qemu

aio.h (25931B)

---

 /*
  * QEMU aio implementation
  *
  * Copyright IBM, Corp. 2008
  *
  * Authors:
  *  Anthony Liguori   <aliguori@us.ibm.com>
  *
  * This work is licensed under the terms of the GNU GPL, version 2.  See
  * the COPYING file in the top-level directory.
  *
  */
 
 #ifndef QEMU_AIO_H
 #define QEMU_AIO_H
 
 #ifdef CONFIG_LINUX_IO_URING
 #include <liburing.h>
 #endif
 #include "qemu/coroutine.h"
 #include "qemu/queue.h"
 #include "qemu/event_notifier.h"
 #include "qemu/thread.h"
 #include "qemu/timer.h"
 
 typedef struct BlockAIOCB BlockAIOCB;
 typedef void BlockCompletionFunc(void *opaque, int ret);
 
 typedef struct AIOCBInfo {
     void (*cancel_async)(BlockAIOCB *acb);
     AioContext *(*get_aio_context)(BlockAIOCB *acb);
     size_t aiocb_size;
 } AIOCBInfo;
 
 struct BlockAIOCB {
     const AIOCBInfo *aiocb_info;
     BlockDriverState *bs;
     BlockCompletionFunc *cb;
     void *opaque;
     int refcnt;
 };
 
 void *qemu_aio_get(const AIOCBInfo *aiocb_info, BlockDriverState *bs,
                    BlockCompletionFunc *cb, void *opaque);
 void qemu_aio_unref(void *p);
 void qemu_aio_ref(void *p);
 
 typedef struct AioHandler AioHandler;
 typedef QLIST_HEAD(, AioHandler) AioHandlerList;
 typedef void QEMUBHFunc(void *opaque);
 typedef bool AioPollFn(void *opaque);
 typedef void IOHandler(void *opaque);
 
 struct Coroutine;
 struct ThreadPool;
 struct LinuxAioState;
 struct LuringState;
 
 /* Is polling disabled? */
 bool aio_poll_disabled(AioContext *ctx);
 
 /* Callbacks for file descriptor monitoring implementations */
 typedef struct {
     /*
      * update:
      * @ctx: the AioContext
      * @old_node: the existing handler or NULL if this file descriptor is being
      *            monitored for the first time
      * @new_node: the new handler or NULL if this file descriptor is being
      *            removed
      *
      * Add/remove/modify a monitored file descriptor.
      *
      * Called with ctx->list_lock acquired.
      */
     void (*update)(AioContext *ctx, AioHandler *old_node, AioHandler *new_node);
 
     /*
      * wait:
      * @ctx: the AioContext
      * @ready_list: list for handlers that become ready
      * @timeout: maximum duration to wait, in nanoseconds
      *
      * Wait for file descriptors to become ready and place them on ready_list.
      *
      * Called with ctx->list_lock incremented but not locked.
      *
      * Returns: number of ready file descriptors.
      */
     int (*wait)(AioContext *ctx, AioHandlerList *ready_list, int64_t timeout);
 
     /*
      * need_wait:
      * @ctx: the AioContext
      *
      * Tell aio_poll() when to stop userspace polling early because ->wait()
      * has fds ready.
      *
      * File descriptor monitoring implementations that cannot poll fd readiness
      * from userspace should use aio_poll_disabled() here.  This ensures that
      * file descriptors are not starved by handlers that frequently make
      * progress via userspace polling.
      *
      * Returns: true if ->wait() should be called, false otherwise.
      */
     bool (*need_wait)(AioContext *ctx);
 } FDMonOps;
 
 /*
  * Each aio_bh_poll() call carves off a slice of the BH list, so that newly
  * scheduled BHs are not processed until the next aio_bh_poll() call.  All
  * active aio_bh_poll() calls chain their slices together in a list, so that
  * nested aio_bh_poll() calls process all scheduled bottom halves.
  */
 typedef QSLIST_HEAD(, QEMUBH) BHList;
 typedef struct BHListSlice BHListSlice;
 struct BHListSlice {
     BHList bh_list;
     QSIMPLEQ_ENTRY(BHListSlice) next;
 };
 
 typedef QSLIST_HEAD(, AioHandler) AioHandlerSList;
 
 struct AioContext {
     GSource source;
 
