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 /* io_uring ring size */
  22 #define MAX_ENTRIES 128
  23
  24 typedef struct LuringAIOCB {
  25     Coroutine *co;
  26     struct io_uring_sqe sqeq;
  27     ssize_t ret;
  28     QEMUIOVector *qiov;
  29     bool is_read;
  30     QSIMPLEQ_ENTRY(LuringAIOCB) next;
  31
  32     /*
  33      * Buffered reads may require resubmission, see
  34      * luring_resubmit_short_read().
  35      */
  36     int total_read;
  37     QEMUIOVector resubmit_qiov;
  38 } LuringAIOCB;
  39
  40 typedef struct LuringQueue {
  41     int plugged;
  42     unsigned int in_queue;
  43     unsigned int in_flight;
  44     bool blocked;
  45     QSIMPLEQ_HEAD(, LuringAIOCB) submit_queue;
  46 } LuringQueue;
  47
  48 typedef struct LuringState {
  49     AioContext *aio_context;
  50
  51     struct io_uring ring;
  52
  53     /* io queue for submit at batch.  Protected by AioContext lock. */
  54     LuringQueue io_q;
  55
  56     /* I/O completion processing.  Only runs in I/O thread.  */
  57     QEMUBH *completion_bh;
  58 } LuringState;
  59
  60 /**
  61  * luring_resubmit:
  62  *
  63  * Resubmit a request by appending it to submit_queue.  The caller must ensure
  64  * that ioq_submit() is called later so that submit_queue requests are started.
  65  */
  66 static void luring_resubmit(LuringState *s, LuringAIOCB *luringcb)
  67 {
  68     QSIMPLEQ_INSERT_TAIL(&s->io_q.submit_queue, luringcb, next);
  69     s->io_q.in_queue++;
  70 }
  71
  72 /**
  73  * luring_resubmit_short_read:
  74  *
  75  * Before Linux commit 9d93a3f5a0c ("io_uring: punt short reads to async
  76  * context") a buffered I/O request with the start of the file range in the
  77  * page cache could result in a short read.  Applications need to resubmit the
  78  * remaining read request.
  79  *
  80  * This is a slow path but recent kernels never take it.
  81  */
  82 static void luring_resubmit_short_read(LuringState *s, LuringAIOCB *luringcb,
  83                                        int nread)
  84 {
  85     QEMUIOVector *resubmit_qiov;
  86     size_t remaining;
  87
  88     trace_luring_resubmit_short_read(s, luringcb, nread);
  89
  90     /* Update read position */
  91     luringcb->total_read = nread;
  92     remaining = luringcb->qiov->size - luringcb->total_read;
  93
  94     /* Shorten qiov */
  95     resubmit_qiov = &luringcb->resubmit_qiov;
  96     if (resubmit_qiov->iov == NULL) {
  97         qemu_iovec_init(resubmit_qiov, luringcb->qiov->niov);
  98     } else {
  99         qemu_iovec_reset(resubmit_qiov);
 100     }
 101     qemu_iovec_concat(resubmit_qiov, luringcb->qiov, luringcb->total_read,
 102                       remaining);
 103
 104     /* Update sqe */
 105     luringcb->sqeq.off = nread;
 106     luringcb->sqeq.addr = (__u64)(uintptr_t)luringcb->resubmit_qiov.iov;
 107     luringcb->sqeq.len = luringcb->resubmit_qiov.niov;
 108
 109     luring_resubmit(s, luringcb);
 110 }
 111
 112 /**
 113  * luring_process_completions:
 114  * @s: AIO state
 115  *
 116  * Fetches completed I/O requests, consumes cqes and invokes their callbacks
 117  * The function is somewhat tricky because it supports nested event loops, for
 118  * example when a request callback invokes aio_poll().
 119  *
 120  * Function schedules BH completion so it  can be called again in a nested
 121  * event loop.  When there are no events left  to complete the BH is being
 122  * canceled.
