/* 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;

        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->cookie = &fscache_fsdef_index;
        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);