/*
   *	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.

   *	Copyright 2018 Christoph Hellwig.

   *
   *	See ../COPYING for licensing terms.
   */

  #define pr_fmt(fmt) "%s: " fmt, __func__

  #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/refcount.h>

  #include <linux/uio.h>

  #include <linux/sched/signal.h>

  #include <linux/fs.h>
  #include <linux/file.h>
  #include <linux/mm.h>
  #include <linux/mman.h>

  #include <linux/mmu_context.h>

  #include <linux/percpu.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 <linux/migrate.h>
  #include <linux/ramfs.h>

  #include <linux/percpu-refcount.h>

  #include <linux/mount.h>

  #include <linux/pseudo_fs.h>

  
  #include <asm/kmap_types.h>

  #include <linux/uaccess.h>

  #include <linux/nospec.h>

  #include "internal.h"

  #define KIOCB_KEY		0

  #define AIO_RING_MAGIC			0xa10a10a1
  #define AIO_RING_COMPAT_FEATURES	1
  #define AIO_RING_INCOMPAT_FEATURES	0
  struct aio_ring {
  	unsigned	id;	/* kernel internal index number */
  	unsigned	nr;	/* number of io_events */

  	unsigned	head;	/* Written to by userland or under ring_lock
  				 * mutex by aio_read_events_ring(). */

  	unsigned	tail;
  
  	unsigned	magic;
  	unsigned	compat_features;
  	unsigned	incompat_features;
  	unsigned	header_length;	/* size of aio_ring */
  
  
  	struct io_event		io_events[0];
  }; /* 128 bytes + ring size */

  /*
   * Plugging is meant to work with larger batches of IOs. If we don't
   * have more than the below, then don't bother setting up a plug.
   */
  #define AIO_PLUG_THRESHOLD	2

  #define AIO_RING_PAGES	8

  struct kioctx_table {

  	struct rcu_head		rcu;
  	unsigned		nr;
  	struct kioctx __rcu	*table[];

  };

  struct kioctx_cpu {
  	unsigned		reqs_available;
  };

  struct ctx_rq_wait {
  	struct completion comp;
  	atomic_t count;
  };

  struct kioctx {

  	struct percpu_ref	users;

  	atomic_t		dead;

  	struct percpu_ref	reqs;

  	unsigned long		user_id;

  	struct __percpu kioctx_cpu *cpu;
  
  	/*
  	 * For percpu reqs_available, number of slots we move to/from global
  	 * counter at a time:
  	 */
  	unsigned		req_batch;

  	/*
  	 * This is what userspace passed to io_setup(), it's not used for
  	 * anything but counting against the global max_reqs quota.
  	 *

  	 * The real limit is nr_events - 1, which will be larger (see

  	 * aio_setup_ring())
  	 */

  	unsigned		max_reqs;

  	/* Size of ringbuffer, in units of struct io_event */
  	unsigned		nr_events;

  	unsigned long		mmap_base;
  	unsigned long		mmap_size;
  
  	struct page		**ring_pages;
  	long			nr_pages;

  	struct rcu_work		free_rwork;	/* see free_ioctx() */

  	/*
  	 * signals when all in-flight requests are done
  	 */

  	struct ctx_rq_wait	*rq_wait;

  	struct {

  		/*
  		 * This counts the number of available slots in the ringbuffer,
  		 * so we avoid overflowing it: it's decremented (if positive)
  		 * when allocating a kiocb and incremented when the resulting
  		 * io_event is pulled off the ringbuffer.

  		 *
  		 * We batch accesses to it with a percpu version.

  		 */
  		atomic_t	reqs_available;

  	} ____cacheline_aligned_in_smp;
  
  	struct {
  		spinlock_t	ctx_lock;
  		struct list_head active_reqs;	/* used for cancellation */
  	} ____cacheline_aligned_in_smp;

  	struct {
  		struct mutex	ring_lock;

  		wait_queue_head_t wait;
  	} ____cacheline_aligned_in_smp;

  
  	struct {
  		unsigned	tail;

  		unsigned	completed_events;

  		spinlock_t	completion_lock;

  	} ____cacheline_aligned_in_smp;

  
  	struct page		*internal_pages[AIO_RING_PAGES];

  	struct file		*aio_ring_file;

  
  	unsigned		id;

  };

  /*
   * First field must be the file pointer in all the
   * iocb unions! See also 'struct kiocb' in <linux/fs.h>
   */

  struct fsync_iocb {

  	struct file		*file;

  	struct work_struct	work;

  	bool			datasync;
  };

  struct poll_iocb {
  	struct file		*file;
  	struct wait_queue_head	*head;
  	__poll_t		events;

  	bool			done;

  	bool			cancelled;
  	struct wait_queue_entry	wait;
  	struct work_struct	work;
  };

  /*
   * NOTE! Each of the iocb union members has the file pointer
   * as the first entry in their struct definition. So you can
   * access the file pointer through any of the sub-structs,
   * or directly as just 'ki_filp' in this struct.
   */

  struct aio_kiocb {

  	union {

  		struct file		*ki_filp;

  		struct kiocb		rw;

  		struct fsync_iocb	fsync;

  		struct poll_iocb	poll;

  	};

  
  	struct kioctx		*ki_ctx;
  	kiocb_cancel_fn		*ki_cancel;

  	struct io_event		ki_res;

  
  	struct list_head	ki_list;	/* the aio core uses this
  						 * for cancellation */

  	refcount_t		ki_refcnt;

  
  	/*
  	 * If the aio_resfd field of the userspace iocb is not zero,
  	 * this is the underlying eventfd context to deliver events to.
  	 */
  	struct eventfd_ctx	*ki_eventfd;
  };

