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 */
  58     LaioQueue io_q;
  59
  60     /* I/O completion processing */
  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             qemu_coroutine_enter(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     if (!s->io_q.plugged && !QSIMPLEQ_EMPTY(&s->io_q.pending)) {
 238         ioq_submit(s);
 239     }
 240 }
 241
 242 static void qemu_laio_completion_bh(void *opaque)
 243 {
 244     LinuxAioState *s = opaque;
 245
 246     qemu_laio_process_completions_and_submit(s);
 247 }
 248
 249 static void qemu_laio_completion_cb(EventNotifier *e)
 250 {
 251     LinuxAioState *s = container_of(e, LinuxAioState, e);
 252
 253     if (event_notifier_test_and_clear(&s->e)) {
 254         qemu_laio_process_completions_and_submit(s);
 255     }
 256 }
 257
 258 static bool qemu_laio_poll_cb(void *opaque)
 259 {
 260     EventNotifier *e = opaque;
 261     LinuxAioState *s = container_of(e, LinuxAioState, e);
 262     struct io_event *events;
 263
 264     if (!io_getevents_peek(s->ctx, &events)) {
 265         return false;
 266     }
 267
 268     qemu_laio_process_completions_and_submit(s);
 269     return true;
 270 }
 271
 272 static void laio_cancel(BlockAIOCB *blockacb)
 273 {
 274     struct qemu_laiocb *laiocb = (struct qemu_laiocb *)blockacb;
 275     struct io_event event;
 276     int ret;
 277
 278     if (laiocb->ret != -EINPROGRESS) {
 279         return;
 280     }
 281     ret = io_cancel(laiocb->ctx->ctx, &laiocb->iocb, &event);
 282     laiocb->ret = -ECANCELED;
 283     if (ret != 0) {
 284         /* iocb is not cancelled, cb will be called by the event loop later */
 285         return;
 286     }
 287
 288     laiocb->common.cb(laiocb->common.opaque, laiocb->ret);
 289 }
 290
 291 static const AIOCBInfo laio_aiocb_info = {
 292     .aiocb_size         = sizeof(struct qemu_laiocb),
 293     .cancel_async       = laio_cancel,
 294 };
 295
 296 static void ioq_init(LaioQueue *io_q)
 297 {
 298     QSIMPLEQ_INIT(&io_q->pending);
 299     io_q->plugged = 0;
 300     io_q->in_queue = 0;
 301     io_q->in_flight = 0;
 302     io_q->blocked = false;
 303 }
 304
 305 static void ioq_submit(LinuxAioState *s)
 306 {
 307     int ret, len;
 308     struct qemu_laiocb *aiocb;
 309     struct iocb *iocbs[MAX_EVENTS];
 310     QSIMPLEQ_HEAD(, qemu_laiocb) completed;
 311
 312     do {
 313         if (s->io_q.in_flight >= MAX_EVENTS) {
 314             break;
 315         }
 316         len = 0;
 317         QSIMPLEQ_FOREACH(aiocb, &s->io_q.pending, next) {
 318             iocbs[len++] = &aiocb->iocb;
 319             if (s->io_q.in_flight + len >= MAX_EVENTS) {
 320                 break;
 321             }
 322         }
 323
 324         ret = io_submit(s->ctx, len, iocbs);
 325         if (ret == -EAGAIN) {
 326             break;
 327         }
 328         if (ret < 0) {
 329             /* Fail the first request, retry the rest */
 330             aiocb = QSIMPLEQ_FIRST(&s->io_q.pending);
 331             QSIMPLEQ_REMOVE_HEAD(&s->io_q.pending, next);
 332             s->io_q.in_queue--;
 333             aiocb->ret = ret;
 334             qemu_laio_process_completion(aiocb);
 335             continue;
 336         }
 337
 338         s->io_q.in_flight += ret;
 339         s->io_q.in_queue  -= ret;
 340         aiocb = container_of(iocbs[ret - 1], struct qemu_laiocb, iocb);
 341         QSIMPLEQ_SPLIT_AFTER(&s->io_q.pending, aiocb, next, &completed);
 342     } while (ret == len && !QSIMPLEQ_EMPTY(&s->io_q.pending));
 343     s->io_q.blocked = (s->io_q.in_queue > 0);
 344
 345     if (s->io_q.in_flight) {
 346         /* We can try to complete something just right away if there are
 347          * still requests in-flight. */
 348         qemu_laio_process_completions(s);
 349         /*
 350          * Even we have completed everything (in_flight == 0), the queue can
 351          * have still pended requests (in_queue > 0).  We do not attempt to
 352          * repeat submission to avoid IO hang.  The reason is simple: s->e is
 353          * still set and completion callback will be called shortly and all
 354          * pended requests will be submitted from there.
