text: /* FS-Cache cache handling
   *
   * Copyright (C) 2007 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 CACHE
  #include <linux/module.h>
  #include <linux/slab.h>
  #include "internal.h"
  
  LIST_HEAD(fscache_cache_list);
  DECLARE_RWSEM(fscache_addremove_sem);
  DECLARE_WAIT_QUEUE_HEAD(fscache_cache_cleared_wq);
  EXPORT_SYMBOL(fscache_cache_cleared_wq);
  
  static LIST_HEAD(fscache_cache_tag_list);
  
  /*
   * look up a cache tag
   */
  struct fscache_cache_tag *__fscache_lookup_cache_tag(const char *name)
  {
  	struct fscache_cache_tag *tag, *xtag;
  
  	/* firstly check for the existence of the tag under read lock */
  	down_read(&fscache_addremove_sem);
  
  	list_for_each_entry(tag, &fscache_cache_tag_list, link) {
  		if (strcmp(tag->name, name) == 0) {
  			atomic_inc(&tag->usage);
  			up_read(&fscache_addremove_sem);
  			return tag;
  		}
  	}
  
  	up_read(&fscache_addremove_sem);
  
  	/* the tag does not exist - create a candidate */
  	xtag = kzalloc(sizeof(*xtag) + strlen(name) + 1, GFP_KERNEL);
  	if (!xtag)
  		/* return a dummy tag if out of memory */
  		return ERR_PTR(-ENOMEM);
  
  	atomic_set(&xtag->usage, 1);
  	strcpy(xtag->name, name);
  
  	/* write lock, search again and add if still not present */
  	down_write(&fscache_addremove_sem);
  
  	list_for_each_entry(tag, &fscache_cache_tag_list, link) {
  		if (strcmp(tag->name, name) == 0) {
  			atomic_inc(&tag->usage);
  			up_write(&fscache_addremove_sem);
  			kfree(xtag);
  			return tag;
  		}
  	}
  
  	list_add_tail(&xtag->link, &fscache_cache_tag_list);
  	up_write(&fscache_addremove_sem);
  	return xtag;
  }
  
  /*
   * release a reference to a cache tag
   */
  void __fscache_release_cache_tag(struct fscache_cache_tag *tag)
  {
  	if (tag != ERR_PTR(-ENOMEM)) {
  		down_write(&fscache_addremove_sem);
  
  		if (atomic_dec_and_test(&tag->usage))
  			list_del_init(&tag->link);
  		else
  			tag = NULL;
  
  		up_write(&fscache_addremove_sem);
  
  		kfree(tag);
  	}
  }
  
  /*
   * select a cache in which to store an object
   * - the cache addremove semaphore must be at least read-locked by the caller
   * - the object will never be an index
   */
  struct fscache_cache *fscache_select_cache_for_object(
  	struct fscache_cookie *cookie)
  {
  	struct fscache_cache_tag *tag;
  	struct fscache_object *object;
  	struct fscache_cache *cache;
  
  	_enter("");
  
  	if (list_empty(&fscache_cache_list)) {
  		_leave(" = NULL [no cache]");
  		return NULL;
  	}
  
  	/* we check the parent to determine the cache to use */
  	spin_lock(&cookie->lock);
  
  	/* the first in the parent's backing list should be the preferred
  	 * cache */
  	if (!hlist_empty(&cookie->backing_objects)) {
  		object = hlist_entry(cookie->backing_objects.first,
  				     struct fscache_object, cookie_link);
  
  		cache = object->cache;
  		if (fscache_object_is_dying(object) ||
  		    test_bit(FSCACHE_IOERROR, &cache->flags))
  			cache = NULL;
  
  		spin_unlock(&cookie->lock);
  		_leave(" = %p [parent]", cache);
  		return cache;
  	}
  
  	/* the parent is unbacked */
  	if (cookie->type != FSCACHE_COOKIE_TYPE_INDEX) {
  		/* cookie not an index and is unbacked */
  		spin_unlock(&cookie->lock);
  		_leave(" = NULL [cookie ub,ni]");
  		return NULL;
  	}
  
  	spin_unlock(&cookie->lock);
  
  	if (!cookie->def->select_cache)
  		goto no_preference;
  
  	/* ask the netfs for its preference */
  	tag = cookie->def->select_cache(cookie->parent->netfs_data,
  					cookie->netfs_data);
  	if (!tag)
  		goto no_preference;
  
  	if (tag == ERR_PTR(-ENOMEM)) {
  		_leave(" = NULL [nomem tag]");
  		return NULL;
  	}
  
  	if (!tag->cache) {
  		_leave(" = NULL [unbacked tag]");
  		return NULL;
  	}
  
  	if (test_bit(FSCACHE_IOERROR, &tag->cache->flags))
  		return NULL;
  
