/* Cache page management and data I/O routines
   *
   * Copyright (C) 2004-2008 Red Hat, Inc. All Rights Reserved.
   * Written by David Howells (dhowells@redhat.com)
   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public License
   * as published by the Free Software Foundation; either version
   * 2 of the License, or (at your option) any later version.
   */
  
  #define FSCACHE_DEBUG_LEVEL PAGE
  #include <linux/module.h>
  #include <linux/fscache-cache.h>
  #include <linux/buffer_head.h>
  #include <linux/pagevec.h>

  #include <linux/slab.h>

  #include "internal.h"
  
  /*
   * check to see if a page is being written to the cache
   */
  bool __fscache_check_page_write(struct fscache_cookie *cookie, struct page *page)
  {
  	void *val;
  
  	rcu_read_lock();
  	val = radix_tree_lookup(&cookie->stores, page->index);
  	rcu_read_unlock();
  
  	return val != NULL;
  }
  EXPORT_SYMBOL(__fscache_check_page_write);
  
  /*
   * wait for a page to finish being written to the cache
   */
  void __fscache_wait_on_page_write(struct fscache_cookie *cookie, struct page *page)
  {
  	wait_queue_head_t *wq = bit_waitqueue(&cookie->flags, 0);
  
  	wait_event(*wq, !__fscache_check_page_write(cookie, page));
  }
  EXPORT_SYMBOL(__fscache_wait_on_page_write);
  
  /*

   * decide whether a page can be released, possibly by cancelling a store to it
   * - we're allowed to sleep if __GFP_WAIT is flagged
   */
  bool __fscache_maybe_release_page(struct fscache_cookie *cookie,
  				  struct page *page,
  				  gfp_t gfp)
  {
  	struct page *xpage;
  	void *val;
  
  	_enter("%p,%p,%x", cookie, page, gfp);
  
  	rcu_read_lock();
  	val = radix_tree_lookup(&cookie->stores, page->index);
  	if (!val) {
  		rcu_read_unlock();
  		fscache_stat(&fscache_n_store_vmscan_not_storing);
  		__fscache_uncache_page(cookie, page);
  		return true;
  	}
  
  	/* see if the page is actually undergoing storage - if so we can't get
  	 * rid of it till the cache has finished with it */
  	if (radix_tree_tag_get(&cookie->stores, page->index,
  			       FSCACHE_COOKIE_STORING_TAG)) {
  		rcu_read_unlock();
  		goto page_busy;
  	}
  
  	/* the page is pending storage, so we attempt to cancel the store and
  	 * discard the store request so that the page can be reclaimed */
  	spin_lock(&cookie->stores_lock);
  	rcu_read_unlock();
  
  	if (radix_tree_tag_get(&cookie->stores, page->index,
  			       FSCACHE_COOKIE_STORING_TAG)) {
  		/* the page started to undergo storage whilst we were looking,
  		 * so now we can only wait or return */
  		spin_unlock(&cookie->stores_lock);
  		goto page_busy;
  	}
  
  	xpage = radix_tree_delete(&cookie->stores, page->index);
  	spin_unlock(&cookie->stores_lock);
  
  	if (xpage) {
  		fscache_stat(&fscache_n_store_vmscan_cancelled);
  		fscache_stat(&fscache_n_store_radix_deletes);
  		ASSERTCMP(xpage, ==, page);
  	} else {
  		fscache_stat(&fscache_n_store_vmscan_gone);
  	}
  
  	wake_up_bit(&cookie->flags, 0);
  	if (xpage)
  		page_cache_release(xpage);
  	__fscache_uncache_page(cookie, page);
  	return true;
  
  page_busy:
  	/* we might want to wait here, but that could deadlock the allocator as

  	 * the work threads writing to the cache may all end up sleeping

  	 * on memory allocation */
  	fscache_stat(&fscache_n_store_vmscan_busy);
  	return false;
  }
  EXPORT_SYMBOL(__fscache_maybe_release_page);
  
  /*

   * note that a page has finished being written to the cache
   */

  static void fscache_end_page_write(struct fscache_object *object,
  				   struct page *page)

