linux/fs/fscache/cache.c
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   1/* FS-Cache cache handling
   2 *
   3 * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
   4 * Written by David Howells (dhowells@redhat.com)
   5 *
   6 * This program is free software; you can redistribute it and/or
   7 * modify it under the terms of the GNU General Public License
   8 * as published by the Free Software Foundation; either version
   9 * 2 of the License, or (at your option) any later version.
  10 */
  11
  12#define FSCACHE_DEBUG_LEVEL CACHE
  13#include <linux/module.h>
  14#include <linux/slab.h>
  15#include "internal.h"
  16
  17LIST_HEAD(fscache_cache_list);
  18DECLARE_RWSEM(fscache_addremove_sem);
  19DECLARE_WAIT_QUEUE_HEAD(fscache_cache_cleared_wq);
  20EXPORT_SYMBOL(fscache_cache_cleared_wq);
  21
  22static LIST_HEAD(fscache_cache_tag_list);
  23
  24/*
  25 * look up a cache tag
  26 */
  27struct fscache_cache_tag *__fscache_lookup_cache_tag(const char *name)
  28{
  29        struct fscache_cache_tag *tag, *xtag;
  30
  31        /* firstly check for the existence of the tag under read lock */
  32        down_read(&fscache_addremove_sem);
  33
  34        list_for_each_entry(tag, &fscache_cache_tag_list, link) {
  35                if (strcmp(tag->name, name) == 0) {
  36                        atomic_inc(&tag->usage);
  37                        up_read(&fscache_addremove_sem);
  38                        return tag;
  39                }
  40        }
  41
  42        up_read(&fscache_addremove_sem);
  43
  44        /* the tag does not exist - create a candidate */
  45        xtag = kzalloc(sizeof(*xtag) + strlen(name) + 1, GFP_KERNEL);
  46        if (!xtag)
  47                /* return a dummy tag if out of memory */
  48                return ERR_PTR(-ENOMEM);
  49
  50        atomic_set(&xtag->usage, 1);
  51        strcpy(xtag->name, name);
  52
  53        /* write lock, search again and add if still not present */
  54        down_write(&fscache_addremove_sem);
  55
  56        list_for_each_entry(tag, &fscache_cache_tag_list, link) {
  57                if (strcmp(tag->name, name) == 0) {
  58                        atomic_inc(&tag->usage);
  59                        up_write(&fscache_addremove_sem);
  60                        kfree(xtag);
  61                        return tag;
  62                }
  63        }
  64
  65        list_add_tail(&xtag->link, &fscache_cache_tag_list);
  66        up_write(&fscache_addremove_sem);
  67        return xtag;
  68}
  69
  70/*
  71 * release a reference to a cache tag
  72 */
  73void __fscache_release_cache_tag(struct fscache_cache_tag *tag)
  74{
  75        if (tag != ERR_PTR(-ENOMEM)) {
  76                down_write(&fscache_addremove_sem);
  77
  78                if (atomic_dec_and_test(&tag->usage))
  79                        list_del_init(&tag->link);
  80                else
  81                        tag = NULL;
  82
  83                up_write(&fscache_addremove_sem);
  84
  85                kfree(tag);
  86        }
  87}
  88
  89/*
  90 * select a cache in which to store an object
  91 * - the cache addremove semaphore must be at least read-locked by the caller
  92 * - the object will never be an index
  93 */
  94struct fscache_cache *fscache_select_cache_for_object(
  95        struct fscache_cookie *cookie)
  96{
  97        struct fscache_cache_tag *tag;
  98        struct fscache_object *object;
  99        struct fscache_cache *cache;
 100
 101        _enter("");
 102
 103        if (list_empty(&fscache_cache_list)) {
 104                _leave(" = NULL [no cache]");
 105                return NULL;
 106        }
 107
 108        /* we check the parent to determine the cache to use */
 109        spin_lock(&cookie->lock);
 110
