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 #define MAX_QUEUED_IO  128
  32
  33 struct qemu_laiocb {
  34     BlockAIOCB common;
  35     Coroutine *co;
  36     LinuxAioState *ctx;
  37     struct iocb iocb;
  38     ssize_t ret;
  39     size_t nbytes;
  40     QEMUIOVector *qiov;
  41     bool is_read;
  42     QSIMPLEQ_ENTRY(qemu_laiocb) next;
  43 };
  44
  45 typedef struct {
  46     int plugged;
  47     unsigned int n;
  48     bool blocked;
  49     QSIMPLEQ_HEAD(, qemu_laiocb) pending;
  50 } LaioQueue;
  51
  52 struct LinuxAioState {
  53     io_context_t ctx;
  54     EventNotifier e;
  55
  56     /* io queue for submit at batch */
  57     LaioQueue io_q;
  58
  59     /* I/O completion processing */
  60     QEMUBH *completion_bh;
  61     struct io_event events[MAX_EVENTS];
  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 = -EINVAL;
  91             }
  92         }
  93     }
  94
  95     laiocb->ret = ret;
  96     if (laiocb->co) {
  97         qemu_coroutine_enter(laiocb->co, NULL);
  98     } else {
  99         laiocb->common.cb(laiocb->common.opaque, ret);
 100         qemu_aio_unref(laiocb);
 101     }
 102 }
 103
 104 /* The completion BH fetches completed I/O requests and invokes their
 105  * callbacks.
 106  *
 107  * The function is somewhat tricky because it supports nested event loops, for
 108  * example when a request callback invokes aio_poll().  In order to do this,
 109  * the completion events array and index are kept in LinuxAioState.  The BH
 110  * reschedules itself as long as there are completions pending so it will
 111  * either be called again in a nested event loop or will be called after all
 112  * events have been completed.  When there are no events left to complete, the
 113  * BH returns without rescheduling.
 114  */
 115 static void qemu_laio_completion_bh(void *opaque)
 116 {
 117     LinuxAioState *s = opaque;
 118
 119     /* Fetch more completion events when empty */
 120     if (s->event_idx == s->event_max) {
 121         do {
 122             struct timespec ts = { 0 };
 123             s->event_max = io_getevents(s->ctx, MAX_EVENTS, MAX_EVENTS,
 124                                         s->events, &ts);
 125         } while (s->event_max == -EINTR);
 126
 127         s->event_idx = 0;
 128         if (s->event_max <= 0) {
 129             s->event_max = 0;
 130             return; /* no more events */
 131         }
 132     }
 133
 134     /* Reschedule so nested event loops see currently pending completions */
 135     qemu_bh_schedule(s->completion_bh);
 136
 137     /* Process completion events */
 138     while (s->event_idx < s->event_max) {
 139         struct iocb *iocb = s->events[s->event_idx].obj;
 140         struct qemu_laiocb *laiocb =
 141                 container_of(iocb, struct qemu_laiocb, iocb);
 142
 143         laiocb->ret = io_event_ret(&s->events[s->event_idx]);
 144         s->event_idx++;
 145
 146         qemu_laio_process_completion(laiocb);
 147     }
 148
 149     if (!s->io_q.plugged && !QSIMPLEQ_EMPTY(&s->io_q.pending)) {
 150         ioq_submit(s);
 151     }
 152
 153     qemu_bh_cancel(s->completion_bh);
 154 }
 155
 156 static void qemu_laio_completion_cb(EventNotifier *e)
 157 {
 158     LinuxAioState *s = container_of(e, LinuxAioState, e);
 159
 160     if (event_notifier_test_and_clear(&s->e)) {
 161         qemu_laio_completion_bh(s);
 162     }
 163 }
 164
 165 static void laio_cancel(BlockAIOCB *blockacb)
 166 {
 167     struct qemu_laiocb *laiocb = (struct qemu_laiocb *)blockacb;
 168     struct io_event event;
 169     int ret;
 170
 171     if (laiocb->ret != -EINPROGRESS) {
 172         return;
 173     }
 174     ret = io_cancel(laiocb->ctx->ctx, &laiocb->iocb, &event);
 175     laiocb->ret = -ECANCELED;
 176     if (ret != 0) {
 177         /* iocb is not cancelled, cb will be called by the event loop later */
 178         return;
 179     }
 180
 181     laiocb->common.cb(laiocb->common.opaque, laiocb->ret);
 182 }
 183
 184 static const AIOCBInfo laio_aiocb_info = {
 185     .aiocb_size         = sizeof(struct qemu_laiocb),
 186     .cancel_async       = laio_cancel,
 187 };
 188
 189 static void ioq_init(LaioQueue *io_q)
 190 {
 191     QSIMPLEQ_INIT(&io_q->pending);
 192     io_q->plugged = 0;
 193     io_q->n = 0;
 194     io_q->blocked = false;
 195 }
 196
 197 static void ioq_submit(LinuxAioState *s)
 198 {
 199     int ret, len;
 200     struct qemu_laiocb *aiocb;
 201     struct iocb *iocbs[MAX_QUEUED_IO];
 202     QSIMPLEQ_HEAD(, qemu_laiocb) completed;
 203
 204     do {
 205         len = 0;
 206         QSIMPLEQ_FOREACH(aiocb, &s->io_q.pending, next) {
 207             iocbs[len++] = &aiocb->iocb;
 208             if (len == MAX_QUEUED_IO) {
 209                 break;