     /* Used by AioContext users to protect from multi-threaded access.  */
     QemuRecMutex lock;
 
     /* The list of registered AIO handlers.  Protected by ctx->list_lock. */
     AioHandlerList aio_handlers;
 
     /* The list of AIO handlers to be deleted.  Protected by ctx->list_lock. */
     AioHandlerList deleted_aio_handlers;
 
     /* Used to avoid unnecessary event_notifier_set calls in aio_notify;
      * only written from the AioContext home thread, or under the BQL in
      * the case of the main AioContext.  However, it is read from any
      * thread so it is still accessed with atomic primitives.
      *
      * If this field is 0, everything (file descriptors, bottom halves,
      * timers) will be re-evaluated before the next blocking poll() or
      * io_uring wait; therefore, the event_notifier_set call can be
      * skipped.  If it is non-zero, you may need to wake up a concurrent
      * aio_poll or the glib main event loop, making event_notifier_set
      * necessary.
      *
      * Bit 0 is reserved for GSource usage of the AioContext, and is 1
      * between a call to aio_ctx_prepare and the next call to aio_ctx_check.
      * Bits 1-31 simply count the number of active calls to aio_poll
      * that are in the prepare or poll phase.
      *
      * The GSource and aio_poll must use a different mechanism because
      * there is no certainty that a call to GSource's prepare callback
      * (via g_main_context_prepare) is indeed followed by check and
      * dispatch.  It's not clear whether this would be a bug, but let's
      * play safe and allow it---it will just cause extra calls to
      * event_notifier_set until the next call to dispatch.
      *
      * Instead, the aio_poll calls include both the prepare and the
      * dispatch phase, hence a simple counter is enough for them.
      */
     uint32_t notify_me;
 
     /* A lock to protect between QEMUBH and AioHandler adders and deleter,
      * and to ensure that no callbacks are removed while we're walking and
      * dispatching them.
      */
     QemuLockCnt list_lock;
 
     /* Bottom Halves pending aio_bh_poll() processing */
     BHList bh_list;
 
     /* Chained BH list slices for each nested aio_bh_poll() call */
     QSIMPLEQ_HEAD(, BHListSlice) bh_slice_list;
 
     /* Used by aio_notify.
      *
      * "notified" is used to avoid expensive event_notifier_test_and_clear
      * calls.  When it is clear, the EventNotifier is clear, or one thread
      * is going to clear "notified" before processing more events.  False
      * positives are possible, i.e. "notified" could be set even though the
      * EventNotifier is clear.
      *
      * Note that event_notifier_set *cannot* be optimized the same way.  For
      * more information on the problem that would result, see "#ifdef BUG2"
      * in the docs/aio_notify_accept.promela formal model.
      */
     bool notified;
     EventNotifier notifier;
 
     QSLIST_HEAD(, Coroutine) scheduled_coroutines;
     QEMUBH *co_schedule_bh;
 
     int thread_pool_min;
     int thread_pool_max;
     /* Thread pool for performing work and receiving completion callbacks.
      * Has its own locking.
      */
     struct ThreadPool *thread_pool;
 
 #ifdef CONFIG_LINUX_AIO
     /*
      * State for native Linux AIO.  Uses aio_context_acquire/release for
      * locking.
      */
     struct LinuxAioState *linux_aio;
 #endif
 #ifdef CONFIG_LINUX_IO_URING
     /*
      * State for Linux io_uring.  Uses aio_context_acquire/release for
      * locking.
      */
     struct LuringState *linux_io_uring;
 
     /* State for file descriptor monitoring using Linux io_uring */
     struct io_uring fdmon_io_uring;
     AioHandlerSList submit_list;
 #endif
 
