xref: /openbmc/qemu/include/block/aio.h (revision b13e49bc)
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     /* Thread pool for performing work and receiving completion callbacks.
196      * Has its own locking.
197      */
198     struct ThreadPool *thread_pool;
199 
200 #ifdef CONFIG_LINUX_AIO
201     /*
202      * State for native Linux AIO.  Uses aio_context_acquire/release for
203      * locking.
204      */
205     struct LinuxAioState *linux_aio;
206 #endif
207 #ifdef CONFIG_LINUX_IO_URING
208     /*
209      * State for Linux io_uring.  Uses aio_context_acquire/release for
210      * locking.
211      */
212     struct LuringState *linux_io_uring;
213 
214     /* State for file descriptor monitoring using Linux io_uring */
215     struct io_uring fdmon_io_uring;
216     AioHandlerSList submit_list;
217 #endif
218 
219     /* TimerLists for calling timers - one per clock type.  Has its own
220      * locking.
221      */
222     QEMUTimerListGroup tlg;
223 
224     int external_disable_cnt;
225 
226     /* Number of AioHandlers without .io_poll() */
227     int poll_disable_cnt;
228 
229     /* Polling mode parameters */
230     int64_t poll_ns;        /* current polling time in nanoseconds */
231     int64_t poll_max_ns;    /* maximum polling time in nanoseconds */
232     int64_t poll_grow;      /* polling time growth factor */
233     int64_t poll_shrink;    /* polling time shrink factor */
234 
235     /* AIO engine parameters */
236     int64_t aio_max_batch;  /* maximum number of requests in a batch */
237 
238     /*
239      * List of handlers participating in userspace polling.  Protected by
240      * ctx->list_lock.  Iterated and modified mostly by the event loop thread
241      * from aio_poll() with ctx->list_lock incremented.  aio_set_fd_handler()
242      * only touches the list to delete nodes if ctx->list_lock's count is zero.
243      */
244     AioHandlerList poll_aio_handlers;
245 
246     /* Are we in polling mode or monitoring file descriptors? */
247     bool poll_started;
248 
249     /* epoll(7) state used when built with CONFIG_EPOLL */
250     int epollfd;
251 
252     const FDMonOps *fdmon_ops;
253 };
254 
255 /**
256  * aio_context_new: Allocate a new AioContext.
257  *
258  * AioContext provide a mini event-loop that can be waited on synchronously.
259  * They also provide bottom halves, a service to execute a piece of code
260  * as soon as possible.
261  */
262 AioContext *aio_context_new(Error **errp);
263 
264 /**
265  * aio_context_ref:
266  * @ctx: The AioContext to operate on.
267  *
268  * Add a reference to an AioContext.
269  */
270 void aio_context_ref(AioContext *ctx);
271 
272 /**
273  * aio_context_unref:
274  * @ctx: The AioContext to operate on.
275  *
276  * Drop a reference to an AioContext.
277  */
278 void aio_context_unref(AioContext *ctx);
279 
280 /* Take ownership of the AioContext.  If the AioContext will be shared between
281  * threads, and a thread does not want to be interrupted, it will have to
282  * take ownership around calls to aio_poll().  Otherwise, aio_poll()
283  * automatically takes care of calling aio_context_acquire and
284  * aio_context_release.
285  *
286  * Note that this is separate from bdrv_drained_begin/bdrv_drained_end.  A
287  * thread still has to call those to avoid being interrupted by the guest.
288  *
289  * Bottom halves, timers and callbacks can be created or removed without
290  * acquiring the AioContext.
291  */
292 void aio_context_acquire(AioContext *ctx);
293 
294 /* Relinquish ownership of the AioContext. */
295 void aio_context_release(AioContext *ctx);
296 
297 /**
298  * aio_bh_schedule_oneshot_full: Allocate a new bottom half structure that will
299  * run only once and as soon as possible.
300  *
301  * @name: A human-readable identifier for debugging purposes.
302  */
303 void aio_bh_schedule_oneshot_full(AioContext *ctx, QEMUBHFunc *cb, void *opaque,
304                                   const char *name);
305 
306 /**
307  * aio_bh_schedule_oneshot: Allocate a new bottom half structure that will run
308  * only once and as soon as possible.
309  *
310  * A convenience wrapper for aio_bh_schedule_oneshot_full() that uses cb as the
311  * name string.
