engines/skeleton_external.c

/*
 * Skeleton for a sample external io engine
 *
 * Should be compiled with:
 *
 * gcc -Wall -O2 -g -shared -rdynamic -fPIC -o engine.o engine.c
 *
 */
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <assert.h>

#include "../fio.h"

/*
 * The core of the module is identical to the ones included with fio,
 * read those. You cannot use register_ioengine() and unregister_ioengine()
 * for external modules, they should be gotten through dlsym()
 */

/*
 * The ->event() hook is called to match an event number with an io_u.
 * After the core has called ->getevents() and it has returned eg 3,
 * the ->event() hook must return the 3 events that have completed for
 * subsequent calls to ->event() with [0-2]. Required.
 */
static struct io_u *fio_skeleton_event(struct thread_data *td, int event)
{
	return NULL;
}

/*
 * The ->getevents() hook is used to reap completion events from an async
 * io engine. It returns the number of completed events since the last call,
 * which may then be retrieved by calling the ->event() hook with the event
 * numbers. Required.
 */
static int fio_skeleton_getevents(struct thread_data *td, unsigned int min,
				  unsigned int max, const struct timespec *t)
{
	return 0;
}

/*
 * The ->cancel() hook attempts to cancel the io_u. Only relevant for
 * async io engines, and need not be supported.
 */
static int fio_skeleton_cancel(struct thread_data *td, struct io_u *io_u)
{
	return 0;
}

/*
 * The ->queue() hook is responsible for initiating io on the io_u
 * being passed in. If the io engine is a synchronous one, io may complete
 * before ->queue() returns. Required.
 *
 * The io engine must transfer in the direction noted by io_u->ddir
 * to the buffer pointed to by io_u->xfer_buf for as many bytes as
 * io_u->xfer_buflen. Residual data count may be set in io_u->resid
 * for a short read/write.
 */
static int fio_skeleton_queue(struct thread_data *td, struct io_u *io_u)
{
	/*
	 * Double sanity check to catch errant write on a readonly setup
	 */
	fio_ro_check(td, io_u);

	/*
	 * Could return FIO_Q_QUEUED for a queued request,
	 * FIO_Q_COMPLETED for a completed request, and FIO_Q_BUSY
	 * if we could queue no more at this point (you'd have to
	 * define ->commit() to handle that.
	 */
	return FIO_Q_COMPLETED;
}

/*
 * The ->prep() function is called for each io_u prior to being submitted
 * with ->queue(). This hook allows the io engine to perform any
 * preparatory actions on the io_u, before being submitted. Not required.
 */
static int fio_skeleton_prep(struct thread_data *td, struct io_u *io_u)
{
	return 0;
}

/*
 * The init function is called once per thread/process, and should set up
 * any structures that this io engine requires to keep track of io. Not
 * required.
 */
static int fio_skeleton_init(struct thread_data *td)
{
	return 0;
}

/*
 * This is paired with the ->init() function and is called when a thread is
 * done doing io. Should tear down anything setup by the ->init() function.
 * Not required.
 */
static void fio_skeleton_cleanup(struct thread_data *td)
{
}

/*
 * Hook for opening the given file. Unless the engine has special
 * needs, it usually just provides generic_open_file() as the handler.
 */
static int fio_skeleton_open(struct thread_data *td, struct fio_file *f)
{
	return generic_open_file(td, f);
}

/*
 * Hook for closing a file. See fio_skeleton_open().
 */
static int fio_skeleton_close(struct thread_data *td, struct fio_file *f)
{
	return generic_close_file(td, f);
}

/*
 * Note that the structure is exported, so that fio can get it via
 * dlsym(..., "ioengine"); for (and only for) external engines.
 */
struct ioengine_ops ioengine = {
	.name		= "engine_name",
	.version	= FIO_IOOPS_VERSION,
	.init		= fio_skeleton_init,
	.prep		= fio_skeleton_prep,
	.queue		= fio_skeleton_queue,
	.cancel		= fio_skeleton_cancel,
	.getevents	= fio_skeleton_getevents,
	.event		= fio_skeleton_event,
	.cleanup	= fio_skeleton_cleanup,
	.open_file	= fio_skeleton_open,
	.close_file	= fio_skeleton_close,
};