/*
 *      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\n", (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\n", 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\n", 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)


/* __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)
{
        unsigned nr_events = ctx->max_reqs;

        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\n", ctx);
        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);
        }
}

#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;

        /* Prevent overflows */
        if ((nr_events > (0x10000000U / sizeof(struct io_event))) ||
            (nr_events > (0x10000000U / sizeof(struct kiocb)))) {
                pr_debug("ENOMEM: nr_events too high\n");
                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 */
        spin_lock(&aio_nr_lock);
        if (aio_nr + ctx->max_reqs > aio_max_nr ||
            aio_nr + ctx->max_reqs < aio_nr)
                ctx->max_reqs = 0;
        else
                aio_nr += ctx->max_reqs;
        spin_unlock(&aio_nr_lock);
        if (ctx->max_reqs == 0)
                goto out_cleanup;

        /* now link into global list. */
        write_lock(&mm->ioctx_list_lock);
        ctx->next = mm->ioctx_list;
        mm->ioctx_list = ctx;
        write_unlock(&mm->ioctx_list_lock);

        dprintk("aio: allocated ioctx %p[%ld]: mm=%p mask=0x%x\n",
                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\n", 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 = mm->ioctx_list;
        mm->ioctx_list = NULL;
        while (ctx) {
                struct kioctx *next = ctx->next;
                ctx->next = NULL;
                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\n",
                                atomic_read(&ctx->users), ctx->dead,
                                ctx->reqs_active);
                put_ioctx(ctx);
                ctx = next;
        }
}

/* 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 = ERR_PTR(-EINVAL);

        /* 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 (!IS_ERR(req->ki_eventfd))
                fput(req->ki_eventfd);
        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 */
                __fput(req->ki_filp);

                /* 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)
{
        dprintk(KERN_DEBUG "aio_put(%p): f_count=%ld\n",
                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;

        /* Must be done under the lock to serialise against cancellation.
         * Call this aio_fput as it duplicates fput via the fput_work.
         */
        if (unlikely(atomic_long_dec_and_test(&req->ki_filp->f_count))) {
                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 kioctx *ioctx;
        struct mm_struct *mm;

        mm = current->mm;
        read_lock(&mm->ioctx_list_lock);
        for (ioctx = mm->ioctx_list; ioctx; ioctx = ioctx->next)
                if (likely(ioctx->user_id == ctx_id && !ioctx->dead)) {
                        get_ioctx(ioctx);
                        break;
                }
        read_unlock(&mm->ioctx_list_lock);

        return ioctx;
}

/*
 * 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\n");
                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\n",
                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]\n", 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 (!IS_ERR(iocb->ki_eventfd))
                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\n",
                 (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\n", 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\n",
                        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.\n");
                        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.\n");
                        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;
        struct kioctx **tmp;
        int was_dead;

        /* delete the entry from the list is someone else hasn't already */
        write_lock(&mm->ioctx_list_lock);
        was_dead = ioctx->dead;
        ioctx->dead = 1;
        for (tmp = &mm->ioctx_list; *tmp && *tmp != ioctx;
             tmp = &(*tmp)->next)
                ;
        if (*tmp)
                *tmp = ioctx->next;
        write_unlock(&mm->ioctx_list_lock);

        dprintk("aio_release(%p)\n", 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\n",
                         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\n");
        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\n");
                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\n");
                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\n");
                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);
                        goto out_put_req;
                }
        }

        ret = put_user(req->ki_key, &user_iocb->aio_key);
        if (unlikely(ret)) {
                dprintk("EFAULT: aio_key\n");
                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\n");
                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\n");
                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);