 210             }
 211         }
 212
 213         ret = io_submit(s->ctx, len, iocbs);
 214         if (ret == -EAGAIN) {
 215             break;
 216         }
 217         if (ret < 0) {
 218             abort();
 219         }
 220
 221         s->io_q.n -= ret;
 222         aiocb = container_of(iocbs[ret - 1], struct qemu_laiocb, iocb);
 223         QSIMPLEQ_SPLIT_AFTER(&s->io_q.pending, aiocb, next, &completed);
 224     } while (ret == len && !QSIMPLEQ_EMPTY(&s->io_q.pending));
 225     s->io_q.blocked = (s->io_q.n > 0);
 226 }
 227
 228 void laio_io_plug(BlockDriverState *bs, LinuxAioState *s)
 229 {
 230     assert(!s->io_q.plugged);
 231     s->io_q.plugged = 1;
 232 }
 233
 234 void laio_io_unplug(BlockDriverState *bs, LinuxAioState *s)
 235 {
 236     assert(s->io_q.plugged);
 237     s->io_q.plugged = 0;
 238     if (!s->io_q.blocked && !QSIMPLEQ_EMPTY(&s->io_q.pending)) {
 239         ioq_submit(s);
 240     }
 241 }
 242
 243 static int laio_do_submit(int fd, struct qemu_laiocb *laiocb, off_t offset,
 244                           int type)
 245 {
 246     LinuxAioState *s = laiocb->ctx;
 247     struct iocb *iocbs = &laiocb->iocb;
 248     QEMUIOVector *qiov = laiocb->qiov;
 249
 250     switch (type) {
 251     case QEMU_AIO_WRITE:
 252         io_prep_pwritev(iocbs, fd, qiov->iov, qiov->niov, offset);
 253         break;
 254     case QEMU_AIO_READ:
 255         io_prep_preadv(iocbs, fd, qiov->iov, qiov->niov, offset);
 256         break;
 257     /* Currently Linux kernel does not support other operations */
 258     default:
 259         fprintf(stderr, "%s: invalid AIO request type 0x%x.\n",
 260                         __func__, type);
 261         return -EIO;
 262     }
 263     io_set_eventfd(&laiocb->iocb, event_notifier_get_fd(&s->e));
 264
 265     QSIMPLEQ_INSERT_TAIL(&s->io_q.pending, laiocb, next);
 266     s->io_q.n++;
 267     if (!s->io_q.blocked &&
 268         (!s->io_q.plugged || s->io_q.n >= MAX_QUEUED_IO)) {
 269         ioq_submit(s);
 270     }
 271
 272     return 0;
 273 }
 274
 275 int coroutine_fn laio_co_submit(BlockDriverState *bs, LinuxAioState *s, int fd,
 276                                 uint64_t offset, QEMUIOVector *qiov, int type)
 277 {
 278     int ret;
 279     struct qemu_laiocb laiocb = {
 280         .co         = qemu_coroutine_self(),
 281         .nbytes     = qiov->size,
 282         .ctx        = s,
 283         .is_read    = (type == QEMU_AIO_READ),
 284         .qiov       = qiov,
 285     };
 286
 287     ret = laio_do_submit(fd, &laiocb, offset, type);
 288     if (ret < 0) {
 289         return ret;
 290     }
 291
 292     qemu_coroutine_yield();
 293     return laiocb.ret;
 294 }
 295
 296 BlockAIOCB *laio_submit(BlockDriverState *bs, LinuxAioState *s, int fd,
 297         int64_t sector_num, QEMUIOVector *qiov, int nb_sectors,
 298         BlockCompletionFunc *cb, void *opaque, int type)
 299 {
 300     struct qemu_laiocb *laiocb;
 301     off_t offset = sector_num * BDRV_SECTOR_SIZE;
 302     int ret;
 303
 304     laiocb = qemu_aio_get(&laio_aiocb_info, bs, cb, opaque);
 305     laiocb->nbytes = nb_sectors * BDRV_SECTOR_SIZE;
 306     laiocb->ctx = s;
 307     laiocb->ret = -EINPROGRESS;
 308     laiocb->is_read = (type == QEMU_AIO_READ);
 309     laiocb->qiov = qiov;
 310
 311     ret = laio_do_submit(fd, laiocb, offset, type);
 312     if (ret < 0) {
 313         qemu_aio_unref(laiocb);
 314         return NULL;
 315     }
 316
 317     return &laiocb->common;
 318 }
 319
 320 void laio_detach_aio_context(LinuxAioState *s, AioContext *old_context)
 321 {
 322     aio_set_event_notifier(old_context, &s->e, false, NULL);
 323     qemu_bh_delete(s->completion_bh);
 324 }
 325
 326 void laio_attach_aio_context(LinuxAioState *s, AioContext *new_context)
 327 {
 328     s->completion_bh = aio_bh_new(new_context, qemu_laio_completion_bh, s);
 329     aio_set_event_notifier(new_context, &s->e, false,
 330                            qemu_laio_completion_cb);
 331 }
 332
 333 LinuxAioState *laio_init(void)
 334 {
 335     LinuxAioState *s;
 336
 337     s = g_malloc0(sizeof(*s));
 338     if (event_notifier_init(&s->e, false) < 0) {
 339         goto out_free_state;
 340     }
 341
 342     if (io_setup(MAX_EVENTS, &s->ctx) != 0) {
 343         goto out_close_efd;
 344     }
 345
 346     ioq_init(&s->io_q);
 347
 348     return s;
 349
 350 out_close_efd:
 351     event_notifier_cleanup(&s->e);
 352 out_free_state:
 353     g_free(s);
 354     return NULL;
 355 }
 356
 357 void laio_cleanup(LinuxAioState *s)
 358 {
 359     event_notifier_cleanup(&s->e);
 360
 361     if (io_destroy(s->ctx) != 0) {
 362         fprintf(stderr, "%s: destroy AIO context %p failed\n",
 363                         __func__, &s->ctx);
 364     }
 365     g_free(s);
 366 }