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