block/linux-aio.c

   1 /*
   2  * Linux native AIO support.
   3  *
   4  * Copyright (C) 2009 IBM, Corp.
   5  * Copyright (C) 2009 Red Hat, Inc.
   6  *
   7  * This work is licensed under the terms of the GNU GPL, version 2 or later.
   8  * See the COPYING file in the top-level directory.
   9  */
  10 #include "qemu/osdep.h"
  11 #include "qemu-common.h"
  12 #include "block/aio.h"
  13 #include "qemu/queue.h"
  14 #include "block/block.h"
  15 #include "block/raw-aio.h"
  16 #include "qemu/event_notifier.h"
  17 #include "qemu/coroutine.h"
  18 #include "qapi/error.h"
  19
  20 #include <libaio.h>
  21
  22 /*
  23  * Queue size (per-device).
  24  *
  25  * XXX: eventually we need to communicate this to the guest and/or make it
  26  *      tunable by the guest.  If we get more outstanding requests at a time
  27  *      than this we will get EAGAIN from io_submit which is communicated to
  28  *      the guest as an I/O error.
  29  */
  30 #define MAX_EVENTS 128
  31
  32 struct qemu_laiocb {
  33     BlockAIOCB common;
  34     Coroutine *co;
  35     LinuxAioState *ctx;
  36     struct iocb iocb;
  37     ssize_t ret;
  38     size_t nbytes;
  39     QEMUIOVector *qiov;
  40     bool is_read;
  41     QSIMPLEQ_ENTRY(qemu_laiocb) next;
  42 };
  43
  44 typedef struct {
  45     int plugged;
  46     unsigned int in_queue;
  47     unsigned int in_flight;
  48     bool blocked;
  49     QSIMPLEQ_HEAD(, qemu_laiocb) pending;
  50 } LaioQueue;
  51
  52 struct LinuxAioState {
  53     AioContext *aio_context;
  54
  55     io_context_t ctx;
  56     EventNotifier e;
  57
  58     /* io queue for submit at batch.  Protected by AioContext lock. */
  59     LaioQueue io_q;
  60
  61     /* I/O completion processing.  Only runs in I/O thread.  */
  62     QEMUBH *completion_bh;
  63     int event_idx;
  64     int event_max;
  65 };
  66
  67 static void ioq_submit(LinuxAioState *s);
  68
  69 static inline ssize_t io_event_ret(struct io_event *ev)
  70 {
  71     return (ssize_t)(((uint64_t)ev->res2 << 32) | ev->res);
  72 }
  73
  74 /*
  75  * Completes an AIO request (calls the callback and frees the ACB).
  76  */
  77 static void qemu_laio_process_completion(struct qemu_laiocb *laiocb)
  78 {
  79     int ret;
  80
  81     ret = laiocb->ret;
  82     if (ret != -ECANCELED) {
  83         if (ret == laiocb->nbytes) {
  84             ret = 0;
  85         } else if (ret >= 0) {
  86             /* Short reads mean EOF, pad with zeros. */
  87             if (laiocb->is_read) {
  88                 qemu_iovec_memset(laiocb->qiov, ret, 0,
  89                     laiocb->qiov->size - ret);
  90             } else {
  91                 ret = -ENOSPC;
  92             }
  93         }
  94     }
  95
  96     laiocb->ret = ret;
  97     if (laiocb->co) {
  98         /* If the coroutine is already entered it must be in ioq_submit() and
  99          * will notice laio->ret has been filled in when it eventually runs
 100          * later.  Coroutines cannot be entered recursively so avoid doing
 101          * that!
 102          */
 103         if (!qemu_coroutine_entered(laiocb->co)) {
 104             aio_co_wake(laiocb->co);
 105         }
 106     } else {
 107         laiocb->common.cb(laiocb->common.opaque, ret);
 108         qemu_aio_unref(laiocb);
 109     }
 110 }
 111
 112 /**
 113  * aio_ring buffer which is shared between userspace and kernel.
 114  *
 115  * This copied from linux/fs/aio.c, common header does not exist
 116  * but AIO exists for ages so we assume ABI is stable.
 117  */
 118 struct aio_ring {
 119     unsigned    id;    /* kernel internal index number */
 120     unsigned    nr;    /* number of io_events */
 121     unsigned    head;  /* Written to by userland or by kernel. */
 122     unsigned    tail;
 123
 124     unsigned    magic;
 125     unsigned    compat_features;
 126     unsigned    incompat_features;
 127     unsigned    header_length;  /* size of aio_ring */
 128
 129     struct io_event io_events[0];
 130 };
 131
 132 /**
 133  * io_getevents_peek:
 134  * @ctx: AIO context
 135  * @events: pointer on events array, output value
 136
 137  * Returns the number of completed events and sets a pointer
 138  * on events array.  This function does not update the internal
 139  * ring buffer, only reads head and tail.  When @events has been
 140  * processed io_getevents_commit() must be called.