  {

  	struct fscache_cookie *cookie;
  	struct page *xpage = NULL;

  	spin_lock(&object->lock);
  	cookie = object->cookie;
  	if (cookie) {
  		/* delete the page from the tree if it is now no longer
  		 * pending */
  		spin_lock(&cookie->stores_lock);

  		radix_tree_tag_clear(&cookie->stores, page->index,
  				     FSCACHE_COOKIE_STORING_TAG);

  		if (!radix_tree_tag_get(&cookie->stores, page->index,
  					FSCACHE_COOKIE_PENDING_TAG)) {
  			fscache_stat(&fscache_n_store_radix_deletes);
  			xpage = radix_tree_delete(&cookie->stores, page->index);
  		}

  		spin_unlock(&cookie->stores_lock);
  		wake_up_bit(&cookie->flags, 0);
  	}
  	spin_unlock(&object->lock);
  	if (xpage)
  		page_cache_release(xpage);

  }
  
  /*
   * actually apply the changed attributes to a cache object
   */
  static void fscache_attr_changed_op(struct fscache_operation *op)
  {
  	struct fscache_object *object = op->object;

  	int ret;

  
  	_enter("{OBJ%x OP%x}", object->debug_id, op->debug_id);
  
  	fscache_stat(&fscache_n_attr_changed_calls);

  	if (fscache_object_is_active(object)) {

  		fscache_stat(&fscache_n_cop_attr_changed);

  		ret = object->cache->ops->attr_changed(object);

  		fscache_stat_d(&fscache_n_cop_attr_changed);

  		if (ret < 0)
  			fscache_abort_object(object);
  	}

  
  	_leave("");
  }
  
  /*
   * notification that the attributes on an object have changed
   */
  int __fscache_attr_changed(struct fscache_cookie *cookie)
  {
  	struct fscache_operation *op;
  	struct fscache_object *object;
  
  	_enter("%p", cookie);
  
  	ASSERTCMP(cookie->def->type, !=, FSCACHE_COOKIE_TYPE_INDEX);
  
  	fscache_stat(&fscache_n_attr_changed);
  
  	op = kzalloc(sizeof(*op), GFP_KERNEL);
  	if (!op) {
  		fscache_stat(&fscache_n_attr_changed_nomem);
  		_leave(" = -ENOMEM");
  		return -ENOMEM;
  	}

  	fscache_operation_init(op, fscache_attr_changed_op, NULL);
  	op->flags = FSCACHE_OP_ASYNC | (1 << FSCACHE_OP_EXCLUSIVE);

  
  	spin_lock(&cookie->lock);
  
  	if (hlist_empty(&cookie->backing_objects))
  		goto nobufs;
  	object = hlist_entry(cookie->backing_objects.first,
  			     struct fscache_object, cookie_link);
  
  	if (fscache_submit_exclusive_op(object, op) < 0)
  		goto nobufs;
  	spin_unlock(&cookie->lock);
  	fscache_stat(&fscache_n_attr_changed_ok);
  	fscache_put_operation(op);
  	_leave(" = 0");
  	return 0;
  
  nobufs:
  	spin_unlock(&cookie->lock);
  	kfree(op);
  	fscache_stat(&fscache_n_attr_changed_nobufs);
  	_leave(" = %d", -ENOBUFS);
  	return -ENOBUFS;
  }
  EXPORT_SYMBOL(__fscache_attr_changed);
  
  /*

   * release a retrieval op reference
   */
  static void fscache_release_retrieval_op(struct fscache_operation *_op)
  {
  	struct fscache_retrieval *op =
  		container_of(_op, struct fscache_retrieval, op);
  
  	_enter("{OP%x}", op->op.debug_id);
  
  	fscache_hist(fscache_retrieval_histogram, op->start_time);
  	if (op->context)
  		fscache_put_context(op->op.object->cookie, op->context);
  
  	_leave("");
  }
  
  /*
   * allocate a retrieval op
   */
  static struct fscache_retrieval *fscache_alloc_retrieval(
  	struct address_space *mapping,
  	fscache_rw_complete_t end_io_func,
  	void *context)
  {
  	struct fscache_retrieval *op;
  
  	/* allocate a retrieval operation and attempt to submit it */
  	op = kzalloc(sizeof(*op), GFP_NOIO);
  	if (!op) {
  		fscache_stat(&fscache_n_retrievals_nomem);
  		return NULL;
  	}

  	fscache_operation_init(&op->op, NULL, fscache_release_retrieval_op);

  	op->op.flags	= FSCACHE_OP_MYTHREAD | (1 << FSCACHE_OP_WAITING);
  	op->mapping	= mapping;
  	op->end_io_func	= end_io_func;
  	op->context	= context;
  	op->start_time	= jiffies;

