2 * QEMU aio implementation
4 * Copyright IBM, Corp. 2008
7 * Anthony Liguori <aliguori@us.ibm.com>
9 * This work is licensed under the terms of the GNU GPL, version 2. See
10 * the COPYING file in the top-level directory.
17 #ifdef CONFIG_LINUX_IO_URING
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"
26 typedef struct BlockAIOCB BlockAIOCB
;
27 typedef void BlockCompletionFunc(void *opaque
, int ret
);
29 typedef struct AIOCBInfo
{
30 void (*cancel_async
)(BlockAIOCB
*acb
);
31 AioContext
*(*get_aio_context
)(BlockAIOCB
*acb
);
36 const AIOCBInfo
*aiocb_info
;
38 BlockCompletionFunc
*cb
;
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
);
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
);
59 /* Is polling disabled? */
60 bool aio_poll_disabled(AioContext
*ctx
);
62 /* Callbacks for file descriptor monitoring implementations */
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
72 * Add/remove/modify a monitored file descriptor.
74 * Called with ctx->list_lock acquired.
76 void (*update
)(AioContext
*ctx
, AioHandler
*old_node
, AioHandler
*new_node
);
80 * @ctx: the AioContext
81 * @ready_list: list for handlers that become ready
82 * @timeout: maximum duration to wait, in nanoseconds
84 * Wait for file descriptors to become ready and place them on ready_list.
86 * Called with ctx->list_lock incremented but not locked.
88 * Returns: number of ready file descriptors.
90 int (*wait
)(AioContext
*ctx
, AioHandlerList
*ready_list
, int64_t timeout
);
94 * @ctx: the AioContext
96 * Tell aio_poll() when to stop userspace polling early because ->wait()
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.
104 * Returns: true if ->wait() should be called, false otherwise.
106 bool (*need_wait
)(AioContext
*ctx
);
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.
115 typedef QSLIST_HEAD(, QEMUBH
) BHList
;
116 typedef struct BHListSlice BHListSlice
;
119 QSIMPLEQ_ENTRY(BHListSlice
) next
;
122 typedef QSLIST_HEAD(, AioHandler
) AioHandlerSList
;
127 /* Used by AioContext users to protect from multi-threaded access. */
130 /* The list of registered AIO handlers. Protected by ctx->list_lock. */
131 AioHandlerList aio_handlers
;
133 /* The list of AIO handlers to be deleted. Protected by ctx->list_lock. */
134 AioHandlerList deleted_aio_handlers
;
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.
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
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.
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.
160 * Instead, the aio_poll calls include both the prepare and the
161 * dispatch phase, hence a simple counter is enough for them.
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
169 QemuLockCnt list_lock
;
171 /* Bottom Halves pending aio_bh_poll() processing */
174 /* Chained BH list slices for each nested aio_bh_poll() call */
175 QSIMPLEQ_HEAD(, BHListSlice
) bh_slice_list
;
177 /* Used by aio_notify.
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.
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.
190 EventNotifier notifier
;
192 QSLIST_HEAD(, Coroutine
) scheduled_coroutines
;
193 QEMUBH
*co_schedule_bh
;
195 /* Thread pool for performing work and receiving completion callbacks.
196 * Has its own locking.
198 struct ThreadPool
*thread_pool
;
200 #ifdef CONFIG_LINUX_AIO
202 * State for native Linux AIO. Uses aio_context_acquire/release for
205 struct LinuxAioState
*linux_aio
;
207 #ifdef CONFIG_LINUX_IO_URING
209 * State for Linux io_uring. Uses aio_context_acquire/release for
212 struct LuringState
*linux_io_uring
;
214 /* State for file descriptor monitoring using Linux io_uring */
215 struct io_uring fdmon_io_uring
;
216 AioHandlerSList submit_list
;
219 /* TimerLists for calling timers - one per clock type. Has its own
222 QEMUTimerListGroup tlg
;
224 int external_disable_cnt
;
226 /* Number of AioHandlers without .io_poll() */
227 int poll_disable_cnt
;
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 */
236 * List of handlers participating in userspace polling. Protected by
237 * ctx->list_lock. Iterated and modified mostly by the event loop thread
238 * from aio_poll() with ctx->list_lock incremented. aio_set_fd_handler()
239 * only touches the list to delete nodes if ctx->list_lock's count is zero.
