block/linux-aio.c - qemu - Git at Google

 /*
  * Linux native AIO support.
  *
  * Copyright (C) 2009 IBM, Corp.
  * Copyright (C) 2009 Red Hat, Inc.
  *
  * This work is licensed under the terms of the GNU GPL, version 2 or later.
  * See the COPYING file in the top-level directory.
  */
 #include "qemu-common.h"
 #include "block/aio.h"
 #include "qemu/queue.h"
 #include "block/raw-aio.h"
 #include "qemu/event_notifier.h"

 #include <libaio.h>

 /*
  * Queue size (per-device).
  *
  * XXX: eventually we need to communicate this to the guest and/or make it
  *      tunable by the guest.  If we get more outstanding requests at a time
  *      than this we will get EAGAIN from io_submit which is communicated to
  *      the guest as an I/O error.
  */
 #define MAX_EVENTS 128

 #define MAX_QUEUED_IO  128

 struct qemu_laiocb {
     BlockAIOCB common;
     struct qemu_laio_state *ctx;
     struct iocb iocb;
     ssize_t ret;
     size_t nbytes;
     QEMUIOVector *qiov;
     bool is_read;
     QSIMPLEQ_ENTRY(qemu_laiocb) next;
 };

 typedef struct {
     int plugged;
     unsigned int n;
     bool blocked;
     QSIMPLEQ_HEAD(, qemu_laiocb) pending;
 } LaioQueue;

 struct qemu_laio_state {
     io_context_t ctx;
     EventNotifier e;

     /* io queue for submit at batch */
     LaioQueue io_q;

     /* I/O completion processing */
     QEMUBH *completion_bh;
     struct io_event events[MAX_EVENTS];
     int event_idx;
     int event_max;
 };

 static void ioq_submit(struct qemu_laio_state *s);

 static inline ssize_t io_event_ret(struct io_event *ev)
 {
     return (ssize_t)(((uint64_t)ev->res2 << 32) | ev->res);
 }

 /*
  * Completes an AIO request (calls the callback and frees the ACB).
  */
 static void qemu_laio_process_completion(struct qemu_laio_state *s,
     struct qemu_laiocb *laiocb)
 {
     int ret;

     ret = laiocb->ret;
     if (ret != -ECANCELED) {
         if (ret == laiocb->nbytes) {
             ret = 0;
         } else if (ret >= 0) {
             /* Short reads mean EOF, pad with zeros. */
             if (laiocb->is_read) {
                 qemu_iovec_memset(laiocb->qiov, ret, 0,
                     laiocb->qiov->size - ret);
             } else {
                 ret = -EINVAL;
             }
         }
     }
     laiocb->common.cb(laiocb->common.opaque, ret);

     qemu_aio_unref(laiocb);
 }

 /* The completion BH fetches completed I/O requests and invokes their
  * callbacks.
  *
  * The function is somewhat tricky because it supports nested event loops, for
  * example when a request callback invokes aio_poll().  In order to do this,
  * the completion events array and index are kept in qemu_laio_state.  The BH
  * reschedules itself as long as there are completions pending so it will
  * either be called again in a nested event loop or will be called after all
  * events have been completed.  When there are no events left to complete, the
  * BH returns without rescheduling.
  */
 static void qemu_laio_completion_bh(void *opaque)
 {
     struct qemu_laio_state *s = opaque;

     /* Fetch more completion events when empty */
     if (s->event_idx == s->event_max) {
         do {
             struct timespec ts = { 0 };
             s->event_max = io_getevents(s->ctx, MAX_EVENTS, MAX_EVENTS,
                                         s->events, &ts);
         } while (s->event_max == -EINTR);

         s->event_idx = 0;
         if (s->event_max <= 0) {
             s->event_max = 0;
             return; /* no more events */
         }
     }

     /* Reschedule so nested event loops see currently pending completions */
     qemu_bh_schedule(s->completion_bh);