 355          */
 356     }
 357 }
 358
 359 void laio_io_plug(BlockDriverState *bs, LinuxAioState *s)
 360 {
 361     s->io_q.plugged++;
 362 }
 363
 364 void laio_io_unplug(BlockDriverState *bs, LinuxAioState *s)
 365 {
 366     assert(s->io_q.plugged);
 367     if (--s->io_q.plugged == 0 &&
 368         !s->io_q.blocked && !QSIMPLEQ_EMPTY(&s->io_q.pending)) {
 369         ioq_submit(s);
 370     }
 371 }
 372
 373 static int laio_do_submit(int fd, struct qemu_laiocb *laiocb, off_t offset,
 374                           int type)
 375 {
 376     LinuxAioState *s = laiocb->ctx;
 377     struct iocb *iocbs = &laiocb->iocb;
 378     QEMUIOVector *qiov = laiocb->qiov;
 379
 380     switch (type) {
 381     case QEMU_AIO_WRITE:
 382         io_prep_pwritev(iocbs, fd, qiov->iov, qiov->niov, offset);
 383         break;
 384     case QEMU_AIO_READ:
 385         io_prep_preadv(iocbs, fd, qiov->iov, qiov->niov, offset);
 386         break;
 387     /* Currently Linux kernel does not support other operations */
 388     default:
 389         fprintf(stderr, "%s: invalid AIO request type 0x%x.\n",
 390                         __func__, type);
 391         return -EIO;
 392     }
 393     io_set_eventfd(&laiocb->iocb, event_notifier_get_fd(&s->e));
 394
 395     QSIMPLEQ_INSERT_TAIL(&s->io_q.pending, laiocb, next);
 396     s->io_q.in_queue++;
 397     if (!s->io_q.blocked &&
 398         (!s->io_q.plugged ||
 399          s->io_q.in_flight + s->io_q.in_queue >= MAX_EVENTS)) {
 400         ioq_submit(s);
 401     }
 402
 403     return 0;
 404 }
 405
 406 int coroutine_fn laio_co_submit(BlockDriverState *bs, LinuxAioState *s, int fd,
 407                                 uint64_t offset, QEMUIOVector *qiov, int type)
 408 {
 409     int ret;
 410     struct qemu_laiocb laiocb = {
 411         .co         = qemu_coroutine_self(),
 412         .nbytes     = qiov->size,
 413         .ctx        = s,
 414         .ret        = -EINPROGRESS,
 415         .is_read    = (type == QEMU_AIO_READ),
 416         .qiov       = qiov,
 417     };
 418
 419     ret = laio_do_submit(fd, &laiocb, offset, type);
 420     if (ret < 0) {
 421         return ret;
 422     }
 423
 424     if (laiocb.ret == -EINPROGRESS) {
 425         qemu_coroutine_yield();
 426     }
 427     return laiocb.ret;
 428 }
 429
 430 BlockAIOCB *laio_submit(BlockDriverState *bs, LinuxAioState *s, int fd,
 431         int64_t sector_num, QEMUIOVector *qiov, int nb_sectors,
 432         BlockCompletionFunc *cb, void *opaque, int type)
 433 {
 434     struct qemu_laiocb *laiocb;
 435     off_t offset = sector_num * BDRV_SECTOR_SIZE;
 436     int ret;
 437
 438     laiocb = qemu_aio_get(&laio_aiocb_info, bs, cb, opaque);
 439     laiocb->nbytes = nb_sectors * BDRV_SECTOR_SIZE;
 440     laiocb->ctx = s;
 441     laiocb->ret = -EINPROGRESS;
 442     laiocb->is_read = (type == QEMU_AIO_READ);
 443     laiocb->qiov = qiov;
 444
 445     ret = laio_do_submit(fd, laiocb, offset, type);
 446     if (ret < 0) {
 447         qemu_aio_unref(laiocb);
 448         return NULL;
 449     }
 450
 451     return &laiocb->common;
 452 }
 453
 454 void laio_detach_aio_context(LinuxAioState *s, AioContext *old_context)
 455 {
 456     aio_set_event_notifier(old_context, &s->e, false, NULL, NULL);
 457     qemu_bh_delete(s->completion_bh);
 458 }
 459
 460 void laio_attach_aio_context(LinuxAioState *s, AioContext *new_context)
 461 {
 462     s->aio_context = new_context;
 463     s->completion_bh = aio_bh_new(new_context, qemu_laio_completion_bh, s);
 464     aio_set_event_notifier(new_context, &s->e, false,
 465                            qemu_laio_completion_cb,
 466                            qemu_laio_poll_cb);
 467 }
 468
 469 LinuxAioState *laio_init(void)
 470 {
 471     LinuxAioState *s;
 472
 473     s = g_malloc0(sizeof(*s));
 474     if (event_notifier_init(&s->e, false) < 0) {
 475         goto out_free_state;
 476     }
 477
 478     if (io_setup(MAX_EVENTS, &s->ctx) != 0) {
 479         goto out_close_efd;
 480     }
 481
 482     ioq_init(&s->io_q);
 483
 484     return s;
 485
 486 out_close_efd:
 487     event_notifier_cleanup(&s->e);
 488 out_free_state:
 489     g_free(s);
 490     return NULL;
 491 }
 492
 493 void laio_cleanup(LinuxAioState *s)
 494 {
 495     event_notifier_cleanup(&s->e);
 496
 497     if (io_destroy(s->ctx) != 0) {
 498         fprintf(stderr, "%s: destroy AIO context %p failed\n",
 499                         __func__, &s->ctx);
 500     }
 501     g_free(s);
 502 }