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     struct io_event events[MAX_EVENTS];
  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         qemu_coroutine_enter(laiocb->co);
  99     } else {
 100         laiocb->common.cb(laiocb->common.opaque, ret);
 101         qemu_aio_unref(laiocb);
 102     }
 103 }
 104
 105 /* The completion BH fetches completed I/O requests and invokes their
 106  * callbacks.
 107  *
 108  * The function is somewhat tricky because it supports nested event loops, for
 109  * example when a request callback invokes aio_poll().  In order to do this,
 110  * the completion events array and index are kept in LinuxAioState.  The BH
 111  * reschedules itself as long as there are completions pending so it will
 112  * either be called again in a nested event loop or will be called after all
 113  * events have been completed.  When there are no events left to complete, the
 114  * BH returns without rescheduling.
 115  */
 116 static void qemu_laio_completion_bh(void *opaque)
 117 {
 118     LinuxAioState *s = opaque;
 119
 120     /* Fetch more completion events when empty */
 121     if (s->event_idx == s->event_max) {
 122         do {
 123             struct timespec ts = { 0 };
 124             s->event_max = io_getevents(s->ctx, MAX_EVENTS, MAX_EVENTS,
 125                                         s->events, &ts);
 126         } while (s->event_max == -EINTR);
 127
 128         s->event_idx = 0;
 129         if (s->event_max <= 0) {
 130             s->event_max = 0;
 131             return; /* no more events */
 132         }
 133         s->io_q.in_flight -= s->event_max;
 134     }
 135
 136     /* Reschedule so nested event loops see currently pending completions */
 137     qemu_bh_schedule(s->completion_bh);
 138
 139     /* Process completion events */
 140     while (s->event_idx < s->event_max) {
 141         struct iocb *iocb = s->events[s->event_idx].obj;
 142         struct qemu_laiocb *laiocb =
 143                 container_of(iocb, struct qemu_laiocb, iocb);
 144
 145         laiocb->ret = io_event_ret(&s->events[s->event_idx]);
 146         s->event_idx++;
 147
 148         qemu_laio_process_completion(laiocb);
 149     }
 150
 151     if (!s->io_q.plugged && !QSIMPLEQ_EMPTY(&s->io_q.pending)) {
 152         ioq_submit(s);
 153     }
 154
 155     qemu_bh_cancel(s->completion_bh);
 156 }
 157
 158 static void qemu_laio_completion_cb(EventNotifier *e)
 159 {
 160     LinuxAioState *s = container_of(e, LinuxAioState, e);
 161
 162     if (event_notifier_test_and_clear(&s->e)) {
 163         qemu_laio_completion_bh(s);
 164     }
 165 }
 166
 167 static void laio_cancel(BlockAIOCB *blockacb)
 168 {
 169     struct qemu_laiocb *laiocb = (struct qemu_laiocb *)blockacb;
 170     struct io_event event;
 171     int ret;
 172
 173     if (laiocb->ret != -EINPROGRESS) {
 174         return;
 175     }
 176     ret = io_cancel(laiocb->ctx->ctx, &laiocb->iocb, &event);
 177     laiocb->ret = -ECANCELED;
 178     if (ret != 0) {
 179         /* iocb is not cancelled, cb will be called by the event loop later */
 180         return;
 181     }
 182
 183     laiocb->common.cb(laiocb->common.opaque, laiocb->ret);
 184 }
 185
 186 static const AIOCBInfo laio_aiocb_info = {
 187     .aiocb_size         = sizeof(struct qemu_laiocb),
 188     .cancel_async       = laio_cancel,
 189 };
 190
 191 static void ioq_init(LaioQueue *io_q)
 192 {
 193     QSIMPLEQ_INIT(&io_q->pending);
 194     io_q->plugged = 0;
 195     io_q->in_queue = 0;
 196     io_q->in_flight = 0;
 197     io_q->blocked = false;
 198 }
 199
 200 static void ioq_submit(LinuxAioState *s)
 201 {
 202     int ret, len;
 203     struct qemu_laiocb *aiocb;
 204     struct iocb *iocbs[MAX_EVENTS];
 205     QSIMPLEQ_HEAD(, qemu_laiocb) completed;
 206
 207     do {
 208         if (s->io_q.in_flight >= MAX_EVENTS) {
 209             break;
 210         }
 211         len = 0;
 212         QSIMPLEQ_FOREACH(aiocb, &s->io_q.pending, next) {
 213             iocbs[len++] = &aiocb->iocb;
 214             if (s->io_q.in_flight + len >= MAX_EVENTS) {
 215                 break;
 216             }
 217         }
 218
 219         ret = io_submit(s->ctx, len, iocbs);
 220         if (ret == -EAGAIN) {
 221             break;
 222         }
 223         if (ret < 0) {
 224             abort();
 225         }
 226
 227         s->io_q.in_flight += ret;
 228         s->io_q.in_queue  -= ret;
 229         aiocb = container_of(iocbs[ret - 1], struct qemu_laiocb, iocb);