  /*------ 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 vfsmount *aio_mnt;
  
  static const struct file_operations aio_ring_fops;
  static const struct address_space_operations aio_ctx_aops;
  
  static struct file *aio_private_file(struct kioctx *ctx, loff_t nr_pages)
  {

  	struct file *file;

  	struct inode *inode = alloc_anon_inode(aio_mnt->mnt_sb);

  	if (IS_ERR(inode))
  		return ERR_CAST(inode);

  
  	inode->i_mapping->a_ops = &aio_ctx_aops;
  	inode->i_mapping->private_data = ctx;
  	inode->i_size = PAGE_SIZE * nr_pages;

  	file = alloc_file_pseudo(inode, aio_mnt, "[aio]",
  				O_RDWR, &aio_ring_fops);

  	if (IS_ERR(file))

  		iput(inode);

  	return file;
  }

  static int aio_init_fs_context(struct fs_context *fc)

  {

  	if (!init_pseudo(fc, AIO_RING_MAGIC))
  		return -ENOMEM;
  	fc->s_iflags |= SB_I_NOEXEC;
  	return 0;

  }

  /* 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)
  {

  	static struct file_system_type aio_fs = {
  		.name		= "aio",

  		.init_fs_context = aio_init_fs_context,

  		.kill_sb	= kill_anon_super,
  	};
  	aio_mnt = kern_mount(&aio_fs);
  	if (IS_ERR(aio_mnt))
  		panic("Failed to create aio fs mount.");

  	kiocb_cachep = KMEM_CACHE(aio_kiocb, SLAB_HWCACHE_ALIGN|SLAB_PANIC);

  	kioctx_cachep = KMEM_CACHE(kioctx,SLAB_HWCACHE_ALIGN|SLAB_PANIC);

  	return 0;
  }

  __initcall(aio_setup);

  static void put_aio_ring_file(struct kioctx *ctx)
  {
  	struct file *aio_ring_file = ctx->aio_ring_file;

  	struct address_space *i_mapping;

  	if (aio_ring_file) {

  		truncate_setsize(file_inode(aio_ring_file), 0);

  
  		/* Prevent further access to the kioctx from migratepages */

  		i_mapping = aio_ring_file->f_mapping;

  		spin_lock(&i_mapping->private_lock);
  		i_mapping->private_data = NULL;

  		ctx->aio_ring_file = NULL;

  		spin_unlock(&i_mapping->private_lock);

  
  		fput(aio_ring_file);
  	}
  }

  static void aio_free_ring(struct kioctx *ctx)
  {

  	int i;

  	/* Disconnect the kiotx from the ring file.  This prevents future
  	 * accesses to the kioctx from page migration.
  	 */
  	put_aio_ring_file(ctx);

  	for (i = 0; i < ctx->nr_pages; i++) {

  		struct page *page;

  		pr_debug("pid(%d) [%d] page->count=%d
  ", current->pid, i,
  				page_count(ctx->ring_pages[i]));

  		page = ctx->ring_pages[i];
  		if (!page)
  			continue;
  		ctx->ring_pages[i] = NULL;
  		put_page(page);

  	}

  	if (ctx->ring_pages && ctx->ring_pages != ctx->internal_pages) {

  		kfree(ctx->ring_pages);

  		ctx->ring_pages = NULL;
  	}

  }

  static int aio_ring_mremap(struct vm_area_struct *vma)

  {

  	struct file *file = vma->vm_file;

  	struct mm_struct *mm = vma->vm_mm;
  	struct kioctx_table *table;

  	int i, res = -EINVAL;

  
  	spin_lock(&mm->ioctx_lock);
  	rcu_read_lock();
  	table = rcu_dereference(mm->ioctx_table);
  	for (i = 0; i < table->nr; i++) {
  		struct kioctx *ctx;

  		ctx = rcu_dereference(table->table[i]);

  		if (ctx && ctx->aio_ring_file == file) {

  			if (!atomic_read(&ctx->dead)) {
  				ctx->user_id = ctx->mmap_base = vma->vm_start;
  				res = 0;
  			}

  			break;
  		}
  	}
  
  	rcu_read_unlock();
  	spin_unlock(&mm->ioctx_lock);

  	return res;

  }

  static const struct vm_operations_struct aio_ring_vm_ops = {
  	.mremap		= aio_ring_mremap,
  #if IS_ENABLED(CONFIG_MMU)
  	.fault		= filemap_fault,
  	.map_pages	= filemap_map_pages,
  	.page_mkwrite	= filemap_page_mkwrite,
  #endif
  };
  
  static int aio_ring_mmap(struct file *file, struct vm_area_struct *vma)
  {
  	vma->vm_flags |= VM_DONTEXPAND;
  	vma->vm_ops = &aio_ring_vm_ops;
  	return 0;
  }

  static const struct file_operations aio_ring_fops = {
  	.mmap = aio_ring_mmap,
  };

  #if IS_ENABLED(CONFIG_MIGRATION)

  static int aio_migratepage(struct address_space *mapping, struct page *new,
  			struct page *old, enum migrate_mode mode)
  {

  	struct kioctx *ctx;

  	unsigned long flags;

  	pgoff_t idx;

  	int rc;

  	/*
  	 * We cannot support the _NO_COPY case here, because copy needs to
  	 * happen under the ctx->completion_lock. That does not work with the
  	 * migration workflow of MIGRATE_SYNC_NO_COPY.
  	 */
  	if (mode == MIGRATE_SYNC_NO_COPY)
  		return -EINVAL;

  	rc = 0;

  	/* mapping->private_lock here protects against the kioctx teardown.  */

  	spin_lock(&mapping->private_lock);
  	ctx = mapping->private_data;

  	if (!ctx) {
  		rc = -EINVAL;
  		goto out;
  	}
  
  	/* The ring_lock mutex.  The prevents aio_read_events() from writing
  	 * to the ring's head, and prevents page migration from mucking in
  	 * a partially initialized kiotx.
  	 */
  	if (!mutex_trylock(&ctx->ring_lock)) {
  		rc = -EAGAIN;
  		goto out;
  	}
  
  	idx = old->index;
  	if (idx < (pgoff_t)ctx->nr_pages) {
  		/* Make sure the old page hasn't already been changed */
  		if (ctx->ring_pages[idx] != old)
  			rc = -EAGAIN;

  	} else
  		rc = -EINVAL;

  
  	if (rc != 0)

  		goto out_unlock;

  	/* Writeback must be complete */
  	BUG_ON(PageWriteback(old));

  	get_page(new);

  	rc = migrate_page_move_mapping(mapping, new, old, 1);

  	if (rc != MIGRATEPAGE_SUCCESS) {

  		put_page(new);

  		goto out_unlock;

  	}

  	/* Take completion_lock to prevent other writes to the ring buffer
  	 * while the old page is copied to the new.  This prevents new
  	 * events from being lost.