  	INIT_LIST_HEAD(&op->to_do);
  	return op;
  }
  
  /*
   * wait for a deferred lookup to complete
   */
  static int fscache_wait_for_deferred_lookup(struct fscache_cookie *cookie)
  {
  	unsigned long jif;
  
  	_enter("");
  
  	if (!test_bit(FSCACHE_COOKIE_LOOKING_UP, &cookie->flags)) {
  		_leave(" = 0 [imm]");
  		return 0;
  	}
  
  	fscache_stat(&fscache_n_retrievals_wait);
  
  	jif = jiffies;
  	if (wait_on_bit(&cookie->flags, FSCACHE_COOKIE_LOOKING_UP,
  			fscache_wait_bit_interruptible,
  			TASK_INTERRUPTIBLE) != 0) {
  		fscache_stat(&fscache_n_retrievals_intr);
  		_leave(" = -ERESTARTSYS");
  		return -ERESTARTSYS;
  	}
  
  	ASSERT(!test_bit(FSCACHE_COOKIE_LOOKING_UP, &cookie->flags));
  
  	smp_rmb();
  	fscache_hist(fscache_retrieval_delay_histogram, jif);
  	_leave(" = 0 [dly]");
  	return 0;
  }
  
  /*

   * wait for an object to become active (or dead)
   */
  static int fscache_wait_for_retrieval_activation(struct fscache_object *object,
  						 struct fscache_retrieval *op,
  						 atomic_t *stat_op_waits,
  						 atomic_t *stat_object_dead)
  {
  	int ret;
  
  	if (!test_bit(FSCACHE_OP_WAITING, &op->op.flags))
  		goto check_if_dead;
  
  	_debug(">>> WT");
  	fscache_stat(stat_op_waits);
  	if (wait_on_bit(&op->op.flags, FSCACHE_OP_WAITING,
  			fscache_wait_bit_interruptible,
  			TASK_INTERRUPTIBLE) < 0) {
  		ret = fscache_cancel_op(&op->op);
  		if (ret == 0)
  			return -ERESTARTSYS;
  
  		/* it's been removed from the pending queue by another party,
  		 * so we should get to run shortly */
  		wait_on_bit(&op->op.flags, FSCACHE_OP_WAITING,
  			    fscache_wait_bit, TASK_UNINTERRUPTIBLE);
  	}
  	_debug("<<< GO");
  
  check_if_dead:
  	if (unlikely(fscache_object_is_dead(object))) {
  		fscache_stat(stat_object_dead);
  		return -ENOBUFS;
  	}
  	return 0;
  }
  
  /*

   * read a page from the cache or allocate a block in which to store it
   * - we return:
   *   -ENOMEM	- out of memory, nothing done
   *   -ERESTARTSYS - interrupted
   *   -ENOBUFS	- no backing object available in which to cache the block
   *   -ENODATA	- no data available in the backing object for this block
   *   0		- dispatched a read - it'll call end_io_func() when finished
   */
  int __fscache_read_or_alloc_page(struct fscache_cookie *cookie,
  				 struct page *page,
  				 fscache_rw_complete_t end_io_func,
  				 void *context,
  				 gfp_t gfp)
  {
  	struct fscache_retrieval *op;
  	struct fscache_object *object;
  	int ret;
  
  	_enter("%p,%p,,,", cookie, page);
  
  	fscache_stat(&fscache_n_retrievals);
  
  	if (hlist_empty(&cookie->backing_objects))
  		goto nobufs;
  
  	ASSERTCMP(cookie->def->type, !=, FSCACHE_COOKIE_TYPE_INDEX);
  	ASSERTCMP(page, !=, NULL);
  
  	if (fscache_wait_for_deferred_lookup(cookie) < 0)
  		return -ERESTARTSYS;
  
  	op = fscache_alloc_retrieval(page->mapping, end_io_func, context);
  	if (!op) {
  		_leave(" = -ENOMEM");
  		return -ENOMEM;
  	}
  
  	spin_lock(&cookie->lock);
  
  	if (hlist_empty(&cookie->backing_objects))
  		goto nobufs_unlock;
  	object = hlist_entry(cookie->backing_objects.first,
  			     struct fscache_object, cookie_link);
  
  	ASSERTCMP(object->state, >, FSCACHE_OBJECT_LOOKING_UP);

  	atomic_inc(&object->n_reads);
  	set_bit(FSCACHE_OP_DEC_READ_CNT, &op->op.flags);

  	if (fscache_submit_op(object, &op->op) < 0)
  		goto nobufs_unlock;
  	spin_unlock(&cookie->lock);
  
  	fscache_stat(&fscache_n_retrieval_ops);
  
