     .strong_runtime_opts    = null_strong_runtime_opts,
 307 };
 308
 309 static void bdrv_null_init(void)
 310 {
 311     bdrv_register(&bdrv_null_co);
 312     bdrv_register(&bdrv_null_aio);
 313 }
 314
 315 block_init(bdrv_null_init);