linux/mm/cleancache.c
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   1/*
   2 * Cleancache frontend
   3 *
   4 * This code provides the generic "frontend" layer to call a matching
   5 * "backend" driver implementation of cleancache.  See
   6 * Documentation/vm/cleancache.txt for more information.
   7 *
   8 * Copyright (C) 2009-2010 Oracle Corp. All rights reserved.
   9 * Author: Dan Magenheimer
  10 *
  11 * This work is licensed under the terms of the GNU GPL, version 2.
  12 */
  13
  14#include <linux/module.h>
  15#include <linux/fs.h>
  16#include <linux/exportfs.h>
  17#include <linux/mm.h>
  18#include <linux/debugfs.h>
  19#include <linux/cleancache.h>
  20
  21/*
  22 * cleancache_ops is set by cleancache_ops_register to contain the pointers
  23 * to the cleancache "backend" implementation functions.
  24 */
  25static struct cleancache_ops *cleancache_ops __read_mostly;
  26
  27/*
  28 * Counters available via /sys/kernel/debug/frontswap (if debugfs is
  29 * properly configured.  These are for information only so are not protected
  30 * against increment races.
  31 */
  32static u64 cleancache_succ_gets;
  33static u64 cleancache_failed_gets;
  34static u64 cleancache_puts;
  35static u64 cleancache_invalidates;
  36
  37/*
  38 * When no backend is registered all calls to init_fs and init_shared_fs
  39 * are registered and fake poolids (FAKE_FS_POOLID_OFFSET or
  40 * FAKE_SHARED_FS_POOLID_OFFSET, plus offset in the respective array
  41 * [shared_|]fs_poolid_map) are given to the respective super block
  42 * (sb->cleancache_poolid) and no tmem_pools are created. When a backend
  43 * registers with cleancache the previous calls to init_fs and init_shared_fs
  44 * are executed to create tmem_pools and set the respective poolids. While no
  45 * backend is registered all "puts", "gets" and "flushes" are ignored or failed.
  46 */
  47#define MAX_INITIALIZABLE_FS 32
  48#define FAKE_FS_POOLID_OFFSET 1000
  49#define FAKE_SHARED_FS_POOLID_OFFSET 2000
  50
  51#define FS_NO_BACKEND (-1)
  52#define FS_UNKNOWN (-2)
  53static int fs_poolid_map[MAX_INITIALIZABLE_FS];
  54static int shared_fs_poolid_map[MAX_INITIALIZABLE_FS];
  55static char *uuids[MAX_INITIALIZABLE_FS];
  56/*
  57 * Mutex for the [shared_|]fs_poolid_map to guard against multiple threads
  58 * invoking umount (and ending in __cleancache_invalidate_fs) and also multiple
  59 * threads calling mount (and ending up in __cleancache_init_[shared|]fs).
  60 */
  61static DEFINE_MUTEX(poolid_mutex);
  62/*
  63 * When set to false (default) all calls to the cleancache functions, except
  64 * the __cleancache_invalidate_fs and __cleancache_init_[shared|]fs are guarded
  65 * by the if (!cleancache_ops) return. This means multiple threads (from
  66 * different filesystems) will be checking cleancache_ops. The usage of a
  67 * bool instead of a atomic_t or a bool guarded by a spinlock is OK - we are
  68 * OK if the time between the backend's have been initialized (and
  69 * cleancache_ops has been set to not NULL) and when the filesystems start
  70 * actually calling the backends. The inverse (when unloading) is obviously
  71 * not good - but this shim does not do that (yet).
  72 */
  73
  74/*
  75 * The backends and filesystems work all asynchronously. This is b/c the
  76 * backends can be built as modules.
  77 * The usual sequence of events is:
  78 *      a) mount /      -> __cleancache_init_fs is called. We set the
  79 *              [shared_|]fs_poolid_map and uuids for.
  80 *
  81 *      b). user does I/Os -> we call the rest of __cleancache_* functions
  82 *              which return immediately as cleancache_ops is false.
  83 *
  84 *      c). modprobe zcache -> cleancache_register_ops. We init the backend
  85 *              and set cleancache_ops to true, and for any fs_poolid_map
  86 *              (which is set by __cleancache_init_fs) we initialize the poolid.
  87 *
  88 *      d). user does I/Os -> now that cleancache_ops is true all the
  89 *              __cleancache_* functions can call the backend. They all check
  90 *              that fs_poolid_map is valid and if so invoke the backend.
