include/block/aio.h

   1 /*
   2  * QEMU aio implementation
   3  *
   4  * Copyright IBM, Corp. 2008
   5  *
   6  * Authors:
   7  *  Anthony Liguori   <aliguori@us.ibm.com>
   8  *
   9  * This work is licensed under the terms of the GNU GPL, version 2.  See
  10  * the COPYING file in the top-level directory.
  11  *
  12  */
  13
  14 #ifndef QEMU_AIO_H
  15 #define QEMU_AIO_H
  16
  17 #ifdef CONFIG_LINUX_IO_URING
  18 #include <liburing.h>
  19 #endif
  20 #include "qemu/coroutine.h"
  21 #include "qemu/queue.h"
  22 #include "qemu/event_notifier.h"
  23 #include "qemu/thread.h"
  24 #include "qemu/timer.h"
  25
  26 typedef struct BlockAIOCB BlockAIOCB;
  27 typedef void BlockCompletionFunc(void *opaque, int ret);
  28
  29 typedef struct AIOCBInfo {
  30     void (*cancel_async)(BlockAIOCB *acb);
  31     AioContext *(*get_aio_context)(BlockAIOCB *acb);
  32     size_t aiocb_size;
  33 } AIOCBInfo;
  34
  35 struct BlockAIOCB {
  36     const AIOCBInfo *aiocb_info;
  37     BlockDriverState *bs;
  38     BlockCompletionFunc *cb;
  39     void *opaque;
  40     int refcnt;
  41 };
  42
  43 void *qemu_aio_get(const AIOCBInfo *aiocb_info, BlockDriverState *bs,
  44                    BlockCompletionFunc *cb, void *opaque);
  45 void qemu_aio_unref(void *p);
  46 void qemu_aio_ref(void *p);
  47
  48 typedef struct AioHandler AioHandler;
  49 typedef QLIST_HEAD(, AioHandler) AioHandlerList;
  50 typedef void QEMUBHFunc(void *opaque);
  51 typedef bool AioPollFn(void *opaque);
  52 typedef void IOHandler(void *opaque);
  53
  54 struct Coroutine;
  55 struct ThreadPool;
  56 struct LinuxAioState;
  57 struct LuringState;
  58
  59 /* Is polling disabled? */
  60 bool aio_poll_disabled(AioContext *ctx);
  61
  62 /* Callbacks for file descriptor monitoring implementations */
  63 typedef struct {
  64     /*
  65      * update:
  66      * @ctx: the AioContext
  67      * @old_node: the existing handler or NULL if this file descriptor is being
  68      *            monitored for the first time
  69      * @new_node: the new handler or NULL if this file descriptor is being
  70      *            removed
  71      *
  72      * Add/remove/modify a monitored file descriptor.
  73      *
  74      * Called with ctx->list_lock acquired.
  75      */
  76     void (*update)(AioContext *ctx, AioHandler *old_node, AioHandler *new_node);
  77
  78     /*
  79      * wait:
  80      * @ctx: the AioContext
  81      * @ready_list: list for handlers that become ready
  82      * @timeout: maximum duration to wait, in nanoseconds
  83      *
  84      * Wait for file descriptors to become ready and place them on ready_list.
  85      *
  86      * Called with ctx->list_lock incremented but not locked.
  87      *
  88      * Returns: number of ready file descriptors.
  89      */
  90     int (*wait)(AioContext *ctx, AioHandlerList *ready_list, int64_t timeout);
  91
  92     /*
  93      * need_wait:
  94      * @ctx: the AioContext
  95      *
  96      * Tell aio_poll() when to stop userspace polling early because ->wait()
  97      * has fds ready.
  98      *
  99      * File descriptor monitoring implementations that cannot poll fd readiness
 100      * from userspace should use aio_poll_disabled() here.  This ensures that
 101      * file descriptors are not starved by handlers that frequently make
 102      * progress via userspace polling.
