async.c

   1 /*
   2  * QEMU System Emulator
   3  *
   4  * Copyright (c) 2003-2008 Fabrice Bellard
   5  *
   6  * Permission is hereby granted, free of charge, to any person obtaining a copy
   7  * of this software and associated documentation files (the "Software"), to deal
   8  * in the Software without restriction, including without limitation the rights
   9  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  10  * copies of the Software, and to permit persons to whom the Software is
  11  * furnished to do so, subject to the following conditions:
  12  *
  13  * The above copyright notice and this permission notice shall be included in
  14  * all copies or substantial portions of the Software.
  15  *
  16  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  17  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  18  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
  19  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  20  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  21  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  22  * THE SOFTWARE.
  23  */
  24
  25 #include "qemu/osdep.h"
  26 #include "qapi/error.h"
  27 #include "qemu-common.h"
  28 #include "block/aio.h"
  29 #include "block/thread-pool.h"
  30 #include "qemu/main-loop.h"
  31 #include "qemu/atomic.h"
  32 #include "block/raw-aio.h"
  33
  34 /***********************************************************/
  35 /* bottom halves (can be seen as timers which expire ASAP) */
  36
  37 struct QEMUBH {
  38     AioContext *ctx;
  39     QEMUBHFunc *cb;
  40     void *opaque;
  41     QEMUBH *next;
  42     bool scheduled;
  43     bool idle;
  44     bool deleted;
  45 };
  46
  47 QEMUBH *aio_bh_new(AioContext *ctx, QEMUBHFunc *cb, void *opaque)
  48 {
  49     QEMUBH *bh;
  50     bh = g_new(QEMUBH, 1);
  51     *bh = (QEMUBH){
  52         .ctx = ctx,
  53         .cb = cb,
  54         .opaque = opaque,
  55     };
  56     qemu_mutex_lock(&ctx->bh_lock);
  57     bh->next = ctx->first_bh;
  58     /* Make sure that the members are ready before putting bh into list */
  59     smp_wmb();
  60     ctx->first_bh = bh;
  61     qemu_mutex_unlock(&ctx->bh_lock);
  62     return bh;
  63 }
  64
  65 void aio_bh_call(QEMUBH *bh)
  66 {
  67     bh->cb(bh->opaque);
  68 }
  69
  70 /* Multiple occurrences of aio_bh_poll cannot be called concurrently */
  71 int aio_bh_poll(AioContext *ctx)
  72 {
  73     QEMUBH *bh, **bhp, *next;
  74     int ret;
  75
  76     ctx->walking_bh++;
  77
  78     ret = 0;
  79     for (bh = ctx->first_bh; bh; bh = next) {
  80         /* Make sure that fetching bh happens before accessing its members */
  81         smp_read_barrier_depends();
  82         next = bh->next;
  83         /* The atomic_xchg is paired with the one in qemu_bh_schedule.  The
  84          * implicit memory barrier ensures that the callback sees all writes
  85          * done by the scheduling thread.  It also ensures that the scheduling
  86          * thread sees the zero before bh->cb has run, and thus will call
  87          * aio_notify again if necessary.
  88          */
  89         if (!bh->deleted && atomic_xchg(&bh->scheduled, 0)) {
  90             /* Idle BHs and the notify BH don't count as progress */
  91             if (!bh->idle && bh != ctx->notify_dummy_bh) {
  92                 ret = 1;
  93             }
  94             bh->idle = 0;
  95             aio_bh_call(bh);
  96         }
  97     }
  98
  99     ctx->walking_bh--;
 100
 101     /* remove deleted bhs */
 102     if (!ctx->walking_bh) {
 103         qemu_mutex_lock(&ctx->bh_lock);
 104         bhp = &ctx->first_bh;
 105         while (*bhp) {
 106             bh = *bhp;
 107             if (bh->deleted) {
 108                 *bhp = bh->next;
 109                 g_free(bh);
 110             } else {
 111                 bhp = &bh->next;
 112             }
 113         }
 114         qemu_mutex_unlock(&ctx->bh_lock);
 115     }
 116
 117     return ret;
 118 }
 119
 120 void qemu_bh_schedule_idle(QEMUBH *bh)
 121 {
 122     bh->idle = 1;
 123     /* Make sure that idle & any writes needed by the callback are done
 124      * before the locations are read in the aio_bh_poll.
