block/io_uring.c

   1 /*
   2  * Linux io_uring support.
   3  *
   4  * Copyright (C) 2009 IBM, Corp.
   5  * Copyright (C) 2009 Red Hat, Inc.
   6  * Copyright (C) 2019 Aarushi Mehta
   7  *
   8  * This work is licensed under the terms of the GNU GPL, version 2 or later.
   9  * See the COPYING file in the top-level directory.
  10  */
  11 #include "qemu/osdep.h"
  12 #include <liburing.h>
  13 #include "block/aio.h"
  14 #include "qemu/queue.h"
  15 #include "block/block.h"
  16 #include "block/raw-aio.h"
  17 #include "qemu/coroutine.h"
  18 #include "qapi/error.h"
  19 #include "trace.h"
  20
  21 /* Only used for assertions.  */
  22 #include "qemu/coroutine_int.h"
  23
  24 /* io_uring ring size */
  25 #define MAX_ENTRIES 128
  26
  27 typedef struct LuringAIOCB {
  28     Coroutine *co;
  29     struct io_uring_sqe sqeq;
  30     ssize_t ret;
  31     QEMUIOVector *qiov;
  32     bool is_read;
  33     QSIMPLEQ_ENTRY(LuringAIOCB) next;
  34
  35     /*
  36      * Buffered reads may require resubmission, see
  37      * luring_resubmit_short_read().
  38      */
  39     int total_read;
  40     QEMUIOVector resubmit_qiov;
  41 } LuringAIOCB;
  42
  43 typedef struct LuringQueue {
  44     int plugged;
  45     unsigned int in_queue;
  46     unsigned int in_flight;
  47     bool blocked;
  48     QSIMPLEQ_HEAD(, LuringAIOCB) submit_queue;
  49 } LuringQueue;
  50
  51 typedef struct LuringState {
  52     AioContext *aio_context;
  53
  54     struct io_uring ring;
  55
  56     /* No locking required, only accessed from AioContext home thread */
  57     LuringQueue io_q;
  58
  59     QEMUBH *completion_bh;
  60 } LuringState;
  61
  62 /**
  63  * luring_resubmit:
  64  *
  65  * Resubmit a request by appending it to submit_queue.  The caller must ensure
  66  * that ioq_submit() is called later so that submit_queue requests are started.
  67  */
  68 static void luring_resubmit(LuringState *s, LuringAIOCB *luringcb)
  69 {
  70     QSIMPLEQ_INSERT_TAIL(&s->io_q.submit_queue, luringcb, next);
  71     s->io_q.in_queue++;
  72 }
  73
  74 /**
  75  * luring_resubmit_short_read:
  76  *
  77  * Short reads are rare but may occur. The remaining read request needs to be
  78  * resubmitted.
  79  */
  80 static void luring_resubmit_short_read(LuringState *s, LuringAIOCB *luringcb,
  81                                        int nread)
  82 {
  83     QEMUIOVector *resubmit_qiov;
  84     size_t remaining;
  85
  86     trace_luring_resubmit_short_read(s, luringcb, nread);
  87
  88     /* Update read position */
  89     luringcb->total_read += nread;
  90     remaining = luringcb->qiov->size - luringcb->total_read;
  91
  92     /* Shorten qiov */
  93     resubmit_qiov = &luringcb->resubmit_qiov;
  94     if (resubmit_qiov->iov == NULL) {
  95         qemu_iovec_init(resubmit_qiov, luringcb->qiov->niov);
  96     } else {
  97         qemu_iovec_reset(resubmit_qiov);
  98     }
  99     qemu_iovec_concat(resubmit_qiov, luringcb->qiov, luringcb->total_read,
 100                       remaining);
 101
 102     /* Update sqe */
 103     luringcb->sqeq.off += nread;
 104     luringcb->sqeq.addr = (__u64)(uintptr_t)luringcb->resubmit_qiov.iov;
 105     luringcb->sqeq.len = luringcb->resubmit_qiov.niov;
 106
 107     luring_resubmit(s, luringcb);
 108 }
 109
 110 /**
 111  * luring_process_completions:
 112  * @s: AIO state
 113  *
 114  * Fetches completed I/O requests, consumes cqes and invokes their callbacks
 115  * The function is somewhat tricky because it supports nested event loops, for
 116  * example when a request callback invokes aio_poll().