  	_leave(" = %p [specific]", tag->cache);
  	return tag->cache;
  
  no_preference:
  	/* netfs has no preference - just select first cache */
  	cache = list_entry(fscache_cache_list.next,
  			   struct fscache_cache, link);
  	_leave(" = %p [first]", cache);
  	return cache;
  }
  
  /**
   * fscache_init_cache - Initialise a cache record
   * @cache: The cache record to be initialised
   * @ops: The cache operations to be installed in that record
   * @idfmt: Format string to define identifier
   * @...: sprintf-style arguments
   *
   * Initialise a record of a cache and fill in the name.
   *
   * See Documentation/filesystems/caching/backend-api.txt for a complete
   * description.
   */
  void fscache_init_cache(struct fscache_cache *cache,
  			const struct fscache_cache_ops *ops,
  			const char *idfmt,
  			...)
  {
  	va_list va;
  
  	memset(cache, 0, sizeof(*cache));
  
  	cache->ops = ops;
  
  	va_start(va, idfmt);
  	vsnprintf(cache->identifier, sizeof(cache->identifier), idfmt, va);
  	va_end(va);
  
  	INIT_WORK(&cache->op_gc, fscache_operation_gc);
  	INIT_LIST_HEAD(&cache->link);
  	INIT_LIST_HEAD(&cache->object_list);
  	INIT_LIST_HEAD(&cache->op_gc_list);
  	spin_lock_init(&cache->object_list_lock);
  	spin_lock_init(&cache->op_gc_list_lock);
  }
  EXPORT_SYMBOL(fscache_init_cache);
  
  /**
   * fscache_add_cache - Declare a cache as being open for business
   * @cache: The record describing the cache
   * @ifsdef: The record of the cache object describing the top-level index
   * @tagname: The tag describing this cache
   *
   * Add a cache to the system, making it available for netfs's to use.
   *
   * See Documentation/filesystems/caching/backend-api.txt for a complete
   * description.
   */
  int fscache_add_cache(struct fscache_cache *cache,
  		      struct fscache_object *ifsdef,
  		      const char *tagname)
  {
  	struct fscache_cache_tag *tag;
  
  	ASSERTCMP(ifsdef->cookie, ==, &fscache_fsdef_index);
  	BUG_ON(!cache->ops);
  	BUG_ON(!ifsdef);
  
  	cache->flags = 0;
  	ifsdef->event_mask =
  		((1 << NR_FSCACHE_OBJECT_EVENTS) - 1) &
  		~(1 << FSCACHE_OBJECT_EV_CLEARED);
  	__set_bit(FSCACHE_OBJECT_IS_AVAILABLE, &ifsdef->flags);
  
  	if (!tagname)
  		tagname = cache->identifier;
  
  	BUG_ON(!tagname[0]);
  
  	_enter("{%s.%s},,%s", cache->ops->name, cache->identifier, tagname);
  
  	/* we use the cache tag to uniquely identify caches */
  	tag = __fscache_lookup_cache_tag(tagname);
  	if (IS_ERR(tag))
  		goto nomem;
  
  	if (test_and_set_bit(FSCACHE_TAG_RESERVED, &tag->flags))
  		goto tag_in_use;
  
  	cache->kobj = kobject_create_and_add(tagname, fscache_root);
  	if (!cache->kobj)
  		goto error;
  
  	ifsdef->cache = cache;
  	cache->fsdef = ifsdef;
  
  	down_write(&fscache_addremove_sem);
  
  	tag->cache = cache;
  	cache->tag = tag;
  
  	/* add the cache to the list */
  	list_add(&cache->link, &fscache_cache_list);
  
  	/* add the cache's netfs definition index object to the cache's
  	 * list */
  	spin_lock(&cache->object_list_lock);
  	list_add_tail(&ifsdef->cache_link, &cache->object_list);
  	spin_unlock(&cache->object_list_lock);
  	fscache_objlist_add(ifsdef);
  
  	/* add the cache's netfs definition index object to the top level index
  	 * cookie as a known backing object */
  	spin_lock(&fscache_fsdef_index.lock);
  
  	hlist_add_head(&ifsdef->cookie_link,
  		       &fscache_fsdef_index.backing_objects);
  
  	atomic_inc(&fscache_fsdef_index.usage);
  
  	/* done */
  	spin_unlock(&fscache_fsdef_index.lock);
  	up_write(&fscache_addremove_sem);
  
  	pr_notice("Cache \"%s\" added (type %s)\n",
  		  cache->tag->name, cache->ops->name);
  	kobject_uevent(cache->kobj, KOBJ_ADD);
  