  	/* pin the netfs read context in case we need to do the actual netfs
  	 * read because we've encountered a cache read failure */
  	fscache_get_context(object->cookie, op->context);
  
  	/* we wait for the operation to become active, and then process it
  	 * *here*, in this thread, and not in the thread pool */

  	ret = fscache_wait_for_retrieval_activation(
  		object, op,
  		__fscache_stat(&fscache_n_retrieval_op_waits),
  		__fscache_stat(&fscache_n_retrievals_object_dead));
  	if (ret < 0)
  		goto error;

  
  	/* ask the cache to honour the operation */
  	if (test_bit(FSCACHE_COOKIE_NO_DATA_YET, &object->cookie->flags)) {

  		fscache_stat(&fscache_n_cop_allocate_page);

  		ret = object->cache->ops->allocate_page(op, page, gfp);

  		fscache_stat_d(&fscache_n_cop_allocate_page);

  		if (ret == 0)
  			ret = -ENODATA;
  	} else {

  		fscache_stat(&fscache_n_cop_read_or_alloc_page);

  		ret = object->cache->ops->read_or_alloc_page(op, page, gfp);

  		fscache_stat_d(&fscache_n_cop_read_or_alloc_page);

  	}

  error:

  	if (ret == -ENOMEM)
  		fscache_stat(&fscache_n_retrievals_nomem);
  	else if (ret == -ERESTARTSYS)
  		fscache_stat(&fscache_n_retrievals_intr);
  	else if (ret == -ENODATA)
  		fscache_stat(&fscache_n_retrievals_nodata);
  	else if (ret < 0)
  		fscache_stat(&fscache_n_retrievals_nobufs);
  	else
  		fscache_stat(&fscache_n_retrievals_ok);
  
  	fscache_put_retrieval(op);
  	_leave(" = %d", ret);
  	return ret;
  
  nobufs_unlock:
  	spin_unlock(&cookie->lock);
  	kfree(op);
  nobufs:
  	fscache_stat(&fscache_n_retrievals_nobufs);
  	_leave(" = -ENOBUFS");
  	return -ENOBUFS;
  }
  EXPORT_SYMBOL(__fscache_read_or_alloc_page);
  
  /*
   * read a list of page from the cache or allocate a block in which to store
   * them
   * - we return:
   *   -ENOMEM	- out of memory, some pages may be being read
   *   -ERESTARTSYS - interrupted, some pages may be being read
   *   -ENOBUFS	- no backing object or space available in which to cache any
   *                pages not being read
   *   -ENODATA	- no data available in the backing object for some or all of
   *                the pages
   *   0		- dispatched a read on all pages
   *
   * end_io_func() will be called for each page read from the cache as it is
   * finishes being read
   *
   * any pages for which a read is dispatched will be removed from pages and
   * nr_pages
   */
  int __fscache_read_or_alloc_pages(struct fscache_cookie *cookie,
  				  struct address_space *mapping,
  				  struct list_head *pages,
  				  unsigned *nr_pages,
  				  fscache_rw_complete_t end_io_func,
  				  void *context,
  				  gfp_t gfp)
  {

  	struct fscache_retrieval *op;
  	struct fscache_object *object;
  	int ret;
  
  	_enter("%p,,%d,,,", cookie, *nr_pages);
  
  	fscache_stat(&fscache_n_retrievals);
  
  	if (hlist_empty(&cookie->backing_objects))
  		goto nobufs;
  
  	ASSERTCMP(cookie->def->type, !=, FSCACHE_COOKIE_TYPE_INDEX);
  	ASSERTCMP(*nr_pages, >, 0);
  	ASSERT(!list_empty(pages));
  
  	if (fscache_wait_for_deferred_lookup(cookie) < 0)
  		return -ERESTARTSYS;
  
  	op = fscache_alloc_retrieval(mapping, end_io_func, context);
  	if (!op)
  		return -ENOMEM;
  
  	spin_lock(&cookie->lock);
  
  	if (hlist_empty(&cookie->backing_objects))
  		goto nobufs_unlock;
  	object = hlist_entry(cookie->backing_objects.first,
  			     struct fscache_object, cookie_link);

  	atomic_inc(&object->n_reads);
  	set_bit(FSCACHE_OP_DEC_READ_CNT, &op->op.flags);

  	if (fscache_submit_op(object, &op->op) < 0)
  		goto nobufs_unlock;
  	spin_unlock(&cookie->lock);
  
  	fscache_stat(&fscache_n_retrieval_ops);
  