312  */
313 #define aio_bh_schedule_oneshot(ctx, cb, opaque) \
314     aio_bh_schedule_oneshot_full((ctx), (cb), (opaque), (stringify(cb)))
315 
316 /**
317  * aio_bh_new_full: Allocate a new bottom half structure.
318  *
319  * Bottom halves are lightweight callbacks whose invocation is guaranteed
320  * to be wait-free, thread-safe and signal-safe.  The #QEMUBH structure
321  * is opaque and must be allocated prior to its use.
322  *
323  * @name: A human-readable identifier for debugging purposes.
324  */
325 QEMUBH *aio_bh_new_full(AioContext *ctx, QEMUBHFunc *cb, void *opaque,
326                         const char *name);
327 
328 /**
329  * aio_bh_new: Allocate a new bottom half structure
330  *
331  * A convenience wrapper for aio_bh_new_full() that uses the cb as the name
332  * string.
333  */
334 #define aio_bh_new(ctx, cb, opaque) \
335     aio_bh_new_full((ctx), (cb), (opaque), (stringify(cb)))
336 
337 /**
338  * aio_notify: Force processing of pending events.
339  *
340  * Similar to signaling a condition variable, aio_notify forces
341  * aio_poll to exit, so that the next call will re-examine pending events.
342  * The caller of aio_notify will usually call aio_poll again very soon,
343  * or go through another iteration of the GLib main loop.  Hence, aio_notify
344  * also has the side effect of recalculating the sets of file descriptors
345  * that the main loop waits for.
346  *
347  * Calling aio_notify is rarely necessary, because for example scheduling
348  * a bottom half calls it already.
349  */
350 void aio_notify(AioContext *ctx);
351 
352 /**
353  * aio_notify_accept: Acknowledge receiving an aio_notify.
354  *
355  * aio_notify() uses an EventNotifier in order to wake up a sleeping
356  * aio_poll() or g_main_context_iteration().  Calls to aio_notify() are
357  * usually rare, but the AioContext has to clear the EventNotifier on
358  * every aio_poll() or g_main_context_iteration() in order to avoid
359  * busy waiting.  This event_notifier_test_and_clear() cannot be done
360  * using the usual aio_context_set_event_notifier(), because it must
361  * be done before processing all events (file descriptors, bottom halves,
362  * timers).
363  *
364  * aio_notify_accept() is an optimized event_notifier_test_and_clear()
365  * that is specific to an AioContext's notifier; it is used internally
366  * to clear the EventNotifier only if aio_notify() had been called.
367  */
368 void aio_notify_accept(AioContext *ctx);
369 
370 /**
371  * aio_bh_call: Executes callback function of the specified BH.
372  */
373 void aio_bh_call(QEMUBH *bh);
374 
375 /**
376  * aio_bh_poll: Poll bottom halves for an AioContext.
377  *
378  * These are internal functions used by the QEMU main loop.
379  * And notice that multiple occurrences of aio_bh_poll cannot
380  * be called concurrently
381  */
382 int aio_bh_poll(AioContext *ctx);
383 
384 /**
385  * qemu_bh_schedule: Schedule a bottom half.
386  *
387  * Scheduling a bottom half interrupts the main loop and causes the
388  * execution of the callback that was passed to qemu_bh_new.
389  *
390  * Bottom halves that are scheduled from a bottom half handler are instantly
391  * invoked.  This can create an infinite loop if a bottom half handler
392  * schedules itself.
393  *
394  * @bh: The bottom half to be scheduled.
395  */
396 void qemu_bh_schedule(QEMUBH *bh);
397 
398 /**
399  * qemu_bh_cancel: Cancel execution of a bottom half.
400  *
401  * Canceling execution of a bottom half undoes the effect of calls to
402  * qemu_bh_schedule without freeing its resources yet.  While cancellation
403  * itself is also wait-free and thread-safe, it can of course race with the
404  * loop that executes bottom halves unless you are holding the iothread
405  * mutex.  This makes it mostly useless if you are not holding the mutex.
406  *
407  * @bh: The bottom half to be canceled.
408  */
409 void qemu_bh_cancel(QEMUBH *bh);
410 
411 /**
412  *qemu_bh_delete: Cancel execution of a bottom half and free its resources.
413  *
414  * Deleting a bottom half frees the memory that was allocated for it by
415  * qemu_bh_new.  It also implies canceling the bottom half if it was
416  * scheduled.