 117  *
 118  * Function schedules BH completion so it  can be called again in a nested
 119  * event loop.  When there are no events left  to complete the BH is being
 120  * canceled.
 121  *
 122  */
 123 static void luring_process_completions(LuringState *s)
 124 {
 125     struct io_uring_cqe *cqes;
 126     int total_bytes;
 127     /*
 128      * Request completion callbacks can run the nested event loop.
 129      * Schedule ourselves so the nested event loop will "see" remaining
 130      * completed requests and process them.  Without this, completion
 131      * callbacks that wait for other requests using a nested event loop
 132      * would hang forever.
 133      *
 134      * This workaround is needed because io_uring uses poll_wait, which
 135      * is woken up when new events are added to the uring, thus polling on
 136      * the same uring fd will block unless more events are received.
 137      *
 138      * Other leaf block drivers (drivers that access the data themselves)
 139      * are networking based, so they poll sockets for data and run the
 140      * correct coroutine.
 141      */
 142     qemu_bh_schedule(s->completion_bh);
 143
 144     while (io_uring_peek_cqe(&s->ring, &cqes) == 0) {
 145         LuringAIOCB *luringcb;
 146         int ret;
 147
 148         if (!cqes) {
 149             break;
 150         }
 151
 152         luringcb = io_uring_cqe_get_data(cqes);
 153         ret = cqes->res;
 154         io_uring_cqe_seen(&s->ring, cqes);
 155         cqes = NULL;
 156
 157         /* Change counters one-by-one because we can be nested. */
 158         s->io_q.in_flight--;
 159         trace_luring_process_completion(s, luringcb, ret);
 160
 161         /* total_read is non-zero only for resubmitted read requests */
 162         total_bytes = ret + luringcb->total_read;
 163
 164         if (ret < 0) {
 165             /*
 166              * Only writev/readv/fsync requests on regular files or host block
 167              * devices are submitted. Therefore -EAGAIN is not expected but it's
 168              * known to happen sometimes with Linux SCSI. Submit again and hope
 169              * the request completes successfully.
 170              *
 171              * For more information, see:
 172              * https://lore.kernel.org/io-uring/20210727165811.284510-3-axboe@kernel.dk/T/#u
 173              *
 174              * If the code is changed to submit other types of requests in the
 175              * future, then this workaround may need to be extended to deal with
 176              * genuine -EAGAIN results that should not be resubmitted
 177              * immediately.
 178              */
 179             if (ret == -EINTR || ret == -EAGAIN) {
 180                 luring_resubmit(s, luringcb);
 181                 continue;
 182             }
 183         } else if (!luringcb->qiov) {
 184             goto end;
 185         } else if (total_bytes == luringcb->qiov->size) {
 186             ret = 0;
 187         /* Only read/write */
 188         } else {
 189             /* Short Read/Write */
 190             if (luringcb->is_read) {
 191                 if (ret > 0) {
 192                     luring_resubmit_short_read(s, luringcb, ret);
 193                     continue;
 194                 } else {
 195                     /* Pad with zeroes */
 196                     qemu_iovec_memset(luringcb->qiov, total_bytes, 0,
 197                                       luringcb->qiov->size - total_bytes);
 198                     ret = 0;
 199                 }
 200             } else {
 201                 ret = -ENOSPC;
 202             }
 203         }
 204 end:
 205         luringcb->ret = ret;
 206         qemu_iovec_destroy(&luringcb->resubmit_qiov);
 207
 208         /*
 209          * If the coroutine is already entered it must be in ioq_submit()
 210          * and will notice luringcb->ret has been filled in when it
 211          * eventually runs later. Coroutines cannot be entered recursively
 212          * so avoid doing that!