  	/* pin the netfs read context in case we need to do the actual netfs
  	 * read because we've encountered a cache read failure */
  	fscache_get_context(object->cookie, op->context);
  
  	/* we wait for the operation to become active, and then process it
  	 * *here*, in this thread, and not in the thread pool */

  	ret = fscache_wait_for_retrieval_activation(
  		object, op,
  		__fscache_stat(&fscache_n_retrieval_op_waits),
  		__fscache_stat(&fscache_n_retrievals_object_dead));
  	if (ret < 0)
  		goto error;

  
  	/* ask the cache to honour the operation */

  	if (test_bit(FSCACHE_COOKIE_NO_DATA_YET, &object->cookie->flags)) {
  		fscache_stat(&fscache_n_cop_allocate_pages);
  		ret = object->cache->ops->allocate_pages(
  			op, pages, nr_pages, gfp);
  		fscache_stat_d(&fscache_n_cop_allocate_pages);
  	} else {
  		fscache_stat(&fscache_n_cop_read_or_alloc_pages);
  		ret = object->cache->ops->read_or_alloc_pages(
  			op, pages, nr_pages, gfp);
  		fscache_stat_d(&fscache_n_cop_read_or_alloc_pages);
  	}

  error:

  	if (ret == -ENOMEM)
  		fscache_stat(&fscache_n_retrievals_nomem);
  	else if (ret == -ERESTARTSYS)
  		fscache_stat(&fscache_n_retrievals_intr);
  	else if (ret == -ENODATA)
  		fscache_stat(&fscache_n_retrievals_nodata);
  	else if (ret < 0)
  		fscache_stat(&fscache_n_retrievals_nobufs);
  	else
  		fscache_stat(&fscache_n_retrievals_ok);
  
  	fscache_put_retrieval(op);
  	_leave(" = %d", ret);
  	return ret;
  
  nobufs_unlock:
  	spin_unlock(&cookie->lock);
  	kfree(op);
  nobufs:
  	fscache_stat(&fscache_n_retrievals_nobufs);
  	_leave(" = -ENOBUFS");
  	return -ENOBUFS;
  }
  EXPORT_SYMBOL(__fscache_read_or_alloc_pages);
  
  /*
   * allocate a block in the cache on which to store a page
   * - we return:
   *   -ENOMEM	- out of memory, nothing done
   *   -ERESTARTSYS - interrupted
   *   -ENOBUFS	- no backing object available in which to cache the block
   *   0		- block allocated
   */
  int __fscache_alloc_page(struct fscache_cookie *cookie,
  			 struct page *page,
  			 gfp_t gfp)
  {
  	struct fscache_retrieval *op;
  	struct fscache_object *object;
  	int ret;
  
  	_enter("%p,%p,,,", cookie, page);
  
  	fscache_stat(&fscache_n_allocs);
  
  	if (hlist_empty(&cookie->backing_objects))
  		goto nobufs;
  
  	ASSERTCMP(cookie->def->type, !=, FSCACHE_COOKIE_TYPE_INDEX);
  	ASSERTCMP(page, !=, NULL);
  
  	if (fscache_wait_for_deferred_lookup(cookie) < 0)
  		return -ERESTARTSYS;
  
  	op = fscache_alloc_retrieval(page->mapping, NULL, NULL);
  	if (!op)
  		return -ENOMEM;
  
  	spin_lock(&cookie->lock);
  
  	if (hlist_empty(&cookie->backing_objects))
  		goto nobufs_unlock;
  	object = hlist_entry(cookie->backing_objects.first,
  			     struct fscache_object, cookie_link);
  
  	if (fscache_submit_op(object, &op->op) < 0)
  		goto nobufs_unlock;
  	spin_unlock(&cookie->lock);
  
  	fscache_stat(&fscache_n_alloc_ops);

  	ret = fscache_wait_for_retrieval_activation(
  		object, op,
  		__fscache_stat(&fscache_n_alloc_op_waits),
  		__fscache_stat(&fscache_n_allocs_object_dead));
  	if (ret < 0)
  		goto error;