 141  */
 142 static inline unsigned int io_getevents_peek(io_context_t ctx,
 143                                              struct io_event **events)
 144 {
 145     struct aio_ring *ring = (struct aio_ring *)ctx;
 146     unsigned int head = ring->head, tail = ring->tail;
 147     unsigned int nr;
 148
 149     nr = tail >= head ? tail - head : ring->nr - head;
 150     *events = ring->io_events + head;
 151     /* To avoid speculative loads of s->events[i] before observing tail.
 152        Paired with smp_wmb() inside linux/fs/aio.c: aio_complete(). */
 153     smp_rmb();
 154
 155     return nr;
 156 }
 157
 158 /**
 159  * io_getevents_commit:
 160  * @ctx: AIO context
 161  * @nr: the number of events on which head should be advanced
 162  *
 163  * Advances head of a ring buffer.
 164  */
 165 static inline void io_getevents_commit(io_context_t ctx, unsigned int nr)
 166 {
 167     struct aio_ring *ring = (struct aio_ring *)ctx;
 168
 169     if (nr) {
 170         ring->head = (ring->head + nr) % ring->nr;
 171     }
 172 }
 173
 174 /**
 175  * io_getevents_advance_and_peek:
 176  * @ctx: AIO context
 177  * @events: pointer on events array, output value
 178  * @nr: the number of events on which head should be advanced
 179  *
 180  * Advances head of a ring buffer and returns number of elements left.
 181  */
 182 static inline unsigned int
 183 io_getevents_advance_and_peek(io_context_t ctx,
 184                               struct io_event **events,
 185                               unsigned int nr)
 186 {
 187     io_getevents_commit(ctx, nr);
 188     return io_getevents_peek(ctx, events);
 189 }
 190
 191 /**
 192  * qemu_laio_process_completions:
 193  * @s: AIO state
 194  *
 195  * Fetches completed I/O requests and invokes their callbacks.
 196  *
 197  * The function is somewhat tricky because it supports nested event loops, for
 198  * example when a request callback invokes aio_poll().  In order to do this,
 199  * indices are kept in LinuxAioState.  Function schedules BH completion so it
 200  * can be called again in a nested event loop.  When there are no events left
 201  * to complete the BH is being canceled.
 202  */
 203 static void qemu_laio_process_completions(LinuxAioState *s)
 204 {
 205     struct io_event *events;
 206
 207     /* Reschedule so nested event loops see currently pending completions */
 208     qemu_bh_schedule(s->completion_bh);
 209
 210     while ((s->event_max = io_getevents_advance_and_peek(s->ctx, &events,
 211                                                          s->event_idx))) {
 212         for (s->event_idx = 0; s->event_idx < s->event_max; ) {
 213             struct iocb *iocb = events[s->event_idx].obj;
 214             struct qemu_laiocb *laiocb =
 215                 container_of(iocb, struct qemu_laiocb, iocb);
 216
 217             laiocb->ret = io_event_ret(&events[s->event_idx]);
 218
 219             /* Change counters one-by-one because we can be nested. */
 220             s->io_q.in_flight--;
 221             s->event_idx++;
 222             qemu_laio_process_completion(laiocb);
 223         }
 224     }
 225
 226     qemu_bh_cancel(s->completion_bh);
 227
 228     /* If we are nested we have to notify the level above that we are done
 229      * by setting event_max to zero, upper level will then jump out of it's
 230      * own `for` loop.  If we are the last all counters droped to zero. */
 231     s->event_max = 0;
 232     s->event_idx = 0;
 233 }
 234
 235 static void qemu_laio_process_completions_and_submit(LinuxAioState *s)
 236 {
 237     qemu_laio_process_completions(s);
 238
 239     aio_context_acquire(s->aio_context);
 240     if (!s->io_q.plugged && !QSIMPLEQ_EMPTY(&s->io_q.pending)) {
 241         ioq_submit(s);
 242     }
 243     aio_context_release(s->aio_context);
