aio.c

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/*
 *  An async IO implementation for Linux
 *  Written by Benjamin LaHaise <[email protected]>
 *
 *  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/export.h>
#include <linux/syscalls.h>
#include <linux/backing-dev.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/mmu_context.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 <linux/blkdev.h>
#include <linux/compat.h>

#include <asm/kmap_types.h>
#include <asm/uaccess.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;

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 = alloc_workqueue("aio", 0, 1);  /* used to limit concurrency */
    BUG_ON(!aio_wq);

    pr_debug("aio_setup: sizeof(struct page) = %d\n", (int)sizeof(struct page));

    return 0;
}
__initcall(aio_setup);

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) {
        BUG_ON(ctx->mm != current->mm);
        vm_munmap(info->mmap_base, info->mmap_size);
    }

    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_pgoff(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]);
    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);

    return 0;
}


/* aio_ring_event: returns a pointer to the event at the given index from
 * kmap_atomic().  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) ({                 \
    unsigned pos = (nr) + AIO_EVENTS_OFFSET;            \
    struct io_event *__event;                   \
    __event = kmap_atomic(                      \
            (info)->ring_pages[pos / AIO_EVENTS_PER_PAGE]); \
    __event += pos % AIO_EVENTS_PER_PAGE;               \
    __event;                            \
})

#define put_aio_ring_event(event) do {      \
    struct io_event *__event = (event); \
    (void)__event;              \
    kunmap_atomic((void *)((unsigned long)__event & PAGE_MASK)); \
} while(0)

static void ctx_rcu_free(struct rcu_head *head)
{
    struct kioctx *ctx = container_of(head, struct kioctx, rcu_head);
    kmem_cache_free(kioctx_cachep, ctx);
}

/* __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_sync(&ctx->wq);
    aio_free_ring(ctx);
    mmdrop(ctx->mm);
    ctx->mm = NULL;
    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);
    }
    pr_debug("__put_ioctx: freeing %p\n", ctx);
    call_rcu(&ctx->rcu_head, ctx_rcu_free);
}

static inline int try_get_ioctx(struct kioctx *kioctx)
{
    return atomic_inc_not_zero(&kioctx->users);
}

static inline void put_ioctx(struct kioctx *kioctx)
{
    BUG_ON(atomic_read(&kioctx->users) <= 0);
    if (unlikely(atomic_dec_and_test(&kioctx->users)))
        __put_ioctx(kioctx);
}

/* 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 err = -ENOMEM;

    /* 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 (!nr_events || (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, 2);
    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 + nr_events > aio_max_nr ||
        aio_nr + nr_events < aio_nr) {
        spin_unlock(&aio_nr_lock);
        goto out_cleanup;
    }
    aio_nr += ctx->max_reqs;
    spin_unlock(&aio_nr_lock);

    /* 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\n",
        ctx, ctx->user_id, current->mm, ctx->ring_info.nr);
    return ctx;

out_cleanup:
    err = -EAGAIN;
    aio_free_ring(ctx);
out_freectx:
    mmdrop(mm);
    kmem_cache_free(kioctx_cachep, ctx);
    dprintk("aio: error allocating ioctx %d\n", err);
    return ERR_PTR(err);
}

/* kill_ctx
 *  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 kill_ctx(struct kioctx *ctx)
{
    int (*cancel)(struct kiocb *, struct io_event *);
    struct task_struct *tsk = current;
    DECLARE_WAITQUEUE(wait, tsk);
    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);
        }
    }

    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;
}
EXPORT_SYMBOL(wait_on_sync_kiocb);

/* 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);

        kill_ctx(ctx);

        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);
        /*
         * We don't need to bother with munmap() here -
         * exit_mmap(mm) is coming and it'll unmap everything.
         * Since aio_free_ring() uses non-zero ->mmap_size
         * as indicator that it needs to unmap the area,
         * just set it to 0; aio_free_ring() is the only
         * place that uses ->mmap_size, so it's safe.
         * That way we get all munmap done to current->mm -
         * all other callers have ctx->mm == current->mm.
         */
        ctx->ring_info.mmap_size = 0;
        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;