  
  	/* ask the cache to honour the operation */

  	fscache_stat(&fscache_n_cop_allocate_page);

  	ret = object->cache->ops->allocate_page(op, page, gfp);

  	fscache_stat_d(&fscache_n_cop_allocate_page);

  error:
  	if (ret == -ERESTARTSYS)
  		fscache_stat(&fscache_n_allocs_intr);
  	else if (ret < 0)

  		fscache_stat(&fscache_n_allocs_nobufs);
  	else
  		fscache_stat(&fscache_n_allocs_ok);
  
  	fscache_put_retrieval(op);
  	_leave(" = %d", ret);
  	return ret;
  
  nobufs_unlock:
  	spin_unlock(&cookie->lock);
  	kfree(op);
  nobufs:
  	fscache_stat(&fscache_n_allocs_nobufs);
  	_leave(" = -ENOBUFS");
  	return -ENOBUFS;
  }
  EXPORT_SYMBOL(__fscache_alloc_page);
  
  /*
   * release a write op reference
   */
  static void fscache_release_write_op(struct fscache_operation *_op)
  {
  	_enter("{OP%x}", _op->debug_id);
  }
  
  /*
   * perform the background storage of a page into the cache
   */
  static void fscache_write_op(struct fscache_operation *_op)
  {
  	struct fscache_storage *op =
  		container_of(_op, struct fscache_storage, op);
  	struct fscache_object *object = op->op.object;

  	struct fscache_cookie *cookie;

  	struct page *page;
  	unsigned n;
  	void *results[1];
  	int ret;
  
  	_enter("{OP%x,%d}", op->op.debug_id, atomic_read(&op->op.usage));

  	spin_lock(&object->lock);

  	cookie = object->cookie;

  	if (!fscache_object_is_active(object) || !cookie) {

  		spin_unlock(&object->lock);

  		_leave("");
  		return;
  	}

  	spin_lock(&cookie->stores_lock);

  	fscache_stat(&fscache_n_store_calls);
  
  	/* find a page to store */
  	page = NULL;
  	n = radix_tree_gang_lookup_tag(&cookie->stores, results, 0, 1,
  				       FSCACHE_COOKIE_PENDING_TAG);
  	if (n != 1)
  		goto superseded;
  	page = results[0];
  	_debug("gang %d [%lx]", n, page->index);

  	if (page->index > op->store_limit) {
  		fscache_stat(&fscache_n_store_pages_over_limit);

  		goto superseded;

  	}

  	radix_tree_tag_set(&cookie->stores, page->index,
  			   FSCACHE_COOKIE_STORING_TAG);
  	radix_tree_tag_clear(&cookie->stores, page->index,
  			     FSCACHE_COOKIE_PENDING_TAG);

  	spin_unlock(&cookie->stores_lock);

  	spin_unlock(&object->lock);

  	fscache_stat(&fscache_n_store_pages);
  	fscache_stat(&fscache_n_cop_write_page);
  	ret = object->cache->ops->write_page(op, page);
  	fscache_stat_d(&fscache_n_cop_write_page);

  	fscache_end_page_write(object, page);
  	if (ret < 0) {

  		fscache_abort_object(object);
  	} else {
  		fscache_enqueue_operation(&op->op);

  	}
  
  	_leave("");
  	return;
  
  superseded:
  	/* this writer is going away and there aren't any more things to
  	 * write */
  	_debug("cease");

  	spin_unlock(&cookie->stores_lock);

  	clear_bit(FSCACHE_OBJECT_PENDING_WRITE, &object->flags);
  	spin_unlock(&object->lock);

  	_leave("");
  }
  
  /*
   * request a page be stored in the cache
   * - returns:
   *   -ENOMEM	- out of memory, nothing done
   *   -ENOBUFS	- no backing object available in which to cache the page
   *   0		- dispatched a write - it'll call end_io_func() when finished
   *
   * if the cookie still has a backing object at this point, that object can be
   * in one of a few states with respect to storage processing:
   *
   *  (1) negative lookup, object not yet created (FSCACHE_COOKIE_CREATING is
   *      set)
   *
   *	(a) no writes yet (set FSCACHE_COOKIE_PENDING_FILL and queue deferred
   *	    fill op)
   *
   *	(b) writes deferred till post-creation (mark page for writing and
   *	    return immediately)
   *
   *  (2) negative lookup, object created, initial fill being made from netfs
   *      (FSCACHE_COOKIE_INITIAL_FILL is set)
   *
   *	(a) fill point not yet reached this page (mark page for writing and
   *          return)
   *
   *	(b) fill point passed this page (queue op to store this page)
   *
   *  (3) object extant (queue op to store this page)
   *
   * any other state is invalid
   */
  int __fscache_write_page(struct fscache_cookie *cookie,
  			 struct page *page,
  			 gfp_t gfp)
  {
  	struct fscache_storage *op;
  	struct fscache_object *object;
  	int ret;
  
