qemu/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 "block/block_int.h"
  14
  15 #define NULL_OPT_LATENCY "latency-ns"
  16
  17 typedef struct {
  18     int64_t length;
  19     int64_t latency_ns;
  20 } BDRVNullState;
  21
  22 static QemuOptsList runtime_opts = {
  23     .name = "null",
  24     .head = QTAILQ_HEAD_INITIALIZER(runtime_opts.head),
  25     .desc = {
  26         {
  27             .name = "filename",
  28             .type = QEMU_OPT_STRING,
  29             .help = "",
  30         },
  31         {
  32             .name = BLOCK_OPT_SIZE,
  33             .type = QEMU_OPT_SIZE,
  34             .help = "size of the null block",
  35         },
  36         {
  37             .name = NULL_OPT_LATENCY,
  38             .type = QEMU_OPT_NUMBER,
  39             .help = "nanoseconds (approximated) to wait "
  40                     "before completing request",
  41         },
  42         { /* end of list */ }
  43     },
  44 };
  45
  46 static int null_file_open(BlockDriverState *bs, QDict *options, int flags,
  47                           Error **errp)
  48 {
  49     QemuOpts *opts;
  50     BDRVNullState *s = bs->opaque;
  51     int ret = 0;
  52
  53     opts = qemu_opts_create(&runtime_opts, NULL, 0, &error_abort);
  54     qemu_opts_absorb_qdict(opts, options, &error_abort);
  55     s->length =
  56         qemu_opt_get_size(opts, BLOCK_OPT_SIZE, 1 << 30);
  57     s->latency_ns =
  58         qemu_opt_get_number(opts, NULL_OPT_LATENCY, 0);
  59     if (s->latency_ns < 0) {
  60         error_setg(errp, "latency-ns is invalid");
  61         ret = -EINVAL;
  62     }
  63     qemu_opts_del(opts);
  64     return ret;
  65 }
  66
  67 static void null_close(BlockDriverState *bs)
  68 {
  69 }
  70
  71 static int64_t null_getlength(BlockDriverState *bs)
  72 {
  73     BDRVNullState *s = bs->opaque;
  74     return s->length;
  75 }
  76
  77 static coroutine_fn int null_co_common(BlockDriverState *bs)
  78 {
  79     BDRVNullState *s = bs->opaque;
  80
  81     if (s->latency_ns) {
  82         co_aio_sleep_ns(bdrv_get_aio_context(bs), QEMU_CLOCK_REALTIME,
  83                         s->latency_ns);
  84     }
  85     return 0;
  86 }
  87
  88 static coroutine_fn int null_co_readv(BlockDriverState *bs,
  89                                       int64_t sector_num, int nb_sectors,
  90                                       QEMUIOVector *qiov)
  91 {
  92     return null_co_common(bs);
  93 }
  94
  95 static coroutine_fn int null_co_writev(BlockDriverState *bs,
  96                                        int64_t sector_num, int nb_sectors,
  97                                        QEMUIOVector *qiov)
  98 {
  99     return null_co_common(bs);
 100 }
 101
 102 static coroutine_fn int null_co_flush(BlockDriverState *bs)
 103 {
 104     return null_co_common(bs);
 105 }
 106
 107 typedef struct {
 108     BlockAIOCB common;
 109     QEMUBH *bh;
 110     QEMUTimer timer;
 111 } NullAIOCB;
 112
 113 static const AIOCBInfo null_aiocb_info = {
 114     .aiocb_size = sizeof(NullAIOCB),
 115 };
 116
 117 static void null_bh_cb(void *opaque)
 118 {
 119     NullAIOCB *acb = opaque;
 120     acb->common.cb(acb->common.opaque, 0);
 121     qemu_bh_delete(acb->bh);
 122     qemu_aio_unref(acb);
 123 }
 124
 125 static void null_timer_cb(void *opaque)
 126 {
 127     NullAIOCB *acb = opaque;
 128     acb->common.cb(acb->common.opaque, 0);
 129     timer_deinit(&acb->timer);
