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 "qemu-common.h"
  14 #include "block/aio.h"
  15 #include "qemu/queue.h"
  16 #include "block/block.h"
  17 #include "block/raw-aio.h"
  18 #include "qemu/coroutine.h"
  19 #include "qapi/error.h"
  20 #include "trace.h"
  21
  22 /* io_uring ring size */
  23 #define MAX_ENTRIES 128
  24
  25 typedef struct LuringAIOCB {
  26     Coroutine *co;
  27     struct io_uring_sqe sqeq;
  28     ssize_t ret;
  29     QEMUIOVector *qiov;
  30     bool is_read;
  31     QSIMPLEQ_ENTRY(LuringAIOCB) next;
  32
  33     /*
  34      * Buffered reads may require resubmission, see
  35      * luring_resubmit_short_read().
  36      */
  37     int total_read;
  38     QEMUIOVector resubmit_qiov;
  39 } LuringAIOCB;
  40
  41 typedef struct LuringQueue {
  42     int plugged;
  43     unsigned int in_queue;
  44     unsigned int in_flight;
  45     bool blocked;
  46     QSIMPLEQ_HEAD(, LuringAIOCB) submit_queue;
  47 } LuringQueue;
  48
  49 typedef struct LuringState {
  50     AioContext *aio_context;
  51
  52     struct io_uring ring;
  53
  54     /* io queue for submit at batch.  Protected by AioContext lock. */
  55     LuringQueue io_q;
  56
  57     /* I/O completion processing.  Only runs in I/O thread.  */
  58     QEMUBH *completion_bh;
  59 } LuringState;
  60
  61 /**
  62  * luring_resubmit:
  63  *
  64  * Resubmit a request by appending it to submit_queue.  The caller must ensure
  65  * that ioq_submit() is called later so that submit_queue requests are started.
  66  */
  67 static void luring_resubmit(LuringState *s, LuringAIOCB *luringcb)
  68 {
  69     QSIMPLEQ_INSERT_TAIL(&s->io_q.submit_queue, luringcb, next);
  70     s->io_q.in_queue++;
  71 }
  72
  73 /**
  74  * luring_resubmit_short_read:
  75  *
  76  * Before Linux commit 9d93a3f5a0c ("io_uring: punt short reads to async
  77  * context") a buffered I/O request with the start of the file range in the
  78  * page cache could result in a short read.  Applications need to resubmit the
  79  * remaining read request.
  80  *
  81  * This is a slow path but recent kernels never take it.
  82  */
  83 static void luring_resubmit_short_read(LuringState *s, LuringAIOCB *luringcb,
  84                                        int nread)
  85 {
  86     QEMUIOVector *resubmit_qiov;
  87     size_t remaining;
  88
  89     trace_luring_resubmit_short_read(s, luringcb, nread);
  90
  91     /* Update read position */
  92     luringcb->total_read = nread;
  93     remaining = luringcb->qiov->size - luringcb->total_read;
  94
  95     /* Shorten qiov */
  96     resubmit_qiov = &luringcb->resubmit_qiov;
  97     if (resubmit_qiov->iov == NULL) {
  98         qemu_iovec_init(resubmit_qiov, luringcb->qiov->niov);
  99     } else {
 100         qemu_iovec_reset(resubmit_qiov);
 101     }
 102     qemu_iovec_concat(resubmit_qiov, luringcb->qiov, luringcb->total_read,
 103                       remaining);
 104
 105     /* Update sqe */
 106     luringcb->sqeq.off = nread;
 107     luringcb->sqeq.addr = (__u64)(uintptr_t)luringcb->resubmit_qiov.iov;
 108     luringcb->sqeq.len = luringcb->resubmit_qiov.niov;
 109
 110     luring_resubmit(s, luringcb);
 111 }
 112
 113 /**
 114  * luring_process_completions:
 115  * @s: AIO state
 116  *
 117  * Fetches completed I/O requests, consumes cqes and invokes their callbacks
 118  * The function is somewhat tricky because it supports nested event loops, for
 119  * example when a request callback invokes aio_poll().
 120  *
 121  * Function schedules BH completion so it  can be called again in a nested
 122  * event loop.  When there are no events left  to complete the BH is being
 123  * canceled.
 124  *
 125  */
 126 static void luring_process_completions(LuringState *s)
 127 {
 128     struct io_uring_cqe *cqes;
 129     int total_bytes;
 130     /*
 131      * Request completion callbacks can run the nested event loop.
 132      * Schedule ourselves so the nested event loop will "see" remaining
 133      * completed requests and process them.  Without this, completion
 134      * callbacks that wait for other requests using a nested event loop
 135      * would hang forever.
 136      *
 137      * This workaround is needed because io_uring uses poll_wait, which
 138      * is woken up when new events are added to the uring, thus polling on
 139      * the same uring fd will block unless more events are received.
 140      *
 141      * Other leaf block drivers (drivers that access the data themselves)
 142      * are networking based, so they poll sockets for data and run the
 143      * correct coroutine.