 103      *
 104      * Returns: true if ->wait() should be called, false otherwise.
 105      */
 106     bool (*need_wait)(AioContext *ctx);
 107 } FDMonOps;
 108
 109 /*
 110  * Each aio_bh_poll() call carves off a slice of the BH list, so that newly
 111  * scheduled BHs are not processed until the next aio_bh_poll() call.  All
 112  * active aio_bh_poll() calls chain their slices together in a list, so that
 113  * nested aio_bh_poll() calls process all scheduled bottom halves.
 114  */
 115 typedef QSLIST_HEAD(, QEMUBH) BHList;
 116 typedef struct BHListSlice BHListSlice;
 117 struct BHListSlice {
 118     BHList bh_list;
 119     QSIMPLEQ_ENTRY(BHListSlice) next;
 120 };
 121
 122 typedef QSLIST_HEAD(, AioHandler) AioHandlerSList;
 123
 124 struct AioContext {
 125     GSource source;
 126
 127     /* Used by AioContext users to protect from multi-threaded access.  */
 128     QemuRecMutex lock;
 129
 130     /* The list of registered AIO handlers.  Protected by ctx->list_lock. */
 131     AioHandlerList aio_handlers;
 132
 133     /* The list of AIO handlers to be deleted.  Protected by ctx->list_lock. */
 134     AioHandlerList deleted_aio_handlers;
 135
 136     /* Used to avoid unnecessary event_notifier_set calls in aio_notify;
 137      * only written from the AioContext home thread, or under the BQL in
 138      * the case of the main AioContext.  However, it is read from any
 139      * thread so it is still accessed with atomic primitives.
 140      *
 141      * If this field is 0, everything (file descriptors, bottom halves,
 142      * timers) will be re-evaluated before the next blocking poll() or
 143      * io_uring wait; therefore, the event_notifier_set call can be
 144      * skipped.  If it is non-zero, you may need to wake up a concurrent
 145      * aio_poll or the glib main event loop, making event_notifier_set
 146      * necessary.
 147      *
 148      * Bit 0 is reserved for GSource usage of the AioContext, and is 1
 149      * between a call to aio_ctx_prepare and the next call to aio_ctx_check.
 150      * Bits 1-31 simply count the number of active calls to aio_poll
 151      * that are in the prepare or poll phase.
 152      *
 153      * The GSource and aio_poll must use a different mechanism because
 154      * there is no certainty that a call to GSource's prepare callback
 155      * (via g_main_context_prepare) is indeed followed by check and
 156      * dispatch.  It's not clear whether this would be a bug, but let's
 157      * play safe and allow it---it will just cause extra calls to
 158      * event_notifier_set until the next call to dispatch.
 159      *
 160      * Instead, the aio_poll calls include both the prepare and the
 161      * dispatch phase, hence a simple counter is enough for them.
 162      */
 163     uint32_t notify_me;
 164
 165     /* A lock to protect between QEMUBH and AioHandler adders and deleter,
 166      * and to ensure that no callbacks are removed while we're walking and
 167      * dispatching them.
 168      */
 169     QemuLockCnt list_lock;
 170
 171     /* Bottom Halves pending aio_bh_poll() processing */
 172     BHList bh_list;
 173
 174     /* Chained BH list slices for each nested aio_bh_poll() call */
 175     QSIMPLEQ_HEAD(, BHListSlice) bh_slice_list;
 176
 177     /* Used by aio_notify.
 178      *
 179      * "notified" is used to avoid expensive event_notifier_test_and_clear
 180      * calls.  When it is clear, the EventNotifier is clear, or one thread
 181      * is going to clear "notified" before processing more events.  False
 182      * positives are possible, i.e. "notified" could be set even though the
 183      * EventNotifier is clear.
 184      *
 185      * Note that event_notifier_set *cannot* be optimized the same way.  For
 186      * more information on the problem that would result, see "#ifdef BUG2"
 187      * in the docs/aio_notify_accept.promela formal model.