  	 */

  	spin_lock_irqsave(&ctx->completion_lock, flags);
  	migrate_page_copy(new, old);
  	BUG_ON(ctx->ring_pages[idx] != old);
  	ctx->ring_pages[idx] = new;
  	spin_unlock_irqrestore(&ctx->completion_lock, flags);

  	/* The old page is no longer accessible. */
  	put_page(old);

  out_unlock:
  	mutex_unlock(&ctx->ring_lock);
  out:
  	spin_unlock(&mapping->private_lock);

  	return rc;

  }

  #endif

  static const struct address_space_operations aio_ctx_aops = {

  	.set_page_dirty = __set_page_dirty_no_writeback,

  #if IS_ENABLED(CONFIG_MIGRATION)

  	.migratepage	= aio_migratepage,

  #endif

  };

  static int aio_setup_ring(struct kioctx *ctx, unsigned int nr_events)

  {
  	struct aio_ring *ring;

  	struct mm_struct *mm = current->mm;

  	unsigned long size, unused;

  	int nr_pages;

  	int i;
  	struct file *file;

  
  	/* 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 = PFN_UP(size);

  	if (nr_pages < 0)
  		return -EINVAL;

  	file = aio_private_file(ctx, nr_pages);

  	if (IS_ERR(file)) {
  		ctx->aio_ring_file = NULL;

  		return -ENOMEM;

  	}

  	ctx->aio_ring_file = file;
  	nr_events = (PAGE_SIZE * nr_pages - sizeof(struct aio_ring))
  			/ sizeof(struct io_event);
  
  	ctx->ring_pages = ctx->internal_pages;
  	if (nr_pages > AIO_RING_PAGES) {
  		ctx->ring_pages = kcalloc(nr_pages, sizeof(struct page *),
  					  GFP_KERNEL);
  		if (!ctx->ring_pages) {
  			put_aio_ring_file(ctx);
  			return -ENOMEM;
  		}
  	}

  	for (i = 0; i < nr_pages; i++) {
  		struct page *page;

  		page = find_or_create_page(file->f_mapping,

  					   i, GFP_HIGHUSER | __GFP_ZERO);
  		if (!page)
  			break;
  		pr_debug("pid(%d) page[%d]->count=%d
  ",
  			 current->pid, i, page_count(page));
  		SetPageUptodate(page);

  		unlock_page(page);

  
  		ctx->ring_pages[i] = page;

  	}

  	ctx->nr_pages = i;

  	if (unlikely(i != nr_pages)) {
  		aio_free_ring(ctx);

  		return -ENOMEM;

  	}

  	ctx->mmap_size = nr_pages * PAGE_SIZE;
  	pr_debug("attempting mmap of %lu bytes
  ", ctx->mmap_size);

  	if (down_write_killable(&mm->mmap_sem)) {
  		ctx->mmap_size = 0;
  		aio_free_ring(ctx);
  		return -EINTR;
  	}

  	ctx->mmap_base = do_mmap_pgoff(ctx->aio_ring_file, 0, ctx->mmap_size,
  				       PROT_READ | PROT_WRITE,

  				       MAP_SHARED, 0, &unused, NULL);

  	up_write(&mm->mmap_sem);

  	if (IS_ERR((void *)ctx->mmap_base)) {

  		ctx->mmap_size = 0;

  		aio_free_ring(ctx);

  		return -ENOMEM;

  	}

  	pr_debug("mmap address: 0x%08lx
  ", ctx->mmap_base);

  	ctx->user_id = ctx->mmap_base;
  	ctx->nr_events = nr_events; /* trusted copy */

  	ring = kmap_atomic(ctx->ring_pages[0]);

  	ring->nr = nr_events;	/* user copy */

  	ring->id = ~0U;

  	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);

  	flush_dcache_page(ctx->ring_pages[0]);

  
  	return 0;
  }

  #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)

  void kiocb_set_cancel_fn(struct kiocb *iocb, kiocb_cancel_fn *cancel)

  {

  	struct aio_kiocb *req = container_of(iocb, struct aio_kiocb, rw);

  	struct kioctx *ctx = req->ki_ctx;
  	unsigned long flags;

  	if (WARN_ON_ONCE(!list_empty(&req->ki_list)))
  		return;

  	spin_lock_irqsave(&ctx->ctx_lock, flags);
  	list_add_tail(&req->ki_list, &ctx->active_reqs);

  	req->ki_cancel = cancel;

  	spin_unlock_irqrestore(&ctx->ctx_lock, flags);
  }
  EXPORT_SYMBOL(kiocb_set_cancel_fn);

  /*
   * free_ioctx() should be RCU delayed to synchronize against the RCU
   * protected lookup_ioctx() and also needs process context to call

   * aio_free_ring().  Use rcu_work.