  	_enter("%p,%x,", cookie, (u32) page->flags);
  
  	ASSERTCMP(cookie->def->type, !=, FSCACHE_COOKIE_TYPE_INDEX);
  	ASSERT(PageFsCache(page));
  
  	fscache_stat(&fscache_n_stores);
  
  	op = kzalloc(sizeof(*op), GFP_NOIO);
  	if (!op)
  		goto nomem;

  	fscache_operation_init(&op->op, fscache_write_op,
  			       fscache_release_write_op);
  	op->op.flags = FSCACHE_OP_ASYNC | (1 << FSCACHE_OP_WAITING);

  
  	ret = radix_tree_preload(gfp & ~__GFP_HIGHMEM);
  	if (ret < 0)
  		goto nomem_free;
  
  	ret = -ENOBUFS;
  	spin_lock(&cookie->lock);
  
  	if (hlist_empty(&cookie->backing_objects))
  		goto nobufs;
  	object = hlist_entry(cookie->backing_objects.first,
  			     struct fscache_object, cookie_link);
  	if (test_bit(FSCACHE_IOERROR, &object->cache->flags))
  		goto nobufs;
  
  	/* add the page to the pending-storage radix tree on the backing
  	 * object */
  	spin_lock(&object->lock);

  	spin_lock(&cookie->stores_lock);

  
  	_debug("store limit %llx", (unsigned long long) object->store_limit);
  
  	ret = radix_tree_insert(&cookie->stores, page->index, page);
  	if (ret < 0) {
  		if (ret == -EEXIST)
  			goto already_queued;
  		_debug("insert failed %d", ret);
  		goto nobufs_unlock_obj;
  	}
  
  	radix_tree_tag_set(&cookie->stores, page->index,
  			   FSCACHE_COOKIE_PENDING_TAG);
  	page_cache_get(page);
  
  	/* we only want one writer at a time, but we do need to queue new
  	 * writers after exclusive ops */
  	if (test_and_set_bit(FSCACHE_OBJECT_PENDING_WRITE, &object->flags))
  		goto already_pending;

  	spin_unlock(&cookie->stores_lock);

  	spin_unlock(&object->lock);
  
  	op->op.debug_id	= atomic_inc_return(&fscache_op_debug_id);
  	op->store_limit = object->store_limit;
  
  	if (fscache_submit_op(object, &op->op) < 0)
  		goto submit_failed;
  
  	spin_unlock(&cookie->lock);
  	radix_tree_preload_end();
  	fscache_stat(&fscache_n_store_ops);
  	fscache_stat(&fscache_n_stores_ok);

  	/* the work queue now carries its own ref on the object */

  	fscache_put_operation(&op->op);
  	_leave(" = 0");
  	return 0;
  
  already_queued:
  	fscache_stat(&fscache_n_stores_again);
  already_pending:

  	spin_unlock(&cookie->stores_lock);

  	spin_unlock(&object->lock);
  	spin_unlock(&cookie->lock);
  	radix_tree_preload_end();
  	kfree(op);
  	fscache_stat(&fscache_n_stores_ok);
  	_leave(" = 0");
  	return 0;
  
  submit_failed:

  	spin_lock(&cookie->stores_lock);

  	radix_tree_delete(&cookie->stores, page->index);

  	spin_unlock(&cookie->stores_lock);

  	page_cache_release(page);
  	ret = -ENOBUFS;
  	goto nobufs;
  
  nobufs_unlock_obj:

  	spin_unlock(&cookie->stores_lock);

  	spin_unlock(&object->lock);
  nobufs:
  	spin_unlock(&cookie->lock);
  	radix_tree_preload_end();
  	kfree(op);
  	fscache_stat(&fscache_n_stores_nobufs);
  	_leave(" = -ENOBUFS");
  	return -ENOBUFS;
  
  nomem_free:
  	kfree(op);
  nomem:
  	fscache_stat(&fscache_n_stores_oom);
  	_leave(" = -ENOMEM");
  	return -ENOMEM;
  }
  EXPORT_SYMBOL(__fscache_write_page);
  