 111        /* the first in the parent's backing list should be the preferred
 112         * cache */
 113        if (!hlist_empty(&cookie->backing_objects)) {
 114                object = hlist_entry(cookie->backing_objects.first,
 115                                     struct fscache_object, cookie_link);
 116
 117                cache = object->cache;
 118                if (object->state >= FSCACHE_OBJECT_DYING ||
 119                    test_bit(FSCACHE_IOERROR, &cache->flags))
 120                        cache = NULL;
 121
 122                spin_unlock(&cookie->lock);
 123                _leave(" = %p [parent]", cache);
 124                return cache;
 125        }
 126
 127        /* the parent is unbacked */
 128        if (cookie->def->type != FSCACHE_COOKIE_TYPE_INDEX) {
 129                /* cookie not an index and is unbacked */
 130                spin_unlock(&cookie->lock);
 131                _leave(" = NULL [cookie ub,ni]");
 132                return NULL;
 133        }
 134
 135        spin_unlock(&cookie->lock);
 136
 137        if (!cookie->def->select_cache)
 138                goto no_preference;
 139
 140        /* ask the netfs for its preference */
 141        tag = cookie->def->select_cache(cookie->parent->netfs_data,
 142                                        cookie->netfs_data);
 143        if (!tag)
 144                goto no_preference;
 145
 146        if (tag == ERR_PTR(-ENOMEM)) {
 147                _leave(" = NULL [nomem tag]");
 148                return NULL;
 149        }
 150
 151        if (!tag->cache) {
 152                _leave(" = NULL [unbacked tag]");
 153                return NULL;
 154        }
 155
 156        if (test_bit(FSCACHE_IOERROR, &tag->cache->flags))
 157                return NULL;
 158
 159        _leave(" = %p [specific]", tag->cache);
 160        return tag->cache;
 161
 162no_preference:
 163        /* netfs has no preference - just select first cache */
 164        cache = list_entry(fscache_cache_list.next,
 165                           struct fscache_cache, link);
 166        _leave(" = %p [first]", cache);
 167        return cache;
 168}
 169
 170/**
 171 * fscache_init_cache - Initialise a cache record
 172 * @cache: The cache record to be initialised
 173 * @ops: The cache operations to be installed in that record
 174 * @idfmt: Format string to define identifier
 175 * @...: sprintf-style arguments
 176 *
 177 * Initialise a record of a cache and fill in the name.
 178 *
 179 * See Documentation/filesystems/caching/backend-api.txt for a complete
 180 * description.
 181 */
 182void fscache_init_cache(struct fscache_cache *cache,
 183                        const struct fscache_cache_ops *ops,
 184                        const char *idfmt,
 185                        ...)
 186{
 187        va_list va;
 188
 189        memset(cache, 0, sizeof(*cache));
 190
 191        cache->ops = ops;
 192
 193        va_start(va, idfmt);
 194        vsnprintf(cache->identifier, sizeof(cache->identifier), idfmt, va);
 195        va_end(va);
 196
 197        INIT_WORK(&cache->op_gc, fscache_operation_gc);
 198        INIT_LIST_HEAD(&cache->link);
 199        INIT_LIST_HEAD(&cache->object_list);
 200        INIT_LIST_HEAD(&cache->op_gc_list);
 201        spin_lock_init(&cache->object_list_lock);
 202        spin_lock_init(&cache->op_gc_list_lock);
 203}
 204EXPORT_SYMBOL(fscache_init_cache);
 205
 206/**
 207 * fscache_add_cache - Declare a cache as being open for business
 208 * @cache: The record describing the cache
 209 * @ifsdef: The record of the cache object describing the top-level index
 210 * @tagname: The tag describing this cache
 211 *
 212 * Add a cache to the system, making it available for netfs's to use.
 213 *
 214 * See Documentation/filesystems/caching/backend-api.txt for a complete
 215 * description.