   */

  static void free_ioctx(struct work_struct *work)

  {

  	struct kioctx *ctx = container_of(to_rcu_work(work), struct kioctx,
  					  free_rwork);

  	pr_debug("freeing %p
  ", ctx);

  	aio_free_ring(ctx);

  	free_percpu(ctx->cpu);

  	percpu_ref_exit(&ctx->reqs);
  	percpu_ref_exit(&ctx->users);

  	kmem_cache_free(kioctx_cachep, ctx);
  }

  static void free_ioctx_reqs(struct percpu_ref *ref)
  {
  	struct kioctx *ctx = container_of(ref, struct kioctx, reqs);

  	/* At this point we know that there are no any in-flight requests */

  	if (ctx->rq_wait && atomic_dec_and_test(&ctx->rq_wait->count))
  		complete(&ctx->rq_wait->comp);

  	/* Synchronize against RCU protected table->table[] dereferences */

  	INIT_RCU_WORK(&ctx->free_rwork, free_ioctx);
  	queue_rcu_work(system_wq, &ctx->free_rwork);

  }

  /*
   * When this function runs, the kioctx has been removed from the "hash table"
   * and ctx->users has dropped to 0, so we know no more kiocbs can be submitted -
   * now it's safe to cancel any that need to be.
   */

  static void free_ioctx_users(struct percpu_ref *ref)

  {

  	struct kioctx *ctx = container_of(ref, struct kioctx, users);

  	struct aio_kiocb *req;

  
  	spin_lock_irq(&ctx->ctx_lock);
  
  	while (!list_empty(&ctx->active_reqs)) {
  		req = list_first_entry(&ctx->active_reqs,

  				       struct aio_kiocb, ki_list);

  		req->ki_cancel(&req->rw);

  		list_del_init(&req->ki_list);

  	}
  
  	spin_unlock_irq(&ctx->ctx_lock);

  	percpu_ref_kill(&ctx->reqs);
  	percpu_ref_put(&ctx->reqs);

  }

  static int ioctx_add_table(struct kioctx *ctx, struct mm_struct *mm)
  {
  	unsigned i, new_nr;
  	struct kioctx_table *table, *old;
  	struct aio_ring *ring;
  
  	spin_lock(&mm->ioctx_lock);

  	table = rcu_dereference_raw(mm->ioctx_table);

  
  	while (1) {
  		if (table)
  			for (i = 0; i < table->nr; i++)

  				if (!rcu_access_pointer(table->table[i])) {

  					ctx->id = i;

  					rcu_assign_pointer(table->table[i], ctx);

  					spin_unlock(&mm->ioctx_lock);

  					/* While kioctx setup is in progress,
  					 * we are protected from page migration
  					 * changes ring_pages by ->ring_lock.
  					 */

  					ring = kmap_atomic(ctx->ring_pages[0]);
  					ring->id = ctx->id;
  					kunmap_atomic(ring);
  					return 0;
  				}
  
  		new_nr = (table ? table->nr : 1) * 4;

  		spin_unlock(&mm->ioctx_lock);
  
  		table = kzalloc(sizeof(*table) + sizeof(struct kioctx *) *
  				new_nr, GFP_KERNEL);
  		if (!table)
  			return -ENOMEM;
  
  		table->nr = new_nr;
  
  		spin_lock(&mm->ioctx_lock);

  		old = rcu_dereference_raw(mm->ioctx_table);

  
  		if (!old) {
  			rcu_assign_pointer(mm->ioctx_table, table);
  		} else if (table->nr > old->nr) {
  			memcpy(table->table, old->table,
  			       old->nr * sizeof(struct kioctx *));
  
  			rcu_assign_pointer(mm->ioctx_table, table);
  			kfree_rcu(old, rcu);
  		} else {
  			kfree(table);
  			table = old;
  		}
  	}
  }

  static void aio_nr_sub(unsigned nr)
  {
  	spin_lock(&aio_nr_lock);
  	if (WARN_ON(aio_nr - nr > aio_nr))
  		aio_nr = 0;
  	else
  		aio_nr -= nr;
  	spin_unlock(&aio_nr_lock);
  }

  /* 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 = current->mm;

  	struct kioctx *ctx;

  	int err = -ENOMEM;

  	/*

  	 * Store the original nr_events -- what userspace passed to io_setup(),
  	 * for counting against the global limit -- before it changes.
  	 */
  	unsigned int max_reqs = nr_events;
  
  	/*

  	 * We keep track of the number of available ringbuffer slots, to prevent
  	 * overflow (reqs_available), and we also use percpu counters for this.
  	 *
  	 * So since up to half the slots might be on other cpu's percpu counters
  	 * and unavailable, double nr_events so userspace sees what they
  	 * expected: additionally, we move req_batch slots to/from percpu
  	 * counters at a time, so make sure that isn't 0:
  	 */
  	nr_events = max(nr_events, num_possible_cpus() * 4);
  	nr_events *= 2;

  	/* Prevent overflows */

  	if (nr_events > (0x10000000U / sizeof(struct io_event))) {

  		pr_debug("ENOMEM: nr_events too high
  ");
  		return ERR_PTR(-EINVAL);
  	}

  	if (!nr_events || (unsigned long)max_reqs > aio_max_nr)

  		return ERR_PTR(-EAGAIN);

  	ctx = kmem_cache_zalloc(kioctx_cachep, GFP_KERNEL);

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

  	ctx->max_reqs = max_reqs;

  	spin_lock_init(&ctx->ctx_lock);

  	spin_lock_init(&ctx->completion_lock);

  	mutex_init(&ctx->ring_lock);

  	/* Protect against page migration throughout kiotx setup by keeping
  	 * the ring_lock mutex held until setup is complete. */
  	mutex_lock(&ctx->ring_lock);

  	init_waitqueue_head(&ctx->wait);
  