    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;

    return req;
}

/*
 * struct kiocb's are allocated in batches to reduce the number of
 * times the ctx lock is acquired and released.
 */
#define KIOCB_BATCH_SIZE    32L
struct kiocb_batch {
    struct list_head head;
    long count; /* number of requests left to allocate */
};

static void kiocb_batch_init(struct kiocb_batch *batch, long total)
{
    INIT_LIST_HEAD(&batch->head);
    batch->count = total;
}

static void kiocb_batch_free(struct kioctx *ctx, struct kiocb_batch *batch)
{
    struct kiocb *req, *n;

    if (list_empty(&batch->head))
        return;

    spin_lock_irq(&ctx->ctx_lock);
    list_for_each_entry_safe(req, n, &batch->head, ki_batch) {
        list_del(&req->ki_batch);
        list_del(&req->ki_list);
        kmem_cache_free(kiocb_cachep, req);
        ctx->reqs_active--;
    }
    if (unlikely(!ctx->reqs_active && ctx->dead))
        wake_up_all(&ctx->wait);
    spin_unlock_irq(&ctx->ctx_lock);
}

/*
 * Allocate a batch of kiocbs.  This avoids taking and dropping the
 * context lock a lot during setup.
 */
static int kiocb_batch_refill(struct kioctx *ctx, struct kiocb_batch *batch)
{
    unsigned short allocated, to_alloc;
    long avail;
    struct kiocb *req, *n;
    struct aio_ring *ring;

    to_alloc = min(batch->count, KIOCB_BATCH_SIZE);
    for (allocated = 0; allocated < to_alloc; allocated++) {
        req = __aio_get_req(ctx);
        if (!req)
            /* allocation failed, go with what we've got */
            break;
        list_add(&req->ki_batch, &batch->head);
    }

    if (allocated == 0)
        goto out;

    spin_lock_irq(&ctx->ctx_lock);
    ring = kmap_atomic(ctx->ring_info.ring_pages[0]);

    avail = aio_ring_avail(&ctx->ring_info, ring) - ctx->reqs_active;
    BUG_ON(avail < 0);
    if (avail < allocated) {
        /* Trim back the number of requests. */
        list_for_each_entry_safe(req, n, &batch->head, ki_batch) {
            list_del(&req->ki_batch);
            kmem_cache_free(kiocb_cachep, req);
            if (--allocated <= avail)
                break;
        }
    }

    batch->count -= allocated;
    list_for_each_entry(req, &batch->head, ki_batch) {
        list_add(&req->ki_list, &ctx->active_reqs);
        ctx->reqs_active++;
    }

    kunmap_atomic(ring);
    spin_unlock_irq(&ctx->ctx_lock);

out:
    return allocated;
}

static inline struct kiocb *aio_get_req(struct kioctx *ctx,
                    struct kiocb_batch *batch)
{
    struct kiocb *req;

    if (list_empty(&batch->head))
        if (kiocb_batch_refill(ctx, batch) == 0)
            return NULL;
    req = list_first_entry(&batch->head, struct kiocb, ki_batch);
    list_del(&req->ki_batch);
    return req;
}

static inline void really_put_req(struct kioctx *ctx, struct kiocb *req)
{
    assert_spin_locked(&ctx->ctx_lock);

    if (req->ki_eventfd != NULL)
        eventfd_ctx_put(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_all(&ctx->wait);
}

/* __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;

    fput(req->ki_filp);
    req->ki_filp = NULL;
    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;
}
EXPORT_SYMBOL(aio_put_req);

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) {
        /*
         * RCU protects us against accessing freed memory but
         * we have to be careful not to get a reference when the
         * reference count already dropped to 0 (ctx->dead test
         * is unreliable because of races).
         */
        if (ctx->user_id == ctx_id && !ctx->dead && try_get_ioctx(ctx)){
            ret = ctx;
            break;
        }
    }

    rcu_read_unlock();
    return ret;
}

/*
 * 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) {
        /*
         * There's no easy way to restart the syscall since other AIO's
         * may be already running. Just fail this IO with EINTR.
         */
        if (unlikely(ret == -ERESTARTSYS || ret == -ERESTARTNOINTR ||
                 ret == -ERESTARTNOHAND || ret == -ERESTART_RESTARTBLOCK))
            ret = -EINTR;
        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_all_iocbs:
 *  Process all pending retries queued on the ioctx
 *  run list, and keep running them until the list
 *  stays empty.
 * Assumes it is operating within the aio issuer's mm context.
 */
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; no point using non-zero delay
     */
    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;

    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
 *      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]);

    tail = info->tail;
    event = aio_ring_event(info, tail);
    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);
    kunmap_atomic(ring);