  91 *
  92 *      e). umount /    -> __cleancache_invalidate_fs, the fs_poolid_map is
  93 *              reset (which is the second check in the __cleancache_* ops
  94 *              to call the backend).
  95 *
  96 * The sequence of event could also be c), followed by a), and d). and e). The
  97 * c) would not happen anymore. There is also the chance of c), and one thread
  98 * doing a) + d), and another doing e). For that case we depend on the
  99 * filesystem calling __cleancache_invalidate_fs in the proper sequence (so
 100 * that it handles all I/Os before it invalidates the fs (which is last part
 101 * of unmounting process).
 102 *
 103 * Note: The acute reader will notice that there is no "rmmod zcache" case.
 104 * This is b/c the functionality for that is not yet implemented and when
 105 * done, will require some extra locking not yet devised.
 106 */
 107
 108/*
 109 * Register operations for cleancache, returning previous thus allowing
 110 * detection of multiple backends and possible nesting.
 111 */
 112struct cleancache_ops *cleancache_register_ops(struct cleancache_ops *ops)
 113{
 114        struct cleancache_ops *old = cleancache_ops;
 115        int i;
 116
 117        mutex_lock(&poolid_mutex);
 118        for (i = 0; i < MAX_INITIALIZABLE_FS; i++) {
 119                if (fs_poolid_map[i] == FS_NO_BACKEND)
 120                        fs_poolid_map[i] = ops->init_fs(PAGE_SIZE);
 121                if (shared_fs_poolid_map[i] == FS_NO_BACKEND)
 122                        shared_fs_poolid_map[i] = ops->init_shared_fs
 123                                        (uuids[i], PAGE_SIZE);
 124        }
 125        /*
 126         * We MUST set cleancache_ops _after_ we have called the backends
 127         * init_fs or init_shared_fs functions. Otherwise the compiler might
 128         * re-order where cleancache_ops is set in this function.
 129         */
 130        barrier();
 131        cleancache_ops = ops;
 132        mutex_unlock(&poolid_mutex);
 133        return old;
 134}
 135EXPORT_SYMBOL(cleancache_register_ops);
 136
 137/* Called by a cleancache-enabled filesystem at time of mount */
 138void __cleancache_init_fs(struct super_block *sb)
 139{
 140        int i;
 141
 142        mutex_lock(&poolid_mutex);
 143        for (i = 0; i < MAX_INITIALIZABLE_FS; i++) {
 144                if (fs_poolid_map[i] == FS_UNKNOWN) {
 145                        sb->cleancache_poolid = i + FAKE_FS_POOLID_OFFSET;
 146                        if (cleancache_ops)
 147                                fs_poolid_map[i] = cleancache_ops->init_fs(PAGE_SIZE);
 148                        else
 149                                fs_poolid_map[i] = FS_NO_BACKEND;
 150                        break;
 151                }
 152        }
 153        mutex_unlock(&poolid_mutex);
 154}
 155EXPORT_SYMBOL(__cleancache_init_fs);
 156
 157/* Called by a cleancache-enabled clustered filesystem at time of mount */
 158void __cleancache_init_shared_fs(char *uuid, struct super_block *sb)
 159{
 160        int i;
 161
 162        mutex_lock(&poolid_mutex);
 163        for (i = 0; i < MAX_INITIALIZABLE_FS; i++) {
 164                if (shared_fs_poolid_map[i] == FS_UNKNOWN) {
 165                        sb->cleancache_poolid = i + FAKE_SHARED_FS_POOLID_OFFSET;
 166                        uuids[i] = uuid;
 167                        if (cleancache_ops)
 168                                shared_fs_poolid_map[i] = cleancache_ops->init_shared_fs
 169                                                (uuid, PAGE_SIZE);
 170                        else
 171                                shared_fs_poolid_map[i] = FS_NO_BACKEND;
 172                        break;
 173                }
 174        }
 175        mutex_unlock(&poolid_mutex);
 176}
 177EXPORT_SYMBOL(__cleancache_init_shared_fs);
 178
 179/*
 180 * If the filesystem uses exportable filehandles, use the filehandle as
 181 * the key, else use the inode number.