     /* TimerLists for calling timers - one per clock type.  Has its own
      * locking.
      */
     QEMUTimerListGroup tlg;
 
     int external_disable_cnt;
 
     /* Number of AioHandlers without .io_poll() */
     int poll_disable_cnt;
 
     /* Polling mode parameters */
     int64_t poll_ns;        /* current polling time in nanoseconds */
     int64_t poll_max_ns;    /* maximum polling time in nanoseconds */
     int64_t poll_grow;      /* polling time growth factor */
     int64_t poll_shrink;    /* polling time shrink factor */
 
     /* AIO engine parameters */
     int64_t aio_max_batch;  /* maximum number of requests in a batch */
 
     /*
      * List of handlers participating in userspace polling.  Protected by
      * ctx->list_lock.  Iterated and modified mostly by the event loop thread
      * from aio_poll() with ctx->list_lock incremented.  aio_set_fd_handler()
      * only touches the list to delete nodes if ctx->list_lock's count is zero.
      */
     AioHandlerList poll_aio_handlers;
 
     /* Are we in polling mode or monitoring file descriptors? */
     bool poll_started;
 
     /* epoll(7) state used when built with CONFIG_EPOLL */
     int epollfd;
 
     const FDMonOps *fdmon_ops;
 };
 
 /**
  * aio_context_new: Allocate a new AioContext.
  *
  * AioContext provide a mini event-loop that can be waited on synchronously.
  * They also provide bottom halves, a service to execute a piece of code
  * as soon as possible.
  */
 AioContext *aio_context_new(Error **errp);
 
 /**
  * aio_context_ref:
  * @ctx: The AioContext to operate on.
  *
  * Add a reference to an AioContext.
  */
 void aio_context_ref(AioContext *ctx);
 
 /**
  * aio_context_unref:
  * @ctx: The AioContext to operate on.
  *
  * Drop a reference to an AioContext.
  */
 void aio_context_unref(AioContext *ctx);
 
 /* Take ownership of the AioContext.  If the AioContext will be shared between
  * threads, and a thread does not want to be interrupted, it will have to
  * take ownership around calls to aio_poll().  Otherwise, aio_poll()
  * automatically takes care of calling aio_context_acquire and
  * aio_context_release.
  *
  * Note that this is separate from bdrv_drained_begin/bdrv_drained_end.  A
  * thread still has to call those to avoid being interrupted by the guest.
  *
  * Bottom halves, timers and callbacks can be created or removed without
  * acquiring the AioContext.
  */
 void aio_context_acquire(AioContext *ctx);
 
 /* Relinquish ownership of the AioContext. */
 void aio_context_release(AioContext *ctx);
 
 /**
  * aio_bh_schedule_oneshot_full: Allocate a new bottom half structure that will
  * run only once and as soon as possible.
  *
  * @name: A human-readable identifier for debugging purposes.
  */
 void aio_bh_schedule_oneshot_full(AioContext *ctx, QEMUBHFunc *cb, void *opaque,
                                   const char *name);
 
 /**
  * aio_bh_schedule_oneshot: Allocate a new bottom half structure that will run
  * only once and as soon as possible.
  *
  * A convenience wrapper for aio_bh_schedule_oneshot_full() that uses cb as the
  * name string.
  */
 #define aio_bh_schedule_oneshot(ctx, cb, opaque) \
     aio_bh_schedule_oneshot_full((ctx), (cb), (opaque), (stringify(cb)))
 
 /**
  * aio_bh_new_full: Allocate a new bottom half structure.
  *
  * Bottom halves are lightweight callbacks whose invocation is guaranteed
  * to be wait-free, thread-safe and signal-safe.  The #QEMUBH structure
  * is opaque and must be allocated prior to its use.
  *
  * @name: A human-readable identifier for debugging purposes.
  */
 QEMUBH *aio_bh_new_full(AioContext *ctx, QEMUBHFunc *cb, void *opaque,
                         const char *name);
 