417  * This func is async. The bottom half will do the delete action at the finial
418  * end.
419  *
420  * @bh: The bottom half to be deleted.
421  */
422 void qemu_bh_delete(QEMUBH *bh);
423 
424 /* Return whether there are any pending callbacks from the GSource
425  * attached to the AioContext, before g_poll is invoked.
426  *
427  * This is used internally in the implementation of the GSource.
428  */
429 bool aio_prepare(AioContext *ctx);
430 
431 /* Return whether there are any pending callbacks from the GSource
432  * attached to the AioContext, after g_poll is invoked.
433  *
434  * This is used internally in the implementation of the GSource.
435  */
436 bool aio_pending(AioContext *ctx);
437 
438 /* Dispatch any pending callbacks from the GSource attached to the AioContext.
439  *
440  * This is used internally in the implementation of the GSource.
441  */
442 void aio_dispatch(AioContext *ctx);
443 
444 /* Progress in completing AIO work to occur.  This can issue new pending
445  * aio as a result of executing I/O completion or bh callbacks.
446  *
447  * Return whether any progress was made by executing AIO or bottom half
448  * handlers.  If @blocking == true, this should always be true except
449  * if someone called aio_notify.
450  *
451  * If there are no pending bottom halves, but there are pending AIO
452  * operations, it may not be possible to make any progress without
453  * blocking.  If @blocking is true, this function will wait until one
454  * or more AIO events have completed, to ensure something has moved
455  * before returning.
456  */
457 bool aio_poll(AioContext *ctx, bool blocking);
458 
459 /* Register a file descriptor and associated callbacks.  Behaves very similarly
460  * to qemu_set_fd_handler.  Unlike qemu_set_fd_handler, these callbacks will
461  * be invoked when using aio_poll().
462  *
463  * Code that invokes AIO completion functions should rely on this function
464  * instead of qemu_set_fd_handler[2].
465  */
466 void aio_set_fd_handler(AioContext *ctx,
467                         int fd,
468                         bool is_external,
469                         IOHandler *io_read,
470                         IOHandler *io_write,
471                         AioPollFn *io_poll,
472                         IOHandler *io_poll_ready,
473                         void *opaque);
474 
475 /* Set polling begin/end callbacks for a file descriptor that has already been
476  * registered with aio_set_fd_handler.  Do nothing if the file descriptor is
477  * not registered.
478  */
479 void aio_set_fd_poll(AioContext *ctx, int fd,
480                      IOHandler *io_poll_begin,
481                      IOHandler *io_poll_end);
482 
483 /* Register an event notifier and associated callbacks.  Behaves very similarly
484  * to event_notifier_set_handler.  Unlike event_notifier_set_handler, these callbacks
485  * will be invoked when using aio_poll().
486  *
487  * Code that invokes AIO completion functions should rely on this function
488  * instead of event_notifier_set_handler.
489  */
490 void aio_set_event_notifier(AioContext *ctx,
491                             EventNotifier *notifier,
492                             bool is_external,
493                             EventNotifierHandler *io_read,
494                             AioPollFn *io_poll,
495                             EventNotifierHandler *io_poll_ready);
496 
497 /* Set polling begin/end callbacks for an event notifier that has already been
498  * registered with aio_set_event_notifier.  Do nothing if the event notifier is
499  * not registered.
500  */
501 void aio_set_event_notifier_poll(AioContext *ctx,
502                                  EventNotifier *notifier,
503                                  EventNotifierHandler *io_poll_begin,
504                                  EventNotifierHandler *io_poll_end);
505 
506 /* Return a GSource that lets the main loop poll the file descriptors attached
507  * to this AioContext.
