cache.c

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/* FS-Cache cache handling
 *
 * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells ([email protected])
 *
 * 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 (object->state >= FSCACHE_OBJECT_DYING ||
            test_bit(FSCACHE_IOERROR, &cache->flags))
            cache = NULL;

        spin_unlock(&cookie->lock);
        _leave(" = %p [parent]", cache);
        return cache;
    }

    /* the parent is unbacked */
    if (cookie->def->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;
}

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);

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 = ULONG_MAX & ~(1 << FSCACHE_OBJECT_EV_CLEARED);
    ifsdef->state = FSCACHE_OBJECT_ACTIVE;

    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);

    printk(KERN_NOTICE "FS-Cache: 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:
    printk(KERN_ERR "FS-Cache: 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);

void fscache_io_error(struct fscache_cache *cache)
{
    set_bit(FSCACHE_IOERROR, &cache->flags);

    printk(KERN_ERR "FS-Cache: 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;

    spin_lock(&cache->object_list_lock);

    while (!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);

        spin_lock(&object->lock);
        spin_unlock(&cache->object_list_lock);
        fscache_raise_event(object, FSCACHE_OBJECT_EV_WITHDRAW);
        spin_unlock(&object->lock);

        cond_resched();
        spin_lock(&cache->object_list_lock);
    }

    spin_unlock(&cache->object_list_lock);
}

void fscache_withdraw_cache(struct fscache_cache *cache)
{
    LIST_HEAD(dying_objects);

    _enter("");

    printk(KERN_NOTICE "FS-Cache: 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);