241 AioHandlerList poll_aio_handlers
;
243 /* Are we in polling mode or monitoring file descriptors? */
246 /* epoll(7) state used when built with CONFIG_EPOLL */
249 const FDMonOps
*fdmon_ops
;
253 * aio_context_new: Allocate a new AioContext.
255 * AioContext provide a mini event-loop that can be waited on synchronously.
256 * They also provide bottom halves, a service to execute a piece of code
257 * as soon as possible.
259 AioContext
*aio_context_new(Error
**errp
);
263 * @ctx: The AioContext to operate on.
265 * Add a reference to an AioContext.
267 void aio_context_ref(AioContext
*ctx
);
271 * @ctx: The AioContext to operate on.
273 * Drop a reference to an AioContext.
275 void aio_context_unref(AioContext
*ctx
);
277 /* Take ownership of the AioContext. If the AioContext will be shared between
278 * threads, and a thread does not want to be interrupted, it will have to
279 * take ownership around calls to aio_poll(). Otherwise, aio_poll()
280 * automatically takes care of calling aio_context_acquire and
281 * aio_context_release.
283 * Note that this is separate from bdrv_drained_begin/bdrv_drained_end. A
284 * thread still has to call those to avoid being interrupted by the guest.
286 * Bottom halves, timers and callbacks can be created or removed without
287 * acquiring the AioContext.
289 void aio_context_acquire(AioContext
*ctx
);
291 /* Relinquish ownership of the AioContext. */
292 void aio_context_release(AioContext
*ctx
);
295 * aio_bh_schedule_oneshot: Allocate a new bottom half structure that will run
296 * only once and as soon as possible.
298 void aio_bh_schedule_oneshot(AioContext
*ctx
, QEMUBHFunc
*cb
, void *opaque
);
301 * aio_bh_new: Allocate a new bottom half structure.
303 * Bottom halves are lightweight callbacks whose invocation is guaranteed
304 * to be wait-free, thread-safe and signal-safe. The #QEMUBH structure
305 * is opaque and must be allocated prior to its use.
307 QEMUBH
*aio_bh_new(AioContext
*ctx
, QEMUBHFunc
*cb
, void *opaque
);
310 * aio_notify: Force processing of pending events.
312 * Similar to signaling a condition variable, aio_notify forces
313 * aio_poll to exit, so that the next call will re-examine pending events.
314 * The caller of aio_notify will usually call aio_poll again very soon,
315 * or go through another iteration of the GLib main loop. Hence, aio_notify
316 * also has the side effect of recalculating the sets of file descriptors
317 * that the main loop waits for.
319 * Calling aio_notify is rarely necessary, because for example scheduling
320 * a bottom half calls it already.
322 void aio_notify(AioContext
*ctx
);
325 * aio_notify_accept: Acknowledge receiving an aio_notify.
327 * aio_notify() uses an EventNotifier in order to wake up a sleeping
328 * aio_poll() or g_main_context_iteration(). Calls to aio_notify() are
329 * usually rare, but the AioContext has to clear the EventNotifier on
330 * every aio_poll() or g_main_context_iteration() in order to avoid
331 * busy waiting. This event_notifier_test_and_clear() cannot be done
332 * using the usual aio_context_set_event_notifier(), because it must
333 * be done before processing all events (file descriptors, bottom halves,
336 * aio_notify_accept() is an optimized event_notifier_test_and_clear()
337 * that is specific to an AioContext's notifier; it is used internally
338 * to clear the EventNotifier only if aio_notify() had been called.
340 void aio_notify_accept(AioContext
*ctx
);
343 * aio_bh_call: Executes callback function of the specified BH.