 /**
  * aio_bh_new: Allocate a new bottom half structure
  *
  * A convenience wrapper for aio_bh_new_full() that uses the cb as the name
  * string.
  */
 #define aio_bh_new(ctx, cb, opaque) \
     aio_bh_new_full((ctx), (cb), (opaque), (stringify(cb)))
 
 /**
  * aio_notify: Force processing of pending events.
  *
  * Similar to signaling a condition variable, aio_notify forces
  * aio_poll to exit, so that the next call will re-examine pending events.
  * The caller of aio_notify will usually call aio_poll again very soon,
  * or go through another iteration of the GLib main loop.  Hence, aio_notify
  * also has the side effect of recalculating the sets of file descriptors
  * that the main loop waits for.
  *
  * Calling aio_notify is rarely necessary, because for example scheduling
  * a bottom half calls it already.
  */
 void aio_notify(AioContext *ctx);
 
 /**
  * aio_notify_accept: Acknowledge receiving an aio_notify.
  *
  * aio_notify() uses an EventNotifier in order to wake up a sleeping
  * aio_poll() or g_main_context_iteration().  Calls to aio_notify() are
  * usually rare, but the AioContext has to clear the EventNotifier on
  * every aio_poll() or g_main_context_iteration() in order to avoid
  * busy waiting.  This event_notifier_test_and_clear() cannot be done
  * using the usual aio_context_set_event_notifier(), because it must
  * be done before processing all events (file descriptors, bottom halves,
  * timers).
  *
  * aio_notify_accept() is an optimized event_notifier_test_and_clear()
  * that is specific to an AioContext's notifier; it is used internally
  * to clear the EventNotifier only if aio_notify() had been called.
  */
 void aio_notify_accept(AioContext *ctx);
 
 /**
  * aio_bh_call: Executes callback function of the specified BH.
  */
 void aio_bh_call(QEMUBH *bh);
 
 /**
  * aio_bh_poll: Poll bottom halves for an AioContext.
  *
  * These are internal functions used by the QEMU main loop.
  * And notice that multiple occurrences of aio_bh_poll cannot
  * be called concurrently
  */
 int aio_bh_poll(AioContext *ctx);
 
 /**
  * qemu_bh_schedule: Schedule a bottom half.
  *
  * Scheduling a bottom half interrupts the main loop and causes the
  * execution of the callback that was passed to qemu_bh_new.
  *
  * Bottom halves that are scheduled from a bottom half handler are instantly
  * invoked.  This can create an infinite loop if a bottom half handler
  * schedules itself.
  *
  * @bh: The bottom half to be scheduled.
  */
 void qemu_bh_schedule(QEMUBH *bh);
 
 /**
  * qemu_bh_cancel: Cancel execution of a bottom half.
  *
  * Canceling execution of a bottom half undoes the effect of calls to
  * qemu_bh_schedule without freeing its resources yet.  While cancellation
  * itself is also wait-free and thread-safe, it can of course race with the
  * loop that executes bottom halves unless you are holding the iothread
  * mutex.  This makes it mostly useless if you are not holding the mutex.
  *
  * @bh: The bottom half to be canceled.
  */
 void qemu_bh_cancel(QEMUBH *bh);
 
 /**
  *qemu_bh_delete: Cancel execution of a bottom half and free its resources.
  *
  * Deleting a bottom half frees the memory that was allocated for it by
  * qemu_bh_new.  It also implies canceling the bottom half if it was
  * scheduled.
  * This func is async. The bottom half will do the delete action at the finial
  * end.
  *
  * @bh: The bottom half to be deleted.
  */
 void qemu_bh_delete(QEMUBH *bh);
 
 /* Return whether there are any pending callbacks from the GSource
  * attached to the AioContext, before g_poll is invoked.
  *
  * This is used internally in the implementation of the GSource.
  */
 bool aio_prepare(AioContext *ctx);
 