 125      */
 126     atomic_mb_set(&bh->scheduled, 1);
 127 }
 128
 129 void qemu_bh_schedule(QEMUBH *bh)
 130 {
 131     AioContext *ctx;
 132
 133     ctx = bh->ctx;
 134     bh->idle = 0;
 135     /* The memory barrier implicit in atomic_xchg makes sure that:
 136      * 1. idle & any writes needed by the callback are done before the
 137      *    locations are read in the aio_bh_poll.
 138      * 2. ctx is loaded before scheduled is set and the callback has a chance
 139      *    to execute.
 140      */
 141     if (atomic_xchg(&bh->scheduled, 1) == 0) {
 142         aio_notify(ctx);
 143     }
 144 }
 145
 146
 147 /* This func is async.
 148  */
 149 void qemu_bh_cancel(QEMUBH *bh)
 150 {
 151     bh->scheduled = 0;
 152 }
 153
 154 /* This func is async.The bottom half will do the delete action at the finial
 155  * end.
 156  */
 157 void qemu_bh_delete(QEMUBH *bh)
 158 {
 159     bh->scheduled = 0;
 160     bh->deleted = 1;
 161 }
 162
 163 int64_t
 164 aio_compute_timeout(AioContext *ctx)
 165 {
 166     int64_t deadline;
 167     int timeout = -1;
 168     QEMUBH *bh;
 169
 170     for (bh = ctx->first_bh; bh; bh = bh->next) {
 171         if (!bh->deleted && bh->scheduled) {
 172             if (bh->idle) {
 173                 /* idle bottom halves will be polled at least
 174                  * every 10ms */
 175                 timeout = 10000000;
 176             } else {
 177                 /* non-idle bottom halves will be executed
 178                  * immediately */
 179                 return 0;
 180             }
 181         }
 182     }
 183
 184     deadline = timerlistgroup_deadline_ns(&ctx->tlg);
 185     if (deadline == 0) {
 186         return 0;
 187     } else {
 188         return qemu_soonest_timeout(timeout, deadline);
 189     }
 190 }
 191
 192 static gboolean
 193 aio_ctx_prepare(GSource *source, gint    *timeout)
 194 {
 195     AioContext *ctx = (AioContext *) source;
 196
 197     atomic_or(&ctx->notify_me, 1);
 198
 199     /* We assume there is no timeout already supplied */
 200     *timeout = qemu_timeout_ns_to_ms(aio_compute_timeout(ctx));
 201
 202     if (aio_prepare(ctx)) {
 203         *timeout = 0;
 204     }
 205
 206     return *timeout == 0;
 207 }
 208
 209 static gboolean
 210 aio_ctx_check(GSource *source)
 211 {
 212     AioContext *ctx = (AioContext *) source;
 213     QEMUBH *bh;
 214
 215     atomic_and(&ctx->notify_me, ~1);
 216     aio_notify_accept(ctx);
 217
 218     for (bh = ctx->first_bh; bh; bh = bh->next) {
 219         if (!bh->deleted && bh->scheduled) {
 220             return true;
 221         }
 222     }
 223     return aio_pending(ctx) || (timerlistgroup_deadline_ns(&ctx->tlg) == 0);
 224 }
 225
 226 static gboolean
 227 aio_ctx_dispatch(GSource     *source,
 228                  GSourceFunc  callback,
 229                  gpointer     user_data)
 230 {
 231     AioContext *ctx = (AioContext *) source;
 232
 233     assert(callback == NULL);
 234     aio_dispatch(ctx);
 235     return true;
 236 }
 237
 238 static void
 239 aio_ctx_finalize(GSource     *source)
 240 {
 241     AioContext *ctx = (AioContext *) source;
 242
 243     qemu_bh_delete(ctx->notify_dummy_bh);
 244     thread_pool_free(ctx->thread_pool);
 245
 246 #ifdef CONFIG_LINUX_AIO
 247     if (ctx->linux_aio) {
 248         laio_detach_aio_context(ctx->linux_aio, ctx);
 249         laio_cleanup(ctx->linux_aio);
 250         ctx->linux_aio = NULL;
 251     }
 252 #endif
 253
 254     qemu_mutex_lock(&ctx->bh_lock);
 255     while (ctx->first_bh) {
 256         QEMUBH *next = ctx->first_bh->next;
 257
 258         /* qemu_bh_delete() must have been called on BHs in this AioContext */
 259         assert(ctx->first_bh->deleted);
 260
 261         g_free(ctx->first_bh);