  	INIT_LIST_HEAD(&ctx->active_reqs);

  	if (percpu_ref_init(&ctx->users, free_ioctx_users, 0, GFP_KERNEL))

  		goto err;

  	if (percpu_ref_init(&ctx->reqs, free_ioctx_reqs, 0, GFP_KERNEL))

  		goto err;

  	ctx->cpu = alloc_percpu(struct kioctx_cpu);
  	if (!ctx->cpu)

  		goto err;

  	err = aio_setup_ring(ctx, nr_events);

  	if (err < 0)

  		goto err;

  	atomic_set(&ctx->reqs_available, ctx->nr_events - 1);

  	ctx->req_batch = (ctx->nr_events - 1) / (num_possible_cpus() * 4);

  	if (ctx->req_batch < 1)
  		ctx->req_batch = 1;

  	/* 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) {

  		spin_unlock(&aio_nr_lock);

  		err = -EAGAIN;

  		goto err_ctx;

  	}
  	aio_nr += ctx->max_reqs;

  	spin_unlock(&aio_nr_lock);

  	percpu_ref_get(&ctx->users);	/* io_setup() will drop this ref */
  	percpu_ref_get(&ctx->reqs);	/* free_ioctx_users() will drop this */

  	err = ioctx_add_table(ctx, mm);
  	if (err)

  		goto err_cleanup;

  	/* Release the ring_lock mutex now that all setup is complete. */
  	mutex_unlock(&ctx->ring_lock);

  	pr_debug("allocated ioctx %p[%ld]: mm=%p mask=0x%x
  ",

  		 ctx, ctx->user_id, mm, ctx->nr_events);

  	return ctx;

  err_cleanup:
  	aio_nr_sub(ctx->max_reqs);

  err_ctx:

  	atomic_set(&ctx->dead, 1);
  	if (ctx->mmap_size)
  		vm_munmap(ctx->mmap_base, ctx->mmap_size);

  	aio_free_ring(ctx);

  err:

  	mutex_unlock(&ctx->ring_lock);

  	free_percpu(ctx->cpu);

  	percpu_ref_exit(&ctx->reqs);
  	percpu_ref_exit(&ctx->users);

  	kmem_cache_free(kioctx_cachep, ctx);

  	pr_debug("error allocating ioctx %d
  ", err);

  	return ERR_PTR(err);

  }

  /* kill_ioctx
   *	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 int kill_ioctx(struct mm_struct *mm, struct kioctx *ctx,

  		      struct ctx_rq_wait *wait)

  {

  	struct kioctx_table *table;

  	spin_lock(&mm->ioctx_lock);
  	if (atomic_xchg(&ctx->dead, 1)) {
  		spin_unlock(&mm->ioctx_lock);

  		return -EINVAL;

  	}

  	table = rcu_dereference_raw(mm->ioctx_table);

  	WARN_ON(ctx != rcu_access_pointer(table->table[ctx->id]));
  	RCU_INIT_POINTER(table->table[ctx->id], NULL);

  	spin_unlock(&mm->ioctx_lock);

  	/* free_ioctx_reqs() will do the necessary RCU synchronization */

  	wake_up_all(&ctx->wait);

  	/*
  	 * It'd be more correct to do this in free_ioctx(), after all
  	 * the outstanding kiocbs have finished - but by then io_destroy
  	 * has already returned, so io_setup() could potentially return
  	 * -EAGAIN with no ioctxs actually in use (as far as userspace
  	 *  could tell).
  	 */
  	aio_nr_sub(ctx->max_reqs);

  	if (ctx->mmap_size)
  		vm_munmap(ctx->mmap_base, ctx->mmap_size);

  	ctx->rq_wait = wait;

  	percpu_ref_kill(&ctx->users);
  	return 0;

  }

  /*
   * 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.
   *
   * There may be outstanding kiocbs, but free_ioctx() will explicitly wait on
   * them.

   */

  void exit_aio(struct mm_struct *mm)

  {

  	struct kioctx_table *table = rcu_dereference_raw(mm->ioctx_table);

  	struct ctx_rq_wait wait;
  	int i, skipped;

  	if (!table)
  		return;

  	atomic_set(&wait.count, table->nr);
  	init_completion(&wait.comp);
  
  	skipped = 0;

  	for (i = 0; i < table->nr; ++i) {

  		struct kioctx *ctx =
  			rcu_dereference_protected(table->table[i], true);

  		if (!ctx) {
  			skipped++;

  			continue;

  		}

  		/*

  		 * We don't need to bother with munmap() here - exit_mmap(mm)
  		 * is coming and it'll unmap everything. And we simply can't,
  		 * this is not necessarily our ->mm.
  		 * Since kill_ioctx() uses non-zero ->mmap_size as indicator
  		 * that it needs to unmap the area, just set it to 0.

  		 */

  		ctx->mmap_size = 0;

  		kill_ioctx(mm, ctx, &wait);
  	}

  	if (!atomic_sub_and_test(skipped, &wait.count)) {

  		/* Wait until all IO for the context are done. */

  		wait_for_completion(&wait.comp);

  	}

  
  	RCU_INIT_POINTER(mm->ioctx_table, NULL);
  	kfree(table);

  }

  static void put_reqs_available(struct kioctx *ctx, unsigned nr)
  {
  	struct kioctx_cpu *kcpu;

  	unsigned long flags;

  	local_irq_save(flags);

  	kcpu = this_cpu_ptr(ctx->cpu);

  	kcpu->reqs_available += nr;

  	while (kcpu->reqs_available >= ctx->req_batch * 2) {
  		kcpu->reqs_available -= ctx->req_batch;
  		atomic_add(ctx->req_batch, &ctx->reqs_available);
  	}

  	local_irq_restore(flags);

  }

  static bool __get_reqs_available(struct kioctx *ctx)

