/*
   *	An async IO implementation for Linux
   *	Written by Benjamin LaHaise <bcrl@kvack.org>
   *
   *	Implements an efficient asynchronous io interface.
   *
   *	Copyright 2000, 2001, 2002 Red Hat, Inc.  All Rights Reserved.
   *
   *	See ../COPYING for licensing terms.
   */
  #include <linux/kernel.h>
  #include <linux/init.h>
  #include <linux/errno.h>
  #include <linux/time.h>
  #include <linux/aio_abi.h>
  #include <linux/module.h>
  #include <linux/syscalls.h>

  #include <linux/uio.h>

  
  #define DEBUG 0
  
  #include <linux/sched.h>
  #include <linux/fs.h>
  #include <linux/file.h>
  #include <linux/mm.h>
  #include <linux/mman.h>
  #include <linux/slab.h>
  #include <linux/timer.h>
  #include <linux/aio.h>
  #include <linux/highmem.h>
  #include <linux/workqueue.h>
  #include <linux/security.h>

  #include <linux/eventfd.h>

  
  #include <asm/kmap_types.h>
  #include <asm/uaccess.h>
  #include <asm/mmu_context.h>
  
  #if DEBUG > 1
  #define dprintk		printk
  #else
  #define dprintk(x...)	do { ; } while (0)
  #endif

  /*------ sysctl variables----*/

  static DEFINE_SPINLOCK(aio_nr_lock);
  unsigned long aio_nr;		/* current system wide number of aio requests */
  unsigned long aio_max_nr = 0x10000; /* system wide maximum number of aio requests */

  /*----end sysctl variables---*/

  static struct kmem_cache	*kiocb_cachep;
  static struct kmem_cache	*kioctx_cachep;

  
  static struct workqueue_struct *aio_wq;
  
  /* Used for rare fput completion. */

  static void aio_fput_routine(struct work_struct *);
  static DECLARE_WORK(fput_work, aio_fput_routine);

  
  static DEFINE_SPINLOCK(fput_lock);

  static LIST_HEAD(fput_head);

  static void aio_kick_handler(struct work_struct *);

  static void aio_queue_work(struct kioctx *);

  
  /* aio_setup
   *	Creates the slab caches used by the aio routines, panic on
   *	failure as this is done early during the boot sequence.
   */
  static int __init aio_setup(void)
  {

  	kiocb_cachep = KMEM_CACHE(kiocb, SLAB_HWCACHE_ALIGN|SLAB_PANIC);
  	kioctx_cachep = KMEM_CACHE(kioctx,SLAB_HWCACHE_ALIGN|SLAB_PANIC);

  
  	aio_wq = create_workqueue("aio");
  
  	pr_debug("aio_setup: sizeof(struct page) = %d
  ", (int)sizeof(struct page));
  
  	return 0;
  }
  
  static void aio_free_ring(struct kioctx *ctx)
  {
  	struct aio_ring_info *info = &ctx->ring_info;
  	long i;
  
  	for (i=0; i<info->nr_pages; i++)
  		put_page(info->ring_pages[i]);
  
  	if (info->mmap_size) {
  		down_write(&ctx->mm->mmap_sem);
  		do_munmap(ctx->mm, info->mmap_base, info->mmap_size);
  		up_write(&ctx->mm->mmap_sem);
  	}
  
  	if (info->ring_pages && info->ring_pages != info->internal_pages)
  		kfree(info->ring_pages);
  	info->ring_pages = NULL;
  	info->nr = 0;
  }
  
  static int aio_setup_ring(struct kioctx *ctx)
  {
  	struct aio_ring *ring;
  	struct aio_ring_info *info = &ctx->ring_info;
  	unsigned nr_events = ctx->max_reqs;
  	unsigned long size;
  	int nr_pages;
  
  	/* Compensate for the ring buffer's head/tail overlap entry */
  	nr_events += 2;	/* 1 is required, 2 for good luck */
  
  	size = sizeof(struct aio_ring);
  	size += sizeof(struct io_event) * nr_events;
  	nr_pages = (size + PAGE_SIZE-1) >> PAGE_SHIFT;
  
  	if (nr_pages < 0)
  		return -EINVAL;
  
  	nr_events = (PAGE_SIZE * nr_pages - sizeof(struct aio_ring)) / sizeof(struct io_event);
  
  	info->nr = 0;
  	info->ring_pages = info->internal_pages;
  	if (nr_pages > AIO_RING_PAGES) {

  		info->ring_pages = kcalloc(nr_pages, sizeof(struct page *), GFP_KERNEL);

  		if (!info->ring_pages)
  			return -ENOMEM;

  	}
  
  	info->mmap_size = nr_pages * PAGE_SIZE;
  	dprintk("attempting mmap of %lu bytes
  ", info->mmap_size);
  	down_write(&ctx->mm->mmap_sem);
  	info->mmap_base = do_mmap(NULL, 0, info->mmap_size, 

  				  PROT_READ|PROT_WRITE, MAP_ANONYMOUS|MAP_PRIVATE,

  				  0);
  	if (IS_ERR((void *)info->mmap_base)) {
  		up_write(&ctx->mm->mmap_sem);

  		info->mmap_size = 0;
  		aio_free_ring(ctx);
  		return -EAGAIN;
  	}
  
  	dprintk("mmap address: 0x%08lx
  ", info->mmap_base);
  	info->nr_pages = get_user_pages(current, ctx->mm,
  					info->mmap_base, nr_pages, 
  					1, 0, info->ring_pages, NULL);
  	up_write(&ctx->mm->mmap_sem);
  
  	if (unlikely(info->nr_pages != nr_pages)) {
  		aio_free_ring(ctx);
  		return -EAGAIN;
  	}
  
  	ctx->user_id = info->mmap_base;
  
  	info->nr = nr_events;		/* trusted copy */
  
  	ring = kmap_atomic(info->ring_pages[0], KM_USER0);
  	ring->nr = nr_events;	/* user copy */
  	ring->id = ctx->user_id;
  	ring->head = ring->tail = 0;
  	ring->magic = AIO_RING_MAGIC;
  	ring->compat_features = AIO_RING_COMPAT_FEATURES;
  	ring->incompat_features = AIO_RING_INCOMPAT_FEATURES;
  	ring->header_length = sizeof(struct aio_ring);
  	kunmap_atomic(ring, KM_USER0);
  
  	return 0;
  }
  
  
  /* aio_ring_event: returns a pointer to the event at the given index from
   * kmap_atomic(, km).  Release the pointer with put_aio_ring_event();
   */
  #define AIO_EVENTS_PER_PAGE	(PAGE_SIZE / sizeof(struct io_event))
  #define AIO_EVENTS_FIRST_PAGE	((PAGE_SIZE - sizeof(struct aio_ring)) / sizeof(struct io_event))
  #define AIO_EVENTS_OFFSET	(AIO_EVENTS_PER_PAGE - AIO_EVENTS_FIRST_PAGE)
  
  #define aio_ring_event(info, nr, km) ({					\
  	unsigned pos = (nr) + AIO_EVENTS_OFFSET;			\
  	struct io_event *__event;					\
  	__event = kmap_atomic(						\
  			(info)->ring_pages[pos / AIO_EVENTS_PER_PAGE], km); \
  	__event += pos % AIO_EVENTS_PER_PAGE;				\
  	__event;							\
  })
  
  #define put_aio_ring_event(event, km) do {	\
  	struct io_event *__event = (event);	\
  	(void)__event;				\
  	kunmap_atomic((void *)((unsigned long)__event & PAGE_MASK), km); \
  } while(0)

  static void ctx_rcu_free(struct rcu_head *head)
  {
  	struct kioctx *ctx = container_of(head, struct kioctx, rcu_head);
  	unsigned nr_events = ctx->max_reqs;
  
  	kmem_cache_free(kioctx_cachep, ctx);
  
  	if (nr_events) {
  		spin_lock(&aio_nr_lock);
  		BUG_ON(aio_nr - nr_events > aio_nr);
  		aio_nr -= nr_events;
  		spin_unlock(&aio_nr_lock);
  	}
  }

  
  /* __put_ioctx
   *	Called when the last user of an aio context has gone away,
   *	and the struct needs to be freed.
   */
  static void __put_ioctx(struct kioctx *ctx)
  {