508  */
509 GSource *aio_get_g_source(AioContext *ctx);
510 
511 /* Return the ThreadPool bound to this AioContext */
512 struct ThreadPool *aio_get_thread_pool(AioContext *ctx);
513 
514 /* Setup the LinuxAioState bound to this AioContext */
515 struct LinuxAioState *aio_setup_linux_aio(AioContext *ctx, Error **errp);
516 
517 /* Return the LinuxAioState bound to this AioContext */
518 struct LinuxAioState *aio_get_linux_aio(AioContext *ctx);
519 
520 /* Setup the LuringState bound to this AioContext */
521 struct LuringState *aio_setup_linux_io_uring(AioContext *ctx, Error **errp);
522 
523 /* Return the LuringState bound to this AioContext */
524 struct LuringState *aio_get_linux_io_uring(AioContext *ctx);
525 /**
526  * aio_timer_new_with_attrs:
527  * @ctx: the aio context
528  * @type: the clock type
529  * @scale: the scale
530  * @attributes: 0, or one to multiple OR'ed QEMU_TIMER_ATTR_<id> values
531  *              to assign
532  * @cb: the callback to call on timer expiry
533  * @opaque: the opaque pointer to pass to the callback
534  *
535  * Allocate a new timer (with attributes) attached to the context @ctx.
536  * The function is responsible for memory allocation.
537  *
538  * The preferred interface is aio_timer_init or aio_timer_init_with_attrs.
539  * Use that unless you really need dynamic memory allocation.
540  *
541  * Returns: a pointer to the new timer
542  */
543 static inline QEMUTimer *aio_timer_new_with_attrs(AioContext *ctx,
544                                                   QEMUClockType type,
545                                                   int scale, int attributes,
546                                                   QEMUTimerCB *cb, void *opaque)
547 {
548     return timer_new_full(&ctx->tlg, type, scale, attributes, cb, opaque);
549 }
550 
551 /**
552  * aio_timer_new:
553  * @ctx: the aio context
554  * @type: the clock type
555  * @scale: the scale
556  * @cb: the callback to call on timer expiry
557  * @opaque: the opaque pointer to pass to the callback
558  *
559  * Allocate a new timer attached to the context @ctx.
560  * See aio_timer_new_with_attrs for details.
561  *
562  * Returns: a pointer to the new timer
563  */
564 static inline QEMUTimer *aio_timer_new(AioContext *ctx, QEMUClockType type,
565                                        int scale,
566                                        QEMUTimerCB *cb, void *opaque)
567 {
568     return timer_new_full(&ctx->tlg, type, scale, 0, cb, opaque);
569 }
570 
571 /**
572  * aio_timer_init_with_attrs:
573  * @ctx: the aio context
574  * @ts: the timer
575  * @type: the clock type
576  * @scale: the scale
577  * @attributes: 0, or one to multiple OR'ed QEMU_TIMER_ATTR_<id> values
578  *              to assign
579  * @cb: the callback to call on timer expiry
580  * @opaque: the opaque pointer to pass to the callback
581  *
582  * Initialise a new timer (with attributes) attached to the context @ctx.
583  * The caller is responsible for memory allocation.
584  */
585 static inline void aio_timer_init_with_attrs(AioContext *ctx,
586                                              QEMUTimer *ts, QEMUClockType type,
587                                              int scale, int attributes,
588                                              QEMUTimerCB *cb, void *opaque)
589 {
590     timer_init_full(ts, &ctx->tlg, type, scale, attributes, cb, opaque);
591 }
592 
593 /**
594  * aio_timer_init:
595  * @ctx: the aio context
596  * @ts: the timer
597  * @type: the clock type
598  * @scale: the scale
599  * @cb: the callback to call on timer expiry
600  * @opaque: the opaque pointer to pass to the callback
601  *
602  * Initialise a new timer attached to the context @ctx.
603  * See aio_timer_init_with_attrs for details.
604  */
605 static inline void aio_timer_init(AioContext *ctx,
606                                   QEMUTimer *ts, QEMUClockType type,
607                                   int scale,
608                                   QEMUTimerCB *cb, void *opaque)
609 {
610     timer_init_full(ts, &ctx->tlg, type, scale, 0, cb, opaque);
611 }
612 
613 /**
614  * aio_compute_timeout:
615  * @ctx: the aio context
616  *
617  * Compute the timeout that a blocking aio_poll should use.
618  */
619 int64_t aio_compute_timeout(AioContext *ctx);
620 
621 /**
622  * aio_disable_external:
623  * @ctx: the aio context
624  *
625  * Disable the further processing of external clients.
626  */
627 static inline void aio_disable_external(AioContext *ctx)
628 {
629     qatomic_inc(&ctx->external_disable_cnt);
630 }
631 
632 /**
633  * aio_enable_external:
634  * @ctx: the aio context
635  *
636  * Enable the processing of external clients.