  {
  	struct kioctx_cpu *kcpu;
  	bool ret = false;

  	unsigned long flags;

  	local_irq_save(flags);

  	kcpu = this_cpu_ptr(ctx->cpu);

  	if (!kcpu->reqs_available) {
  		int old, avail = atomic_read(&ctx->reqs_available);
  
  		do {
  			if (avail < ctx->req_batch)
  				goto out;
  
  			old = avail;
  			avail = atomic_cmpxchg(&ctx->reqs_available,
  					       avail, avail - ctx->req_batch);
  		} while (avail != old);
  
  		kcpu->reqs_available += ctx->req_batch;
  	}
  
  	ret = true;
  	kcpu->reqs_available--;
  out:

  	local_irq_restore(flags);

  	return ret;
  }

  /* refill_reqs_available
   *	Updates the reqs_available reference counts used for tracking the
   *	number of free slots in the completion ring.  This can be called
   *	from aio_complete() (to optimistically update reqs_available) or
   *	from aio_get_req() (the we're out of events case).  It must be
   *	called holding ctx->completion_lock.
   */
  static void refill_reqs_available(struct kioctx *ctx, unsigned head,
                                    unsigned tail)
  {
  	unsigned events_in_ring, completed;
  
  	/* Clamp head since userland can write to it. */
  	head %= ctx->nr_events;
  	if (head <= tail)
  		events_in_ring = tail - head;
  	else
  		events_in_ring = ctx->nr_events - (head - tail);
  
  	completed = ctx->completed_events;
  	if (events_in_ring < completed)
  		completed -= events_in_ring;
  	else
  		completed = 0;
  
  	if (!completed)
  		return;
  
  	ctx->completed_events -= completed;
  	put_reqs_available(ctx, completed);
  }
  
  /* user_refill_reqs_available
   *	Called to refill reqs_available when aio_get_req() encounters an
   *	out of space in the completion ring.
   */
  static void user_refill_reqs_available(struct kioctx *ctx)
  {
  	spin_lock_irq(&ctx->completion_lock);
  	if (ctx->completed_events) {
  		struct aio_ring *ring;
  		unsigned head;
  
  		/* Access of ring->head may race with aio_read_events_ring()
  		 * here, but that's okay since whether we read the old version
  		 * or the new version, and either will be valid.  The important
  		 * part is that head cannot pass tail since we prevent
  		 * aio_complete() from updating tail by holding
  		 * ctx->completion_lock.  Even if head is invalid, the check
  		 * against ctx->completed_events below will make sure we do the
  		 * safe/right thing.
  		 */
  		ring = kmap_atomic(ctx->ring_pages[0]);
  		head = ring->head;
  		kunmap_atomic(ring);
  
  		refill_reqs_available(ctx, head, ctx->tail);
  	}
  
  	spin_unlock_irq(&ctx->completion_lock);
  }

  static bool get_reqs_available(struct kioctx *ctx)
  {
  	if (__get_reqs_available(ctx))
  		return true;
  	user_refill_reqs_available(ctx);
  	return __get_reqs_available(ctx);
  }

  /* aio_get_req

   *	Allocate a slot for an aio request.
   * Returns NULL if no requests are free.

   *
   * The refcount is initialized to 2 - one for the async op completion,
   * one for the synchronous code that does this.

   */

  static inline struct aio_kiocb *aio_get_req(struct kioctx *ctx)

  {

  	struct aio_kiocb *req;

  	req = kmem_cache_alloc(kiocb_cachep, GFP_KERNEL);

  	if (unlikely(!req))

  		return NULL;

  	if (unlikely(!get_reqs_available(ctx))) {

  		kmem_cache_free(kiocb_cachep, req);

  		return NULL;
  	}

  	percpu_ref_get(&ctx->reqs);

  	req->ki_ctx = ctx;

  	INIT_LIST_HEAD(&req->ki_list);

  	refcount_set(&req->ki_refcnt, 2);

  	req->ki_eventfd = NULL;

  	return req;

  }

  static struct kioctx *lookup_ioctx(unsigned long ctx_id)

  {

  	struct aio_ring __user *ring  = (void __user *)ctx_id;

  	struct mm_struct *mm = current->mm;

  	struct kioctx *ctx, *ret = NULL;

  	struct kioctx_table *table;
  	unsigned id;
  
  	if (get_user(id, &ring->id))
  		return NULL;

  	rcu_read_lock();

  	table = rcu_dereference(mm->ioctx_table);

  	if (!table || id >= table->nr)
  		goto out;

  	id = array_index_nospec(id, table->nr);

  	ctx = rcu_dereference(table->table[id]);

  	if (ctx && ctx->user_id == ctx_id) {

  		if (percpu_ref_tryget_live(&ctx->users))
  			ret = ctx;

  	}
  out:

  	rcu_read_unlock();

  	return ret;

  }

  static inline void iocb_destroy(struct aio_kiocb *iocb)
  {

  	if (iocb->ki_eventfd)
  		eventfd_ctx_put(iocb->ki_eventfd);

  	if (iocb->ki_filp)
  		fput(iocb->ki_filp);
  	percpu_ref_put(&iocb->ki_ctx->reqs);
  	kmem_cache_free(kiocb_cachep, iocb);
  }

  /* aio_complete
   *	Called when the io request on the given iocb is complete.

