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/*

 * 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

#include "qemu-common.h"

#include "qemu/queue.h"

#include "qemu/event_notifier.h"

typedef struct BlockDriverAIOCB BlockDriverAIOCB;

typedef void BlockDriverCompletionFunc(void *opaque, int ret);

typedef struct AIOCBInfo {

    void (*cancel)(BlockDriverAIOCB *acb);

    size_t aiocb_size;

} AIOCBInfo;

struct BlockDriverAIOCB {

    const AIOCBInfo *aiocb_info;

    BlockDriverState *bs;

    BlockDriverCompletionFunc *cb;

    void *opaque;

};

void *qemu_aio_get(const AIOCBInfo *aiocb_info, BlockDriverState *bs,

                   BlockDriverCompletionFunc *cb, void *opaque);

void qemu_aio_release(void *p);

typedef struct AioHandler AioHandler;

typedef void QEMUBHFunc(void *opaque);

typedef void IOHandler(void *opaque);

typedef struct AioContext {

    GSource source;

    /* The list of registered AIO handlers */

    QLIST_HEAD(, AioHandler) aio_handlers;

    /* This is a simple lock used to protect the aio_handlers list.

     * Specifically, it's used to ensure that no callbacks are removed while

     * we're walking and dispatching callbacks.

     */

    int walking_handlers;

    /* Anchor of the list of Bottom Halves belonging to the context */

    struct QEMUBH *first_bh;

    /* A simple lock used to protect the first_bh list, and ensure that

     * no callbacks are removed while we're walking and dispatching callbacks.

     */

    int walking_bh;

    /* Used for aio_notify.  */

    EventNotifier notifier;

} AioContext;

/* Returns 1 if there are still outstanding AIO requests; 0 otherwise */

typedef int (AioFlushEventNotifierHandler)(EventNotifier *e);

/**

 * 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(void);

/**

 * 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);

/**

 * aio_bh_new: 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.

 */

QEMUBH *aio_bh_new(AioContext *ctx, QEMUBHFunc *cb, void *opaque);

/**

 * aio_notify: Force processing of pending events.

 *

 * Similar to signaling a condition variable, aio_notify forces

 * aio_wait to exit, so that the next call will re-examine pending events.

 * The caller of aio_notify will usually call aio_wait 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_bh_poll: Poll bottom halves for an AioContext.

 *

 * These are internal functions used by the QEMU main loop.

 */

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.

 *

 * @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.

 *

 * This is used internally in the implementation of the GSource.

 */

bool aio_pending(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.

 *

 * If there is no pending AIO operation or completion (bottom half),

 * return false.  If there are pending bottom halves, return true.

 *

 * 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.

 *

 * If @blocking is false, this function will also return false if the

 * function cannot make any progress without blocking.

 */

bool aio_poll(AioContext *ctx, bool blocking);

#ifdef CONFIG_POSIX

/* Returns 1 if there are still outstanding AIO requests; 0 otherwise */

typedef int (AioFlushHandler)(void *opaque);

/* Register a file descriptor and associated callbacks.  Behaves very similarly

 * to qemu_set_fd_handler2.  Unlike qemu_set_fd_handler2, these callbacks will

 * be invoked when using qemu_aio_wait().

 *

 * 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,

                        IOHandler *io_read,

                        IOHandler *io_write,

                        AioFlushHandler *io_flush,

                        void *opaque);

#endif

/* 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 qemu_aio_wait().

 *

 * 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,

                            EventNotifierHandler *io_read,

                            AioFlushEventNotifierHandler *io_flush);

/* Return a GSource that lets the main loop poll the file descriptors attached

 * to this AioContext.

 */

GSource *aio_get_g_source(AioContext *ctx);

/* Functions to operate on the main QEMU AioContext.  */

bool qemu_aio_wait(void);

void qemu_aio_set_event_notifier(EventNotifier *notifier,

                                 EventNotifierHandler *io_read,

                                 AioFlushEventNotifierHandler *io_flush);

#ifdef CONFIG_POSIX

void qemu_aio_set_fd_handler(int fd,

                             IOHandler *io_read,

                             IOHandler *io_write,

                             AioFlushHandler *io_flush,

                             void *opaque);

#endif

#endif