    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 (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;
}
EXPORT_SYMBOL(aio_complete);

/* 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]);
    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);
        *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);
    }
    spin_unlock(&info->ring_lock);

out:
    kunmap_atomic(ring);
    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;
    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)\n", ioctx);
    if (likely(!was_dead))
        put_ioctx(ioctx);   /* twice for the list */

    kill_ctx(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_all(&ioctx->wait);
}

/* 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)
            io_destroy(ioctx);
        put_ioctx(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 -EINVAL 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);
        put_ioctx(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, bool compat)
{
    ssize_t ret;

#ifdef CONFIG_COMPAT
    if (compat)
        ret = compat_rw_copy_check_uvector(type,
                (struct compat_iovec __user *)kiocb->ki_buf,
                kiocb->ki_nbytes, 1, &kiocb->ki_inline_vec,
                &kiocb->ki_iovec);
    else
#endif
        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;

    ret = rw_verify_area(type, kiocb->ki_filp, &kiocb->ki_pos, ret);
    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(int type, struct file * file, struct kiocb *kiocb)
{
    int bytes;

    bytes = rw_verify_area(type, file, &kiocb->ki_pos, kiocb->ki_left);
    if (bytes < 0)
        return bytes;

    kiocb->ki_iovec = &kiocb->ki_inline_vec;
    kiocb->ki_iovec->iov_base = kiocb->ki_buf;
    kiocb->ki_iovec->iov_len = bytes;
    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, bool compat)
{
    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 = aio_setup_single_vector(READ, file, 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 = aio_setup_single_vector(WRITE, file, 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 = aio_setup_vectored_rw(READ, kiocb, compat);
        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 = aio_setup_vectored_rw(WRITE, kiocb, compat);
        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;
}

static int io_submit_one(struct kioctx *ctx, struct iocb __user *user_iocb,
             struct iocb *iocb, struct kiocb_batch *batch,
             bool compat)
{
    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, batch);  /* 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_ctx_fdget((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\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;

    ret = aio_setup_iocb(req, compat);

    if (ret)
        goto out_put_req;

    spin_lock_irq(&ctx->ctx_lock);
    /*
     * We could have raced with io_destroy() and are currently holding a
     * reference to ctx which should be destroyed. We cannot submit IO
     * since ctx gets freed as soon as io_submit() puts its reference.  The
     * check here is reliable: io_destroy() sets ctx->dead before waiting
     * for outstanding IO and the barrier between these two is realized by
     * unlock of mm->ioctx_lock and lock of ctx->ctx_lock.  Analogously we
     * increment ctx->reqs_active before checking for ctx->dead and the
     * barrier is realized by unlock and lock of ctx->ctx_lock. Thus if we
     * don't see ctx->dead set here, io_destroy() waits for our IO to
     * finish.
     */
    if (ctx->dead) {
        spin_unlock_irq(&ctx->ctx_lock);
        ret = -EINVAL;
        goto out_put_req;
    }
    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;
}

long do_io_submit(aio_context_t ctx_id, long nr,
          struct iocb __user *__user *iocbpp, bool compat)
{
    struct kioctx *ctx;
    long ret = 0;
    int i = 0;
    struct blk_plug plug;
    struct kiocb_batch batch;

    if (unlikely(nr < 0))
        return -EINVAL;

    if (unlikely(nr > LONG_MAX/sizeof(*iocbpp)))
        nr = LONG_MAX/sizeof(*iocbpp);

    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;
    }

    kiocb_batch_init(&batch, nr);

    blk_start_plug(&plug);

    /*
     * 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, &batch, compat);
        if (ret)
            break;
    }
    blk_finish_plug(&plug);

    kiocb_batch_free(ctx, &batch);
    put_ioctx(ctx);
    return i ? i : 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)
{
    return do_io_submit(ctx_id, nr, iocbpp, 0);
}

/* 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. If
 *  it succeeds, the number of read events is returned. May fail with
 *  -EINVAL if ctx_id is invalid, if min_nr is out of range, if nr is
 *  out of range, if timeout is out of range.  May fail with -EFAULT
 *  if any of the memory specified is invalid.  May return 0 or
 *  < min_nr if the timeout specified by timeout has elapsed
 *  before sufficient events are available, where timeout == NULL
 *  specifies an infinite timeout. Note that the timeout pointed to by
 *  timeout 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))
            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;
}