   */

  static void aio_complete(struct aio_kiocb *iocb)

  {
  	struct kioctx	*ctx = iocb->ki_ctx;

  	struct aio_ring	*ring;

  	struct io_event	*ev_page, *event;

  	unsigned tail, pos, head;

  	unsigned long	flags;

  	/*

  	 * Add a completion event to the ring buffer. Must be done holding

  	 * ctx->completion_lock to prevent other code from messing with the tail

  	 * pointer since we might be called from irq context.
  	 */
  	spin_lock_irqsave(&ctx->completion_lock, flags);

  	tail = ctx->tail;

  	pos = tail + AIO_EVENTS_OFFSET;

  	if (++tail >= ctx->nr_events)

  		tail = 0;

  	ev_page = kmap_atomic(ctx->ring_pages[pos / AIO_EVENTS_PER_PAGE]);

  	event = ev_page + pos % AIO_EVENTS_PER_PAGE;

  	*event = iocb->ki_res;

  	kunmap_atomic(ev_page);

  	flush_dcache_page(ctx->ring_pages[pos / AIO_EVENTS_PER_PAGE]);

  	pr_debug("%p[%u]: %p: %p %Lx %Lx %Lx
  ", ctx, tail, iocb,
  		 (void __user *)(unsigned long)iocb->ki_res.obj,
  		 iocb->ki_res.data, iocb->ki_res.res, iocb->ki_res.res2);

  
  	/* after flagging the request as done, we
  	 * must never even look at it again
  	 */
  	smp_wmb();	/* make event visible before updating tail */

  	ctx->tail = tail;

  	ring = kmap_atomic(ctx->ring_pages[0]);

  	head = ring->head;

  	ring->tail = tail;

  	kunmap_atomic(ring);

  	flush_dcache_page(ctx->ring_pages[0]);

  	ctx->completed_events++;
  	if (ctx->completed_events > 1)
  		refill_reqs_available(ctx, head, tail);

  	spin_unlock_irqrestore(&ctx->completion_lock, flags);

  	pr_debug("added to ring %p at [%u]
  ", 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)

  		eventfd_signal(iocb->ki_eventfd, 1);

  	/*
  	 * 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);

  }
  
  static inline void iocb_put(struct aio_kiocb *iocb)
  {
  	if (refcount_dec_and_test(&iocb->ki_refcnt)) {
  		aio_complete(iocb);
  		iocb_destroy(iocb);
  	}

  }

  /* aio_read_events_ring

   *	Pull an event off of the ioctx's event ring.  Returns the number of
   *	events fetched

   */

  static long aio_read_events_ring(struct kioctx *ctx,
  				 struct io_event __user *event, long nr)

  {

  	struct aio_ring *ring;

  	unsigned head, tail, pos;

  	long ret = 0;
  	int copy_ret;

  	/*
  	 * The mutex can block and wake us up and that will cause
  	 * wait_event_interruptible_hrtimeout() to schedule without sleeping
  	 * and repeat. This should be rare enough that it doesn't cause
  	 * peformance issues. See the comment in read_events() for more detail.
  	 */
  	sched_annotate_sleep();

  	mutex_lock(&ctx->ring_lock);

  	/* Access to ->ring_pages here is protected by ctx->ring_lock. */

  	ring = kmap_atomic(ctx->ring_pages[0]);

  	head = ring->head;

  	tail = ring->tail;

  	kunmap_atomic(ring);

  	/*
  	 * Ensure that once we've read the current tail pointer, that
  	 * we also see the events that were stored up to the tail.
  	 */
  	smp_rmb();

  	pr_debug("h%u t%u m%u
  ", head, tail, ctx->nr_events);

  	if (head == tail)

  		goto out;

  	head %= ctx->nr_events;
  	tail %= ctx->nr_events;

  	while (ret < nr) {
  		long avail;
  		struct io_event *ev;
  		struct page *page;

  		avail = (head <= tail ?  tail : ctx->nr_events) - head;
  		if (head == tail)

  			break;

  		pos = head + AIO_EVENTS_OFFSET;

  		page = ctx->ring_pages[pos / AIO_EVENTS_PER_PAGE];

  		pos %= AIO_EVENTS_PER_PAGE;

  		avail = min(avail, nr - ret);
  		avail = min_t(long, avail, AIO_EVENTS_PER_PAGE - pos);

  		ev = kmap(page);
  		copy_ret = copy_to_user(event + ret, ev + pos,
  					sizeof(*ev) * avail);
  		kunmap(page);
  
  		if (unlikely(copy_ret)) {
  			ret = -EFAULT;
  			goto out;
  		}
  
  		ret += avail;
  		head += avail;

  		head %= ctx->nr_events;

  	}

  	ring = kmap_atomic(ctx->ring_pages[0]);

  	ring->head = head;

  	kunmap_atomic(ring);

  	flush_dcache_page(ctx->ring_pages[0]);

  	pr_debug("%li  h%u t%u
  ", ret, head, tail);

  out:

  	mutex_unlock(&ctx->ring_lock);

  	return ret;
  }

  static bool aio_read_events(struct kioctx *ctx, long min_nr, long nr,
  			    struct io_event __user *event, long *i)

  {

  	long ret = aio_read_events_ring(ctx, event + *i, nr - *i);

  	if (ret > 0)
  		*i += ret;

  	if (unlikely(atomic_read(&ctx->dead)))
  		ret = -EINVAL;

  	if (!*i)
  		*i = ret;

  	return ret < 0 || *i >= min_nr;

  }

  static long read_events(struct kioctx *ctx, long min_nr, long nr,

  			struct io_event __user *event,

  			ktime_t until)

  {

  	long ret = 0;

  	/*
  	 * Note that aio_read_events() is being called as the conditional - i.e.
  	 * we're calling it after prepare_to_wait() has set task state to
  	 * TASK_INTERRUPTIBLE.
  	 *
  	 * But aio_read_events() can block, and if it blocks it's going to flip
  	 * the task state back to TASK_RUNNING.
  	 *
  	 * This should be ok, provided it doesn't flip the state back to
  	 * TASK_RUNNING and return 0 too much - that causes us to spin. That
  	 * will only happen if the mutex_lock() call blocks, and we then find
  	 * the ringbuffer empty. So in practice we should be ok, but it's
  	 * something to be aware of when touching this code.
  	 */

  	if (until == 0)

  		aio_read_events(ctx, min_nr, nr, event, &ret);
  	else
  		wait_event_interruptible_hrtimeout(ctx->wait,
  				aio_read_events(ctx, min_nr, nr, event, &ret),
  				until);

  	return ret;