 182 */
 183static int cleancache_get_key(struct inode *inode,
 184                              struct cleancache_filekey *key)
 185{
 186        int (*fhfn)(struct inode *, __u32 *fh, int *, struct inode *);
 187        int len = 0, maxlen = CLEANCACHE_KEY_MAX;
 188        struct super_block *sb = inode->i_sb;
 189
 190        key->u.ino = inode->i_ino;
 191        if (sb->s_export_op != NULL) {
 192                fhfn = sb->s_export_op->encode_fh;
 193                if  (fhfn) {
 194                        len = (*fhfn)(inode, &key->u.fh[0], &maxlen, NULL);
 195                        if (len <= FILEID_ROOT || len == FILEID_INVALID)
 196                                return -1;
 197                        if (maxlen > CLEANCACHE_KEY_MAX)
 198                                return -1;
 199                }
 200        }
 201        return 0;
 202}
 203
 204/*
 205 * Returns a pool_id that is associated with a given fake poolid.
 206 */
 207static int get_poolid_from_fake(int fake_pool_id)
 208{
 209        if (fake_pool_id >= FAKE_SHARED_FS_POOLID_OFFSET)
 210                return shared_fs_poolid_map[fake_pool_id -
 211                        FAKE_SHARED_FS_POOLID_OFFSET];
 212        else if (fake_pool_id >= FAKE_FS_POOLID_OFFSET)
 213                return fs_poolid_map[fake_pool_id - FAKE_FS_POOLID_OFFSET];
 214        return FS_NO_BACKEND;
 215}
 216
 217/*
 218 * "Get" data from cleancache associated with the poolid/inode/index
 219 * that were specified when the data was put to cleanache and, if
 220 * successful, use it to fill the specified page with data and return 0.
 221 * The pageframe is unchanged and returns -1 if the get fails.
 222 * Page must be locked by caller.
 223 *
 224 * The function has two checks before any action is taken - whether
 225 * a backend is registered and whether the sb->cleancache_poolid
 226 * is correct.
 227 */
 228int __cleancache_get_page(struct page *page)
 229{
 230        int ret = -1;
 231        int pool_id;
 232        int fake_pool_id;
 233        struct cleancache_filekey key = { .u.key = { 0 } };
 234
 235        if (!cleancache_ops) {
 236                cleancache_failed_gets++;
 237                goto out;
 238        }
 239
 240        VM_BUG_ON(!PageLocked(page));
 241        fake_pool_id = page->mapping->host->i_sb->cleancache_poolid;
 242        if (fake_pool_id < 0)
 243                goto out;
 244        pool_id = get_poolid_from_fake(fake_pool_id);
 245
 246        if (cleancache_get_key(page->mapping->host, &key) < 0)
 247                goto out;
 248
 249        if (pool_id >= 0)
 250                ret = cleancache_ops->get_page(pool_id,
 251                                key, page->index, page);
 252        if (ret == 0)
 253                cleancache_succ_gets++;
 254        else
 255                cleancache_failed_gets++;
 256out:
 257        return ret;
 258}
 259EXPORT_SYMBOL(__cleancache_get_page);
 260
 261/*
 262 * "Put" data from a page to cleancache and associate it with the
 263 * (previously-obtained per-filesystem) poolid and the page's,
 264 * inode and page index.  Page must be locked.  Note that a put_page
 265 * always "succeeds", though a subsequent get_page may succeed or fail.
 266 *
 267 * The function has two checks before any action is taken - whether
 268 * a backend is registered and whether the sb->cleancache_poolid
 269 * is correct.
 270 */
 271void __cleancache_put_page(struct page *page)
 272{
 273        int pool_id;
 274        int fake_pool_id;
 275        struct cleancache_filekey key = { .u.key = { 0 } };
 276
 277        if (!cleancache_ops) {
 278                cleancache_puts++;
 279                return;
 280        }
 281
 282        VM_BUG_ON(!PageLocked(page));
 283        fake_pool_id = page->mapping->host->i_sb->cleancache_poolid;
 284        if (fake_pool_id < 0)
 285                return;
 286
 287        pool_id = get_poolid_from_fake(fake_pool_id);
 288
 289        if (pool_id >= 0 &&
 290                cleancache_get_key(page->mapping->host, &key) >= 0) {
 291                cleancache_ops->put_page(pool_id, key, page->index, page);
 292                cleancache_puts++;
 293        }
 294}
 295EXPORT_SYMBOL(__cleancache_put_page);
 296
 297/*
 298 * Invalidate any data from cleancache associated with the poolid and the
 299 * page's inode and page index so that a subsequent "get" will fail.
 300 *
 301 * The function has two checks before any action is taken - whether
 302 * a backend is registered and whether the sb->cleancache_poolid
 303 * is correct.