 /* Return whether there are any pending callbacks from the GSource
  * attached to the AioContext, after g_poll is invoked.
  *
  * This is used internally in the implementation of the GSource.
  */
 bool aio_pending(AioContext *ctx);
 
 /* Dispatch any pending callbacks from the GSource attached to the AioContext.
  *
  * This is used internally in the implementation of the GSource.
  */
 void aio_dispatch(AioContext *ctx);
 
 /* Progress in completing AIO work to occur.  This can issue new pending
  * aio as a result of executing I/O completion or bh callbacks.
  *
  * Return whether any progress was made by executing AIO or bottom half
  * handlers.  If @blocking == true, this should always be true except
  * if someone called aio_notify.
  *
  * If there are no pending bottom halves, but there are pending AIO
  * operations, it may not be possible to make any progress without
  * blocking.  If @blocking is true, this function will wait until one
  * or more AIO events have completed, to ensure something has moved
  * before returning.
  */
 bool aio_poll(AioContext *ctx, bool blocking);
 
 /* Register a file descriptor and associated callbacks.  Behaves very similarly
  * to qemu_set_fd_handler.  Unlike qemu_set_fd_handler, these callbacks will
  * be invoked when using aio_poll().
  *
  * Code that invokes AIO completion functions should rely on this function
  * instead of qemu_set_fd_handler[2].
  */
 void aio_set_fd_handler(AioContext *ctx,
                         int fd,
                         bool is_external,
                         IOHandler *io_read,
                         IOHandler *io_write,
                         AioPollFn *io_poll,
                         IOHandler *io_poll_ready,
                         void *opaque);
 
 /* Set polling begin/end callbacks for a file descriptor that has already been
  * registered with aio_set_fd_handler.  Do nothing if the file descriptor is
  * not registered.
  */
 void aio_set_fd_poll(AioContext *ctx, int fd,
                      IOHandler *io_poll_begin,
                      IOHandler *io_poll_end);
 
 /* Register an event notifier and associated callbacks.  Behaves very similarly
  * to event_notifier_set_handler.  Unlike event_notifier_set_handler, these callbacks
  * will be invoked when using aio_poll().
  *
  * Code that invokes AIO completion functions should rely on this function
  * instead of event_notifier_set_handler.
  */
 void aio_set_event_notifier(AioContext *ctx,
                             EventNotifier *notifier,
                             bool is_external,
                             EventNotifierHandler *io_read,
                             AioPollFn *io_poll,
                             EventNotifierHandler *io_poll_ready);
 
 /* Set polling begin/end callbacks for an event notifier that has already been
  * registered with aio_set_event_notifier.  Do nothing if the event notifier is
  * not registered.
  */
 void aio_set_event_notifier_poll(AioContext *ctx,
                                  EventNotifier *notifier,
                                  EventNotifierHandler *io_poll_begin,
                                  EventNotifierHandler *io_poll_end);
 
 /* Return a GSource that lets the main loop poll the file descriptors attached
  * to this AioContext.
  */
 GSource *aio_get_g_source(AioContext *ctx);
 
 /* Return the ThreadPool bound to this AioContext */
 struct ThreadPool *aio_get_thread_pool(AioContext *ctx);
 
 /* Setup the LinuxAioState bound to this AioContext */
 struct LinuxAioState *aio_setup_linux_aio(AioContext *ctx, Error **errp);
 
 /* Return the LinuxAioState bound to this AioContext */
 struct LinuxAioState *aio_get_linux_aio(AioContext *ctx);
 
 /* Setup the LuringState bound to this AioContext */
 struct LuringState *aio_setup_linux_io_uring(AioContext *ctx, Error **errp);
 