 216 */
 217int fscache_add_cache(struct fscache_cache *cache,
 218                      struct fscache_object *ifsdef,
 219                      const char *tagname)
 220{
 221        struct fscache_cache_tag *tag;
 222
 223        BUG_ON(!cache->ops);
 224        BUG_ON(!ifsdef);
 225
 226        cache->flags = 0;
 227        ifsdef->event_mask = ULONG_MAX & ~(1 << FSCACHE_OBJECT_EV_CLEARED);
 228        ifsdef->state = FSCACHE_OBJECT_ACTIVE;
 229
 230        if (!tagname)
 231                tagname = cache->identifier;
 232
 233        BUG_ON(!tagname[0]);
 234
 235        _enter("{%s.%s},,%s", cache->ops->name, cache->identifier, tagname);
 236
 237        /* we use the cache tag to uniquely identify caches */
 238        tag = __fscache_lookup_cache_tag(tagname);
 239        if (IS_ERR(tag))
 240                goto nomem;
 241
 242        if (test_and_set_bit(FSCACHE_TAG_RESERVED, &tag->flags))
 243                goto tag_in_use;
 244
 245        cache->kobj = kobject_create_and_add(tagname, fscache_root);
 246        if (!cache->kobj)
 247                goto error;
 248
 249        ifsdef->cookie = &fscache_fsdef_index;
 250        ifsdef->cache = cache;
 251        cache->fsdef = ifsdef;
 252
 253        down_write(&fscache_addremove_sem);
 254
 255        tag->cache = cache;
 256        cache->tag = tag;
 257
 258        /* add the cache to the list */
 259        list_add(&cache->link, &fscache_cache_list);
 260
 261        /* add the cache's netfs definition index object to the cache's
 262         * list */
 263        spin_lock(&cache->object_list_lock);
 264        list_add_tail(&ifsdef->cache_link, &cache->object_list);
 265        spin_unlock(&cache->object_list_lock);
 266        fscache_objlist_add(ifsdef);
 267
 268        /* add the cache's netfs definition index object to the top level index
 269         * cookie as a known backing object */
 270        spin_lock(&fscache_fsdef_index.lock);
 271
 272        hlist_add_head(&ifsdef->cookie_link,
 273                       &fscache_fsdef_index.backing_objects);
 274
 275        atomic_inc(&fscache_fsdef_index.usage);
 276
 277        /* done */
 278        spin_unlock(&fscache_fsdef_index.lock);
 279        up_write(&fscache_addremove_sem);
 280
 281        printk(KERN_NOTICE "FS-Cache: Cache \"%s\" added (type %s)\n",
 282               cache->tag->name, cache->ops->name);
 283        kobject_uevent(cache->kobj, KOBJ_ADD);
 284
 285        _leave(" = 0 [%s]", cache->identifier);
 286        return 0;
 287
 288tag_in_use:
 289        printk(KERN_ERR "FS-Cache: Cache tag '%s' already in use\n", tagname);
 290        __fscache_release_cache_tag(tag);
 291        _leave(" = -EXIST");
 292        return -EEXIST;
 293
 294error:
 295        __fscache_release_cache_tag(tag);
 296        _leave(" = -EINVAL");
 297        return -EINVAL;
 298
 299nomem:
 300        _leave(" = -ENOMEM");
 301        return -ENOMEM;
 302}
 303EXPORT_SYMBOL(fscache_add_cache);
 304
 305/**
 306 * fscache_io_error - Note a cache I/O error
 307 * @cache: The record describing the cache
 308 *
 309 * Note that an I/O error occurred in a cache and that it should no longer be
 310 * used for anything.  This also reports the error into the kernel log.
 311 *
 312 * See Documentation/filesystems/caching/backend-api.txt for a complete
 313 * description.