 213          */
 214         assert(luringcb->co->ctx == s->aio_context);
 215         if (!qemu_coroutine_entered(luringcb->co)) {
 216             aio_co_wake(luringcb->co);
 217         }
 218     }
 219     qemu_bh_cancel(s->completion_bh);
 220 }
 221
 222 static int ioq_submit(LuringState *s)
 223 {
 224     int ret = 0;
 225     LuringAIOCB *luringcb, *luringcb_next;
 226
 227     while (s->io_q.in_queue > 0) {
 228         /*
 229          * Try to fetch sqes from the ring for requests waiting in
 230          * the overflow queue
 231          */
 232         QSIMPLEQ_FOREACH_SAFE(luringcb, &s->io_q.submit_queue, next,
 233                               luringcb_next) {
 234             struct io_uring_sqe *sqes = io_uring_get_sqe(&s->ring);
 235             if (!sqes) {
 236                 break;
 237             }
 238             /* Prep sqe for submission */
 239             *sqes = luringcb->sqeq;
 240             QSIMPLEQ_REMOVE_HEAD(&s->io_q.submit_queue, next);
 241         }
 242         ret = io_uring_submit(&s->ring);
 243         trace_luring_io_uring_submit(s, ret);
 244         /* Prevent infinite loop if submission is refused */
 245         if (ret <= 0) {
 246             if (ret == -EAGAIN || ret == -EINTR) {
 247                 continue;
 248             }
 249             break;
 250         }
 251         s->io_q.in_flight += ret;
 252         s->io_q.in_queue  -= ret;
 253     }
 254     s->io_q.blocked = (s->io_q.in_queue > 0);
 255
 256     if (s->io_q.in_flight) {
 257         /*
 258          * We can try to complete something just right away if there are
 259          * still requests in-flight.
 260          */
 261         luring_process_completions(s);
 262     }
 263     return ret;
 264 }
 265
 266 static void luring_process_completions_and_submit(LuringState *s)
 267 {
 268     luring_process_completions(s);
 269
 270     if (!s->io_q.plugged && s->io_q.in_queue > 0) {
 271         ioq_submit(s);
 272     }
 273 }
 274
 275 static void qemu_luring_completion_bh(void *opaque)
 276 {
 277     LuringState *s = opaque;
 278     luring_process_completions_and_submit(s);
 279 }
 280
 281 static void qemu_luring_completion_cb(void *opaque)
 282 {
 283     LuringState *s = opaque;
 284     luring_process_completions_and_submit(s);
 285 }
 286
 287 static bool qemu_luring_poll_cb(void *opaque)
 288 {
 289     LuringState *s = opaque;
 290
 291     return io_uring_cq_ready(&s->ring);
 292 }
 293
 294 static void qemu_luring_poll_ready(void *opaque)
 295 {
 296     LuringState *s = opaque;
 297
 298     luring_process_completions_and_submit(s);
 299 }
 300
 301 static void ioq_init(LuringQueue *io_q)
 302 {
 303     QSIMPLEQ_INIT(&io_q->submit_queue);
 304     io_q->plugged = 0;
 305     io_q->in_queue = 0;
 306     io_q->in_flight = 0;
 307     io_q->blocked = false;
 308 }
 309
 310 void luring_io_plug(void)
 311 {
 312     AioContext *ctx = qemu_get_current_aio_context();
 313     LuringState *s = aio_get_linux_io_uring(ctx);
 314     trace_luring_io_plug(s);
 315     s->io_q.plugged++;
 316 }
 317
 318 void luring_io_unplug(void)
 319 {
 320     AioContext *ctx = qemu_get_current_aio_context();
 321     LuringState *s = aio_get_linux_io_uring(ctx);
 322     assert(s->io_q.plugged);
 323     trace_luring_io_unplug(s, s->io_q.blocked, s->io_q.plugged,
 324                            s->io_q.in_queue, s->io_q.in_flight);
 325     if (--s->io_q.plugged == 0 &&
 326         !s->io_q.blocked && s->io_q.in_queue > 0) {
 327         ioq_submit(s);
 328     }
 329 }
 330
 331 /**
 332  * luring_do_submit:
 333  * @fd: file descriptor for I/O
 334  * @luringcb: AIO control block
 335  * @s: AIO state
 336  * @offset: offset for request
 337  * @type: type of request
 338  *
 339  * Fetches sqes from ring, adds to pending queue and preps them