     /* Process completion events */
     while (s->event_idx < s->event_max) {
         struct iocb *iocb = s->events[s->event_idx].obj;
         struct qemu_laiocb *laiocb =
                 container_of(iocb, struct qemu_laiocb, iocb);

         laiocb->ret = io_event_ret(&s->events[s->event_idx]);
         s->event_idx++;

         qemu_laio_process_completion(s, laiocb);
     }

     if (!s->io_q.plugged && !QSIMPLEQ_EMPTY(&s->io_q.pending)) {
         ioq_submit(s);
     }
 }

 static void qemu_laio_completion_cb(EventNotifier *e)
 {
     struct qemu_laio_state *s = container_of(e, struct qemu_laio_state, e);

     if (event_notifier_test_and_clear(&s->e)) {
         qemu_bh_schedule(s->completion_bh);
     }
 }

 static void laio_cancel(BlockAIOCB *blockacb)
 {
     struct qemu_laiocb *laiocb = (struct qemu_laiocb *)blockacb;
     struct io_event event;
     int ret;

     if (laiocb->ret != -EINPROGRESS) {
         return;
     }
     ret = io_cancel(laiocb->ctx->ctx, &laiocb->iocb, &event);
     laiocb->ret = -ECANCELED;
     if (ret != 0) {
         /* iocb is not cancelled, cb will be called by the event loop later */
         return;
     }

     laiocb->common.cb(laiocb->common.opaque, laiocb->ret);
 }

 static const AIOCBInfo laio_aiocb_info = {
     .aiocb_size         = sizeof(struct qemu_laiocb),
     .cancel_async       = laio_cancel,
 };

 static void ioq_init(LaioQueue *io_q)
 {
     QSIMPLEQ_INIT(&io_q->pending);
     io_q->plugged = 0;
     io_q->n = 0;
     io_q->blocked = false;
 }

 static void ioq_submit(struct qemu_laio_state *s)
 {
     int ret, len;
     struct qemu_laiocb *aiocb;
     struct iocb *iocbs[MAX_QUEUED_IO];
     QSIMPLEQ_HEAD(, qemu_laiocb) completed;

     do {
         len = 0;
         QSIMPLEQ_FOREACH(aiocb, &s->io_q.pending, next) {
             iocbs[len++] = &aiocb->iocb;
             if (len == MAX_QUEUED_IO) {
                 break;
             }
         }

         ret = io_submit(s->ctx, len, iocbs);
         if (ret == -EAGAIN) {
             break;
         }
         if (ret < 0) {
             abort();
         }

         s->io_q.n -= ret;
         aiocb = container_of(iocbs[ret - 1], struct qemu_laiocb, iocb);
         QSIMPLEQ_SPLIT_AFTER(&s->io_q.pending, aiocb, next, &completed);
     } while (ret == len && !QSIMPLEQ_EMPTY(&s->io_q.pending));
     s->io_q.blocked = (s->io_q.n > 0);
 }

 void laio_io_plug(BlockDriverState *bs, void *aio_ctx)
 {
     struct qemu_laio_state *s = aio_ctx;

     s->io_q.plugged++;
 }

 void laio_io_unplug(BlockDriverState *bs, void *aio_ctx, bool unplug)
 {
     struct qemu_laio_state *s = aio_ctx;

     assert(s->io_q.plugged > 0 || !unplug);

     if (unplug && --s->io_q.plugged > 0) {
         return;
     }

     if (!s->io_q.blocked && !QSIMPLEQ_EMPTY(&s->io_q.pending)) {
         ioq_submit(s);
     }
 }

 BlockAIOCB *laio_submit(BlockDriverState *bs, void *aio_ctx, int fd,
         int64_t sector_num, QEMUIOVector *qiov, int nb_sectors,
         BlockCompletionFunc *cb, void *opaque, int type)
 {
     struct qemu_laio_state *s = aio_ctx;
     struct qemu_laiocb *laiocb;
     struct iocb *iocbs;
     off_t offset = sector_num * 512;

     laiocb = qemu_aio_get(&laio_aiocb_info, bs, cb, opaque);
     laiocb->nbytes = nb_sectors * 512;
     laiocb->ctx = s;
     laiocb->ret = -EINPROGRESS;
     laiocb->is_read = (type == QEMU_AIO_READ);
     laiocb->qiov = qiov;

     iocbs = &laiocb->iocb;

     switch (type) {
     case QEMU_AIO_WRITE:
         io_prep_pwritev(iocbs, fd, qiov->iov, qiov->niov, offset);
 	break;
     case QEMU_AIO_READ:
         io_prep_preadv(iocbs, fd, qiov->iov, qiov->niov, offset);
 	break;
     /* Currently Linux kernel does not support other operations */
     default:
         fprintf(stderr, "%s: invalid AIO request type 0x%x.\n",
                         __func__, type);
         goto out_free_aiocb;
     }
     io_set_eventfd(&laiocb->iocb, event_notifier_get_fd(&s->e));