 188      */
 189     bool notified;
 190     EventNotifier notifier;
 191
 192     QSLIST_HEAD(, Coroutine) scheduled_coroutines;
 193     QEMUBH *co_schedule_bh;
 194
 195     int thread_pool_min;
 196     int thread_pool_max;
 197     /* Thread pool for performing work and receiving completion callbacks.
 198      * Has its own locking.
 199      */
 200     struct ThreadPool *thread_pool;
 201
 202 #ifdef CONFIG_LINUX_AIO
 203     /*
 204      * State for native Linux AIO.  Uses aio_context_acquire/release for
 205      * locking.
 206      */
 207     struct LinuxAioState *linux_aio;
 208 #endif
 209 #ifdef CONFIG_LINUX_IO_URING
 210     /*
 211      * State for Linux io_uring.  Uses aio_context_acquire/release for
 212      * locking.
 213      */
 214     struct LuringState *linux_io_uring;
 215
 216     /* State for file descriptor monitoring using Linux io_uring */
 217     struct io_uring fdmon_io_uring;
 218     AioHandlerSList submit_list;
 219 #endif
 220
 221     /* TimerLists for calling timers - one per clock type.  Has its own
 222      * locking.
 223      */
 224     QEMUTimerListGroup tlg;
 225
 226     int external_disable_cnt;
 227
 228     /* Number of AioHandlers without .io_poll() */
 229     int poll_disable_cnt;
 230
 231     /* Polling mode parameters */
 232     int64_t poll_ns;        /* current polling time in nanoseconds */
 233     int64_t poll_max_ns;    /* maximum polling time in nanoseconds */
 234     int64_t poll_grow;      /* polling time growth factor */
 235     int64_t poll_shrink;    /* polling time shrink factor */
 236
 237     /* AIO engine parameters */
 238     int64_t aio_max_batch;  /* maximum number of requests in a batch */
 239
 240     /*
 241      * List of handlers participating in userspace polling.  Protected by
 242      * ctx->list_lock.  Iterated and modified mostly by the event loop thread
 243      * from aio_poll() with ctx->list_lock incremented.  aio_set_fd_handler()
 244      * only touches the list to delete nodes if ctx->list_lock's count is zero.
 245      */
 246     AioHandlerList poll_aio_handlers;
 247
 248     /* Are we in polling mode or monitoring file descriptors? */
 249     bool poll_started;
 250
 251     /* epoll(7) state used when built with CONFIG_EPOLL */
 252     int epollfd;
 253
 254     const FDMonOps *fdmon_ops;
 255 };
 256
 257 /**
 258  * aio_context_new: Allocate a new AioContext.
 259  *
 260  * AioContext provide a mini event-loop that can be waited on synchronously.
 261  * They also provide bottom halves, a service to execute a piece of code
 262  * as soon as possible.
 263  */
 264 AioContext *aio_context_new(Error **errp);
 265
 266 /**
 267  * aio_context_ref:
 268  * @ctx: The AioContext to operate on.
 269  *
 270  * Add a reference to an AioContext.
 271  */
 272 void aio_context_ref(AioContext *ctx);
 273
 274 /**
 275  * aio_context_unref:
 276  * @ctx: The AioContext to operate on.
 277  *
 278  * Drop a reference to an AioContext.
 279  */
 280 void aio_context_unref(AioContext *ctx);
 281
 282 /* Take ownership of the AioContext.  If the AioContext will be shared between
 283  * threads, and a thread does not want to be interrupted, it will have to
 284  * take ownership around calls to aio_poll().  Otherwise, aio_poll()
 285  * automatically takes care of calling aio_context_acquire and
 286  * aio_context_release.
 287  *
 288  * Note that this is separate from bdrv_drained_begin/bdrv_drained_end.  A
 289  * thread still has to call those to avoid being interrupted by the guest.
 290  *
 291  * Bottom halves, timers and callbacks can be created or removed without
 292  * acquiring the AioContext.