  	BUG_ON(ctx->reqs_active);
  
  	cancel_delayed_work(&ctx->wq);
  	cancel_work_sync(&ctx->wq.work);
  	aio_free_ring(ctx);
  	mmdrop(ctx->mm);
  	ctx->mm = NULL;
  	pr_debug("__put_ioctx: freeing %p
  ", ctx);

  	call_rcu(&ctx->rcu_head, ctx_rcu_free);

  }
  
  #define get_ioctx(kioctx) do {						\
  	BUG_ON(atomic_read(&(kioctx)->users) <= 0);			\
  	atomic_inc(&(kioctx)->users);					\
  } while (0)
  #define put_ioctx(kioctx) do {						\
  	BUG_ON(atomic_read(&(kioctx)->users) <= 0);			\
  	if (unlikely(atomic_dec_and_test(&(kioctx)->users))) 		\
  		__put_ioctx(kioctx);					\
  } while (0)

  /* ioctx_alloc
   *	Allocates and initializes an ioctx.  Returns an ERR_PTR if it failed.
   */
  static struct kioctx *ioctx_alloc(unsigned nr_events)
  {
  	struct mm_struct *mm;
  	struct kioctx *ctx;

  	int did_sync = 0;

  
  	/* Prevent overflows */
  	if ((nr_events > (0x10000000U / sizeof(struct io_event))) ||
  	    (nr_events > (0x10000000U / sizeof(struct kiocb)))) {
  		pr_debug("ENOMEM: nr_events too high
  ");
  		return ERR_PTR(-EINVAL);
  	}

  	if ((unsigned long)nr_events > aio_max_nr)

  		return ERR_PTR(-EAGAIN);

  	ctx = kmem_cache_zalloc(kioctx_cachep, GFP_KERNEL);

  	if (!ctx)
  		return ERR_PTR(-ENOMEM);

  	ctx->max_reqs = nr_events;
  	mm = ctx->mm = current->mm;
  	atomic_inc(&mm->mm_count);
  
  	atomic_set(&ctx->users, 1);
  	spin_lock_init(&ctx->ctx_lock);
  	spin_lock_init(&ctx->ring_info.ring_lock);
  	init_waitqueue_head(&ctx->wait);
  
  	INIT_LIST_HEAD(&ctx->active_reqs);
  	INIT_LIST_HEAD(&ctx->run_list);

  	INIT_DELAYED_WORK(&ctx->wq, aio_kick_handler);

  
  	if (aio_setup_ring(ctx) < 0)
  		goto out_freectx;
  
  	/* limit the number of system wide aios */

  	do {
  		spin_lock_bh(&aio_nr_lock);
  		if (aio_nr + nr_events > aio_max_nr ||
  		    aio_nr + nr_events < aio_nr)
  			ctx->max_reqs = 0;
  		else
  			aio_nr += ctx->max_reqs;
  		spin_unlock_bh(&aio_nr_lock);
  		if (ctx->max_reqs || did_sync)
  			break;
  
  		/* wait for rcu callbacks to have completed before giving up */
  		synchronize_rcu();
  		did_sync = 1;
  		ctx->max_reqs = nr_events;
  	} while (1);

  	if (ctx->max_reqs == 0)

  		goto out_cleanup;

  	/* now link into global list. */

  	spin_lock(&mm->ioctx_lock);
  	hlist_add_head_rcu(&ctx->list, &mm->ioctx_list);
  	spin_unlock(&mm->ioctx_lock);

  
  	dprintk("aio: allocated ioctx %p[%ld]: mm=%p mask=0x%x
  ",
  		ctx, ctx->user_id, current->mm, ctx->ring_info.nr);
  	return ctx;
  
  out_cleanup:

  	__put_ioctx(ctx);
  	return ERR_PTR(-EAGAIN);
  
  out_freectx:
  	mmdrop(mm);
  	kmem_cache_free(kioctx_cachep, ctx);
  	ctx = ERR_PTR(-ENOMEM);
  
  	dprintk("aio: error allocating ioctx %p
  ", ctx);
  	return ctx;
  }
  
  /* aio_cancel_all
   *	Cancels all outstanding aio requests on an aio context.  Used 
   *	when the processes owning a context have all exited to encourage 
   *	the rapid destruction of the kioctx.
   */
  static void aio_cancel_all(struct kioctx *ctx)
  {
  	int (*cancel)(struct kiocb *, struct io_event *);
  	struct io_event res;
  	spin_lock_irq(&ctx->ctx_lock);
  	ctx->dead = 1;
  	while (!list_empty(&ctx->active_reqs)) {
  		struct list_head *pos = ctx->active_reqs.next;
  		struct kiocb *iocb = list_kiocb(pos);
  		list_del_init(&iocb->ki_list);
  		cancel = iocb->ki_cancel;
  		kiocbSetCancelled(iocb);
  		if (cancel) {
  			iocb->ki_users++;
  			spin_unlock_irq(&ctx->ctx_lock);
  			cancel(iocb, &res);
  			spin_lock_irq(&ctx->ctx_lock);
  		}
  	}
  	spin_unlock_irq(&ctx->ctx_lock);
  }

  static void wait_for_all_aios(struct kioctx *ctx)

  {
  	struct task_struct *tsk = current;
  	DECLARE_WAITQUEUE(wait, tsk);

  	spin_lock_irq(&ctx->ctx_lock);

  	if (!ctx->reqs_active)

  		goto out;

  
  	add_wait_queue(&ctx->wait, &wait);
  	set_task_state(tsk, TASK_UNINTERRUPTIBLE);
  	while (ctx->reqs_active) {

  		spin_unlock_irq(&ctx->ctx_lock);

  		io_schedule();

  		set_task_state(tsk, TASK_UNINTERRUPTIBLE);

  		spin_lock_irq(&ctx->ctx_lock);

  	}
  	__set_task_state(tsk, TASK_RUNNING);
  	remove_wait_queue(&ctx->wait, &wait);

  
  out:
  	spin_unlock_irq(&ctx->ctx_lock);

  }
  
  /* wait_on_sync_kiocb:
   *	Waits on the given sync kiocb to complete.
   */

  ssize_t wait_on_sync_kiocb(struct kiocb *iocb)

  {
  	while (iocb->ki_users) {
  		set_current_state(TASK_UNINTERRUPTIBLE);
  		if (!iocb->ki_users)
  			break;

  		io_schedule();

  	}
  	__set_current_state(TASK_RUNNING);
  	return iocb->ki_user_data;
  }
  
  /* exit_aio: called when the last user of mm goes away.  At this point, 
   * there is no way for any new requests to be submited or any of the 
   * io_* syscalls to be called on the context.  However, there may be 
   * outstanding requests which hold references to the context; as they 
   * go away, they will call put_ioctx and release any pinned memory
   * associated with the request (held via struct page * references).
   */

  void exit_aio(struct mm_struct *mm)

  {

  	struct kioctx *ctx;
  
  	while (!hlist_empty(&mm->ioctx_list)) {
  		ctx = hlist_entry(mm->ioctx_list.first, struct kioctx, list);
  		hlist_del_rcu(&ctx->list);

  		aio_cancel_all(ctx);
  
  		wait_for_all_aios(ctx);
  		/*

  		 * Ensure we don't leave the ctx on the aio_wq

  		 */

  		cancel_work_sync(&ctx->wq.work);

  
  		if (1 != atomic_read(&ctx->users))
  			printk(KERN_DEBUG
  				"exit_aio:ioctx still alive: %d %d %d
  ",
  				atomic_read(&ctx->users), ctx->dead,
  				ctx->reqs_active);
  		put_ioctx(ctx);

  	}
  }

  /* aio_get_req
   *	Allocate a slot for an aio request.  Increments the users count
   * of the kioctx so that the kioctx stays around until all requests are
   * complete.  Returns NULL if no requests are free.
   *
   * Returns with kiocb->users set to 2.  The io submit code path holds
   * an extra reference while submitting the i/o.
   * This prevents races between the aio code path referencing the
   * req (after submitting it) and aio_complete() freeing the req.
   */

  static struct kiocb *__aio_get_req(struct kioctx *ctx)