 /* Return the LuringState bound to this AioContext */
 struct LuringState *aio_get_linux_io_uring(AioContext *ctx);
 /**
  * aio_timer_new_with_attrs:
  * @ctx: the aio context
  * @type: the clock type
  * @scale: the scale
  * @attributes: 0, or one to multiple OR'ed QEMU_TIMER_ATTR_<id> values
  *              to assign
  * @cb: the callback to call on timer expiry
  * @opaque: the opaque pointer to pass to the callback
  *
  * Allocate a new timer (with attributes) attached to the context @ctx.
  * The function is responsible for memory allocation.
  *
  * The preferred interface is aio_timer_init or aio_timer_init_with_attrs.
  * Use that unless you really need dynamic memory allocation.
  *
  * Returns: a pointer to the new timer
  */
 static inline QEMUTimer *aio_timer_new_with_attrs(AioContext *ctx,
                                                   QEMUClockType type,
                                                   int scale, int attributes,
                                                   QEMUTimerCB *cb, void *opaque)
 {
     return timer_new_full(&ctx->tlg, type, scale, attributes, cb, opaque);
 }
 
 /**
  * aio_timer_new:
  * @ctx: the aio context
  * @type: the clock type
  * @scale: the scale
  * @cb: the callback to call on timer expiry
  * @opaque: the opaque pointer to pass to the callback
  *
  * Allocate a new timer attached to the context @ctx.
  * See aio_timer_new_with_attrs for details.
  *
  * Returns: a pointer to the new timer
  */
 static inline QEMUTimer *aio_timer_new(AioContext *ctx, QEMUClockType type,
                                        int scale,
                                        QEMUTimerCB *cb, void *opaque)
 {
     return timer_new_full(&ctx->tlg, type, scale, 0, cb, opaque);
 }
 
 /**
  * aio_timer_init_with_attrs:
  * @ctx: the aio context
  * @ts: the timer
  * @type: the clock type
  * @scale: the scale
  * @attributes: 0, or one to multiple OR'ed QEMU_TIMER_ATTR_<id> values
  *              to assign
  * @cb: the callback to call on timer expiry
  * @opaque: the opaque pointer to pass to the callback
  *
  * Initialise a new timer (with attributes) attached to the context @ctx.
  * The caller is responsible for memory allocation.
  */
 static inline void aio_timer_init_with_attrs(AioContext *ctx,
                                              QEMUTimer *ts, QEMUClockType type,
                                              int scale, int attributes,
                                              QEMUTimerCB *cb, void *opaque)
 {
     timer_init_full(ts, &ctx->tlg, type, scale, attributes, cb, opaque);
 }
 
 /**
  * aio_timer_init:
  * @ctx: the aio context
  * @ts: the timer
  * @type: the clock type
  * @scale: the scale
  * @cb: the callback to call on timer expiry
  * @opaque: the opaque pointer to pass to the callback
  *
  * Initialise a new timer attached to the context @ctx.
  * See aio_timer_init_with_attrs for details.
  */
 static inline void aio_timer_init(AioContext *ctx,
                                   QEMUTimer *ts, QEMUClockType type,
                                   int scale,
                                   QEMUTimerCB *cb, void *opaque)
 {
     timer_init_full(ts, &ctx->tlg, type, scale, 0, cb, opaque);
 }
 
 /**
  * aio_compute_timeout:
  * @ctx: the aio context
  *
  * Compute the timeout that a blocking aio_poll should use.
  */
 int64_t aio_compute_timeout(AioContext *ctx);
 
 /**
  * aio_disable_external:
  * @ctx: the aio context
  *
  * Disable the further processing of external clients.
  */
 static inline void aio_disable_external(AioContext *ctx)
 {
     qatomic_inc(&ctx->external_disable_cnt);
 }
 
 /**
  * aio_enable_external:
  * @ctx: the aio context
  *
  * Enable the processing of external clients.
  */
 static inline void aio_enable_external(AioContext *ctx)
 {
     int old;
 
     old = qatomic_fetch_dec(&ctx->external_disable_cnt);
     assert(old > 0);
     if (old == 1) {
         /* Kick event loop so it re-arms file descriptors */
         aio_notify(ctx);
     }
 }
 