     QSIMPLEQ_INSERT_TAIL(&s->io_q.pending, laiocb, next);
     s->io_q.n++;
     if (!s->io_q.blocked &&
         (!s->io_q.plugged || s->io_q.n >= MAX_QUEUED_IO)) {
         ioq_submit(s);
     }
     return &laiocb->common;

 out_free_aiocb:
     qemu_aio_unref(laiocb);
     return NULL;
 }

 void laio_detach_aio_context(void *s_, AioContext *old_context)
 {
     struct qemu_laio_state *s = s_;

     aio_set_event_notifier(old_context, &s->e, false, NULL);
     qemu_bh_delete(s->completion_bh);
 }

 void laio_attach_aio_context(void *s_, AioContext *new_context)
 {
     struct qemu_laio_state *s = s_;

     s->completion_bh = aio_bh_new(new_context, qemu_laio_completion_bh, s);
     aio_set_event_notifier(new_context, &s->e, false,
                            qemu_laio_completion_cb);
 }

 void *laio_init(void)
 {
     struct qemu_laio_state *s;

     s = g_malloc0(sizeof(*s));
     if (event_notifier_init(&s->e, false) < 0) {
         goto out_free_state;
     }

     if (io_setup(MAX_EVENTS, &s->ctx) != 0) {
         goto out_close_efd;
     }

     ioq_init(&s->io_q);

     return s;

 out_close_efd:
     event_notifier_cleanup(&s->e);
 out_free_state:
     g_free(s);
     return NULL;
 }

 void laio_cleanup(void *s_)
 {
     struct qemu_laio_state *s = s_;

     event_notifier_cleanup(&s->e);

     if (io_destroy(s->ctx) != 0) {
         fprintf(stderr, "%s: destroy AIO context %p failed\n",
                         __func__, &s->ctx);
     }
     g_free(s);
 }
	/*
	* Linux native AIO support.
	*
	* Copyright (C) 2009 IBM, Corp.
	* Copyright (C) 2009 Red Hat, Inc.
	*
	* This work is licensed under the terms of the GNU GPL, version 2 or later.
	* See the COPYING file in the top-level directory.
	*/
	#include "qemu-common.h"
	#include "block/aio.h"
	#include "qemu/queue.h"
	#include "block/raw-aio.h"
	#include "qemu/event_notifier.h"

	#include <libaio.h>

	/*
	* Queue size (per-device).
	*
	* XXX: eventually we need to communicate this to the guest and/or make it
	* tunable by the guest. If we get more outstanding requests at a time
	* than this we will get EAGAIN from io_submit which is communicated to
	* the guest as an I/O error.
	*/
	#define MAX_EVENTS 128

	#define MAX_QUEUED_IO 128

	struct qemu_laiocb {
	BlockAIOCB common;
	struct qemu_laio_state *ctx;
	struct iocb iocb;
	ssize_t ret;
	size_t nbytes;
	QEMUIOVector *qiov;
	bool is_read;
	QSIMPLEQ_ENTRY(qemu_laiocb) next;
	};

	typedef struct {
	int plugged;
	unsigned int n;
	bool blocked;
	QSIMPLEQ_HEAD(, qemu_laiocb) pending;
	} LaioQueue;

	struct qemu_laio_state {
	io_context_t ctx;
	EventNotifier e;

	/* io queue for submit at batch */
	LaioQueue io_q;

	/* I/O completion processing */
	QEMUBH *completion_bh;
	struct io_event events[MAX_EVENTS];
	int event_idx;
	int event_max;
	};

	static void ioq_submit(struct qemu_laio_state *s);

	static inline ssize_t io_event_ret(struct io_event *ev)
	{
	return (ssize_t)(((uint64_t)ev->res2 << 32) \| ev->res);
	}