  {
  	struct kiocb *req = NULL;
  	struct aio_ring *ring;
  	int okay = 0;
  
  	req = kmem_cache_alloc(kiocb_cachep, GFP_KERNEL);
  	if (unlikely(!req))
  		return NULL;

  	req->ki_flags = 0;

  	req->ki_users = 2;
  	req->ki_key = 0;
  	req->ki_ctx = ctx;
  	req->ki_cancel = NULL;
  	req->ki_retry = NULL;

  	req->ki_dtor = NULL;
  	req->private = NULL;

  	req->ki_iovec = NULL;

  	INIT_LIST_HEAD(&req->ki_run_list);

  	req->ki_eventfd = NULL;

  
  	/* Check if the completion queue has enough free space to
  	 * accept an event from this io.
  	 */
  	spin_lock_irq(&ctx->ctx_lock);
  	ring = kmap_atomic(ctx->ring_info.ring_pages[0], KM_USER0);
  	if (ctx->reqs_active < aio_ring_avail(&ctx->ring_info, ring)) {
  		list_add(&req->ki_list, &ctx->active_reqs);

  		ctx->reqs_active++;
  		okay = 1;
  	}
  	kunmap_atomic(ring, KM_USER0);
  	spin_unlock_irq(&ctx->ctx_lock);
  
  	if (!okay) {
  		kmem_cache_free(kiocb_cachep, req);
  		req = NULL;
  	}
  
  	return req;
  }
  
  static inline struct kiocb *aio_get_req(struct kioctx *ctx)
  {
  	struct kiocb *req;
  	/* Handle a potential starvation case -- should be exceedingly rare as 
  	 * requests will be stuck on fput_head only if the aio_fput_routine is 
  	 * delayed and the requests were the last user of the struct file.
  	 */
  	req = __aio_get_req(ctx);
  	if (unlikely(NULL == req)) {
  		aio_fput_routine(NULL);
  		req = __aio_get_req(ctx);
  	}
  	return req;
  }
  
  static inline void really_put_req(struct kioctx *ctx, struct kiocb *req)
  {

  	assert_spin_locked(&ctx->ctx_lock);

  	if (req->ki_dtor)
  		req->ki_dtor(req);

  	if (req->ki_iovec != &req->ki_inline_vec)
  		kfree(req->ki_iovec);

  	kmem_cache_free(kiocb_cachep, req);
  	ctx->reqs_active--;
  
  	if (unlikely(!ctx->reqs_active && ctx->dead))
  		wake_up(&ctx->wait);
  }

  static void aio_fput_routine(struct work_struct *data)

  {
  	spin_lock_irq(&fput_lock);
  	while (likely(!list_empty(&fput_head))) {
  		struct kiocb *req = list_kiocb(fput_head.next);
  		struct kioctx *ctx = req->ki_ctx;
  
  		list_del(&req->ki_list);
  		spin_unlock_irq(&fput_lock);

  		/* Complete the fput(s) */
  		if (req->ki_filp != NULL)
  			__fput(req->ki_filp);
  		if (req->ki_eventfd != NULL)
  			__fput(req->ki_eventfd);

  
  		/* Link the iocb into the context's free list */
  		spin_lock_irq(&ctx->ctx_lock);
  		really_put_req(ctx, req);
  		spin_unlock_irq(&ctx->ctx_lock);
  
  		put_ioctx(ctx);
  		spin_lock_irq(&fput_lock);
  	}
  	spin_unlock_irq(&fput_lock);
  }
  
  /* __aio_put_req
   *	Returns true if this put was the last user of the request.
   */
  static int __aio_put_req(struct kioctx *ctx, struct kiocb *req)
  {

  	int schedule_putreq = 0;

  	dprintk(KERN_DEBUG "aio_put(%p): f_count=%ld
  ",
  		req, atomic_long_read(&req->ki_filp->f_count));

  	assert_spin_locked(&ctx->ctx_lock);

  	req->ki_users--;

  	BUG_ON(req->ki_users < 0);

  	if (likely(req->ki_users))
  		return 0;
  	list_del(&req->ki_list);		/* remove from active_reqs */
  	req->ki_cancel = NULL;
  	req->ki_retry = NULL;

  	/*
  	 * Try to optimize the aio and eventfd file* puts, by avoiding to
  	 * schedule work in case it is not __fput() time. In normal cases,
  	 * we would not be holding the last reference to the file*, so
  	 * this function will be executed w/out any aio kthread wakeup.

  	 */

  	if (unlikely(atomic_long_dec_and_test(&req->ki_filp->f_count)))
  		schedule_putreq++;
  	else
  		req->ki_filp = NULL;
  	if (req->ki_eventfd != NULL) {
  		if (unlikely(atomic_long_dec_and_test(&req->ki_eventfd->f_count)))
  			schedule_putreq++;
  		else
  			req->ki_eventfd = NULL;
  	}
  	if (unlikely(schedule_putreq)) {

  		get_ioctx(ctx);
  		spin_lock(&fput_lock);
  		list_add(&req->ki_list, &fput_head);
  		spin_unlock(&fput_lock);
  		queue_work(aio_wq, &fput_work);
  	} else
  		really_put_req(ctx, req);
  	return 1;
  }
  
  /* aio_put_req
   *	Returns true if this put was the last user of the kiocb,
   *	false if the request is still in use.
   */

  int aio_put_req(struct kiocb *req)

  {
  	struct kioctx *ctx = req->ki_ctx;
  	int ret;
  	spin_lock_irq(&ctx->ctx_lock);
  	ret = __aio_put_req(ctx, req);
  	spin_unlock_irq(&ctx->ctx_lock);

  	return ret;
  }

  static struct kioctx *lookup_ioctx(unsigned long ctx_id)

  {

  	struct mm_struct *mm = current->mm;

  	struct kioctx *ctx, *ret = NULL;

  	struct hlist_node *n;

  	rcu_read_lock();
  
  	hlist_for_each_entry_rcu(ctx, n, &mm->ioctx_list, list) {
  		if (ctx->user_id == ctx_id && !ctx->dead) {
  			get_ioctx(ctx);

  			ret = ctx;

  			break;
  		}

  	}

  	rcu_read_unlock();

  	return ret;

  }
  
  /*
   * use_mm
   *	Makes the calling kernel thread take on the specified
   *	mm context.
   *	Called by the retry thread execute retries within the
   *	iocb issuer's mm context, so that copy_from/to_user
   *	operations work seamlessly for aio.
   *	(Note: this routine is intended to be called only
   *	from a kernel thread context)
   */
  static void use_mm(struct mm_struct *mm)
  {
  	struct mm_struct *active_mm;
  	struct task_struct *tsk = current;
  
  	task_lock(tsk);

  	active_mm = tsk->active_mm;
  	atomic_inc(&mm->mm_count);
  	tsk->mm = mm;
  	tsk->active_mm = mm;

  	switch_mm(active_mm, mm, tsk);

  	task_unlock(tsk);
  
  	mmdrop(active_mm);
  }
  
  /*
   * unuse_mm
   *	Reverses the effect of use_mm, i.e. releases the
   *	specified mm context which was earlier taken on
   *	by the calling kernel thread
   *	(Note: this routine is intended to be called only
   *	from a kernel thread context)

   */

  static void unuse_mm(struct mm_struct *mm)

  {
  	struct task_struct *tsk = current;
  
  	task_lock(tsk);

  	tsk->mm = NULL;
  	/* active_mm is still 'mm' */
  	enter_lazy_tlb(mm, tsk);
  	task_unlock(tsk);
  }
  
  /*
   * Queue up a kiocb to be retried. Assumes that the kiocb
   * has already been marked as kicked, and places it on
   * the retry run list for the corresponding ioctx, if it
   * isn't already queued. Returns 1 if it actually queued
   * the kiocb (to tell the caller to activate the work
   * queue to process it), or 0, if it found that it was
   * already queued.