 293  */
 294 void aio_context_acquire(AioContext *ctx);
 295
 296 /* Relinquish ownership of the AioContext. */
 297 void aio_context_release(AioContext *ctx);
 298
 299 /**
 300  * aio_bh_schedule_oneshot_full: Allocate a new bottom half structure that will
 301  * run only once and as soon as possible.
 302  *
 303  * @name: A human-readable identifier for debugging purposes.
 304  */
 305 void aio_bh_schedule_oneshot_full(AioContext *ctx, QEMUBHFunc *cb, void *opaque,
 306                                   const char *name);
 307
 308 /**
 309  * aio_bh_schedule_oneshot: Allocate a new bottom half structure that will run
 310  * only once and as soon as possible.
 311  *
 312  * A convenience wrapper for aio_bh_schedule_oneshot_full() that uses cb as the
 313  * name string.
 314  */
 315 #define aio_bh_schedule_oneshot(ctx, cb, opaque) \
 316     aio_bh_schedule_oneshot_full((ctx), (cb), (opaque), (stringify(cb)))
 317
 318 /**
 319  * aio_bh_new_full: Allocate a new bottom half structure.
 320  *
 321  * Bottom halves are lightweight callbacks whose invocation is guaranteed
 322  * to be wait-free, thread-safe and signal-safe.  The #QEMUBH structure
 323  * is opaque and must be allocated prior to its use.
 324  *
 325  * @name: A human-readable identifier for debugging purposes.
 326  */
 327 QEMUBH *aio_bh_new_full(AioContext *ctx, QEMUBHFunc *cb, void *opaque,
 328                         const char *name);
 329
 330 /**
 331  * aio_bh_new: Allocate a new bottom half structure
 332  *
 333  * A convenience wrapper for aio_bh_new_full() that uses the cb as the name
 334  * string.
 335  */
 336 #define aio_bh_new(ctx, cb, opaque) \
 337     aio_bh_new_full((ctx), (cb), (opaque), (stringify(cb)))
 338
 339 /**
 340  * aio_notify: Force processing of pending events.
 341  *
 342  * Similar to signaling a condition variable, aio_notify forces
 343  * aio_poll to exit, so that the next call will re-examine pending events.
 344  * The caller of aio_notify will usually call aio_poll again very soon,
 345  * or go through another iteration of the GLib main loop.  Hence, aio_notify
 346  * also has the side effect of recalculating the sets of file descriptors
 347  * that the main loop waits for.
 348  *
 349  * Calling aio_notify is rarely necessary, because for example scheduling
 350  * a bottom half calls it already.
 351  */
 352 void aio_notify(AioContext *ctx);
 353
 354 /**
 355  * aio_notify_accept: Acknowledge receiving an aio_notify.
 356  *
 357  * aio_notify() uses an EventNotifier in order to wake up a sleeping
 358  * aio_poll() or g_main_context_iteration().  Calls to aio_notify() are
 359  * usually rare, but the AioContext has to clear the EventNotifier on
 360  * every aio_poll() or g_main_context_iteration() in order to avoid
 361  * busy waiting.  This event_notifier_test_and_clear() cannot be done
 362  * using the usual aio_context_set_event_notifier(), because it must
 363  * be done before processing all events (file descriptors, bottom halves,
 364  * timers).
 365  *
 366  * aio_notify_accept() is an optimized event_notifier_test_and_clear()
 367  * that is specific to an AioContext's notifier; it is used internally
 368  * to clear the EventNotifier only if aio_notify() had been called.
 369  */
 370 void aio_notify_accept(AioContext *ctx);
 371
 372 /**
 373  * aio_bh_call: Executes callback function of the specified BH.
 374  */
 375 void aio_bh_call(QEMUBH *bh);
 376
 377 /**
 378  * aio_bh_poll: Poll bottom halves for an AioContext.
 379  *
 380  * These are internal functions used by the QEMU main loop.