 340  *
 341  */
 342 static int luring_do_submit(int fd, LuringAIOCB *luringcb, LuringState *s,
 343                             uint64_t offset, int type)
 344 {
 345     int ret;
 346     struct io_uring_sqe *sqes = &luringcb->sqeq;
 347
 348     switch (type) {
 349     case QEMU_AIO_WRITE:
 350         io_uring_prep_writev(sqes, fd, luringcb->qiov->iov,
 351                              luringcb->qiov->niov, offset);
 352         break;
 353     case QEMU_AIO_READ:
 354         io_uring_prep_readv(sqes, fd, luringcb->qiov->iov,
 355                             luringcb->qiov->niov, offset);
 356         break;
 357     case QEMU_AIO_FLUSH:
 358         io_uring_prep_fsync(sqes, fd, IORING_FSYNC_DATASYNC);
 359         break;
 360     default:
 361         fprintf(stderr, "%s: invalid AIO request type, aborting 0x%x.\n",
 362                         __func__, type);
 363         abort();
 364     }
 365     io_uring_sqe_set_data(sqes, luringcb);
 366
 367     QSIMPLEQ_INSERT_TAIL(&s->io_q.submit_queue, luringcb, next);
 368     s->io_q.in_queue++;
 369     trace_luring_do_submit(s, s->io_q.blocked, s->io_q.plugged,
 370                            s->io_q.in_queue, s->io_q.in_flight);
 371     if (!s->io_q.blocked &&
 372         (!s->io_q.plugged ||
 373          s->io_q.in_flight + s->io_q.in_queue >= MAX_ENTRIES)) {
 374         ret = ioq_submit(s);
 375         trace_luring_do_submit_done(s, ret);
 376         return ret;
 377     }
 378     return 0;
 379 }
 380
 381 int coroutine_fn luring_co_submit(BlockDriverState *bs, int fd, uint64_t offset,
 382                                   QEMUIOVector *qiov, int type)
 383 {
 384     int ret;
 385     AioContext *ctx = qemu_get_current_aio_context();
 386     LuringState *s = aio_get_linux_io_uring(ctx);
 387     LuringAIOCB luringcb = {
 388         .co         = qemu_coroutine_self(),
 389         .ret        = -EINPROGRESS,
 390         .qiov       = qiov,
 391         .is_read    = (type == QEMU_AIO_READ),
 392     };
 393     trace_luring_co_submit(bs, s, &luringcb, fd, offset, qiov ? qiov->size : 0,
 394                            type);
 395     ret = luring_do_submit(fd, &luringcb, s, offset, type);
 396
 397     if (ret < 0) {
 398         return ret;
 399     }
 400
 401     if (luringcb.ret == -EINPROGRESS) {
 402         qemu_coroutine_yield();
 403     }
 404     return luringcb.ret;
 405 }
 406
 407 void luring_detach_aio_context(LuringState *s, AioContext *old_context)
 408 {
 409     aio_set_fd_handler(old_context, s->ring.ring_fd, false,
 410                        NULL, NULL, NULL, NULL, s);
 411     qemu_bh_delete(s->completion_bh);
 412     s->aio_context = NULL;
 413 }
 414
 415 void luring_attach_aio_context(LuringState *s, AioContext *new_context)
 416 {
 417     s->aio_context = new_context;
 418     s->completion_bh = aio_bh_new(new_context, qemu_luring_completion_bh, s);
 419     aio_set_fd_handler(s->aio_context, s->ring.ring_fd, false,
 420                        qemu_luring_completion_cb, NULL,
 421                        qemu_luring_poll_cb, qemu_luring_poll_ready, s);
 422 }
 423
 424 LuringState *luring_init(Error **errp)
 425 {
 426     int rc;
 427     LuringState *s = g_new0(LuringState, 1);
 428     struct io_uring *ring = &s->ring;
 429
 430     trace_luring_init_state(s, sizeof(*s));
 431
 432     rc = io_uring_queue_init(MAX_ENTRIES, ring, 0);
 433     if (rc < 0) {
 434         error_setg_errno(errp, errno, "failed to init linux io_uring ring");
 435         g_free(s);
 436         return NULL;
 437     }
 438
 439     ioq_init(&s->io_q);
 440     return s;
 441
 442 }
 443
 444 void luring_cleanup(LuringState *s)
 445 {
 446     io_uring_queue_exit(&s->ring);
 447     trace_luring_cleanup_state(s);
 448     g_free(s);
 449 }