 123  *
 124  */
 125 static void luring_process_completions(LuringState *s)
 126 {
 127     struct io_uring_cqe *cqes;
 128     int total_bytes;
 129     /*
 130      * Request completion callbacks can run the nested event loop.
 131      * Schedule ourselves so the nested event loop will "see" remaining
 132      * completed requests and process them.  Without this, completion
 133      * callbacks that wait for other requests using a nested event loop
 134      * would hang forever.
 135      *
 136      * This workaround is needed because io_uring uses poll_wait, which
 137      * is woken up when new events are added to the uring, thus polling on
 138      * the same uring fd will block unless more events are received.
 139      *
 140      * Other leaf block drivers (drivers that access the data themselves)
 141      * are networking based, so they poll sockets for data and run the
 142      * correct coroutine.
 143      */
 144     qemu_bh_schedule(s->completion_bh);
 145
 146     while (io_uring_peek_cqe(&s->ring, &cqes) == 0) {
 147         LuringAIOCB *luringcb;
 148         int ret;
 149
 150         if (!cqes) {
 151             break;
 152         }
 153
 154         luringcb = io_uring_cqe_get_data(cqes);
 155         ret = cqes->res;
 156         io_uring_cqe_seen(&s->ring, cqes);
 157         cqes = NULL;
 158
 159         /* Change counters one-by-one because we can be nested. */
 160         s->io_q.in_flight--;
 161         trace_luring_process_completion(s, luringcb, ret);
 162
 163         /* total_read is non-zero only for resubmitted read requests */
 164         total_bytes = ret + luringcb->total_read;
 165
 166         if (ret < 0) {
 167             /*
 168              * Only writev/readv/fsync requests on regular files or host block
 169              * devices are submitted. Therefore -EAGAIN is not expected but it's
 170              * known to happen sometimes with Linux SCSI. Submit again and hope
 171              * the request completes successfully.
 172              *
 173              * For more information, see:
 174              * https://lore.kernel.org/io-uring/20210727165811.284510-3-axboe@kernel.dk/T/#u
 175              *
 176              * If the code is changed to submit other types of requests in the
 177              * future, then this workaround may need to be extended to deal with
 178              * genuine -EAGAIN results that should not be resubmitted
 179              * immediately.
 180              */
 181             if (ret == -EINTR || ret == -EAGAIN) {
 182                 luring_resubmit(s, luringcb);
 183                 continue;
 184             }
 185         } else if (!luringcb->qiov) {
 186             goto end;
 187         } else if (total_bytes == luringcb->qiov->size) {
 188             ret = 0;
 189         /* Only read/write */
 190         } else {
 191             /* Short Read/Write */
 192             if (luringcb->is_read) {
 193                 if (ret > 0) {
 194                     luring_resubmit_short_read(s, luringcb, ret);
 195                     continue;
 196                 } else {
 197                     /* Pad with zeroes */
 198                     qemu_iovec_memset(luringcb->qiov, total_bytes, 0,
 199                                       luringcb->qiov->size - total_bytes);
 200                     ret = 0;
 201                 }
 202             } else {
 203                 ret = -ENOSPC;
 204             }
 205         }
 206 end:
 207         luringcb->ret = ret;
 208         qemu_iovec_destroy(&luringcb->resubmit_qiov);
 209
 210         /*
 211          * If the coroutine is already entered it must be in ioq_submit()
 212          * and will notice luringcb->ret has been filled in when it
 213          * eventually runs later. Coroutines cannot be entered recursively
 214          * so avoid doing that!