 381  * And notice that multiple occurrences of aio_bh_poll cannot
 382  * be called concurrently
 383  */
 384 int aio_bh_poll(AioContext *ctx);
 385
 386 /**
 387  * qemu_bh_schedule: Schedule a bottom half.
 388  *
 389  * Scheduling a bottom half interrupts the main loop and causes the
 390  * execution of the callback that was passed to qemu_bh_new.
 391  *
 392  * Bottom halves that are scheduled from a bottom half handler are instantly
 393  * invoked.  This can create an infinite loop if a bottom half handler
 394  * schedules itself.
 395  *
 396  * @bh: The bottom half to be scheduled.
 397  */
 398 void qemu_bh_schedule(QEMUBH *bh);
 399
 400 /**
 401  * qemu_bh_cancel: Cancel execution of a bottom half.
 402  *
 403  * Canceling execution of a bottom half undoes the effect of calls to
 404  * qemu_bh_schedule without freeing its resources yet.  While cancellation
 405  * itself is also wait-free and thread-safe, it can of course race with the
 406  * loop that executes bottom halves unless you are holding the iothread
 407  * mutex.  This makes it mostly useless if you are not holding the mutex.
 408  *
 409  * @bh: The bottom half to be canceled.
 410  */
 411 void qemu_bh_cancel(QEMUBH *bh);
 412
 413 /**
 414  *qemu_bh_delete: Cancel execution of a bottom half and free its resources.
 415  *
 416  * Deleting a bottom half frees the memory that was allocated for it by
 417  * qemu_bh_new.  It also implies canceling the bottom half if it was
 418  * scheduled.
 419  * This func is async. The bottom half will do the delete action at the finial
 420  * end.
 421  *
 422  * @bh: The bottom half to be deleted.
 423  */
 424 void qemu_bh_delete(QEMUBH *bh);
 425
 426 /* Return whether there are any pending callbacks from the GSource
 427  * attached to the AioContext, before g_poll is invoked.
 428  *
 429  * This is used internally in the implementation of the GSource.
 430  */
 431 bool aio_prepare(AioContext *ctx);
 432
 433 /* Return whether there are any pending callbacks from the GSource
 434  * attached to the AioContext, after g_poll is invoked.
 435  *
 436  * This is used internally in the implementation of the GSource.
 437  */
 438 bool aio_pending(AioContext *ctx);
 439
 440 /* Dispatch any pending callbacks from the GSource attached to the AioContext.
 441  *
 442  * This is used internally in the implementation of the GSource.
 443  */
 444 void aio_dispatch(AioContext *ctx);
 445
 446 /* Progress in completing AIO work to occur.  This can issue new pending
 447  * aio as a result of executing I/O completion or bh callbacks.
 448  *
 449  * Return whether any progress was made by executing AIO or bottom half
 450  * handlers.  If @blocking == true, this should always be true except
 451  * if someone called aio_notify.
 452  *
 453  * If there are no pending bottom halves, but there are pending AIO
 454  * operations, it may not be possible to make any progress without
 455  * blocking.  If @blocking is true, this function will wait until one
 456  * or more AIO events have completed, to ensure something has moved
 457  * before returning.
 458  */
 459 bool aio_poll(AioContext *ctx, bool blocking);
 460
 461 /* Register a file descriptor and associated callbacks.  Behaves very similarly
 462  * to qemu_set_fd_handler.  Unlike qemu_set_fd_handler, these callbacks will
 463  * be invoked when using aio_poll().
 464  *
 465  * Code that invokes AIO completion functions should rely on this function
 466  * instead of qemu_set_fd_handler[2].
 467  */
 468 void aio_set_fd_handler(AioContext *ctx,
 469                         int fd,
 470                         bool is_external,
 471                         IOHandler *io_read,
 472                         IOHandler *io_write,
 473                         AioPollFn *io_poll,
 474                         IOHandler *io_poll_ready,
 475                         void *opaque);
 476
 477 /* Set polling begin/end callbacks for a file descriptor that has already been
 478  * registered with aio_set_fd_handler.  Do nothing if the file descriptor is
 479  * not registered.
