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 "block/block_int.h"
  18
  19 #define NULL_OPT_LATENCY "latency-ns"
  20 #define NULL_OPT_ZEROES  "read-zeroes"
  21
  22 typedef struct {
  23     int64_t length;
  24     int64_t latency_ns;
  25     bool read_zeroes;
  26 } BDRVNullState;
  27
  28 static QemuOptsList runtime_opts = {
  29     .name = "null",
  30     .head = QTAILQ_HEAD_INITIALIZER(runtime_opts.head),
  31     .desc = {
  32         {
  33             .name = "filename",
  34             .type = QEMU_OPT_STRING,
  35             .help = "",
  36         },
  37         {
  38             .name = BLOCK_OPT_SIZE,
  39             .type = QEMU_OPT_SIZE,
  40             .help = "size of the null block",
  41         },
  42         {
  43             .name = NULL_OPT_LATENCY,
  44             .type = QEMU_OPT_NUMBER,
  45             .help = "nanoseconds (approximated) to wait "
  46                     "before completing request",
  47         },
  48         {
  49             .name = NULL_OPT_ZEROES,
  50             .type = QEMU_OPT_BOOL,
  51             .help = "return zeroes when read",
  52         },
  53         { /* end of list */ }
  54     },
  55 };
  56
  57 static int null_file_open(BlockDriverState *bs, QDict *options, int flags,
  58                           Error **errp)
  59 {
  60     QemuOpts *opts;
  61     BDRVNullState *s = bs->opaque;
  62     int ret = 0;
  63
  64     opts = qemu_opts_create(&runtime_opts, NULL, 0, &error_abort);
  65     qemu_opts_absorb_qdict(opts, options, &error_abort);
  66     s->length =
  67         qemu_opt_get_size(opts, BLOCK_OPT_SIZE, 1 << 30);
  68     s->latency_ns =
  69         qemu_opt_get_number(opts, NULL_OPT_LATENCY, 0);
  70     if (s->latency_ns < 0) {
  71         error_setg(errp, "latency-ns is invalid");
  72         ret = -EINVAL;
  73     }
  74     s->read_zeroes = qemu_opt_get_bool(opts, NULL_OPT_ZEROES, false);
  75     qemu_opts_del(opts);
  76     return ret;
  77 }
  78
  79 static void null_close(BlockDriverState *bs)
  80 {
  81 }
  82
  83 static int64_t null_getlength(BlockDriverState *bs)
  84 {
  85     BDRVNullState *s = bs->opaque;
  86     return s->length;
  87 }
  88
  89 static coroutine_fn int null_co_common(BlockDriverState *bs)
  90 {
  91     BDRVNullState *s = bs->opaque;
  92
  93     if (s->latency_ns) {
  94         co_aio_sleep_ns(bdrv_get_aio_context(bs), QEMU_CLOCK_REALTIME,
  95                         s->latency_ns);
  96     }
  97     return 0;
  98 }
  99
 100 static coroutine_fn int null_co_readv(BlockDriverState *bs,
 101                                       int64_t sector_num, int nb_sectors,
 102                                       QEMUIOVector *qiov)
 103 {
 104     BDRVNullState *s = bs->opaque;
 105
 106     if (s->read_zeroes) {
 107         qemu_iovec_memset(qiov, 0, 0, nb_sectors * BDRV_SECTOR_SIZE);
 108     }
 109
 110     return null_co_common(bs);
 111 }
 112
 113 static coroutine_fn int null_co_writev(BlockDriverState *bs,
 114                                        int64_t sector_num, int nb_sectors,
 115                                        QEMUIOVector *qiov)
 116 {
 117     return null_co_common(bs);
 118 }
 119
 120 static coroutine_fn int null_co_flush(BlockDriverState *bs)
 121 {
 122     return null_co_common(bs);
 123 }
 124
 125 typedef struct {
 126     BlockAIOCB common;
 127     QEMUBH *bh;
 128     QEMUTimer timer;
 129 } NullAIOCB;
 130
 131 static const AIOCBInfo null_aiocb_info = {
 132     .aiocb_size = sizeof(NullAIOCB),
 133 };
 134
 135 static void null_bh_cb(void *opaque)
 136 {
 137     NullAIOCB *acb = opaque;
 138     acb->common.cb(acb->common.opaque, 0);
 139     qemu_bh_delete(acb->bh);
 140     qemu_aio_unref(acb);
 141 }
 142
 143 static void null_timer_cb(void *opaque)
 144 {
 145     NullAIOCB *acb = opaque;
 146     acb->common.cb(acb->common.opaque, 0);
 147     timer_deinit(&acb->timer);
 148     qemu_aio_unref(acb);
 149 }
 150
 151 static inline BlockAIOCB *null_aio_common(BlockDriverState *bs,
 152                                           BlockCompletionFunc *cb,
 153                                           void *opaque)
 154 {
 155     NullAIOCB *acb;
 156     BDRVNullState *s = bs->opaque;
 157
 158     acb = qemu_aio_get(&null_aiocb_info, bs, cb, opaque);
 159     /* Only emulate latency after vcpu is running. */
 160     if (s->latency_ns) {
 161         aio_timer_init(bdrv_get_aio_context(bs), &acb->timer,