   */
  static inline int __queue_kicked_iocb(struct kiocb *iocb)
  {
  	struct kioctx *ctx = iocb->ki_ctx;

  	assert_spin_locked(&ctx->ctx_lock);

  	if (list_empty(&iocb->ki_run_list)) {
  		list_add_tail(&iocb->ki_run_list,
  			&ctx->run_list);

  		return 1;
  	}
  	return 0;
  }
  
  /* aio_run_iocb
   *	This is the core aio execution routine. It is
   *	invoked both for initial i/o submission and
   *	subsequent retries via the aio_kick_handler.
   *	Expects to be invoked with iocb->ki_ctx->lock

   *	already held. The lock is released and reacquired

   *	as needed during processing.
   *
   * Calls the iocb retry method (already setup for the
   * iocb on initial submission) for operation specific
   * handling, but takes care of most of common retry
   * execution details for a given iocb. The retry method
   * needs to be non-blocking as far as possible, to avoid
   * holding up other iocbs waiting to be serviced by the
   * retry kernel thread.
   *
   * The trickier parts in this code have to do with
   * ensuring that only one retry instance is in progress
   * for a given iocb at any time. Providing that guarantee
   * simplifies the coding of individual aio operations as
   * it avoids various potential races.
   */
  static ssize_t aio_run_iocb(struct kiocb *iocb)
  {
  	struct kioctx	*ctx = iocb->ki_ctx;
  	ssize_t (*retry)(struct kiocb *);
  	ssize_t ret;

  	if (!(retry = iocb->ki_retry)) {
  		printk("aio_run_iocb: iocb->ki_retry = NULL
  ");
  		return 0;
  	}
  
  	/*
  	 * We don't want the next retry iteration for this
  	 * operation to start until this one has returned and
  	 * updated the iocb state. However, wait_queue functions
  	 * can trigger a kick_iocb from interrupt context in the
  	 * meantime, indicating that data is available for the next
  	 * iteration. We want to remember that and enable the
  	 * next retry iteration _after_ we are through with
  	 * this one.
  	 *
  	 * So, in order to be able to register a "kick", but
  	 * prevent it from being queued now, we clear the kick
  	 * flag, but make the kick code *think* that the iocb is
  	 * still on the run list until we are actually done.
  	 * When we are done with this iteration, we check if
  	 * the iocb was kicked in the meantime and if so, queue
  	 * it up afresh.
  	 */
  
  	kiocbClearKicked(iocb);
  
  	/*
  	 * This is so that aio_complete knows it doesn't need to
  	 * pull the iocb off the run list (We can't just call
  	 * INIT_LIST_HEAD because we don't want a kick_iocb to
  	 * queue this on the run list yet)
  	 */
  	iocb->ki_run_list.next = iocb->ki_run_list.prev = NULL;
  	spin_unlock_irq(&ctx->ctx_lock);
  
  	/* Quit retrying if the i/o has been cancelled */
  	if (kiocbIsCancelled(iocb)) {
  		ret = -EINTR;
  		aio_complete(iocb, ret, 0);
  		/* must not access the iocb after this */
  		goto out;
  	}
  
  	/*
  	 * Now we are all set to call the retry method in async

  	 * context.

  	 */

  	ret = retry(iocb);

  	if (ret != -EIOCBRETRY && ret != -EIOCBQUEUED) {
  		BUG_ON(!list_empty(&iocb->ki_wait.task_list));
  		aio_complete(iocb, ret, 0);

  	}
  out:
  	spin_lock_irq(&ctx->ctx_lock);
  
  	if (-EIOCBRETRY == ret) {
  		/*
  		 * OK, now that we are done with this iteration
  		 * and know that there is more left to go,
  		 * this is where we let go so that a subsequent
  		 * "kick" can start the next iteration
  		 */
  
  		/* will make __queue_kicked_iocb succeed from here on */
  		INIT_LIST_HEAD(&iocb->ki_run_list);
  		/* we must queue the next iteration ourselves, if it
  		 * has already been kicked */
  		if (kiocbIsKicked(iocb)) {
  			__queue_kicked_iocb(iocb);

  
  			/*
  			 * __queue_kicked_iocb will always return 1 here, because
  			 * iocb->ki_run_list is empty at this point so it should
  			 * be safe to unconditionally queue the context into the
  			 * work queue.
  			 */
  			aio_queue_work(ctx);

  		}
  	}
  	return ret;
  }
  
  /*
   * __aio_run_iocbs:
   * 	Process all pending retries queued on the ioctx
   * 	run list.
   * Assumes it is operating within the aio issuer's mm

   * context.

   */
  static int __aio_run_iocbs(struct kioctx *ctx)
  {
  	struct kiocb *iocb;

  	struct list_head run_list;

  	assert_spin_locked(&ctx->ctx_lock);

  	list_replace_init(&ctx->run_list, &run_list);

  	while (!list_empty(&run_list)) {
  		iocb = list_entry(run_list.next, struct kiocb,
  			ki_run_list);
  		list_del(&iocb->ki_run_list);
  		/*
  		 * Hold an extra reference while retrying i/o.
  		 */
  		iocb->ki_users++;       /* grab extra reference */
  		aio_run_iocb(iocb);

  		__aio_put_req(ctx, iocb);

   	}

  	if (!list_empty(&ctx->run_list))
  		return 1;
  	return 0;
  }
  
  static void aio_queue_work(struct kioctx * ctx)
  {
  	unsigned long timeout;
  	/*
  	 * if someone is waiting, get the work started right
  	 * away, otherwise, use a longer delay
  	 */
  	smp_mb();
  	if (waitqueue_active(&ctx->wait))
  		timeout = 1;
  	else
  		timeout = HZ/10;
  	queue_delayed_work(aio_wq, &ctx->wq, timeout);
  }
  
  
  /*
   * aio_run_iocbs:
   * 	Process all pending retries queued on the ioctx
   * 	run list.
   * Assumes it is operating within the aio issuer's mm
   * context.
   */
  static inline void aio_run_iocbs(struct kioctx *ctx)
  {
  	int requeue;
  
  	spin_lock_irq(&ctx->ctx_lock);
  
  	requeue = __aio_run_iocbs(ctx);
  	spin_unlock_irq(&ctx->ctx_lock);
  	if (requeue)
  		aio_queue_work(ctx);
  }
  
  /*
   * just like aio_run_iocbs, but keeps running them until
   * the list stays empty
   */
  static inline void aio_run_all_iocbs(struct kioctx *ctx)
  {
  	spin_lock_irq(&ctx->ctx_lock);
  	while (__aio_run_iocbs(ctx))
  		;
  	spin_unlock_irq(&ctx->ctx_lock);
  }
  
  /*
   * aio_kick_handler:
   * 	Work queue handler triggered to process pending
   * 	retries on an ioctx. Takes on the aio issuer's
   *	mm context before running the iocbs, so that
   *	copy_xxx_user operates on the issuer's address
   *      space.
   * Run on aiod's context.
   */

  static void aio_kick_handler(struct work_struct *work)

  {

  	struct kioctx *ctx = container_of(work, struct kioctx, wq.work);

  	mm_segment_t oldfs = get_fs();

  	struct mm_struct *mm;

  	int requeue;
  
  	set_fs(USER_DS);
  	use_mm(ctx->mm);
  	spin_lock_irq(&ctx->ctx_lock);
  	requeue =__aio_run_iocbs(ctx);

  	mm = ctx->mm;

  	spin_unlock_irq(&ctx->ctx_lock);

   	unuse_mm(mm);

  	set_fs(oldfs);
  	/*
  	 * we're in a worker thread already, don't use queue_delayed_work,
  	 */
  	if (requeue)

  		queue_delayed_work(aio_wq, &ctx->wq, 0);

  }
  
  
  /*
   * Called by kick_iocb to queue the kiocb for retry
   * and if required activate the aio work queue to process
   * it
   */

  static void try_queue_kicked_iocb(struct kiocb *iocb)

  {
   	struct kioctx	*ctx = iocb->ki_ctx;
  	unsigned long flags;
  	int run = 0;

  	/* We're supposed to be the only path putting the iocb back on the run
  	 * list.  If we find that the iocb is *back* on a wait queue already
  	 * than retry has happened before we could queue the iocb.  This also
  	 * means that the retry could have completed and freed our iocb, no
  	 * good. */
  	BUG_ON((!list_empty(&iocb->ki_wait.task_list)));

  
  	spin_lock_irqsave(&ctx->ctx_lock, flags);

  	/* set this inside the lock so that we can't race with aio_run_iocb()
  	 * testing it and putting the iocb on the run list under the lock */
  	if (!kiocbTryKick(iocb))
  		run = __queue_kicked_iocb(iocb);

  	spin_unlock_irqrestore(&ctx->ctx_lock, flags);

  	if (run)

  		aio_queue_work(ctx);