 480  */
 481 void aio_set_fd_poll(AioContext *ctx, int fd,
 482                      IOHandler *io_poll_begin,
 483                      IOHandler *io_poll_end);
 484
 485 /* Register an event notifier and associated callbacks.  Behaves very similarly
 486  * to event_notifier_set_handler.  Unlike event_notifier_set_handler, these callbacks
 487  * will be invoked when using aio_poll().
 488  *
 489  * Code that invokes AIO completion functions should rely on this function
 490  * instead of event_notifier_set_handler.
 491  */
 492 void aio_set_event_notifier(AioContext *ctx,
 493                             EventNotifier *notifier,
 494                             bool is_external,
 495                             EventNotifierHandler *io_read,
 496                             AioPollFn *io_poll,
 497                             EventNotifierHandler *io_poll_ready);
 498
 499 /* Set polling begin/end callbacks for an event notifier that has already been
 500  * registered with aio_set_event_notifier.  Do nothing if the event notifier is
 501  * not registered.
 502  */
 503 void aio_set_event_notifier_poll(AioContext *ctx,
 504                                  EventNotifier *notifier,
 505                                  EventNotifierHandler *io_poll_begin,
 506                                  EventNotifierHandler *io_poll_end);
 507
 508 /* Return a GSource that lets the main loop poll the file descriptors attached
 509  * to this AioContext.
 510  */
 511 GSource *aio_get_g_source(AioContext *ctx);
 512
 513 /* Return the ThreadPool bound to this AioContext */
 514 struct ThreadPool *aio_get_thread_pool(AioContext *ctx);
 515
 516 /* Setup the LinuxAioState bound to this AioContext */
 517 struct LinuxAioState *aio_setup_linux_aio(AioContext *ctx, Error **errp);
 518
 519 /* Return the LinuxAioState bound to this AioContext */
 520 struct LinuxAioState *aio_get_linux_aio(AioContext *ctx);
 521
 522 /* Setup the LuringState bound to this AioContext */
 523 struct LuringState *aio_setup_linux_io_uring(AioContext *ctx, Error **errp);
 524
 525 /* Return the LuringState bound to this AioContext */
 526 struct LuringState *aio_get_linux_io_uring(AioContext *ctx);
 527 /**
 528  * aio_timer_new_with_attrs:
 529  * @ctx: the aio context
 530  * @type: the clock type
 531  * @scale: the scale
 532  * @attributes: 0, or one to multiple OR'ed QEMU_TIMER_ATTR_<id> values
 533  *              to assign
 534  * @cb: the callback to call on timer expiry
 535  * @opaque: the opaque pointer to pass to the callback
 536  *
 537  * Allocate a new timer (with attributes) attached to the context @ctx.
 538  * The function is responsible for memory allocation.
 539  *
 540  * The preferred interface is aio_timer_init or aio_timer_init_with_attrs.
 541  * Use that unless you really need dynamic memory allocation.
 542  *
 543  * Returns: a pointer to the new timer
 544  */
 545 static inline QEMUTimer *aio_timer_new_with_attrs(AioContext *ctx,
 546                                                   QEMUClockType type,
 547                                                   int scale, int attributes,
 548                                                   QEMUTimerCB *cb, void *opaque)
 549 {
 550     return timer_new_full(&ctx->tlg, type, scale, attributes, cb, opaque);
 551 }
 552
 553 /**
 554  * aio_timer_new:
 555  * @ctx: the aio context
 556  * @type: the clock type
 557  * @scale: the scale
 558  * @cb: the callback to call on timer expiry
 559  * @opaque: the opaque pointer to pass to the callback
 560  *
 561  * Allocate a new timer attached to the context @ctx.
 562  * See aio_timer_new_with_attrs for details.
