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     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);