  }
  
  /*
   * kick_iocb:
   *      Called typically from a wait queue callback context
   *      (aio_wake_function) to trigger a retry of the iocb.
   *      The retry is usually executed by aio workqueue
   *      threads (See aio_kick_handler).
   */

  void kick_iocb(struct kiocb *iocb)

  {
  	/* sync iocbs are easy: they can only ever be executing from a 
  	 * single context. */
  	if (is_sync_kiocb(iocb)) {
  		kiocbSetKicked(iocb);
  	        wake_up_process(iocb->ki_obj.tsk);
  		return;
  	}

  	try_queue_kicked_iocb(iocb);

  }
  EXPORT_SYMBOL(kick_iocb);
  
  /* aio_complete
   *	Called when the io request on the given iocb is complete.
   *	Returns true if this is the last user of the request.  The 
   *	only other user of the request can be the cancellation code.
   */

  int aio_complete(struct kiocb *iocb, long res, long res2)

  {
  	struct kioctx	*ctx = iocb->ki_ctx;
  	struct aio_ring_info	*info;
  	struct aio_ring	*ring;
  	struct io_event	*event;
  	unsigned long	flags;
  	unsigned long	tail;
  	int		ret;

  	/*
  	 * Special case handling for sync iocbs:
  	 *  - events go directly into the iocb for fast handling
  	 *  - the sync task with the iocb in its stack holds the single iocb
  	 *    ref, no other paths have a way to get another ref
  	 *  - the sync task helpfully left a reference to itself in the iocb

  	 */
  	if (is_sync_kiocb(iocb)) {

  		BUG_ON(iocb->ki_users != 1);

  		iocb->ki_user_data = res;

  		iocb->ki_users = 0;

  		wake_up_process(iocb->ki_obj.tsk);

  		return 1;

  	}
  
  	info = &ctx->ring_info;
  
  	/* add a completion event to the ring buffer.
  	 * must be done holding ctx->ctx_lock to prevent
  	 * other code from messing with the tail
  	 * pointer since we might be called from irq
  	 * context.
  	 */
  	spin_lock_irqsave(&ctx->ctx_lock, flags);
  
  	if (iocb->ki_run_list.prev && !list_empty(&iocb->ki_run_list))
  		list_del_init(&iocb->ki_run_list);
  
  	/*
  	 * cancelled requests don't get events, userland was given one
  	 * when the event got cancelled.
  	 */
  	if (kiocbIsCancelled(iocb))
  		goto put_rq;
  
  	ring = kmap_atomic(info->ring_pages[0], KM_IRQ1);
  
  	tail = info->tail;
  	event = aio_ring_event(info, tail, KM_IRQ0);

  	if (++tail >= info->nr)
  		tail = 0;

  
  	event->obj = (u64)(unsigned long)iocb->ki_obj.user;
  	event->data = iocb->ki_user_data;
  	event->res = res;
  	event->res2 = res2;
  
  	dprintk("aio_complete: %p[%lu]: %p: %p %Lx %lx %lx
  ",
  		ctx, tail, iocb, iocb->ki_obj.user, iocb->ki_user_data,
  		res, res2);
  
  	/* after flagging the request as done, we
  	 * must never even look at it again
  	 */
  	smp_wmb();	/* make event visible before updating tail */
  
  	info->tail = tail;
  	ring->tail = tail;
  
  	put_aio_ring_event(event, KM_IRQ0);
  	kunmap_atomic(ring, KM_IRQ1);
  
  	pr_debug("added to ring %p at [%lu]
  ", iocb, tail);

  
  	/*
  	 * Check if the user asked us to deliver the result through an
  	 * eventfd. The eventfd_signal() function is safe to be called
  	 * from IRQ context.
  	 */

  	if (iocb->ki_eventfd != NULL)

  		eventfd_signal(iocb->ki_eventfd, 1);

  put_rq:
  	/* everything turned out well, dispose of the aiocb. */
  	ret = __aio_put_req(ctx, iocb);

  	/*
  	 * We have to order our ring_info tail store above and test
  	 * of the wait list below outside the wait lock.  This is
  	 * like in wake_up_bit() where clearing a bit has to be
  	 * ordered with the unlocked test.
  	 */
  	smp_mb();

  	if (waitqueue_active(&ctx->wait))
  		wake_up(&ctx->wait);

  	spin_unlock_irqrestore(&ctx->ctx_lock, flags);

  	return ret;
  }
  
  /* aio_read_evt
   *	Pull an event off of the ioctx's event ring.  Returns the number of 
   *	events fetched (0 or 1 ;-)
   *	FIXME: make this use cmpxchg.
   *	TODO: make the ringbuffer user mmap()able (requires FIXME).
   */
  static int aio_read_evt(struct kioctx *ioctx, struct io_event *ent)
  {
  	struct aio_ring_info *info = &ioctx->ring_info;
  	struct aio_ring *ring;
  	unsigned long head;
  	int ret = 0;
  
  	ring = kmap_atomic(info->ring_pages[0], KM_USER0);
  	dprintk("in aio_read_evt h%lu t%lu m%lu
  ",
  		 (unsigned long)ring->head, (unsigned long)ring->tail,
  		 (unsigned long)ring->nr);
  
  	if (ring->head == ring->tail)
  		goto out;
  
  	spin_lock(&info->ring_lock);
  
  	head = ring->head % info->nr;
  	if (head != ring->tail) {
  		struct io_event *evp = aio_ring_event(info, head, KM_USER1);
  		*ent = *evp;
  		head = (head + 1) % info->nr;
  		smp_mb(); /* finish reading the event before updatng the head */
  		ring->head = head;
  		ret = 1;
  		put_aio_ring_event(evp, KM_USER1);
  	}
  	spin_unlock(&info->ring_lock);
  
  out:
  	kunmap_atomic(ring, KM_USER0);
  	dprintk("leaving aio_read_evt: %d  h%lu t%lu
  ", ret,
  		 (unsigned long)ring->head, (unsigned long)ring->tail);
  	return ret;
  }
  
  struct aio_timeout {
  	struct timer_list	timer;
  	int			timed_out;
  	struct task_struct	*p;
  };
  
  static void timeout_func(unsigned long data)
  {
  	struct aio_timeout *to = (struct aio_timeout *)data;
  
  	to->timed_out = 1;
  	wake_up_process(to->p);
  }
  
  static inline void init_timeout(struct aio_timeout *to)
  {

  	setup_timer_on_stack(&to->timer, timeout_func, (unsigned long) to);

  	to->timed_out = 0;
  	to->p = current;
  }
  
  static inline void set_timeout(long start_jiffies, struct aio_timeout *to,
  			       const struct timespec *ts)
  {
  	to->timer.expires = start_jiffies + timespec_to_jiffies(ts);
  	if (time_after(to->timer.expires, jiffies))
  		add_timer(&to->timer);
  	else
  		to->timed_out = 1;
  }
  
  static inline void clear_timeout(struct aio_timeout *to)
  {
  	del_singleshot_timer_sync(&to->timer);
  }
  
  static int read_events(struct kioctx *ctx,
  			long min_nr, long nr,
  			struct io_event __user *event,
  			struct timespec __user *timeout)
  {
  	long			start_jiffies = jiffies;
  	struct task_struct	*tsk = current;
  	DECLARE_WAITQUEUE(wait, tsk);
  	int			ret;
  	int			i = 0;
  	struct io_event		ent;
  	struct aio_timeout	to;

  	int			retry = 0;
  
  	/* needed to zero any padding within an entry (there shouldn't be 
  	 * any, but C is fun!
  	 */
  	memset(&ent, 0, sizeof(ent));
  retry:
  	ret = 0;
  	while (likely(i < nr)) {
  		ret = aio_read_evt(ctx, &ent);
  		if (unlikely(ret <= 0))
  			break;
  
  		dprintk("read event: %Lx %Lx %Lx %Lx
  ",
  			ent.data, ent.obj, ent.res, ent.res2);
  