 314 */
 315void fscache_io_error(struct fscache_cache *cache)
 316{
 317        set_bit(FSCACHE_IOERROR, &cache->flags);
 318
 319        printk(KERN_ERR "FS-Cache: Cache %s stopped due to I/O error\n",
 320               cache->ops->name);
 321}
 322EXPORT_SYMBOL(fscache_io_error);
 323
 324/*
 325 * request withdrawal of all the objects in a cache
 326 * - all the objects being withdrawn are moved onto the supplied list
 327 */
 328static void fscache_withdraw_all_objects(struct fscache_cache *cache,
 329                                         struct list_head *dying_objects)
 330{
 331        struct fscache_object *object;
 332
 333        spin_lock(&cache->object_list_lock);
 334
 335        while (!list_empty(&cache->object_list)) {
 336                object = list_entry(cache->object_list.next,
 337                                    struct fscache_object, cache_link);
 338                list_move_tail(&object->cache_link, dying_objects);
 339
 340                _debug("withdraw %p", object->cookie);
 341
 342                spin_lock(&object->lock);
 343                spin_unlock(&cache->object_list_lock);
 344                fscache_raise_event(object, FSCACHE_OBJECT_EV_WITHDRAW);
 345                spin_unlock(&object->lock);
 346
 347                cond_resched();
 348                spin_lock(&cache->object_list_lock);
 349        }
 350
 351        spin_unlock(&cache->object_list_lock);
 352}
 353
 354/**
 355 * fscache_withdraw_cache - Withdraw a cache from the active service
 356 * @cache: The record describing the cache
 357 *
 358 * Withdraw a cache from service, unbinding all its cache objects from the
 359 * netfs cookies they're currently representing.
 360 *
 361 * See Documentation/filesystems/caching/backend-api.txt for a complete
 362 * description.
 363 */
 364void fscache_withdraw_cache(struct fscache_cache *cache)
 365{
 366        LIST_HEAD(dying_objects);
 367
 368        _enter("");
 369
 370        printk(KERN_NOTICE "FS-Cache: Withdrawing cache \"%s\"\n",
 371               cache->tag->name);
 372
 373        /* make the cache unavailable for cookie acquisition */
 374        if (test_and_set_bit(FSCACHE_CACHE_WITHDRAWN, &cache->flags))
 375                BUG();
 376
 377        down_write(&fscache_addremove_sem);
 378        list_del_init(&cache->link);
 379        cache->tag->cache = NULL;
 380        up_write(&fscache_addremove_sem);
 381
 382        /* make sure all pages pinned by operations on behalf of the netfs are
 383         * written to disk */
 384        fscache_stat(&fscache_n_cop_sync_cache);
 385        cache->ops->sync_cache(cache);
 386        fscache_stat_d(&fscache_n_cop_sync_cache);
 387
 388        /* dissociate all the netfs pages backed by this cache from the block
 389         * mappings in the cache */
 390        fscache_stat(&fscache_n_cop_dissociate_pages);
 391        cache->ops->dissociate_pages(cache);
 392        fscache_stat_d(&fscache_n_cop_dissociate_pages);
 393
 394        /* we now have to destroy all the active objects pertaining to this
 395         * cache - which we do by passing them off to thread pool to be
 396         * disposed of */
 397        _debug("destroy");
 398
 399        fscache_withdraw_all_objects(cache, &dying_objects);
 400
 401        /* wait for all extant objects to finish their outstanding operations
 402         * and go away */
 403        _debug("wait for finish");
 404        wait_event(fscache_cache_cleared_wq,
 405                   atomic_read(&cache->object_count) == 0);
 406        _debug("wait for clearance");
 407        wait_event(fscache_cache_cleared_wq,
 408                   list_empty(&cache->object_list));
 409        _debug("cleared");
 410        ASSERT(list_empty(&dying_objects));
 411
 412        kobject_put(cache->kobj);
 413
 414        clear_bit(FSCACHE_TAG_RESERVED, &cache->tag->flags);
 415        fscache_release_cache_tag(cache->tag);
 416        cache->tag = NULL;
 417
 418        _leave("");
 419}
 420EXPORT_SYMBOL(fscache_withdraw_cache);
 421
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