345 void aio_bh_call(QEMUBH
*bh
);
348 * aio_bh_poll: Poll bottom halves for an AioContext.
350 * These are internal functions used by the QEMU main loop.
351 * And notice that multiple occurrences of aio_bh_poll cannot
352 * be called concurrently
354 int aio_bh_poll(AioContext
*ctx
);
357 * qemu_bh_schedule: Schedule a bottom half.
359 * Scheduling a bottom half interrupts the main loop and causes the
360 * execution of the callback that was passed to qemu_bh_new.
362 * Bottom halves that are scheduled from a bottom half handler are instantly
363 * invoked. This can create an infinite loop if a bottom half handler
366 * @bh: The bottom half to be scheduled.
368 void qemu_bh_schedule(QEMUBH
*bh
);
371 * qemu_bh_cancel: Cancel execution of a bottom half.
373 * Canceling execution of a bottom half undoes the effect of calls to
374 * qemu_bh_schedule without freeing its resources yet. While cancellation
375 * itself is also wait-free and thread-safe, it can of course race with the
376 * loop that executes bottom halves unless you are holding the iothread
377 * mutex. This makes it mostly useless if you are not holding the mutex.
379 * @bh: The bottom half to be canceled.
381 void qemu_bh_cancel(QEMUBH
*bh
);
384 *qemu_bh_delete: Cancel execution of a bottom half and free its resources.
386 * Deleting a bottom half frees the memory that was allocated for it by
387 * qemu_bh_new. It also implies canceling the bottom half if it was
389 * This func is async. The bottom half will do the delete action at the finial
392 * @bh: The bottom half to be deleted.
394 void qemu_bh_delete(QEMUBH
*bh
);
396 /* Return whether there are any pending callbacks from the GSource
397 * attached to the AioContext, before g_poll is invoked.
399 * This is used internally in the implementation of the GSource.
401 bool aio_prepare(AioContext
*ctx
);
403 /* Return whether there are any pending callbacks from the GSource
404 * attached to the AioContext, after g_poll is invoked.
406 * This is used internally in the implementation of the GSource.
408 bool aio_pending(AioContext
*ctx
);
410 /* Dispatch any pending callbacks from the GSource attached to the AioContext.
412 * This is used internally in the implementation of the GSource.
414 void aio_dispatch(AioContext
*ctx
);
416 /* Progress in completing AIO work to occur. This can issue new pending
417 * aio as a result of executing I/O completion or bh callbacks.
419 * Return whether any progress was made by executing AIO or bottom half
420 * handlers. If @blocking == true, this should always be true except
421 * if someone called aio_notify.
423 * If there are no pending bottom halves, but there are pending AIO
424 * operations, it may not be possible to make any progress without
425 * blocking. If @blocking is true, this function will wait until one
426 * or more AIO events have completed, to ensure something has moved
429 bool aio_poll(AioContext
*ctx
, bool blocking
);
431 /* Register a file descriptor and associated callbacks. Behaves very similarly
432 * to qemu_set_fd_handler. Unlike qemu_set_fd_handler, these callbacks will
433 * be invoked when using aio_poll().
435 * Code that invokes AIO completion functions should rely on this function
436 * instead of qemu_set_fd_handler[2].
438 void aio_set_fd_handler(AioContext
*ctx
,
446 /* Set polling begin/end callbacks for a file descriptor that has already been
447 * registered with aio_set_fd_handler. Do nothing if the file descriptor is
450 void aio_set_fd_poll(AioContext
*ctx
, int fd
,
451 IOHandler
*io_poll_begin
,
452 IOHandler
*io_poll_end
);
454 /* Register an event notifier and associated callbacks. Behaves very similarly
455 * to event_notifier_set_handler. Unlike event_notifier_set_handler, these callbacks
456 * will be invoked when using aio_poll().
458 * Code that invokes AIO completion functions should rely on this function
459 * instead of event_notifier_set_handler.