  		/* Could we split the check in two? */
  		ret = -EFAULT;
  		if (unlikely(copy_to_user(event, &ent, sizeof(ent)))) {
  			dprintk("aio: lost an event due to EFAULT.
  ");
  			break;
  		}
  		ret = 0;
  
  		/* Good, event copied to userland, update counts. */
  		event ++;
  		i ++;
  	}
  
  	if (min_nr <= i)
  		return i;
  	if (ret)
  		return ret;
  
  	/* End fast path */
  
  	/* racey check, but it gets redone */
  	if (!retry && unlikely(!list_empty(&ctx->run_list))) {
  		retry = 1;
  		aio_run_all_iocbs(ctx);
  		goto retry;
  	}
  
  	init_timeout(&to);
  	if (timeout) {
  		struct timespec	ts;
  		ret = -EFAULT;
  		if (unlikely(copy_from_user(&ts, timeout, sizeof(ts))))
  			goto out;
  
  		set_timeout(start_jiffies, &to, &ts);
  	}
  
  	while (likely(i < nr)) {
  		add_wait_queue_exclusive(&ctx->wait, &wait);
  		do {
  			set_task_state(tsk, TASK_INTERRUPTIBLE);
  			ret = aio_read_evt(ctx, &ent);
  			if (ret)
  				break;
  			if (min_nr <= i)
  				break;

  			if (unlikely(ctx->dead)) {
  				ret = -EINVAL;
  				break;
  			}

  			if (to.timed_out)	/* Only check after read evt */
  				break;

  			/* Try to only show up in io wait if there are ops
  			 *  in flight */
  			if (ctx->reqs_active)
  				io_schedule();
  			else
  				schedule();

  			if (signal_pending(tsk)) {
  				ret = -EINTR;
  				break;
  			}
  			/*ret = aio_read_evt(ctx, &ent);*/
  		} while (1) ;
  
  		set_task_state(tsk, TASK_RUNNING);
  		remove_wait_queue(&ctx->wait, &wait);
  
  		if (unlikely(ret <= 0))
  			break;
  
  		ret = -EFAULT;
  		if (unlikely(copy_to_user(event, &ent, sizeof(ent)))) {
  			dprintk("aio: lost an event due to EFAULT.
  ");
  			break;
  		}
  
  		/* Good, event copied to userland, update counts. */
  		event ++;
  		i ++;
  	}
  
  	if (timeout)
  		clear_timeout(&to);
  out:

  	destroy_timer_on_stack(&to.timer);

  	return i ? i : ret;
  }
  
  /* Take an ioctx and remove it from the list of ioctx's.  Protects 
   * against races with itself via ->dead.
   */
  static void io_destroy(struct kioctx *ioctx)
  {
  	struct mm_struct *mm = current->mm;

  	int was_dead;
  
  	/* delete the entry from the list is someone else hasn't already */

  	spin_lock(&mm->ioctx_lock);

  	was_dead = ioctx->dead;
  	ioctx->dead = 1;

  	hlist_del_rcu(&ioctx->list);
  	spin_unlock(&mm->ioctx_lock);

  
  	dprintk("aio_release(%p)
  ", ioctx);
  	if (likely(!was_dead))
  		put_ioctx(ioctx);	/* twice for the list */
  
  	aio_cancel_all(ioctx);
  	wait_for_all_aios(ioctx);

  
  	/*
  	 * Wake up any waiters.  The setting of ctx->dead must be seen
  	 * by other CPUs at this point.  Right now, we rely on the
  	 * locking done by the above calls to ensure this consistency.
  	 */
  	wake_up(&ioctx->wait);

  	put_ioctx(ioctx);	/* once for the lookup */
  }
  
  /* sys_io_setup:
   *	Create an aio_context capable of receiving at least nr_events.
   *	ctxp must not point to an aio_context that already exists, and
   *	must be initialized to 0 prior to the call.  On successful
   *	creation of the aio_context, *ctxp is filled in with the resulting 
   *	handle.  May fail with -EINVAL if *ctxp is not initialized,
   *	if the specified nr_events exceeds internal limits.  May fail 
   *	with -EAGAIN if the specified nr_events exceeds the user's limit 
   *	of available events.  May fail with -ENOMEM if insufficient kernel
   *	resources are available.  May fail with -EFAULT if an invalid
   *	pointer is passed for ctxp.  Will fail with -ENOSYS if not
   *	implemented.
   */

  SYSCALL_DEFINE2(io_setup, unsigned, nr_events, aio_context_t __user *, ctxp)

  {
  	struct kioctx *ioctx = NULL;
  	unsigned long ctx;
  	long ret;
  
  	ret = get_user(ctx, ctxp);
  	if (unlikely(ret))
  		goto out;
  
  	ret = -EINVAL;

  	if (unlikely(ctx || nr_events == 0)) {
  		pr_debug("EINVAL: io_setup: ctx %lu nr_events %u
  ",
  		         ctx, nr_events);

  		goto out;
  	}
  
  	ioctx = ioctx_alloc(nr_events);
  	ret = PTR_ERR(ioctx);
  	if (!IS_ERR(ioctx)) {
  		ret = put_user(ioctx->user_id, ctxp);
  		if (!ret)
  			return 0;
  
  		get_ioctx(ioctx); /* io_destroy() expects us to hold a ref */
  		io_destroy(ioctx);
  	}
  
  out:
  	return ret;
  }
  
  /* sys_io_destroy:
   *	Destroy the aio_context specified.  May cancel any outstanding 
   *	AIOs and block on completion.  Will fail with -ENOSYS if not
   *	implemented.  May fail with -EFAULT if the context pointed to
   *	is invalid.
   */

  SYSCALL_DEFINE1(io_destroy, aio_context_t, ctx)

  {
  	struct kioctx *ioctx = lookup_ioctx(ctx);
  	if (likely(NULL != ioctx)) {
  		io_destroy(ioctx);
  		return 0;
  	}
  	pr_debug("EINVAL: io_destroy: invalid context id
  ");
  	return -EINVAL;
  }

  static void aio_advance_iovec(struct kiocb *iocb, ssize_t ret)

  {

  	struct iovec *iov = &iocb->ki_iovec[iocb->ki_cur_seg];
  
  	BUG_ON(ret <= 0);
  
  	while (iocb->ki_cur_seg < iocb->ki_nr_segs && ret > 0) {
  		ssize_t this = min((ssize_t)iov->iov_len, ret);
  		iov->iov_base += this;
  		iov->iov_len -= this;
  		iocb->ki_left -= this;
  		ret -= this;
  		if (iov->iov_len == 0) {
  			iocb->ki_cur_seg++;
  			iov++;

  		}

  	}

  	/* the caller should not have done more io than what fit in
  	 * the remaining iovecs */
  	BUG_ON(ret > 0 && iocb->ki_left == 0);

  }

  static ssize_t aio_rw_vect_retry(struct kiocb *iocb)

  {
  	struct file *file = iocb->ki_filp;

  	struct address_space *mapping = file->f_mapping;
  	struct inode *inode = mapping->host;
  	ssize_t (*rw_op)(struct kiocb *, const struct iovec *,
  			 unsigned long, loff_t);

  	ssize_t ret = 0;

  	unsigned short opcode;
  
  	if ((iocb->ki_opcode == IOCB_CMD_PREADV) ||
  		(iocb->ki_opcode == IOCB_CMD_PREAD)) {
  		rw_op = file->f_op->aio_read;
  		opcode = IOCB_CMD_PREADV;
  	} else {
  		rw_op = file->f_op->aio_write;
  		opcode = IOCB_CMD_PWRITEV;
  	}

  	/* This matches the pread()/pwrite() logic */
  	if (iocb->ki_pos < 0)
  		return -EINVAL;

  	do {

  		ret = rw_op(iocb, &iocb->ki_iovec[iocb->ki_cur_seg],
  			    iocb->ki_nr_segs - iocb->ki_cur_seg,
  			    iocb->ki_pos);
  		if (ret > 0)
  			aio_advance_iovec(iocb, ret);
  
  	/* retry all partial writes.  retry partial reads as long as its a
  	 * regular file. */
  	} while (ret > 0 && iocb->ki_left > 0 &&
  		 (opcode == IOCB_CMD_PWRITEV ||
  		  (!S_ISFIFO(inode->i_mode) && !S_ISSOCK(inode->i_mode))));