  }

  /* 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: ctx %lu nr_events %u
  ",

  		         ctx, nr_events);

  		goto out;
  	}
  
  	ioctx = ioctx_alloc(nr_events);
  	ret = PTR_ERR(ioctx);
  	if (!IS_ERR(ioctx)) {
  		ret = put_user(ioctx->user_id, ctxp);

  		if (ret)

  			kill_ioctx(current->mm, ioctx, NULL);

  		percpu_ref_put(&ioctx->users);

  	}
  
  out:
  	return ret;
  }

  #ifdef CONFIG_COMPAT
  COMPAT_SYSCALL_DEFINE2(io_setup, unsigned, nr_events, u32 __user *, ctx32p)
  {
  	struct kioctx *ioctx = NULL;
  	unsigned long ctx;
  	long ret;
  
  	ret = get_user(ctx, ctx32p);
  	if (unlikely(ret))
  		goto out;
  
  	ret = -EINVAL;
  	if (unlikely(ctx || nr_events == 0)) {
  		pr_debug("EINVAL: ctx %lu nr_events %u
  ",
  		         ctx, nr_events);
  		goto out;
  	}
  
  	ioctx = ioctx_alloc(nr_events);
  	ret = PTR_ERR(ioctx);
  	if (!IS_ERR(ioctx)) {
  		/* truncating is ok because it's a user address */
  		ret = put_user((u32)ioctx->user_id, ctx32p);
  		if (ret)
  			kill_ioctx(current->mm, ioctx, NULL);
  		percpu_ref_put(&ioctx->users);
  	}
  
  out:
  	return ret;
  }
  #endif

  /* 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)) {

  		struct ctx_rq_wait wait;

  		int ret;

  		init_completion(&wait.comp);
  		atomic_set(&wait.count, 1);

  		/* Pass requests_done to kill_ioctx() where it can be set
  		 * in a thread-safe way. If we try to set it here then we have
  		 * a race condition if two io_destroy() called simultaneously.
  		 */

  		ret = kill_ioctx(current->mm, ioctx, &wait);

  		percpu_ref_put(&ioctx->users);

  
  		/* Wait until all IO for the context are done. Otherwise kernel
  		 * keep using user-space buffers even if user thinks the context
  		 * is destroyed.
  		 */

  		if (!ret)

  			wait_for_completion(&wait.comp);

  		return ret;

  	}

  	pr_debug("EINVAL: invalid context id
  ");

  	return -EINVAL;
  }

  static void aio_remove_iocb(struct aio_kiocb *iocb)
  {
  	struct kioctx *ctx = iocb->ki_ctx;
  	unsigned long flags;
  
  	spin_lock_irqsave(&ctx->ctx_lock, flags);
  	list_del(&iocb->ki_list);
  	spin_unlock_irqrestore(&ctx->ctx_lock, flags);
  }

  static void aio_complete_rw(struct kiocb *kiocb, long res, long res2)
  {
  	struct aio_kiocb *iocb = container_of(kiocb, struct aio_kiocb, rw);

  	if (!list_empty_careful(&iocb->ki_list))
  		aio_remove_iocb(iocb);

  	if (kiocb->ki_flags & IOCB_WRITE) {
  		struct inode *inode = file_inode(kiocb->ki_filp);
  
  		/*
  		 * Tell lockdep we inherited freeze protection from submission
  		 * thread.
  		 */
  		if (S_ISREG(inode->i_mode))
  			__sb_writers_acquired(inode->i_sb, SB_FREEZE_WRITE);
  		file_end_write(kiocb->ki_filp);
  	}

  	iocb->ki_res.res = res;
  	iocb->ki_res.res2 = res2;
  	iocb_put(iocb);

  }

  static int aio_prep_rw(struct kiocb *req, const struct iocb *iocb)

  {
  	int ret;

  	req->ki_complete = aio_complete_rw;

  	req->private = NULL;

  	req->ki_pos = iocb->aio_offset;
  	req->ki_flags = iocb_flags(req->ki_filp);
  	if (iocb->aio_flags & IOCB_FLAG_RESFD)
  		req->ki_flags |= IOCB_EVENTFD;

  	req->ki_hint = ki_hint_validate(file_write_hint(req->ki_filp));

  	if (iocb->aio_flags & IOCB_FLAG_IOPRIO) {
  		/*
  		 * If the IOCB_FLAG_IOPRIO flag of aio_flags is set, then
  		 * aio_reqprio is interpreted as an I/O scheduling
  		 * class and priority.
  		 */
  		ret = ioprio_check_cap(iocb->aio_reqprio);
  		if (ret) {

  			pr_debug("aio ioprio check cap error: %d
  ", ret);

  			return ret;

  		}
  
  		req->ki_ioprio = iocb->aio_reqprio;
  	} else

  		req->ki_ioprio = get_current_ioprio();

  	ret = kiocb_set_rw_flags(req, iocb->aio_rw_flags);
  	if (unlikely(ret))

  		return ret;

  
  	req->ki_flags &= ~IOCB_HIPRI; /* no one is going to poll for this I/O */
  	return 0;

  }

  static ssize_t aio_setup_rw(int rw, const struct iocb *iocb,
  		struct iovec **iovec, bool vectored, bool compat,
  		struct iov_iter *iter)

  {

  	void __user *buf = (void __user *)(uintptr_t)iocb->aio_buf;
  	size_t len = iocb->aio_nbytes;
  
  	if (!vectored) {
  		ssize_t ret = import_single_range(rw, buf, len, *iovec, iter);
  		*iovec = NULL;
  		return ret;
  	}

  #ifdef CONFIG_COMPAT
  	if (compat)

  		return compat_import_iovec(rw, buf, len, UIO_FASTIOV, iovec,
  				iter);

  #endif

  	return import_iovec(rw, buf, len, UIO_FASTIOV, iovec, iter);

  }

  static inline void aio_rw_done(struct kiocb *req, ssize_t ret)