 304 */
 305void __cleancache_invalidate_page(struct address_space *mapping,
 306                                        struct page *page)
 307{
 308        /* careful... page->mapping is NULL sometimes when this is called */
 309        int pool_id;
 310        int fake_pool_id = mapping->host->i_sb->cleancache_poolid;
 311        struct cleancache_filekey key = { .u.key = { 0 } };
 312
 313        if (!cleancache_ops)
 314                return;
 315
 316        if (fake_pool_id >= 0) {
 317                pool_id = get_poolid_from_fake(fake_pool_id);
 318                if (pool_id < 0)
 319                        return;
 320
 321                VM_BUG_ON(!PageLocked(page));
 322                if (cleancache_get_key(mapping->host, &key) >= 0) {
 323                        cleancache_ops->invalidate_page(pool_id,
 324                                        key, page->index);
 325                        cleancache_invalidates++;
 326                }
 327        }
 328}
 329EXPORT_SYMBOL(__cleancache_invalidate_page);
 330
 331/*
 332 * Invalidate all data from cleancache associated with the poolid and the
 333 * mappings's inode so that all subsequent gets to this poolid/inode
 334 * will fail.
 335 *
 336 * The function has two checks before any action is taken - whether
 337 * a backend is registered and whether the sb->cleancache_poolid
 338 * is correct.
 339 */
 340void __cleancache_invalidate_inode(struct address_space *mapping)
 341{
 342        int pool_id;
 343        int fake_pool_id = mapping->host->i_sb->cleancache_poolid;
 344        struct cleancache_filekey key = { .u.key = { 0 } };
 345
 346        if (!cleancache_ops)
 347                return;
 348
 349        if (fake_pool_id < 0)
 350                return;
 351
 352        pool_id = get_poolid_from_fake(fake_pool_id);
 353
 354        if (pool_id >= 0 && cleancache_get_key(mapping->host, &key) >= 0)
 355                cleancache_ops->invalidate_inode(pool_id, key);
 356}
 357EXPORT_SYMBOL(__cleancache_invalidate_inode);
 358
 359/*
 360 * Called by any cleancache-enabled filesystem at time of unmount;
 361 * note that pool_id is surrendered and may be returned by a subsequent
 362 * cleancache_init_fs or cleancache_init_shared_fs.
 363 */
 364void __cleancache_invalidate_fs(struct super_block *sb)
 365{
 366        int index;
 367        int fake_pool_id = sb->cleancache_poolid;
 368        int old_poolid = fake_pool_id;
 369
 370        mutex_lock(&poolid_mutex);
 371        if (fake_pool_id >= FAKE_SHARED_FS_POOLID_OFFSET) {
 372                index = fake_pool_id - FAKE_SHARED_FS_POOLID_OFFSET;
 373                old_poolid = shared_fs_poolid_map[index];
 374                shared_fs_poolid_map[index] = FS_UNKNOWN;
 375                uuids[index] = NULL;
 376        } else if (fake_pool_id >= FAKE_FS_POOLID_OFFSET) {
 377                index = fake_pool_id - FAKE_FS_POOLID_OFFSET;
 378                old_poolid = fs_poolid_map[index];
 379                fs_poolid_map[index] = FS_UNKNOWN;
 380        }
 381        sb->cleancache_poolid = -1;
 382        if (cleancache_ops)
 383                cleancache_ops->invalidate_fs(old_poolid);
 384        mutex_unlock(&poolid_mutex);
 385}
 386EXPORT_SYMBOL(__cleancache_invalidate_fs);
 387
 388static int __init init_cleancache(void)
 389{
 390        int i;
 391
 392#ifdef CONFIG_DEBUG_FS
 393        struct dentry *root = debugfs_create_dir("cleancache", NULL);
 394        if (root == NULL)
 395                return -ENXIO;
 396        debugfs_create_u64("succ_gets", S_IRUGO, root, &cleancache_succ_gets);
 397        debugfs_create_u64("failed_gets", S_IRUGO,
 398                                root, &cleancache_failed_gets);
 399        debugfs_create_u64("puts", S_IRUGO, root, &cleancache_puts);
 400        debugfs_create_u64("invalidates", S_IRUGO,
 401                                root, &cleancache_invalidates);
 402#endif
 403        for (i = 0; i < MAX_INITIALIZABLE_FS; i++) {
 404                fs_poolid_map[i] = FS_UNKNOWN;
 405                shared_fs_poolid_map[i] = FS_UNKNOWN;
 406        }
 407        return 0;
 408}
 409module_init(init_cleancache)
 410
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