  	/* This means we must have transferred all that we could */
  	/* No need to retry anymore */

  	if ((ret == 0) || (iocb->ki_left == 0))
  		ret = iocb->ki_nbytes - iocb->ki_left;

  	/* If we managed to write some out we return that, rather than
  	 * the eventual error. */
  	if (opcode == IOCB_CMD_PWRITEV
  	    && ret < 0 && ret != -EIOCBQUEUED && ret != -EIOCBRETRY
  	    && iocb->ki_nbytes - iocb->ki_left)
  		ret = iocb->ki_nbytes - iocb->ki_left;

  	return ret;
  }
  
  static ssize_t aio_fdsync(struct kiocb *iocb)
  {
  	struct file *file = iocb->ki_filp;
  	ssize_t ret = -EINVAL;
  
  	if (file->f_op->aio_fsync)
  		ret = file->f_op->aio_fsync(iocb, 1);
  	return ret;
  }
  
  static ssize_t aio_fsync(struct kiocb *iocb)
  {
  	struct file *file = iocb->ki_filp;
  	ssize_t ret = -EINVAL;
  
  	if (file->f_op->aio_fsync)
  		ret = file->f_op->aio_fsync(iocb, 0);
  	return ret;
  }

  static ssize_t aio_setup_vectored_rw(int type, struct kiocb *kiocb)
  {
  	ssize_t ret;
  
  	ret = rw_copy_check_uvector(type, (struct iovec __user *)kiocb->ki_buf,
  				    kiocb->ki_nbytes, 1,
  				    &kiocb->ki_inline_vec, &kiocb->ki_iovec);
  	if (ret < 0)
  		goto out;
  
  	kiocb->ki_nr_segs = kiocb->ki_nbytes;
  	kiocb->ki_cur_seg = 0;
  	/* ki_nbytes/left now reflect bytes instead of segs */
  	kiocb->ki_nbytes = ret;
  	kiocb->ki_left = ret;
  
  	ret = 0;
  out:
  	return ret;
  }
  
  static ssize_t aio_setup_single_vector(struct kiocb *kiocb)
  {
  	kiocb->ki_iovec = &kiocb->ki_inline_vec;
  	kiocb->ki_iovec->iov_base = kiocb->ki_buf;
  	kiocb->ki_iovec->iov_len = kiocb->ki_left;
  	kiocb->ki_nr_segs = 1;
  	kiocb->ki_cur_seg = 0;

  	return 0;
  }

  /*
   * aio_setup_iocb:
   *	Performs the initial checks and aio retry method
   *	setup for the kiocb at the time of io submission.
   */

  static ssize_t aio_setup_iocb(struct kiocb *kiocb)

  {
  	struct file *file = kiocb->ki_filp;
  	ssize_t ret = 0;
  
  	switch (kiocb->ki_opcode) {
  	case IOCB_CMD_PREAD:
  		ret = -EBADF;
  		if (unlikely(!(file->f_mode & FMODE_READ)))
  			break;
  		ret = -EFAULT;
  		if (unlikely(!access_ok(VERIFY_WRITE, kiocb->ki_buf,
  			kiocb->ki_left)))
  			break;

  		ret = security_file_permission(file, MAY_READ);
  		if (unlikely(ret))
  			break;

  		ret = aio_setup_single_vector(kiocb);
  		if (ret)
  			break;

  		ret = -EINVAL;
  		if (file->f_op->aio_read)

  			kiocb->ki_retry = aio_rw_vect_retry;

  		break;
  	case IOCB_CMD_PWRITE:
  		ret = -EBADF;
  		if (unlikely(!(file->f_mode & FMODE_WRITE)))
  			break;
  		ret = -EFAULT;
  		if (unlikely(!access_ok(VERIFY_READ, kiocb->ki_buf,
  			kiocb->ki_left)))
  			break;

  		ret = security_file_permission(file, MAY_WRITE);
  		if (unlikely(ret))
  			break;

  		ret = aio_setup_single_vector(kiocb);
  		if (ret)
  			break;
  		ret = -EINVAL;
  		if (file->f_op->aio_write)
  			kiocb->ki_retry = aio_rw_vect_retry;
  		break;
  	case IOCB_CMD_PREADV:
  		ret = -EBADF;
  		if (unlikely(!(file->f_mode & FMODE_READ)))
  			break;
  		ret = security_file_permission(file, MAY_READ);
  		if (unlikely(ret))
  			break;
  		ret = aio_setup_vectored_rw(READ, kiocb);
  		if (ret)
  			break;
  		ret = -EINVAL;
  		if (file->f_op->aio_read)
  			kiocb->ki_retry = aio_rw_vect_retry;
  		break;
  	case IOCB_CMD_PWRITEV:
  		ret = -EBADF;
  		if (unlikely(!(file->f_mode & FMODE_WRITE)))
  			break;
  		ret = security_file_permission(file, MAY_WRITE);
  		if (unlikely(ret))
  			break;
  		ret = aio_setup_vectored_rw(WRITE, kiocb);
  		if (ret)
  			break;

  		ret = -EINVAL;
  		if (file->f_op->aio_write)

  			kiocb->ki_retry = aio_rw_vect_retry;

  		break;
  	case IOCB_CMD_FDSYNC:
  		ret = -EINVAL;
  		if (file->f_op->aio_fsync)
  			kiocb->ki_retry = aio_fdsync;
  		break;
  	case IOCB_CMD_FSYNC:
  		ret = -EINVAL;
  		if (file->f_op->aio_fsync)
  			kiocb->ki_retry = aio_fsync;
  		break;
  	default:
  		dprintk("EINVAL: io_submit: no operation provided
  ");
  		ret = -EINVAL;
  	}
  
  	if (!kiocb->ki_retry)
  		return ret;
  
  	return 0;
  }
  
  /*
   * aio_wake_function:
   * 	wait queue callback function for aio notification,
   * 	Simply triggers a retry of the operation via kick_iocb.
   *
   * 	This callback is specified in the wait queue entry in

   *	a kiocb.

   *
   * Note:
   * This routine is executed with the wait queue lock held.
   * Since kick_iocb acquires iocb->ctx->ctx_lock, it nests
   * the ioctx lock inside the wait queue lock. This is safe
   * because this callback isn't used for wait queues which
   * are nested inside ioctx lock (i.e. ctx->wait)
   */

  static int aio_wake_function(wait_queue_t *wait, unsigned mode,
  			     int sync, void *key)

  {
  	struct kiocb *iocb = container_of(wait, struct kiocb, ki_wait);
  
  	list_del_init(&wait->task_list);
  	kick_iocb(iocb);
  	return 1;
  }

  static int io_submit_one(struct kioctx *ctx, struct iocb __user *user_iocb,

  			 struct iocb *iocb)
  {
  	struct kiocb *req;
  	struct file *file;
  	ssize_t ret;
  
  	/* enforce forwards compatibility on users */

  	if (unlikely(iocb->aio_reserved1 || iocb->aio_reserved2)) {

  		pr_debug("EINVAL: io_submit: reserve field set
  ");
  		return -EINVAL;
  	}
  
  	/* prevent overflows */
  	if (unlikely(
  	    (iocb->aio_buf != (unsigned long)iocb->aio_buf) ||
  	    (iocb->aio_nbytes != (size_t)iocb->aio_nbytes) ||
  	    ((ssize_t)iocb->aio_nbytes < 0)
  	   )) {
  		pr_debug("EINVAL: io_submit: overflow check
  ");
  		return -EINVAL;
  	}
  
  	file = fget(iocb->aio_fildes);
  	if (unlikely(!file))
  		return -EBADF;
  
  	req = aio_get_req(ctx);		/* returns with 2 references to req */
  	if (unlikely(!req)) {
  		fput(file);
  		return -EAGAIN;
  	}

  	req->ki_filp = file;

  	if (iocb->aio_flags & IOCB_FLAG_RESFD) {
  		/*
  		 * If the IOCB_FLAG_RESFD flag of aio_flags is set, get an
  		 * instance of the file* now. The file descriptor must be
  		 * an eventfd() fd, and will be signaled for each completed
  		 * event using the eventfd_signal() function.
  		 */
  		req->ki_eventfd = eventfd_fget((int) iocb->aio_resfd);