 563  *
 564  * Returns: a pointer to the new timer
 565  */
 566 static inline QEMUTimer *aio_timer_new(AioContext *ctx, QEMUClockType type,
 567                                        int scale,
 568                                        QEMUTimerCB *cb, void *opaque)
 569 {
 570     return timer_new_full(&ctx->tlg, type, scale, 0, cb, opaque);
 571 }
 572
 573 /**
 574  * aio_timer_init_with_attrs:
 575  * @ctx: the aio context
 576  * @ts: the timer
 577  * @type: the clock type
 578  * @scale: the scale
 579  * @attributes: 0, or one to multiple OR'ed QEMU_TIMER_ATTR_<id> values
 580  *              to assign
 581  * @cb: the callback to call on timer expiry
 582  * @opaque: the opaque pointer to pass to the callback
 583  *
 584  * Initialise a new timer (with attributes) attached to the context @ctx.
 585  * The caller is responsible for memory allocation.
 586  */
 587 static inline void aio_timer_init_with_attrs(AioContext *ctx,
 588                                              QEMUTimer *ts, QEMUClockType type,
 589                                              int scale, int attributes,
 590                                              QEMUTimerCB *cb, void *opaque)
 591 {
 592     timer_init_full(ts, &ctx->tlg, type, scale, attributes, cb, opaque);
 593 }
 594
 595 /**
 596  * aio_timer_init:
 597  * @ctx: the aio context
 598  * @ts: the timer
 599  * @type: the clock type
 600  * @scale: the scale
 601  * @cb: the callback to call on timer expiry
 602  * @opaque: the opaque pointer to pass to the callback
 603  *
 604  * Initialise a new timer attached to the context @ctx.
 605  * See aio_timer_init_with_attrs for details.
 606  */
 607 static inline void aio_timer_init(AioContext *ctx,
 608                                   QEMUTimer *ts, QEMUClockType type,
 609                                   int scale,
 610                                   QEMUTimerCB *cb, void *opaque)
 611 {
 612     timer_init_full(ts, &ctx->tlg, type, scale, 0, cb, opaque);
 613 }
 614
 615 /**
 616  * aio_compute_timeout:
 617  * @ctx: the aio context
 618  *
 619  * Compute the timeout that a blocking aio_poll should use.
 620  */
 621 int64_t aio_compute_timeout(AioContext *ctx);
 622
 623 /**
 624  * aio_disable_external:
 625  * @ctx: the aio context
 626  *
 627  * Disable the further processing of external clients.
 628  */
 629 static inline void aio_disable_external(AioContext *ctx)
 630 {
 631     qatomic_inc(&ctx->external_disable_cnt);
 632 }
 633
 634 /**
 635  * aio_enable_external:
 636  * @ctx: the aio context
 637  *
 638  * Enable the processing of external clients.
 639  */
 640 static inline void aio_enable_external(AioContext *ctx)
 641 {
 642     int old;
 643
 644     old = qatomic_fetch_dec(&ctx->external_disable_cnt);
 645     assert(old > 0);
 646     if (old == 1) {
 647         /* Kick event loop so it re-arms file descriptors */
 648         aio_notify(ctx);
 649     }
 650 }
 651
 652 /**
 653  * aio_external_disabled:
 654  * @ctx: the aio context
 655  *
 656  * Return true if the external clients are disabled.
 657  */
 658 static inline bool aio_external_disabled(AioContext *ctx)
 659 {
 660     return qatomic_read(&ctx->external_disable_cnt);
 661 }
 662
 663 /**
 664  * aio_node_check:
 665  * @ctx: the aio context
 666  * @is_external: Whether or not the checked node is an external event source.
 667  *
 668  * Check if the node's is_external flag is okay to be polled by the ctx at this
 669  * moment. True means green light.
 670  */
 671 static inline bool aio_node_check(AioContext *ctx, bool is_external)
 672 {
 673     return !is_external || !qatomic_read(&ctx->external_disable_cnt);
 674 }
 675
 676 /**
 677  * aio_co_schedule:
 678  * @ctx: the aio context
 679  * @co: the coroutine
 680  *
 681  * Start a coroutine on a remote AioContext.