 144      */
 145     qemu_bh_schedule(s->completion_bh);
 146
 147     while (io_uring_peek_cqe(&s->ring, &cqes) == 0) {
 148         LuringAIOCB *luringcb;
 149         int ret;
 150
 151         if (!cqes) {
 152             break;
 153         }
 154
 155         luringcb = io_uring_cqe_get_data(cqes);
 156         ret = cqes->res;
 157         io_uring_cqe_seen(&s->ring, cqes);
 158         cqes = NULL;
 159
 160         /* Change counters one-by-one because we can be nested. */
 161         s->io_q.in_flight--;
 162         trace_luring_process_completion(s, luringcb, ret);
 163
 164         /* total_read is non-zero only for resubmitted read requests */
 165         total_bytes = ret + luringcb->total_read;
 166
 167         if (ret < 0) {
 168             if (ret == -EINTR) {
 169                 luring_resubmit(s, luringcb);
 170                 continue;
 171             }
 172         } else if (!luringcb->qiov) {
 173             goto end;
 174         } else if (total_bytes == luringcb->qiov->size) {
 175             ret = 0;
 176         /* Only read/write */
 177         } else {
 178             /* Short Read/Write */
 179             if (luringcb->is_read) {
 180                 if (ret > 0) {
 181                     luring_resubmit_short_read(s, luringcb, ret);
 182                     continue;
 183                 } else {
 184                     /* Pad with zeroes */
 185                     qemu_iovec_memset(luringcb->qiov, total_bytes, 0,
 186                                       luringcb->qiov->size - total_bytes);
 187                     ret = 0;
 188                 }
 189             } else {
 190                 ret = -ENOSPC;;
 191             }
 192         }
 193 end:
 194         luringcb->ret = ret;
 195         qemu_iovec_destroy(&luringcb->resubmit_qiov);
 196
 197         /*
 198          * If the coroutine is already entered it must be in ioq_submit()
 199          * and will notice luringcb->ret has been filled in when it
 200          * eventually runs later. Coroutines cannot be entered recursively
 201          * so avoid doing that!
 202          */
 203         if (!qemu_coroutine_entered(luringcb->co)) {
 204             aio_co_wake(luringcb->co);
 205         }
 206     }
 207     qemu_bh_cancel(s->completion_bh);
 208 }
 209
 210 static int ioq_submit(LuringState *s)
 211 {
 212     int ret = 0;
 213     LuringAIOCB *luringcb, *luringcb_next;
 214
 215     while (s->io_q.in_queue > 0) {
 216         /*
 217          * Try to fetch sqes from the ring for requests waiting in
 218          * the overflow queue
 219          */
 220         QSIMPLEQ_FOREACH_SAFE(luringcb, &s->io_q.submit_queue, next,
 221                               luringcb_next) {
 222             struct io_uring_sqe *sqes = io_uring_get_sqe(&s->ring);
 223             if (!sqes) {
 224                 break;
 225             }
 226             /* Prep sqe for submission */
 227             *sqes = luringcb->sqeq;
 228             QSIMPLEQ_REMOVE_HEAD(&s->io_q.submit_queue, next);
 229         }
 230         ret = io_uring_submit(&s->ring);
 231         trace_luring_io_uring_submit(s, ret);
 232         /* Prevent infinite loop if submission is refused */
 233         if (ret <= 0) {
 234             if (ret == -EAGAIN) {
 235                 continue;
 236             }
 237             break;
 238         }
 239         s->io_q.in_flight += ret;
 240         s->io_q.in_queue  -= ret;
 241     }
 242     s->io_q.blocked = (s->io_q.in_queue > 0);
 243
 244     if (s->io_q.in_flight) {
 245         /*
 246          * We can try to complete something just right away if there are
 247          * still requests in-flight.