  		if (IS_ERR(req->ki_eventfd)) {

  			ret = PTR_ERR(req->ki_eventfd);

  			req->ki_eventfd = NULL;

  			goto out_put_req;
  		}
  	}

  	ret = put_user(req->ki_key, &user_iocb->aio_key);

  	if (unlikely(ret)) {
  		dprintk("EFAULT: aio_key
  ");
  		goto out_put_req;
  	}
  
  	req->ki_obj.user = user_iocb;
  	req->ki_user_data = iocb->aio_data;
  	req->ki_pos = iocb->aio_offset;
  
  	req->ki_buf = (char __user *)(unsigned long)iocb->aio_buf;
  	req->ki_left = req->ki_nbytes = iocb->aio_nbytes;
  	req->ki_opcode = iocb->aio_lio_opcode;
  	init_waitqueue_func_entry(&req->ki_wait, aio_wake_function);
  	INIT_LIST_HEAD(&req->ki_wait.task_list);

  
  	ret = aio_setup_iocb(req);
  
  	if (ret)
  		goto out_put_req;
  
  	spin_lock_irq(&ctx->ctx_lock);

  	aio_run_iocb(req);

  	if (!list_empty(&ctx->run_list)) {

  		/* drain the run list */
  		while (__aio_run_iocbs(ctx))
  			;
  	}

  	spin_unlock_irq(&ctx->ctx_lock);
  	aio_put_req(req);	/* drop extra ref to req */
  	return 0;
  
  out_put_req:
  	aio_put_req(req);	/* drop extra ref to req */
  	aio_put_req(req);	/* drop i/o ref to req */
  	return ret;
  }
  
  /* sys_io_submit:
   *	Queue the nr iocbs pointed to by iocbpp for processing.  Returns
   *	the number of iocbs queued.  May return -EINVAL if the aio_context
   *	specified by ctx_id is invalid, if nr is < 0, if the iocb at
   *	*iocbpp[0] is not properly initialized, if the operation specified
   *	is invalid for the file descriptor in the iocb.  May fail with
   *	-EFAULT if any of the data structures point to invalid data.  May
   *	fail with -EBADF if the file descriptor specified in the first
   *	iocb is invalid.  May fail with -EAGAIN if insufficient resources
   *	are available to queue any iocbs.  Will return 0 if nr is 0.  Will
   *	fail with -ENOSYS if not implemented.
   */

  SYSCALL_DEFINE3(io_submit, aio_context_t, ctx_id, long, nr,
  		struct iocb __user * __user *, iocbpp)

  {
  	struct kioctx *ctx;
  	long ret = 0;
  	int i;
  
  	if (unlikely(nr < 0))
  		return -EINVAL;
  
  	if (unlikely(!access_ok(VERIFY_READ, iocbpp, (nr*sizeof(*iocbpp)))))
  		return -EFAULT;
  
  	ctx = lookup_ioctx(ctx_id);
  	if (unlikely(!ctx)) {
  		pr_debug("EINVAL: io_submit: invalid context id
  ");
  		return -EINVAL;
  	}
  
  	/*
  	 * AKPM: should this return a partial result if some of the IOs were
  	 * successfully submitted?
  	 */
  	for (i=0; i<nr; i++) {
  		struct iocb __user *user_iocb;
  		struct iocb tmp;
  
  		if (unlikely(__get_user(user_iocb, iocbpp + i))) {
  			ret = -EFAULT;
  			break;
  		}
  
  		if (unlikely(copy_from_user(&tmp, user_iocb, sizeof(tmp)))) {
  			ret = -EFAULT;
  			break;
  		}
  
  		ret = io_submit_one(ctx, user_iocb, &tmp);
  		if (ret)
  			break;
  	}
  
  	put_ioctx(ctx);
  	return i ? i : ret;
  }
  
  /* lookup_kiocb
   *	Finds a given iocb for cancellation.

   */

  static struct kiocb *lookup_kiocb(struct kioctx *ctx, struct iocb __user *iocb,
  				  u32 key)

  {
  	struct list_head *pos;

  
  	assert_spin_locked(&ctx->ctx_lock);

  	/* TODO: use a hash or array, this sucks. */
  	list_for_each(pos, &ctx->active_reqs) {
  		struct kiocb *kiocb = list_kiocb(pos);
  		if (kiocb->ki_obj.user == iocb && kiocb->ki_key == key)
  			return kiocb;
  	}
  	return NULL;
  }
  
  /* sys_io_cancel:
   *	Attempts to cancel an iocb previously passed to io_submit.  If
   *	the operation is successfully cancelled, the resulting event is
   *	copied into the memory pointed to by result without being placed
   *	into the completion queue and 0 is returned.  May fail with
   *	-EFAULT if any of the data structures pointed to are invalid.
   *	May fail with -EINVAL if aio_context specified by ctx_id is
   *	invalid.  May fail with -EAGAIN if the iocb specified was not
   *	cancelled.  Will fail with -ENOSYS if not implemented.
   */

  SYSCALL_DEFINE3(io_cancel, aio_context_t, ctx_id, struct iocb __user *, iocb,
  		struct io_event __user *, result)

  {
  	int (*cancel)(struct kiocb *iocb, struct io_event *res);
  	struct kioctx *ctx;
  	struct kiocb *kiocb;
  	u32 key;
  	int ret;
  
  	ret = get_user(key, &iocb->aio_key);
  	if (unlikely(ret))
  		return -EFAULT;
  
  	ctx = lookup_ioctx(ctx_id);
  	if (unlikely(!ctx))
  		return -EINVAL;
  
  	spin_lock_irq(&ctx->ctx_lock);
  	ret = -EAGAIN;
  	kiocb = lookup_kiocb(ctx, iocb, key);
  	if (kiocb && kiocb->ki_cancel) {
  		cancel = kiocb->ki_cancel;
  		kiocb->ki_users ++;
  		kiocbSetCancelled(kiocb);
  	} else
  		cancel = NULL;
  	spin_unlock_irq(&ctx->ctx_lock);
  
  	if (NULL != cancel) {
  		struct io_event tmp;
  		pr_debug("calling cancel
  ");
  		memset(&tmp, 0, sizeof(tmp));
  		tmp.obj = (u64)(unsigned long)kiocb->ki_obj.user;
  		tmp.data = kiocb->ki_user_data;
  		ret = cancel(kiocb, &tmp);
  		if (!ret) {
  			/* Cancellation succeeded -- copy the result
  			 * into the user's buffer.
  			 */
  			if (copy_to_user(result, &tmp, sizeof(tmp)))
  				ret = -EFAULT;
  		}
  	} else

  		ret = -EINVAL;

  
  	put_ioctx(ctx);
  
  	return ret;
  }
  
  /* io_getevents:
   *	Attempts to read at least min_nr events and up to nr events from
   *	the completion queue for the aio_context specified by ctx_id.  May
   *	fail with -EINVAL if ctx_id is invalid, if min_nr is out of range,
   *	if nr is out of range, if when is out of range.  May fail with
   *	-EFAULT if any of the memory specified to is invalid.  May return
   *	0 or < min_nr if no events are available and the timeout specified
   *	by when	has elapsed, where when == NULL specifies an infinite
   *	timeout.  Note that the timeout pointed to by when is relative and
   *	will be updated if not NULL and the operation blocks.  Will fail
   *	with -ENOSYS if not implemented.
   */

  SYSCALL_DEFINE5(io_getevents, aio_context_t, ctx_id,
  		long, min_nr,
  		long, nr,
  		struct io_event __user *, events,
  		struct timespec __user *, timeout)

  {
  	struct kioctx *ioctx = lookup_ioctx(ctx_id);
  	long ret = -EINVAL;
  
  	if (likely(ioctx)) {
  		if (likely(min_nr <= nr && min_nr >= 0 && nr >= 0))
  			ret = read_events(ioctx, min_nr, nr, events, timeout);
  		put_ioctx(ioctx);
  	}

  	asmlinkage_protect(5, ret, ctx_id, min_nr, nr, events, timeout);

  	return ret;
  }
  
  __initcall(aio_setup);
  
  EXPORT_SYMBOL(aio_complete);
  EXPORT_SYMBOL(aio_put_req);
  EXPORT_SYMBOL(wait_on_sync_kiocb);