 262         ctx->first_bh = next;
 263     }
 264     qemu_mutex_unlock(&ctx->bh_lock);
 265
 266     aio_set_event_notifier(ctx, &ctx->notifier, false, NULL);
 267     event_notifier_cleanup(&ctx->notifier);
 268     rfifolock_destroy(&ctx->lock);
 269     qemu_mutex_destroy(&ctx->bh_lock);
 270     timerlistgroup_deinit(&ctx->tlg);
 271 }
 272
 273 static GSourceFuncs aio_source_funcs = {
 274     aio_ctx_prepare,
 275     aio_ctx_check,
 276     aio_ctx_dispatch,
 277     aio_ctx_finalize
 278 };
 279
 280 GSource *aio_get_g_source(AioContext *ctx)
 281 {
 282     g_source_ref(&ctx->source);
 283     return &ctx->source;
 284 }
 285
 286 ThreadPool *aio_get_thread_pool(AioContext *ctx)
 287 {
 288     if (!ctx->thread_pool) {
 289         ctx->thread_pool = thread_pool_new(ctx);
 290     }
 291     return ctx->thread_pool;
 292 }
 293
 294 #ifdef CONFIG_LINUX_AIO
 295 LinuxAioState *aio_get_linux_aio(AioContext *ctx)
 296 {
 297     if (!ctx->linux_aio) {
 298         ctx->linux_aio = laio_init();
 299         laio_attach_aio_context(ctx->linux_aio, ctx);
 300     }
 301     return ctx->linux_aio;
 302 }
 303 #endif
 304
 305 void aio_notify(AioContext *ctx)
 306 {
 307     /* Write e.g. bh->scheduled before reading ctx->notify_me.  Pairs
 308      * with atomic_or in aio_ctx_prepare or atomic_add in aio_poll.
 309      */
 310     smp_mb();
 311     if (ctx->notify_me) {
 312         event_notifier_set(&ctx->notifier);
 313         atomic_mb_set(&ctx->notified, true);
 314     }
 315 }
 316
 317 void aio_notify_accept(AioContext *ctx)
 318 {
 319     if (atomic_xchg(&ctx->notified, false)) {
 320         event_notifier_test_and_clear(&ctx->notifier);
 321     }
 322 }
 323
 324 static void aio_timerlist_notify(void *opaque)
 325 {
 326     aio_notify(opaque);
 327 }
 328
 329 static void aio_rfifolock_cb(void *opaque)
 330 {
 331     AioContext *ctx = opaque;
 332
 333     /* Kick owner thread in case they are blocked in aio_poll() */
 334     qemu_bh_schedule(ctx->notify_dummy_bh);
 335 }
 336
 337 static void notify_dummy_bh(void *opaque)
 338 {
 339     /* Do nothing, we were invoked just to force the event loop to iterate */
 340 }
 341
 342 static void event_notifier_dummy_cb(EventNotifier *e)
 343 {
 344 }
 345
 346 AioContext *aio_context_new(Error **errp)
 347 {
 348     int ret;
 349     AioContext *ctx;
 350
 351     ctx = (AioContext *) g_source_new(&aio_source_funcs, sizeof(AioContext));
 352     aio_context_setup(ctx);
 353
 354     ret = event_notifier_init(&ctx->notifier, false);
 355     if (ret < 0) {
 356         error_setg_errno(errp, -ret, "Failed to initialize event notifier");
 357         goto fail;
 358     }
 359     g_source_set_can_recurse(&ctx->source, true);
 360     aio_set_event_notifier(ctx, &ctx->notifier,
 361                            false,
 362                            (EventNotifierHandler *)
 363                            event_notifier_dummy_cb);
 364 #ifdef CONFIG_LINUX_AIO
 365     ctx->linux_aio = NULL;
 366 #endif
 367     ctx->thread_pool = NULL;
 368     qemu_mutex_init(&ctx->bh_lock);
 369     rfifolock_init(&ctx->lock, aio_rfifolock_cb, ctx);
 370     timerlistgroup_init(&ctx->tlg, aio_timerlist_notify, ctx);
 371
 372     ctx->notify_dummy_bh = aio_bh_new(ctx, notify_dummy_bh, NULL);
 373
 374     return ctx;
 375 fail:
 376     g_source_destroy(&ctx->source);
 377     return NULL;
 378 }
 379
 380 void aio_context_ref(AioContext *ctx)
 381 {
 382     g_source_ref(&ctx->source);
 383 }
 384
 385 void aio_context_unref(AioContext *ctx)
 386 {
 387     g_source_unref(&ctx->source);
 388 }
 389
 390 void aio_context_acquire(AioContext *ctx)
 391 {
 392     rfifolock_lock(&ctx->lock);
 393 }
 394
 395 void aio_context_release(AioContext *ctx)
 396 {
 397     rfifolock_unlock(&ctx->lock);
 398 }