 215          */
 216         if (!qemu_coroutine_entered(luringcb->co)) {
 217             aio_co_wake(luringcb->co);
 218         }
 219     }
 220     qemu_bh_cancel(s->completion_bh);
 221 }
 222
 223 static int ioq_submit(LuringState *s)
 224 {
 225     int ret = 0;
 226     LuringAIOCB *luringcb, *luringcb_next;
 227
 228     while (s->io_q.in_queue > 0) {
 229         /*
 230          * Try to fetch sqes from the ring for requests waiting in
 231          * the overflow queue
 232          */
 233         QSIMPLEQ_FOREACH_SAFE(luringcb, &s->io_q.submit_queue, next,
 234                               luringcb_next) {
 235             struct io_uring_sqe *sqes = io_uring_get_sqe(&s->ring);
 236             if (!sqes) {
 237                 break;
 238             }
 239             /* Prep sqe for submission */
 240             *sqes = luringcb->sqeq;
 241             QSIMPLEQ_REMOVE_HEAD(&s->io_q.submit_queue, next);
 242         }
 243         ret = io_uring_submit(&s->ring);
 244         trace_luring_io_uring_submit(s, ret);
 245         /* Prevent infinite loop if submission is refused */
 246         if (ret <= 0) {
 247             if (ret == -EAGAIN || ret == -EINTR) {
 248                 continue;
 249             }
 250             break;
 251         }
 252         s->io_q.in_flight += ret;
 253         s->io_q.in_queue  -= ret;
 254     }
 255     s->io_q.blocked = (s->io_q.in_queue > 0);
 256
 257     if (s->io_q.in_flight) {
 258         /*
 259          * We can try to complete something just right away if there are
 260          * still requests in-flight.
 261          */
 262         luring_process_completions(s);
 263     }
 264     return ret;
 265 }
 266
 267 static void luring_process_completions_and_submit(LuringState *s)
 268 {
 269     aio_context_acquire(s->aio_context);
 270     luring_process_completions(s);
 271
 272     if (!s->io_q.plugged && s->io_q.in_queue > 0) {
 273         ioq_submit(s);
 274     }
 275     aio_context_release(s->aio_context);
 276 }
 277
 278 static void qemu_luring_completion_bh(void *opaque)
 279 {
 280     LuringState *s = opaque;
 281     luring_process_completions_and_submit(s);
 282 }
 283
 284 static void qemu_luring_completion_cb(void *opaque)
 285 {
 286     LuringState *s = opaque;
 287     luring_process_completions_and_submit(s);
 288 }
 289
 290 static bool qemu_luring_poll_cb(void *opaque)
 291 {
 292     LuringState *s = opaque;
 293
 294     return io_uring_cq_ready(&s->ring);
 295 }
 296
 297 static void qemu_luring_poll_ready(void *opaque)
 298 {
 299     LuringState *s = opaque;
 300
 301     luring_process_completions_and_submit(s);
 302 }
 303
 304 static void ioq_init(LuringQueue *io_q)
 305 {
 306     QSIMPLEQ_INIT(&io_q->submit_queue);
 307     io_q->plugged = 0;
 308     io_q->in_queue = 0;
 309     io_q->in_flight = 0;
 310     io_q->blocked = false;
 311 }
 312
 313 void luring_io_plug(BlockDriverState *bs, LuringState *s)
 314 {
 315     trace_luring_io_plug(s);
 316     s->io_q.plugged++;
 317 }
 318
 319 void luring_io_unplug(BlockDriverState *bs, LuringState *s)
 320 {
 321     assert(s->io_q.plugged);
 322     trace_luring_io_unplug(s, s->io_q.blocked, s->io_q.plugged,
 323                            s->io_q.in_queue, s->io_q.in_flight);
 324     if (--s->io_q.plugged == 0 &&
 325         !s->io_q.blocked && s->io_q.in_queue > 0) {
 326         ioq_submit(s);
 327     }
 328 }
 329
 330 /**
 331  * luring_do_submit:
 332  * @fd: file descriptor for I/O
 333  * @luringcb: AIO control block
 334  * @s: AIO state
 335  * @offset: offset for request
 336  * @type: type of request
 337  *
 338  * Fetches sqes from ring, adds to pending queue and preps them