 244 }
 245
 246 static void qemu_laio_completion_bh(void *opaque)
 247 {
 248     LinuxAioState *s = opaque;
 249
 250     qemu_laio_process_completions_and_submit(s);
 251 }
 252
 253 static void qemu_laio_completion_cb(EventNotifier *e)
 254 {
 255     LinuxAioState *s = container_of(e, LinuxAioState, e);
 256
 257     if (event_notifier_test_and_clear(&s->e)) {
 258         qemu_laio_process_completions_and_submit(s);
 259     }
 260 }
 261
 262 static bool qemu_laio_poll_cb(void *opaque)
 263 {
 264     EventNotifier *e = opaque;
 265     LinuxAioState *s = container_of(e, LinuxAioState, e);
 266     struct io_event *events;
 267
 268     if (!io_getevents_peek(s->ctx, &events)) {
 269         return false;
 270     }
 271
 272     qemu_laio_process_completions_and_submit(s);
 273     return true;
 274 }
 275
 276 static void laio_cancel(BlockAIOCB *blockacb)
 277 {
 278     struct qemu_laiocb *laiocb = (struct qemu_laiocb *)blockacb;
 279     struct io_event event;
 280     int ret;
 281
 282     if (laiocb->ret != -EINPROGRESS) {
 283         return;
 284     }
 285     ret = io_cancel(laiocb->ctx->ctx, &laiocb->iocb, &event);
 286     laiocb->ret = -ECANCELED;
 287     if (ret != 0) {
 288         /* iocb is not cancelled, cb will be called by the event loop later */
 289         return;
 290     }
 291
 292     laiocb->common.cb(laiocb->common.opaque, laiocb->ret);
 293 }
 294
 295 static const AIOCBInfo laio_aiocb_info = {
 296     .aiocb_size         = sizeof(struct qemu_laiocb),
 297     .cancel_async       = laio_cancel,
 298 };
 299
 300 static void ioq_init(LaioQueue *io_q)
 301 {
 302     QSIMPLEQ_INIT(&io_q->pending);
 303     io_q->plugged = 0;
 304     io_q->in_queue = 0;
 305     io_q->in_flight = 0;
 306     io_q->blocked = false;
 307 }
 308
 309 static void ioq_submit(LinuxAioState *s)
 310 {
 311     int ret, len;
 312     struct qemu_laiocb *aiocb;
 313     struct iocb *iocbs[MAX_EVENTS];
 314     QSIMPLEQ_HEAD(, qemu_laiocb) completed;
 315
 316     do {
 317         if (s->io_q.in_flight >= MAX_EVENTS) {
 318             break;
 319         }
 320         len = 0;
 321         QSIMPLEQ_FOREACH(aiocb, &s->io_q.pending, next) {
 322             iocbs[len++] = &aiocb->iocb;
 323             if (s->io_q.in_flight + len >= MAX_EVENTS) {
 324                 break;
 325             }
 326         }
 327
 328         ret = io_submit(s->ctx, len, iocbs);
 329         if (ret == -EAGAIN) {
 330             break;
 331         }
 332         if (ret < 0) {
 333             /* Fail the first request, retry the rest */
 334             aiocb = QSIMPLEQ_FIRST(&s->io_q.pending);
 335             QSIMPLEQ_REMOVE_HEAD(&s->io_q.pending, next);
 336             s->io_q.in_queue--;
 337             aiocb->ret = ret;
 338             qemu_laio_process_completion(aiocb);
 339             continue;
 340         }
 341
 342         s->io_q.in_flight += ret;
 343         s->io_q.in_queue  -= ret;
 344         aiocb = container_of(iocbs[ret - 1], struct qemu_laiocb, iocb);
 345         QSIMPLEQ_SPLIT_AFTER(&s->io_q.pending, aiocb, next, &completed);
 346     } while (ret == len && !QSIMPLEQ_EMPTY(&s->io_q.pending));
 347     s->io_q.blocked = (s->io_q.in_queue > 0);
 348
 349     if (s->io_q.in_flight) {
 350         /* We can try to complete something just right away if there are
 351          * still requests in-flight. */
 352         qemu_laio_process_completions(s);
 353         /*
 354          * Even we have completed everything (in_flight == 0), the queue can
 355          * have still pended requests (in_queue > 0).  We do not attempt to
 356          * repeat submission to avoid IO hang.  The reason is simple: s->e is
 357          * still set and completion callback will be called shortly and all
 358          * pended requests will be submitted from there.