637  */
638 static inline void aio_enable_external(AioContext *ctx)
639 {
640     int old;
641 
642     old = qatomic_fetch_dec(&ctx->external_disable_cnt);
643     assert(old > 0);
644     if (old == 1) {
645         /* Kick event loop so it re-arms file descriptors */
646         aio_notify(ctx);
647     }
648 }
649 
650 /**
651  * aio_external_disabled:
652  * @ctx: the aio context
653  *
654  * Return true if the external clients are disabled.
655  */
656 static inline bool aio_external_disabled(AioContext *ctx)
657 {
658     return qatomic_read(&ctx->external_disable_cnt);
659 }
660 
661 /**
662  * aio_node_check:
663  * @ctx: the aio context
664  * @is_external: Whether or not the checked node is an external event source.
665  *
666  * Check if the node's is_external flag is okay to be polled by the ctx at this
667  * moment. True means green light.
668  */
669 static inline bool aio_node_check(AioContext *ctx, bool is_external)
670 {
671     return !is_external || !qatomic_read(&ctx->external_disable_cnt);
672 }
673 
674 /**
675  * aio_co_schedule:
676  * @ctx: the aio context
677  * @co: the coroutine
678  *
679  * Start a coroutine on a remote AioContext.
680  *
681  * The coroutine must not be entered by anyone else while aio_co_schedule()
682  * is active.  In addition the coroutine must have yielded unless ctx
683  * is the context in which the coroutine is running (i.e. the value of
684  * qemu_get_current_aio_context() from the coroutine itself).
685  */
686 void aio_co_schedule(AioContext *ctx, struct Coroutine *co);
687 
688 /**
689  * aio_co_reschedule_self:
690  * @new_ctx: the new context
691  *
692  * Move the currently running coroutine to new_ctx. If the coroutine is already
693  * running in new_ctx, do nothing.
694  */
695 void coroutine_fn aio_co_reschedule_self(AioContext *new_ctx);
696 
697 /**
698  * aio_co_wake:
699  * @co: the coroutine
700  *
701  * Restart a coroutine on the AioContext where it was running last, thus
702  * preventing coroutines from jumping from one context to another when they
703  * go to sleep.
704  *
705  * aio_co_wake may be executed either in coroutine or non-coroutine
706  * context.  The coroutine must not be entered by anyone else while
707  * aio_co_wake() is active.
708  */
709 void aio_co_wake(struct Coroutine *co);
710 
711 /**
712  * aio_co_enter:
713  * @ctx: the context to run the coroutine
714  * @co: the coroutine to run
715  *
716  * Enter a coroutine in the specified AioContext.
717  */
718 void aio_co_enter(AioContext *ctx, struct Coroutine *co);
719 
720 /**
721  * Return the AioContext whose event loop runs in the current thread.
722  *
723  * If called from an IOThread this will be the IOThread's AioContext.  If
724  * called from the main thread or with the "big QEMU lock" taken it
725  * will be the main loop AioContext.
726  */
727 AioContext *qemu_get_current_aio_context(void);
728 
729 void qemu_set_current_aio_context(AioContext *ctx);
730 
731 /**
732  * aio_context_setup:
733  * @ctx: the aio context
734  *
735  * Initialize the aio context.
736  */
737 void aio_context_setup(AioContext *ctx);
738 
739 /**
740  * aio_context_destroy:
741  * @ctx: the aio context
742  *
743  * Destroy the aio context.
744  */
745 void aio_context_destroy(AioContext *ctx);
746 
747 /* Used internally, do not call outside AioContext code */
748 void aio_context_use_g_source(AioContext *ctx);
749 
750 /**
751  * aio_context_set_poll_params:
752  * @ctx: the aio context
753  * @max_ns: how long to busy poll for, in nanoseconds
754  * @grow: polling time growth factor
755  * @shrink: polling time shrink factor
756  *
757  * Poll mode can be disabled by setting poll_max_ns to 0.
758  */
759 void aio_context_set_poll_params(AioContext *ctx, int64_t max_ns,
760                                  int64_t grow, int64_t shrink,
761                                  Error **errp);
762 
763 /**
764  * aio_context_set_aio_params:
765  * @ctx: the aio context
766  * @max_batch: maximum number of requests in a batch, 0 means that the
767  *             engine will use its default
768  */
769 void aio_context_set_aio_params(AioContext *ctx, int64_t max_batch,
770                                 Error **errp);
771 
772 #endif
773