 339  *
 340  */
 341 static int luring_do_submit(int fd, LuringAIOCB *luringcb, LuringState *s,
 342                             uint64_t offset, int type)
 343 {
 344     int ret;
 345     struct io_uring_sqe *sqes = &luringcb->sqeq;
 346
 347     switch (type) {
 348     case QEMU_AIO_WRITE:
 349         io_uring_prep_writev(sqes, fd, luringcb->qiov->iov,
 350                              luringcb->qiov->niov, offset);
 351         break;
 352     case QEMU_AIO_READ:
 353         io_uring_prep_readv(sqes, fd, luringcb->qiov->iov,
 354                             luringcb->qiov->niov, offset);
 355         break;
 356     case QEMU_AIO_FLUSH:
 357         io_uring_prep_fsync(sqes, fd, IORING_FSYNC_DATASYNC);
 358         break;
 359     default:
 360         fprintf(stderr, "%s: invalid AIO request type, aborting 0x%x.\n",
 361                         __func__, type);
 362         abort();
 363     }
 364     io_uring_sqe_set_data(sqes, luringcb);
 365
 366     QSIMPLEQ_INSERT_TAIL(&s->io_q.submit_queue, luringcb, next);
 367     s->io_q.in_queue++;
 368     trace_luring_do_submit(s, s->io_q.blocked, s->io_q.plugged,
 369                            s->io_q.in_queue, s->io_q.in_flight);
 370     if (!s->io_q.blocked &&
 371         (!s->io_q.plugged ||
 372          s->io_q.in_flight + s->io_q.in_queue >= MAX_ENTRIES)) {
 373         ret = ioq_submit(s);
 374         trace_luring_do_submit_done(s, ret);
 375         return ret;
 376     }
 377     return 0;
 378 }
 379
 380 int coroutine_fn luring_co_submit(BlockDriverState *bs, LuringState *s, int fd,
 381                                   uint64_t offset, QEMUIOVector *qiov, int type)
 382 {
 383     int ret;
 384     LuringAIOCB luringcb = {
 385         .co         = qemu_coroutine_self(),
 386         .ret        = -EINPROGRESS,
 387         .qiov       = qiov,
 388         .is_read    = (type == QEMU_AIO_READ),
 389     };
 390     trace_luring_co_submit(bs, s, &luringcb, fd, offset, qiov ? qiov->size : 0,
 391                            type);
 392     ret = luring_do_submit(fd, &luringcb, s, offset, type);
 393
 394     if (ret < 0) {
 395         return ret;
 396     }
 397
 398     if (luringcb.ret == -EINPROGRESS) {
 399         qemu_coroutine_yield();
 400     }
 401     return luringcb.ret;
 402 }
 403
 404 void luring_detach_aio_context(LuringState *s, AioContext *old_context)
 405 {
 406     aio_set_fd_handler(old_context, s->ring.ring_fd, false,
 407                        NULL, NULL, NULL, NULL, s);
 408     qemu_bh_delete(s->completion_bh);
 409     s->aio_context = NULL;
 410 }
 411
 412 void luring_attach_aio_context(LuringState *s, AioContext *new_context)
 413 {
 414     s->aio_context = new_context;
 415     s->completion_bh = aio_bh_new(new_context, qemu_luring_completion_bh, s);
 416     aio_set_fd_handler(s->aio_context, s->ring.ring_fd, false,
 417                        qemu_luring_completion_cb, NULL,
 418                        qemu_luring_poll_cb, qemu_luring_poll_ready, s);
 419 }
 420
 421 LuringState *luring_init(Error **errp)
 422 {
 423     int rc;
 424     LuringState *s = g_new0(LuringState, 1);
 425     struct io_uring *ring = &s->ring;
 426
 427     trace_luring_init_state(s, sizeof(*s));
 428
 429     rc = io_uring_queue_init(MAX_ENTRIES, ring, 0);
 430     if (rc < 0) {
 431         error_setg_errno(errp, errno, "failed to init linux io_uring ring");
 432         g_free(s);
 433         return NULL;
 434     }
 435
 436     ioq_init(&s->io_q);
 437     return s;
 438
 439 }
 440
 441 void luring_cleanup(LuringState *s)
 442 {
 443     io_uring_queue_exit(&s->ring);
 444     trace_luring_cleanup_state(s);
 445     g_free(s);
 446 }