  /*
   * remove a page from the cache
   */
  void __fscache_uncache_page(struct fscache_cookie *cookie, struct page *page)
  {
  	struct fscache_object *object;
  
  	_enter(",%p", page);
  
  	ASSERTCMP(cookie->def->type, !=, FSCACHE_COOKIE_TYPE_INDEX);
  	ASSERTCMP(page, !=, NULL);
  
  	fscache_stat(&fscache_n_uncaches);
  
  	/* cache withdrawal may beat us to it */
  	if (!PageFsCache(page))
  		goto done;
  
  	/* get the object */
  	spin_lock(&cookie->lock);
  
  	if (hlist_empty(&cookie->backing_objects)) {
  		ClearPageFsCache(page);
  		goto done_unlock;
  	}
  
  	object = hlist_entry(cookie->backing_objects.first,
  			     struct fscache_object, cookie_link);
  
  	/* there might now be stuff on disk we could read */
  	clear_bit(FSCACHE_COOKIE_NO_DATA_YET, &cookie->flags);
  
  	/* only invoke the cache backend if we managed to mark the page
  	 * uncached here; this deals with synchronisation vs withdrawal */
  	if (TestClearPageFsCache(page) &&
  	    object->cache->ops->uncache_page) {
  		/* the cache backend releases the cookie lock */

  		fscache_stat(&fscache_n_cop_uncache_page);

  		object->cache->ops->uncache_page(object, page);

  		fscache_stat_d(&fscache_n_cop_uncache_page);

  		goto done;
  	}
  
  done_unlock:
  	spin_unlock(&cookie->lock);
  done:
  	_leave("");
  }
  EXPORT_SYMBOL(__fscache_uncache_page);
  
  /**
   * fscache_mark_pages_cached - Mark pages as being cached
   * @op: The retrieval op pages are being marked for
   * @pagevec: The pages to be marked
   *
   * Mark a bunch of netfs pages as being cached.  After this is called,
   * the netfs must call fscache_uncache_page() to remove the mark.
   */
  void fscache_mark_pages_cached(struct fscache_retrieval *op,
  			       struct pagevec *pagevec)
  {
  	struct fscache_cookie *cookie = op->op.object->cookie;
  	unsigned long loop;
  
  #ifdef CONFIG_FSCACHE_STATS
  	atomic_add(pagevec->nr, &fscache_n_marks);
  #endif
  
  	for (loop = 0; loop < pagevec->nr; loop++) {
  		struct page *page = pagevec->pages[loop];
  
  		_debug("- mark %p{%lx}", page, page->index);
  		if (TestSetPageFsCache(page)) {
  			static bool once_only;
  			if (!once_only) {
  				once_only = true;
  				printk(KERN_WARNING "FS-Cache:"
  				       " Cookie type %s marked page %lx"
  				       " multiple times
  ",
  				       cookie->def->name, page->index);
  			}
  		}
  	}
  
  	if (cookie->def->mark_pages_cached)
  		cookie->def->mark_pages_cached(cookie->netfs_data,
  					       op->mapping, pagevec);
  	pagevec_reinit(pagevec);
  }
  EXPORT_SYMBOL(fscache_mark_pages_cached);

  
  /*
   * Uncache all the pages in an inode that are marked PG_fscache, assuming them
   * to be associated with the given cookie.
   */
  void __fscache_uncache_all_inode_pages(struct fscache_cookie *cookie,
  				       struct inode *inode)
  {
  	struct address_space *mapping = inode->i_mapping;
  	struct pagevec pvec;
  	pgoff_t next;
  	int i;
  
  	_enter("%p,%p", cookie, inode);
  
  	if (!mapping || mapping->nrpages == 0) {
  		_leave(" [no pages]");
  		return;
  	}
  
  	pagevec_init(&pvec, 0);
  	next = 0;

  	do {
  		if (!pagevec_lookup(&pvec, mapping, next, PAGEVEC_SIZE))
  			break;

  		for (i = 0; i < pagevec_count(&pvec); i++) {
  			struct page *page = pvec.pages[i];

  			next = page->index;

  			if (PageFsCache(page)) {
  				__fscache_wait_on_page_write(cookie, page);
  				__fscache_uncache_page(cookie, page);
  			}
  		}
  		pagevec_release(&pvec);
  		cond_resched();

  	} while (++next);

  
  	_leave("");
  }
  EXPORT_SYMBOL(__fscache_uncache_all_inode_pages);