 162                        QEMU_CLOCK_REALTIME, SCALE_NS,
 163                        null_timer_cb, acb);
 164         timer_mod_ns(&acb->timer,
 165                      qemu_clock_get_ns(QEMU_CLOCK_REALTIME) + s->latency_ns);
 166     } else {
 167         acb->bh = aio_bh_new(bdrv_get_aio_context(bs), null_bh_cb, acb);
 168         qemu_bh_schedule(acb->bh);
 169     }
 170     return &acb->common;
 171 }
 172
 173 static BlockAIOCB *null_aio_readv(BlockDriverState *bs,
 174                                   int64_t sector_num, QEMUIOVector *qiov,
 175                                   int nb_sectors,
 176                                   BlockCompletionFunc *cb,
 177                                   void *opaque)
 178 {
 179     BDRVNullState *s = bs->opaque;
 180
 181     if (s->read_zeroes) {
 182         qemu_iovec_memset(qiov, 0, 0, nb_sectors * BDRV_SECTOR_SIZE);
 183     }
 184
 185     return null_aio_common(bs, cb, opaque);
 186 }
 187
 188 static BlockAIOCB *null_aio_writev(BlockDriverState *bs,
 189                                    int64_t sector_num, QEMUIOVector *qiov,
 190                                    int nb_sectors,
 191                                    BlockCompletionFunc *cb,
 192                                    void *opaque)
 193 {
 194     return null_aio_common(bs, cb, opaque);
 195 }
 196
 197 static BlockAIOCB *null_aio_flush(BlockDriverState *bs,
 198                                   BlockCompletionFunc *cb,
 199                                   void *opaque)
 200 {
 201     return null_aio_common(bs, cb, opaque);
 202 }
 203
 204 static int null_reopen_prepare(BDRVReopenState *reopen_state,
 205                                BlockReopenQueue *queue, Error **errp)
 206 {
 207     return 0;
 208 }
 209
 210 static int64_t coroutine_fn null_co_get_block_status(BlockDriverState *bs,
 211                                                      int64_t sector_num,
 212                                                      int nb_sectors, int *pnum,
 213                                                      BlockDriverState **file)
 214 {
 215     BDRVNullState *s = bs->opaque;
 216     off_t start = sector_num * BDRV_SECTOR_SIZE;
 217
 218     *pnum = nb_sectors;
 219     *file = bs;
 220
 221     if (s->read_zeroes) {
 222         return BDRV_BLOCK_OFFSET_VALID | start | BDRV_BLOCK_ZERO;
 223     } else {
 224         return BDRV_BLOCK_OFFSET_VALID | start;
 225     }
 226 }
 227
 228 static void null_refresh_filename(BlockDriverState *bs, QDict *opts)
 229 {
 230     QINCREF(opts);
 231     qdict_del(opts, "filename");
 232
 233     if (!qdict_size(opts)) {
 234         snprintf(bs->exact_filename, sizeof(bs->exact_filename), "%s://",
 235                  bs->drv->format_name);
 236     }
 237
 238     qdict_put(opts, "driver", qstring_from_str(bs->drv->format_name));
 239     bs->full_open_options = opts;
 240 }
 241
 242 static BlockDriver bdrv_null_co = {
 243     .format_name            = "null-co",
 244     .protocol_name          = "null-co",
 245     .instance_size          = sizeof(BDRVNullState),
 246
 247     .bdrv_file_open         = null_file_open,
 248     .bdrv_close             = null_close,
 249     .bdrv_getlength         = null_getlength,
 250
 251     .bdrv_co_readv          = null_co_readv,
 252     .bdrv_co_writev         = null_co_writev,
 253     .bdrv_co_flush_to_disk  = null_co_flush,
 254     .bdrv_reopen_prepare    = null_reopen_prepare,
 255
 256     .bdrv_co_get_block_status   = null_co_get_block_status,
 257
 258     .bdrv_refresh_filename  = null_refresh_filename,
 259 };
 260
 261 static BlockDriver bdrv_null_aio = {
 262     .format_name            = "null-aio",
 263     .protocol_name          = "null-aio",
 264     .instance_size          = sizeof(BDRVNullState),
 265
 266     .bdrv_file_open         = null_file_open,
 267     .bdrv_close             = null_close,
 268     .bdrv_getlength         = null_getlength,
 269
 270     .bdrv_aio_readv         = null_aio_readv,
 271     .bdrv_aio_writev        = null_aio_writev,
 272     .bdrv_aio_flush         = null_aio_flush,
 273     .bdrv_reopen_prepare    = null_reopen_prepare,
 274
 275     .bdrv_co_get_block_status   = null_co_get_block_status,
 276
 277     .bdrv_refresh_filename  = null_refresh_filename,
 278 };
 279
 280 static void bdrv_null_init(void)
 281 {
 282     bdrv_register(&bdrv_null_co);
 283     bdrv_register(&bdrv_null_aio);
 284 }
 285
 286 block_init(bdrv_null_init);