	/*
	* Completes an AIO request (calls the callback and frees the ACB).
	*/
	static void qemu_laio_process_completion(struct qemu_laio_state *s,
	struct qemu_laiocb *laiocb)
	{
	int ret;

	ret = laiocb->ret;
	if (ret != -ECANCELED) {
	if (ret == laiocb->nbytes) {
	ret = 0;
	} else if (ret >= 0) {
	/* Short reads mean EOF, pad with zeros. */
	if (laiocb->is_read) {
	qemu_iovec_memset(laiocb->qiov, ret, 0,
	laiocb->qiov->size - ret);
	} else {
	ret = -EINVAL;
	}
	}
	}
	laiocb->common.cb(laiocb->common.opaque, ret);

	qemu_aio_unref(laiocb);
	}

	/* The completion BH fetches completed I/O requests and invokes their
	* callbacks.
	*
	* The function is somewhat tricky because it supports nested event loops, for
	* example when a request callback invokes aio_poll(). In order to do this,
	* the completion events array and index are kept in qemu_laio_state. The BH
	* reschedules itself as long as there are completions pending so it will
	* either be called again in a nested event loop or will be called after all
	* events have been completed. When there are no events left to complete, the
	* BH returns without rescheduling.
	*/
	static void qemu_laio_completion_bh(void *opaque)
	{
	struct qemu_laio_state *s = opaque;

	/* Fetch more completion events when empty */
	if (s->event_idx == s->event_max) {
	do {
	struct timespec ts = { 0 };
	s->event_max = io_getevents(s->ctx, MAX_EVENTS, MAX_EVENTS,
	s->events, &ts);
	} while (s->event_max == -EINTR);

	s->event_idx = 0;
	if (s->event_max <= 0) {
	s->event_max = 0;
	return; /* no more events */
	}
	}

	/* Reschedule so nested event loops see currently pending completions */
	qemu_bh_schedule(s->completion_bh);

	/* Process completion events */
	while (s->event_idx < s->event_max) {
	struct iocb *iocb = s->events[s->event_idx].obj;
	struct qemu_laiocb *laiocb =
	container_of(iocb, struct qemu_laiocb, iocb);

	laiocb->ret = io_event_ret(&s->events[s->event_idx]);
	s->event_idx++;

	qemu_laio_process_completion(s, laiocb);
	}

	if (!s->io_q.plugged && !QSIMPLEQ_EMPTY(&s->io_q.pending)) {
	ioq_submit(s);
	}
	}

	static void qemu_laio_completion_cb(EventNotifier *e)
	{
	struct qemu_laio_state *s = container_of(e, struct qemu_laio_state, e);

	if (event_notifier_test_and_clear(&s->e)) {
	qemu_bh_schedule(s->completion_bh);
	}
	}

	static void laio_cancel(BlockAIOCB *blockacb)
	{
	struct qemu_laiocb laiocb = (struct qemu_laiocb )blockacb;
	struct io_event event;
	int ret;

	if (laiocb->ret != -EINPROGRESS) {
	return;
	}
	ret = io_cancel(laiocb->ctx->ctx, &laiocb->iocb, &event);
	laiocb->ret = -ECANCELED;
	if (ret != 0) {
	/* iocb is not cancelled, cb will be called by the event loop later */
	return;
	}

	laiocb->common.cb(laiocb->common.opaque, laiocb->ret);
	}

	static const AIOCBInfo laio_aiocb_info = {
	.aiocb_size = sizeof(struct qemu_laiocb),
	.cancel_async = laio_cancel,
	};

	static void ioq_init(LaioQueue *io_q)
	{
	QSIMPLEQ_INIT(&io_q->pending);
	io_q->plugged = 0;
	io_q->n = 0;
	io_q->blocked = false;
	}

	static void ioq_submit(struct qemu_laio_state *s)
	{
	int ret, len;
	struct qemu_laiocb *aiocb;
	struct iocb *iocbs[MAX_QUEUED_IO];
	QSIMPLEQ_HEAD(, qemu_laiocb) completed;

	do {
	len = 0;
	QSIMPLEQ_FOREACH(aiocb, &s->io_q.pending, next) {
	iocbs[len++] = &aiocb->iocb;
	if (len == MAX_QUEUED_IO) {
	break;
	}
	}

	ret = io_submit(s->ctx, len, iocbs);
	if (ret == -EAGAIN) {
	break;
	}
	if (ret < 0) {
	abort();
	}