 130     qemu_aio_unref(acb);
 131 }
 132
 133 static inline BlockAIOCB *null_aio_common(BlockDriverState *bs,
 134                                           BlockCompletionFunc *cb,
 135                                           void *opaque)
 136 {
 137     NullAIOCB *acb;
 138     BDRVNullState *s = bs->opaque;
 139
 140     acb = qemu_aio_get(&null_aiocb_info, bs, cb, opaque);
 141     /* Only emulate latency after vcpu is running. */
 142     if (s->latency_ns) {
 143         aio_timer_init(bdrv_get_aio_context(bs), &acb->timer,
 144                        QEMU_CLOCK_REALTIME, SCALE_NS,
 145                        null_timer_cb, acb);
 146         timer_mod_ns(&acb->timer,
 147                      qemu_clock_get_ns(QEMU_CLOCK_REALTIME) + s->latency_ns);
 148     } else {
 149         acb->bh = aio_bh_new(bdrv_get_aio_context(bs), null_bh_cb, acb);
 150         qemu_bh_schedule(acb->bh);
 151     }
 152     return &acb->common;
 153 }
 154
 155 static BlockAIOCB *null_aio_readv(BlockDriverState *bs,
 156                                   int64_t sector_num, QEMUIOVector *qiov,
 157                                   int nb_sectors,
 158                                   BlockCompletionFunc *cb,
 159                                   void *opaque)
 160 {
 161     return null_aio_common(bs, cb, opaque);
 162 }
 163
 164 static BlockAIOCB *null_aio_writev(BlockDriverState *bs,
 165                                    int64_t sector_num, QEMUIOVector *qiov,
 166                                    int nb_sectors,
 167                                    BlockCompletionFunc *cb,
 168                                    void *opaque)
 169 {
 170     return null_aio_common(bs, cb, opaque);
 171 }
 172
 173 static BlockAIOCB *null_aio_flush(BlockDriverState *bs,
 174                                   BlockCompletionFunc *cb,
 175                                   void *opaque)
 176 {
 177     return null_aio_common(bs, cb, opaque);
 178 }
 179
 180 static int null_reopen_prepare(BDRVReopenState *reopen_state,
 181                                BlockReopenQueue *queue, Error **errp)
 182 {
 183     return 0;
 184 }
 185
 186 static BlockDriver bdrv_null_co = {
 187     .format_name            = "null-co",
 188     .protocol_name          = "null-co",
 189     .instance_size          = sizeof(BDRVNullState),
 190
 191     .bdrv_file_open         = null_file_open,
 192     .bdrv_close             = null_close,
 193     .bdrv_getlength         = null_getlength,
 194
 195     .bdrv_co_readv          = null_co_readv,
 196     .bdrv_co_writev         = null_co_writev,
 197     .bdrv_co_flush_to_disk  = null_co_flush,
 198     .bdrv_reopen_prepare    = null_reopen_prepare,
 199 };
 200
 201 static BlockDriver bdrv_null_aio = {
 202     .format_name            = "null-aio",
 203     .protocol_name          = "null-aio",
 204     .instance_size          = sizeof(BDRVNullState),
 205
 206     .bdrv_file_open         = null_file_open,
 207     .bdrv_close             = null_close,
 208     .bdrv_getlength         = null_getlength,
 209
 210     .bdrv_aio_readv         = null_aio_readv,
 211     .bdrv_aio_writev        = null_aio_writev,
 212     .bdrv_aio_flush         = null_aio_flush,
 213     .bdrv_reopen_prepare    = null_reopen_prepare,
 214 };
 215
 216 static void bdrv_null_init(void)
 217 {
 218     bdrv_register(&bdrv_null_co);
 219     bdrv_register(&bdrv_null_aio);
 220 }
 221
 222 block_init(bdrv_null_init);