 230         QSIMPLEQ_SPLIT_AFTER(&s->io_q.pending, aiocb, next, &completed);
 231     } while (ret == len && !QSIMPLEQ_EMPTY(&s->io_q.pending));
 232     s->io_q.blocked = (s->io_q.in_queue > 0);
 233 }
 234
 235 void laio_io_plug(BlockDriverState *bs, LinuxAioState *s)
 236 {
 237     s->io_q.plugged++;
 238 }
 239
 240 void laio_io_unplug(BlockDriverState *bs, LinuxAioState *s)
 241 {
 242     assert(s->io_q.plugged);
 243     if (--s->io_q.plugged == 0 &&
 244         !s->io_q.blocked && !QSIMPLEQ_EMPTY(&s->io_q.pending)) {
 245         ioq_submit(s);
 246     }
 247 }
 248
 249 static int laio_do_submit(int fd, struct qemu_laiocb *laiocb, off_t offset,
 250                           int type)
 251 {
 252     LinuxAioState *s = laiocb->ctx;
 253     struct iocb *iocbs = &laiocb->iocb;
 254     QEMUIOVector *qiov = laiocb->qiov;
 255
 256     switch (type) {
 257     case QEMU_AIO_WRITE:
 258         io_prep_pwritev(iocbs, fd, qiov->iov, qiov->niov, offset);
 259         break;
 260     case QEMU_AIO_READ:
 261         io_prep_preadv(iocbs, fd, qiov->iov, qiov->niov, offset);
 262         break;
 263     /* Currently Linux kernel does not support other operations */
 264     default:
 265         fprintf(stderr, "%s: invalid AIO request type 0x%x.\n",
 266                         __func__, type);
 267         return -EIO;
 268     }
 269     io_set_eventfd(&laiocb->iocb, event_notifier_get_fd(&s->e));
 270
 271     QSIMPLEQ_INSERT_TAIL(&s->io_q.pending, laiocb, next);
 272     s->io_q.in_queue++;
 273     if (!s->io_q.blocked &&
 274         (!s->io_q.plugged ||
 275          s->io_q.in_flight + s->io_q.in_queue >= MAX_EVENTS)) {
 276         ioq_submit(s);
 277     }
 278
 279     return 0;
 280 }
 281
 282 int coroutine_fn laio_co_submit(BlockDriverState *bs, LinuxAioState *s, int fd,
 283                                 uint64_t offset, QEMUIOVector *qiov, int type)
 284 {
 285     int ret;
 286     struct qemu_laiocb laiocb = {
 287         .co         = qemu_coroutine_self(),
 288         .nbytes     = qiov->size,
 289         .ctx        = s,
 290         .is_read    = (type == QEMU_AIO_READ),
 291         .qiov       = qiov,
 292     };
 293
 294     ret = laio_do_submit(fd, &laiocb, offset, type);
 295     if (ret < 0) {
 296         return ret;
 297     }
 298
 299     qemu_coroutine_yield();
 300     return laiocb.ret;
 301 }
 302
 303 BlockAIOCB *laio_submit(BlockDriverState *bs, LinuxAioState *s, int fd,
 304         int64_t sector_num, QEMUIOVector *qiov, int nb_sectors,
 305         BlockCompletionFunc *cb, void *opaque, int type)
 306 {
 307     struct qemu_laiocb *laiocb;
 308     off_t offset = sector_num * BDRV_SECTOR_SIZE;
 309     int ret;
 310
 311     laiocb = qemu_aio_get(&laio_aiocb_info, bs, cb, opaque);
 312     laiocb->nbytes = nb_sectors * BDRV_SECTOR_SIZE;
 313     laiocb->ctx = s;
 314     laiocb->ret = -EINPROGRESS;
 315     laiocb->is_read = (type == QEMU_AIO_READ);
 316     laiocb->qiov = qiov;
 317
 318     ret = laio_do_submit(fd, laiocb, offset, type);
 319     if (ret < 0) {
 320         qemu_aio_unref(laiocb);
 321         return NULL;
 322     }
 323
 324     return &laiocb->common;
 325 }
 326
 327 void laio_detach_aio_context(LinuxAioState *s, AioContext *old_context)
 328 {
 329     aio_set_event_notifier(old_context, &s->e, false, NULL);
 330     qemu_bh_delete(s->completion_bh);
 331 }
 332
 333 void laio_attach_aio_context(LinuxAioState *s, AioContext *new_context)
 334 {
 335     s->aio_context = new_context;
 336     s->completion_bh = aio_bh_new(new_context, qemu_laio_completion_bh, s);
 337     aio_set_event_notifier(new_context, &s->e, false,
 338                            qemu_laio_completion_cb);
 339 }
 340
 341 LinuxAioState *laio_init(void)
 342 {
 343     LinuxAioState *s;
 344
 345     s = g_malloc0(sizeof(*s));
 346     if (event_notifier_init(&s->e, false) < 0) {
 347         goto out_free_state;
 348     }
 349
 350     if (io_setup(MAX_EVENTS, &s->ctx) != 0) {
 351         goto out_close_efd;
 352     }
 353
 354     ioq_init(&s->io_q);
 355
 356     return s;
 357
 358 out_close_efd:
 359     event_notifier_cleanup(&s->e);
 360 out_free_state:
 361     g_free(s);
 362     return NULL;
 363 }
 364
 365 void laio_cleanup(LinuxAioState *s)
 366 {
 367     event_notifier_cleanup(&s->e);
 368
 369     if (io_destroy(s->ctx) != 0) {
 370         fprintf(stderr, "%s: destroy AIO context %p failed\n",
 371                         __func__, &s->ctx);
 372     }
 373     g_free(s);
 374 }