  	_leave(" = 0 [%s]", cache->identifier);
  	return 0;
  
  tag_in_use:
  	pr_err("Cache tag '%s' already in use\n", tagname);
  	__fscache_release_cache_tag(tag);
  	_leave(" = -EXIST");
  	return -EEXIST;
  
  error:
  	__fscache_release_cache_tag(tag);
  	_leave(" = -EINVAL");
  	return -EINVAL;
  
  nomem:
  	_leave(" = -ENOMEM");
  	return -ENOMEM;
  }
  EXPORT_SYMBOL(fscache_add_cache);
  
  /**
   * fscache_io_error - Note a cache I/O error
   * @cache: The record describing the cache
   *
   * Note that an I/O error occurred in a cache and that it should no longer be
   * used for anything.  This also reports the error into the kernel log.
   *
   * See Documentation/filesystems/caching/backend-api.txt for a complete
   * description.
   */
  void fscache_io_error(struct fscache_cache *cache)
  {
  	if (!test_and_set_bit(FSCACHE_IOERROR, &cache->flags))
  		pr_err("Cache '%s' stopped due to I/O error\n",
  		       cache->ops->name);
  }
  EXPORT_SYMBOL(fscache_io_error);
  
  /*
   * request withdrawal of all the objects in a cache
   * - all the objects being withdrawn are moved onto the supplied list
   */
  static void fscache_withdraw_all_objects(struct fscache_cache *cache,
  					 struct list_head *dying_objects)
  {
  	struct fscache_object *object;
  
  	while (!list_empty(&cache->object_list)) {
  		spin_lock(&cache->object_list_lock);
  
  		if (!list_empty(&cache->object_list)) {
  			object = list_entry(cache->object_list.next,
  					    struct fscache_object, cache_link);
  			list_move_tail(&object->cache_link, dying_objects);
  
  			_debug("withdraw %p", object->cookie);
  
  			/* This must be done under object_list_lock to prevent
  			 * a race with fscache_drop_object().
  			 */
  			fscache_raise_event(object, FSCACHE_OBJECT_EV_KILL);
  		}
  
  		spin_unlock(&cache->object_list_lock);
  		cond_resched();
  	}
  }
  
  /**
   * fscache_withdraw_cache - Withdraw a cache from the active service
   * @cache: The record describing the cache
   *
   * Withdraw a cache from service, unbinding all its cache objects from the
   * netfs cookies they're currently representing.
   *
   * See Documentation/filesystems/caching/backend-api.txt for a complete
   * description.
   */
  void fscache_withdraw_cache(struct fscache_cache *cache)
  {
  	LIST_HEAD(dying_objects);
  
  	_enter("");
  
  	pr_notice("Withdrawing cache \"%s\"\n",
  		  cache->tag->name);
  
  	/* make the cache unavailable for cookie acquisition */
  	if (test_and_set_bit(FSCACHE_CACHE_WITHDRAWN, &cache->flags))
  		BUG();
  
  	down_write(&fscache_addremove_sem);
  	list_del_init(&cache->link);
  	cache->tag->cache = NULL;
  	up_write(&fscache_addremove_sem);
  
  	/* make sure all pages pinned by operations on behalf of the netfs are
  	 * written to disk */
  	fscache_stat(&fscache_n_cop_sync_cache);
  	cache->ops->sync_cache(cache);
  	fscache_stat_d(&fscache_n_cop_sync_cache);
  
  	/* dissociate all the netfs pages backed by this cache from the block
  	 * mappings in the cache */
  	fscache_stat(&fscache_n_cop_dissociate_pages);
  	cache->ops->dissociate_pages(cache);
  	fscache_stat_d(&fscache_n_cop_dissociate_pages);
  
  	/* we now have to destroy all the active objects pertaining to this
  	 * cache - which we do by passing them off to thread pool to be
  	 * disposed of */
  	_debug("destroy");
  
  	fscache_withdraw_all_objects(cache, &dying_objects);
  
  	/* wait for all extant objects to finish their outstanding operations
  	 * and go away */
  	_debug("wait for finish");
  	wait_event(fscache_cache_cleared_wq,
  		   atomic_read(&cache->object_count) == 0);
  	_debug("wait for clearance");
  	wait_event(fscache_cache_cleared_wq,
  		   list_empty(&cache->object_list));
  	_debug("cleared");
  	ASSERT(list_empty(&dying_objects));
  
  	kobject_put(cache->kobj);
  
  	clear_bit(FSCACHE_TAG_RESERVED, &cache->tag->flags);
  	fscache_release_cache_tag(cache->tag);
  	cache->tag = NULL;
  
  	_leave("");
  }
  EXPORT_SYMBOL(fscache_withdraw_cache);
  