 359          */
 360     }
 361 }
 362
 363 void laio_io_plug(BlockDriverState *bs, LinuxAioState *s)
 364 {
 365     s->io_q.plugged++;
 366 }
 367
 368 void laio_io_unplug(BlockDriverState *bs, LinuxAioState *s)
 369 {
 370     assert(s->io_q.plugged);
 371     if (--s->io_q.plugged == 0 &&
 372         !s->io_q.blocked && !QSIMPLEQ_EMPTY(&s->io_q.pending)) {
 373         ioq_submit(s);
 374     }
 375 }
 376
 377 static int laio_do_submit(int fd, struct qemu_laiocb *laiocb, off_t offset,
 378                           int type)
 379 {
 380     LinuxAioState *s = laiocb->ctx;
 381     struct iocb *iocbs = &laiocb->iocb;
 382     QEMUIOVector *qiov = laiocb->qiov;
 383
 384     switch (type) {
 385     case QEMU_AIO_WRITE:
 386         io_prep_pwritev(iocbs, fd, qiov->iov, qiov->niov, offset);
 387         break;
 388     case QEMU_AIO_READ:
 389         io_prep_preadv(iocbs, fd, qiov->iov, qiov->niov, offset);
 390         break;
 391     /* Currently Linux kernel does not support other operations */
 392     default:
 393         fprintf(stderr, "%s: invalid AIO request type 0x%x.\n",
 394                         __func__, type);
 395         return -EIO;
 396     }
 397     io_set_eventfd(&laiocb->iocb, event_notifier_get_fd(&s->e));
 398
 399     QSIMPLEQ_INSERT_TAIL(&s->io_q.pending, laiocb, next);
 400     s->io_q.in_queue++;
 401     if (!s->io_q.blocked &&
 402         (!s->io_q.plugged ||
 403          s->io_q.in_flight + s->io_q.in_queue >= MAX_EVENTS)) {
 404         ioq_submit(s);
 405     }
 406
 407     return 0;
 408 }
 409
 410 int coroutine_fn laio_co_submit(BlockDriverState *bs, LinuxAioState *s, int fd,
 411                                 uint64_t offset, QEMUIOVector *qiov, int type)
 412 {
 413     int ret;
 414     struct qemu_laiocb laiocb = {
 415         .co         = qemu_coroutine_self(),
 416         .nbytes     = qiov->size,
 417         .ctx        = s,
 418         .ret        = -EINPROGRESS,
 419         .is_read    = (type == QEMU_AIO_READ),
 420         .qiov       = qiov,
 421     };
 422
 423     ret = laio_do_submit(fd, &laiocb, offset, type);
 424     if (ret < 0) {
 425         return ret;
 426     }
 427
 428     if (laiocb.ret == -EINPROGRESS) {
 429         qemu_coroutine_yield();
 430     }
 431     return laiocb.ret;
 432 }
 433
 434 BlockAIOCB *laio_submit(BlockDriverState *bs, LinuxAioState *s, int fd,
 435         int64_t sector_num, QEMUIOVector *qiov, int nb_sectors,
 436         BlockCompletionFunc *cb, void *opaque, int type)
 437 {
 438     struct qemu_laiocb *laiocb;
 439     off_t offset = sector_num * BDRV_SECTOR_SIZE;
 440     int ret;
 441
 442     laiocb = qemu_aio_get(&laio_aiocb_info, bs, cb, opaque);
 443     laiocb->nbytes = nb_sectors * BDRV_SECTOR_SIZE;
 444     laiocb->ctx = s;
 445     laiocb->ret = -EINPROGRESS;
 446     laiocb->is_read = (type == QEMU_AIO_READ);
 447     laiocb->qiov = qiov;
 448
 449     ret = laio_do_submit(fd, laiocb, offset, type);
 450     if (ret < 0) {
 451         qemu_aio_unref(laiocb);
 452         return NULL;
 453     }
 454
 455     return &laiocb->common;
 456 }
 457
 458 void laio_detach_aio_context(LinuxAioState *s, AioContext *old_context)
 459 {
 460     aio_set_event_notifier(old_context, &s->e, false, NULL, NULL);
 461     qemu_bh_delete(s->completion_bh);
 462     s->aio_context = NULL;
 463 }
 464
 465 void laio_attach_aio_context(LinuxAioState *s, AioContext *new_context)
 466 {
 467     s->aio_context = new_context;
 468     s->completion_bh = aio_bh_new(new_context, qemu_laio_completion_bh, s);
 469     aio_set_event_notifier(new_context, &s->e, false,
 470                            qemu_laio_completion_cb,
 471                            qemu_laio_poll_cb);
 472 }
 473
 474 LinuxAioState *laio_init(Error **errp)
 475 {
 476     int rc;
 477     LinuxAioState *s;
 478
 479     s = g_malloc0(sizeof(*s));
 480     rc = event_notifier_init(&s->e, false);
 481     if (rc < 0) {
 482         error_setg_errno(errp, -rc, "failed to to initialize event notifier");
 483         goto out_free_state;
 484     }
 485
 486     rc = io_setup(MAX_EVENTS, &s->ctx);
 487     if (rc < 0) {
 488         error_setg_errno(errp, -rc, "failed to create linux AIO context");
 489         goto out_close_efd;
 490     }
 491
 492     ioq_init(&s->io_q);
 493
 494     return s;
 495
 496 out_close_efd:
 497     event_notifier_cleanup(&s->e);
 498 out_free_state:
 499     g_free(s);
 500     return NULL;
 501 }
 502
 503 void laio_cleanup(LinuxAioState *s)
 504 {
 505     event_notifier_cleanup(&s->e);
 506
 507     if (io_destroy(s->ctx) != 0) {
 508         fprintf(stderr, "%s: destroy AIO context %p failed\n",
 509                         __func__, &s->ctx);
 510     }
 511     g_free(s);
 512 }