461 void aio_set_event_notifier(AioContext
*ctx
,
462 EventNotifier
*notifier
,
464 EventNotifierHandler
*io_read
,
467 /* Set polling begin/end callbacks for an event notifier that has already been
468 * registered with aio_set_event_notifier. Do nothing if the event notifier is
471 void aio_set_event_notifier_poll(AioContext
*ctx
,
472 EventNotifier
*notifier
,
473 EventNotifierHandler
*io_poll_begin
,
474 EventNotifierHandler
*io_poll_end
);
476 /* Return a GSource that lets the main loop poll the file descriptors attached
477 * to this AioContext.
479 GSource
*aio_get_g_source(AioContext
*ctx
);
481 /* Return the ThreadPool bound to this AioContext */
482 struct ThreadPool
*aio_get_thread_pool(AioContext
*ctx
);
484 /* Setup the LinuxAioState bound to this AioContext */
485 struct LinuxAioState
*aio_setup_linux_aio(AioContext
*ctx
, Error
**errp
);
487 /* Return the LinuxAioState bound to this AioContext */
488 struct LinuxAioState
*aio_get_linux_aio(AioContext
*ctx
);
490 /* Setup the LuringState bound to this AioContext */
491 struct LuringState
*aio_setup_linux_io_uring(AioContext
*ctx
, Error
**errp
);
493 /* Return the LuringState bound to this AioContext */
494 struct LuringState
*aio_get_linux_io_uring(AioContext
*ctx
);
496 * aio_timer_new_with_attrs:
497 * @ctx: the aio context
498 * @type: the clock type
500 * @attributes: 0, or one to multiple OR'ed QEMU_TIMER_ATTR_<id> values
502 * @cb: the callback to call on timer expiry
503 * @opaque: the opaque pointer to pass to the callback
505 * Allocate a new timer (with attributes) attached to the context @ctx.
506 * The function is responsible for memory allocation.
508 * The preferred interface is aio_timer_init or aio_timer_init_with_attrs.
509 * Use that unless you really need dynamic memory allocation.
511 * Returns: a pointer to the new timer
513 static inline QEMUTimer
*aio_timer_new_with_attrs(AioContext
*ctx
,
515 int scale
, int attributes
,
516 QEMUTimerCB
*cb
, void *opaque
)
518 return timer_new_full(&ctx
->tlg
, type
, scale
, attributes
, cb
, opaque
);
523 * @ctx: the aio context
524 * @type: the clock type
526 * @cb: the callback to call on timer expiry
527 * @opaque: the opaque pointer to pass to the callback
529 * Allocate a new timer attached to the context @ctx.
530 * See aio_timer_new_with_attrs for details.
532 * Returns: a pointer to the new timer
534 static inline QEMUTimer
*aio_timer_new(AioContext
*ctx
, QEMUClockType type
,
536 QEMUTimerCB
*cb
, void *opaque
)
538 return timer_new_full(&ctx
->tlg
, type
, scale
, 0, cb
, opaque
);
542 * aio_timer_init_with_attrs:
543 * @ctx: the aio context
545 * @type: the clock type
547 * @attributes: 0, or one to multiple OR'ed QEMU_TIMER_ATTR_<id> values
549 * @cb: the callback to call on timer expiry
550 * @opaque: the opaque pointer to pass to the callback
552 * Initialise a new timer (with attributes) attached to the context @ctx.
553 * The caller is responsible for memory allocation.
555 static inline void aio_timer_init_with_attrs(AioContext
*ctx
,
556 QEMUTimer
*ts
, QEMUClockType type
,
557 int scale
, int attributes
,
558 QEMUTimerCB
*cb
, void *opaque
)
560 timer_init_full(ts
, &ctx
->tlg
, type
, scale
, attributes
, cb
, opaque
);
565 * @ctx: the aio context
567 * @type: the clock type
569 * @cb: the callback to call on timer expiry
570 * @opaque: the opaque pointer to pass to the callback
572 * Initialise a new timer attached to the context @ctx.
573 * See aio_timer_init_with_attrs for details.