 248          */
 249         luring_process_completions(s);
 250     }
 251     return ret;
 252 }
 253
 254 static void luring_process_completions_and_submit(LuringState *s)
 255 {
 256     aio_context_acquire(s->aio_context);
 257     luring_process_completions(s);
 258
 259     if (!s->io_q.plugged && s->io_q.in_queue > 0) {
 260         ioq_submit(s);
 261     }
 262     aio_context_release(s->aio_context);
 263 }
 264
 265 static void qemu_luring_completion_bh(void *opaque)
 266 {
 267     LuringState *s = opaque;
 268     luring_process_completions_and_submit(s);
 269 }
 270
 271 static void qemu_luring_completion_cb(void *opaque)
 272 {
 273     LuringState *s = opaque;
 274     luring_process_completions_and_submit(s);
 275 }
 276
 277 static void ioq_init(LuringQueue *io_q)
 278 {
 279     QSIMPLEQ_INIT(&io_q->submit_queue);
 280     io_q->plugged = 0;
 281     io_q->in_queue = 0;
 282     io_q->in_flight = 0;
 283     io_q->blocked = false;
 284 }
 285
 286 void luring_io_plug(BlockDriverState *bs, LuringState *s)
 287 {
 288     trace_luring_io_plug(s);
 289     s->io_q.plugged++;
 290 }
 291
 292 void luring_io_unplug(BlockDriverState *bs, LuringState *s)
 293 {
 294     assert(s->io_q.plugged);
 295     trace_luring_io_unplug(s, s->io_q.blocked, s->io_q.plugged,
 296                            s->io_q.in_queue, s->io_q.in_flight);
 297     if (--s->io_q.plugged == 0 &&
 298         !s->io_q.blocked && s->io_q.in_queue > 0) {
 299         ioq_submit(s);
 300     }
 301 }
 302
 303 /**
 304  * luring_do_submit:
 305  * @fd: file descriptor for I/O
 306  * @luringcb: AIO control block
 307  * @s: AIO state
 308  * @offset: offset for request
 309  * @type: type of request
 310  *
 311  * Fetches sqes from ring, adds to pending queue and preps them
 312  *
 313  */
 314 static int luring_do_submit(int fd, LuringAIOCB *luringcb, LuringState *s,
 315                             uint64_t offset, int type)
 316 {
 317     int ret;
 318     struct io_uring_sqe *sqes = &luringcb->sqeq;
 319
 320     switch (type) {
 321     case QEMU_AIO_WRITE:
 322         io_uring_prep_writev(sqes, fd, luringcb->qiov->iov,
 323                              luringcb->qiov->niov, offset);
 324         break;
 325     case QEMU_AIO_READ:
 326         io_uring_prep_readv(sqes, fd, luringcb->qiov->iov,
 327                             luringcb->qiov->niov, offset);
 328         break;
 329     case QEMU_AIO_FLUSH:
 330         io_uring_prep_fsync(sqes, fd, IORING_FSYNC_DATASYNC);
 331         break;
 332     default:
 333         fprintf(stderr, "%s: invalid AIO request type, aborting 0x%x.\n",
 334                         __func__, type);
 335         abort();
 336     }
 337     io_uring_sqe_set_data(sqes, luringcb);
 338
 339     QSIMPLEQ_INSERT_TAIL(&s->io_q.submit_queue, luringcb, next);
 340     s->io_q.in_queue++;
 341     trace_luring_do_submit(s, s->io_q.blocked, s->io_q.plugged,
 342                            s->io_q.in_queue, s->io_q.in_flight);
 343     if (!s->io_q.blocked &&
 344         (!s->io_q.plugged ||
 345          s->io_q.in_flight + s->io_q.in_queue >= MAX_ENTRIES)) {
 346         ret = ioq_submit(s);
 347         trace_luring_do_submit_done(s, ret);
 348         return ret;
 349     }
 350     return 0;
 351 }
 352
 353 int coroutine_fn luring_co_submit(BlockDriverState *bs, LuringState *s, int fd,
 354                                   uint64_t offset, QEMUIOVector *qiov, int type)
 355 {
 356     int ret;
 357     LuringAIOCB luringcb = {
 358         .co         = qemu_coroutine_self(),
 359         .ret        = -EINPROGRESS,
 360         .qiov       = qiov,
 361         .is_read    = (type == QEMU_AIO_READ),
 362     };
 363     trace_luring_co_submit(bs, s, &luringcb, fd, offset, qiov ? qiov->size : 0,
 364                            type);
 365     ret = luring_do_submit(fd, &luringcb, s, offset, type);
 366
 367     if (ret < 0) {
 368         return ret;
 369     }
 370
 371     if (luringcb.ret == -EINPROGRESS) {
 372         qemu_coroutine_yield();
 373     }
 374     return luringcb.ret;
 375 }
 376
 377 void luring_detach_aio_context(LuringState *s, AioContext *old_context)
 378 {
 379     aio_set_fd_handler(old_context, s->ring.ring_fd, false, NULL, NULL, NULL,
 380                        s);
 381     qemu_bh_delete(s->completion_bh);
 382     s->aio_context = NULL;
 383 }
 384
 385 void luring_attach_aio_context(LuringState *s, AioContext *new_context)
 386 {
 387     s->aio_context = new_context;
 388     s->completion_bh = aio_bh_new(new_context, qemu_luring_completion_bh, s);
 389     aio_set_fd_handler(s->aio_context, s->ring.ring_fd, false,
 390                        qemu_luring_completion_cb, NULL, NULL, s);
 391 }
 392
 393 LuringState *luring_init(Error **errp)
 394 {
 395     int rc;
 396     LuringState *s = g_new0(LuringState, 1);
 397     struct io_uring *ring = &s->ring;
 398
 399     trace_luring_init_state(s, sizeof(*s));
 400
 401     rc = io_uring_queue_init(MAX_ENTRIES, ring, 0);
 402     if (rc < 0) {
 403         error_setg_errno(errp, errno, "failed to init linux io_uring ring");
 404         g_free(s);
 405         return NULL;
 406     }
 407
 408     ioq_init(&s->io_q);
 409     return s;
 410
 411 }
 412
 413 void luring_cleanup(LuringState *s)
 414 {
 415     io_uring_queue_exit(&s->ring);
 416     g_free(s);
 417     trace_luring_cleanup_state(s);
 418 }