	s->io_q.n -= ret;
	aiocb = container_of(iocbs[ret - 1], struct qemu_laiocb, iocb);
	QSIMPLEQ_SPLIT_AFTER(&s->io_q.pending, aiocb, next, &completed);
	} while (ret == len && !QSIMPLEQ_EMPTY(&s->io_q.pending));
	s->io_q.blocked = (s->io_q.n > 0);
	}

	void laio_io_plug(BlockDriverState bs, void aio_ctx)
	{
	struct qemu_laio_state *s = aio_ctx;

	s->io_q.plugged++;
	}

	void laio_io_unplug(BlockDriverState bs, void aio_ctx, bool unplug)
	{
	struct qemu_laio_state *s = aio_ctx;

	assert(s->io_q.plugged > 0 \|\| !unplug);

	if (unplug && --s->io_q.plugged > 0) {
	return;
	}

	if (!s->io_q.blocked && !QSIMPLEQ_EMPTY(&s->io_q.pending)) {
	ioq_submit(s);
	}
	}

	BlockAIOCB laio_submit(BlockDriverState bs, void *aio_ctx, int fd,
	int64_t sector_num, QEMUIOVector *qiov, int nb_sectors,
	BlockCompletionFunc cb, void opaque, int type)
	{
	struct qemu_laio_state *s = aio_ctx;
	struct qemu_laiocb *laiocb;
	struct iocb *iocbs;
	off_t offset = sector_num * 512;

	laiocb = qemu_aio_get(&laio_aiocb_info, bs, cb, opaque);
	laiocb->nbytes = nb_sectors * 512;
	laiocb->ctx = s;
	laiocb->ret = -EINPROGRESS;
	laiocb->is_read = (type == QEMU_AIO_READ);
	laiocb->qiov = qiov;

	iocbs = &laiocb->iocb;

	switch (type) {
	case QEMU_AIO_WRITE:
	io_prep_pwritev(iocbs, fd, qiov->iov, qiov->niov, offset);
	break;
	case QEMU_AIO_READ:
	io_prep_preadv(iocbs, fd, qiov->iov, qiov->niov, offset);
	break;
	/* Currently Linux kernel does not support other operations */
	default:
	fprintf(stderr, "%s: invalid AIO request type 0x%x.\n",
	__func__, type);
	goto out_free_aiocb;
	}
	io_set_eventfd(&laiocb->iocb, event_notifier_get_fd(&s->e));

	QSIMPLEQ_INSERT_TAIL(&s->io_q.pending, laiocb, next);
	s->io_q.n++;
	if (!s->io_q.blocked &&
	(!s->io_q.plugged \|\| s->io_q.n >= MAX_QUEUED_IO)) {
	ioq_submit(s);
	}
	return &laiocb->common;

	out_free_aiocb:
	qemu_aio_unref(laiocb);
	return NULL;
	}

	void laio_detach_aio_context(void s_, AioContext old_context)
	{
	struct qemu_laio_state *s = s_;

	aio_set_event_notifier(old_context, &s->e, false, NULL);
	qemu_bh_delete(s->completion_bh);
	}

	void laio_attach_aio_context(void s_, AioContext new_context)
	{
	struct qemu_laio_state *s = s_;

	s->completion_bh = aio_bh_new(new_context, qemu_laio_completion_bh, s);
	aio_set_event_notifier(new_context, &s->e, false,
	qemu_laio_completion_cb);
	}

	void *laio_init(void)
	{
	struct qemu_laio_state *s;

	s = g_malloc0(sizeof(*s));
	if (event_notifier_init(&s->e, false) < 0) {
	goto out_free_state;
	}

	if (io_setup(MAX_EVENTS, &s->ctx) != 0) {
	goto out_close_efd;
	}

	ioq_init(&s->io_q);

	return s;

	out_close_efd:
	event_notifier_cleanup(&s->e);
	out_free_state:
	g_free(s);
	return NULL;
	}

	void laio_cleanup(void *s_)
	{
	struct qemu_laio_state *s = s_;

	event_notifier_cleanup(&s->e);

	if (io_destroy(s->ctx) != 0) {
	fprintf(stderr, "%s: destroy AIO context %p failed\n",
	__func__, &s->ctx);
	}
	g_free(s);
	}