 /**
  * aio_external_disabled:
  * @ctx: the aio context
  *
  * Return true if the external clients are disabled.
  */
 static inline bool aio_external_disabled(AioContext *ctx)
 {
     return qatomic_read(&ctx->external_disable_cnt);
 }
 
 /**
  * aio_node_check:
  * @ctx: the aio context
  * @is_external: Whether or not the checked node is an external event source.
  *
  * Check if the node's is_external flag is okay to be polled by the ctx at this
  * moment. True means green light.
  */
 static inline bool aio_node_check(AioContext *ctx, bool is_external)
 {
     return !is_external || !qatomic_read(&ctx->external_disable_cnt);
 }
 
 /**
  * aio_co_schedule:
  * @ctx: the aio context
  * @co: the coroutine
  *
  * Start a coroutine on a remote AioContext.
  *
  * The coroutine must not be entered by anyone else while aio_co_schedule()
  * is active.  In addition the coroutine must have yielded unless ctx
  * is the context in which the coroutine is running (i.e. the value of
  * qemu_get_current_aio_context() from the coroutine itself).
  */
 void aio_co_schedule(AioContext *ctx, struct Coroutine *co);
 
 /**
  * aio_co_reschedule_self:
  * @new_ctx: the new context
  *
  * Move the currently running coroutine to new_ctx. If the coroutine is already
  * running in new_ctx, do nothing.
  */
 void coroutine_fn aio_co_reschedule_self(AioContext *new_ctx);
 
 /**
  * aio_co_wake:
  * @co: the coroutine
  *
  * Restart a coroutine on the AioContext where it was running last, thus
  * preventing coroutines from jumping from one context to another when they
  * go to sleep.
  *
  * aio_co_wake may be executed either in coroutine or non-coroutine
  * context.  The coroutine must not be entered by anyone else while
  * aio_co_wake() is active.
  */
 void aio_co_wake(struct Coroutine *co);
 
 /**
  * aio_co_enter:
  * @ctx: the context to run the coroutine
  * @co: the coroutine to run
  *
  * Enter a coroutine in the specified AioContext.
  */
 void aio_co_enter(AioContext *ctx, struct Coroutine *co);
 
 /**
  * Return the AioContext whose event loop runs in the current thread.
  *
  * If called from an IOThread this will be the IOThread's AioContext.  If
  * called from the main thread or with the "big QEMU lock" taken it
  * will be the main loop AioContext.
  */
 AioContext *qemu_get_current_aio_context(void);
 
 void qemu_set_current_aio_context(AioContext *ctx);
 
 /**
  * aio_context_setup:
  * @ctx: the aio context
  *
  * Initialize the aio context.
  */
 void aio_context_setup(AioContext *ctx);
 
 /**
  * aio_context_destroy:
  * @ctx: the aio context
  *
  * Destroy the aio context.
  */
 void aio_context_destroy(AioContext *ctx);
 
 /* Used internally, do not call outside AioContext code */
 void aio_context_use_g_source(AioContext *ctx);
 
 /**
  * aio_context_set_poll_params:
  * @ctx: the aio context
  * @max_ns: how long to busy poll for, in nanoseconds
  * @grow: polling time growth factor
  * @shrink: polling time shrink factor
  *
  * Poll mode can be disabled by setting poll_max_ns to 0.
  */
 void aio_context_set_poll_params(AioContext *ctx, int64_t max_ns,
                                  int64_t grow, int64_t shrink,
                                  Error **errp);
 
 /**
  * aio_context_set_aio_params:
  * @ctx: the aio context
  * @max_batch: maximum number of requests in a batch, 0 means that the
  *             engine will use its default
  */
 void aio_context_set_aio_params(AioContext *ctx, int64_t max_batch,
                                 Error **errp);
 
 /**
  * aio_context_set_thread_pool_params:
  * @ctx: the aio context
  * @min: min number of threads to have readily available in the thread pool
  * @min: max number of threads the thread pool can contain
  */
 void aio_context_set_thread_pool_params(AioContext *ctx, int64_t min,
                                         int64_t max, Error **errp);
 #endif