 682  *
 683  * The coroutine must not be entered by anyone else while aio_co_schedule()
 684  * is active.  In addition the coroutine must have yielded unless ctx
 685  * is the context in which the coroutine is running (i.e. the value of
 686  * qemu_get_current_aio_context() from the coroutine itself).
 687  */
 688 void aio_co_schedule(AioContext *ctx, struct Coroutine *co);
 689
 690 /**
 691  * aio_co_reschedule_self:
 692  * @new_ctx: the new context
 693  *
 694  * Move the currently running coroutine to new_ctx. If the coroutine is already
 695  * running in new_ctx, do nothing.
 696  */
 697 void coroutine_fn aio_co_reschedule_self(AioContext *new_ctx);
 698
 699 /**
 700  * aio_co_wake:
 701  * @co: the coroutine
 702  *
 703  * Restart a coroutine on the AioContext where it was running last, thus
 704  * preventing coroutines from jumping from one context to another when they
 705  * go to sleep.
 706  *
 707  * aio_co_wake may be executed either in coroutine or non-coroutine
 708  * context.  The coroutine must not be entered by anyone else while
 709  * aio_co_wake() is active.
 710  */
 711 void aio_co_wake(struct Coroutine *co);
 712
 713 /**
 714  * aio_co_enter:
 715  * @ctx: the context to run the coroutine
 716  * @co: the coroutine to run
 717  *
 718  * Enter a coroutine in the specified AioContext.
 719  */
 720 void aio_co_enter(AioContext *ctx, struct Coroutine *co);
 721
 722 /**
 723  * Return the AioContext whose event loop runs in the current thread.
 724  *
 725  * If called from an IOThread this will be the IOThread's AioContext.  If
 726  * called from the main thread or with the "big QEMU lock" taken it
 727  * will be the main loop AioContext.
 728  */
 729 AioContext *qemu_get_current_aio_context(void);
 730
 731 void qemu_set_current_aio_context(AioContext *ctx);
 732
 733 /**
 734  * aio_context_setup:
 735  * @ctx: the aio context
 736  *
 737  * Initialize the aio context.
 738  */
 739 void aio_context_setup(AioContext *ctx);
 740
 741 /**
 742  * aio_context_destroy:
 743  * @ctx: the aio context
 744  *
 745  * Destroy the aio context.
 746  */
 747 void aio_context_destroy(AioContext *ctx);
 748
 749 /* Used internally, do not call outside AioContext code */
 750 void aio_context_use_g_source(AioContext *ctx);
 751
 752 /**
 753  * aio_context_set_poll_params:
 754  * @ctx: the aio context
 755  * @max_ns: how long to busy poll for, in nanoseconds
 756  * @grow: polling time growth factor
 757  * @shrink: polling time shrink factor
 758  *
 759  * Poll mode can be disabled by setting poll_max_ns to 0.
 760  */
 761 void aio_context_set_poll_params(AioContext *ctx, int64_t max_ns,
 762                                  int64_t grow, int64_t shrink,
 763                                  Error **errp);
 764
 765 /**
 766  * aio_context_set_aio_params:
 767  * @ctx: the aio context
 768  * @max_batch: maximum number of requests in a batch, 0 means that the
 769  *             engine will use its default
 770  */
 771 void aio_context_set_aio_params(AioContext *ctx, int64_t max_batch,
 772                                 Error **errp);
 773
 774 /**
 775  * aio_context_set_thread_pool_params:
 776  * @ctx: the aio context
 777  * @min: min number of threads to have readily available in the thread pool
 778  * @min: max number of threads the thread pool can contain
 779  */
 780 void aio_context_set_thread_pool_params(AioContext *ctx, int64_t min,
 781                                         int64_t max, Error **errp);
 782 #endif