575 static inline void aio_timer_init(AioContext
*ctx
,
576 QEMUTimer
*ts
, QEMUClockType type
,
578 QEMUTimerCB
*cb
, void *opaque
)
580 timer_init_full(ts
, &ctx
->tlg
, type
, scale
, 0, cb
, opaque
);
584 * aio_compute_timeout:
585 * @ctx: the aio context
587 * Compute the timeout that a blocking aio_poll should use.
589 int64_t aio_compute_timeout(AioContext
*ctx
);
592 * aio_disable_external:
593 * @ctx: the aio context
595 * Disable the further processing of external clients.
597 static inline void aio_disable_external(AioContext
*ctx
)
599 qatomic_inc(&ctx
->external_disable_cnt
);
603 * aio_enable_external:
604 * @ctx: the aio context
606 * Enable the processing of external clients.
608 static inline void aio_enable_external(AioContext
*ctx
)
612 old
= qatomic_fetch_dec(&ctx
->external_disable_cnt
);
615 /* Kick event loop so it re-arms file descriptors */
621 * aio_external_disabled:
622 * @ctx: the aio context
624 * Return true if the external clients are disabled.
626 static inline bool aio_external_disabled(AioContext
*ctx
)
628 return qatomic_read(&ctx
->external_disable_cnt
);
633 * @ctx: the aio context
634 * @is_external: Whether or not the checked node is an external event source.
636 * Check if the node's is_external flag is okay to be polled by the ctx at this
637 * moment. True means green light.
639 static inline bool aio_node_check(AioContext
*ctx
, bool is_external
)
641 return !is_external
|| !qatomic_read(&ctx
->external_disable_cnt
);
646 * @ctx: the aio context
649 * Start a coroutine on a remote AioContext.
651 * The coroutine must not be entered by anyone else while aio_co_schedule()
652 * is active. In addition the coroutine must have yielded unless ctx
653 * is the context in which the coroutine is running (i.e. the value of
654 * qemu_get_current_aio_context() from the coroutine itself).
656 void aio_co_schedule(AioContext
*ctx
, struct Coroutine
*co
);
659 * aio_co_reschedule_self:
660 * @new_ctx: the new context
662 * Move the currently running coroutine to new_ctx. If the coroutine is already
663 * running in new_ctx, do nothing.
665 void coroutine_fn
aio_co_reschedule_self(AioContext
*new_ctx
);
671 * Restart a coroutine on the AioContext where it was running last, thus
672 * preventing coroutines from jumping from one context to another when they
675 * aio_co_wake may be executed either in coroutine or non-coroutine
676 * context. The coroutine must not be entered by anyone else while
677 * aio_co_wake() is active.
679 void aio_co_wake(struct Coroutine
*co
);
683 * @ctx: the context to run the coroutine
684 * @co: the coroutine to run
686 * Enter a coroutine in the specified AioContext.
688 void aio_co_enter(AioContext
*ctx
, struct Coroutine
*co
);
691 * Return the AioContext whose event loop runs in the current thread.
693 * If called from an IOThread this will be the IOThread's AioContext. If
694 * called from another thread it will be the main loop AioContext.
696 AioContext
*qemu_get_current_aio_context(void);
700 * @ctx: the aio context
702 * Initialize the aio context.
704 void aio_context_setup(AioContext
*ctx
);
707 * aio_context_destroy:
708 * @ctx: the aio context
710 * Destroy the aio context.
712 void aio_context_destroy(AioContext
*ctx
);
714 /* Used internally, do not call outside AioContext code */
715 void aio_context_use_g_source(AioContext
*ctx
);
718 * aio_context_set_poll_params:
719 * @ctx: the aio context
720 * @max_ns: how long to busy poll for, in nanoseconds
721 * @grow: polling time growth factor
722 * @shrink: polling time shrink factor
724 * Poll mode can be disabled by setting poll_max_ns to 0.
726 void aio_context_set_poll_params(AioContext
*ctx
, int64_t max_ns
,
727 int64_t grow
, int64_t shrink
,