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.rst 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_register_ops to contain the pointers
  23 * to the cleancache "backend" implementation functions.
  24 */
  25static const struct cleancache_ops *cleancache_ops __read_mostly;
  26
  27/*
  28 * Counters available via /sys/kernel/debug/cleancache (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
  37static void cleancache_register_ops_sb(struct super_block *sb, void *unused)
  38{
  39        switch (sb->cleancache_poolid) {
  40        case CLEANCACHE_NO_BACKEND:
  41                __cleancache_init_fs(sb);
  42                break;
  43        case CLEANCACHE_NO_BACKEND_SHARED:
  44                __cleancache_init_shared_fs(sb);
  45                break;
  46        }
  47}
  48
  49/*
  50 * Register operations for cleancache. Returns 0 on success.
  51 */
  52int cleancache_register_ops(const struct cleancache_ops *ops)
  53{
  54        if (cmpxchg(&cleancache_ops, NULL, ops))
  55                return -EBUSY;
  56
  57        /*
  58         * A cleancache backend can be built as a module and hence loaded after
  59         * a cleancache enabled filesystem has called cleancache_init_fs. To
  60         * handle such a scenario, here we call ->init_fs or ->init_shared_fs
  61         * for each active super block. To differentiate between local and
  62         * shared filesystems, we temporarily initialize sb->cleancache_poolid
  63         * to CLEANCACHE_NO_BACKEND or CLEANCACHE_NO_BACKEND_SHARED
  64         * respectively in case there is no backend registered at the time
  65         * cleancache_init_fs or cleancache_init_shared_fs is called.
  66         *
  67         * Since filesystems can be mounted concurrently with cleancache
  68         * backend registration, we have to be careful to guarantee that all
  69         * cleancache enabled filesystems that has been mounted by the time
  70         * cleancache_register_ops is called has got and all mounted later will
  71         * get cleancache_poolid. This is assured by the following statements
  72         * tied together:
  73         *
  74         * a) iterate_supers skips only those super blocks that has started
  75         *    ->kill_sb
  76         *
  77         * b) if iterate_supers encounters a super block that has not finished
  78         *    ->mount yet, it waits until it is finished
  79         *
  80         * c) cleancache_init_fs is called from ->mount and
  81         *    cleancache_invalidate_fs is called from ->kill_sb
  82         *
  83         * d) we call iterate_supers after cleancache_ops has been set
  84         *
  85         * From a) it follows that if iterate_supers skips a super block, then
  86         * either the super block is already dead, in which case we do not need
  87         * to bother initializing cleancache for it, or it was mounted after we
  88         * initiated iterate_supers. In the latter case, it must have seen
  89         * cleancache_ops set according to d) and initialized cleancache from
  90         * ->mount by itself according to c). This proves that we call
  91         * ->init_fs at least once for each active super block.
  92         *
  93         * From b) and c) it follows that if iterate_supers encounters a super
  94         * block that has already started ->init_fs, it will wait until ->mount
  95         * and hence ->init_fs has finished, then check cleancache_poolid, see
  96         * that it has already been set and therefore do nothing. This proves
  97         * that we call ->init_fs no more than once for each super block.
  98         *
  99         * Combined together, the last two paragraphs prove the function
 100         * correctness.
 101         *
 102         * Note that various cleancache callbacks may proceed before this
 103         * function is called or even concurrently with it, but since
 104         * CLEANCACHE_NO_BACKEND is negative, they will all result in a noop
 105         * until the corresponding ->init_fs has been actually called and
 106         * cleancache_ops has been set.
 107         */
 108        iterate_supers(cleancache_register_ops_sb, NULL);
 109        return 0;
 110}
 111EXPORT_SYMBOL(cleancache_register_ops);
 112
 113/* Called by a cleancache-enabled filesystem at time of mount */
 114void __cleancache_init_fs(struct super_block *sb)
 115{
 116        int pool_id = CLEANCACHE_NO_BACKEND;
 117
 118        if (cleancache_ops) {
 119                pool_id = cleancache_ops->init_fs(PAGE_SIZE);
 120                if (pool_id < 0)
 121                        pool_id = CLEANCACHE_NO_POOL;
 122        }
 123        sb->cleancache_poolid = pool_id;
 124}
 125EXPORT_SYMBOL(__cleancache_init_fs);
 126
 127/* Called by a cleancache-enabled clustered filesystem at time of mount */
 128void __cleancache_init_shared_fs(struct super_block *sb)
 129{
 130        int pool_id = CLEANCACHE_NO_BACKEND_SHARED;
 131
 132        if (cleancache_ops) {
 133                pool_id = cleancache_ops->init_shared_fs(&sb->s_uuid, PAGE_SIZE);
 134                if (pool_id < 0)
 135                        pool_id = CLEANCACHE_NO_POOL;
 136        }
 137        sb->cleancache_poolid = pool_id;
 138}
 139EXPORT_SYMBOL(__cleancache_init_shared_fs);
 140
 141/*
 142 * If the filesystem uses exportable filehandles, use the filehandle as
 143 * the key, else use the inode number.
 144 */
 145static int cleancache_get_key(struct inode *inode,
 146                              struct cleancache_filekey *key)
 147{
 148        int (*fhfn)(struct inode *, __u32 *fh, int *, struct inode *);
 149        int len = 0, maxlen = CLEANCACHE_KEY_MAX;
 150        struct super_block *sb = inode->i_sb;
 151
 152        key->u.ino = inode->i_ino;
 153        if (sb->s_export_op != NULL) {
 154                fhfn = sb->s_export_op->encode_fh;
 155                if  (fhfn) {
 156                        len = (*fhfn)(inode, &key->u.fh[0], &maxlen, NULL);
 157                        if (len <= FILEID_ROOT || len == FILEID_INVALID)
 158                                return -1;
 159                        if (maxlen > CLEANCACHE_KEY_MAX)
 160                                return -1;
 161                }
 162        }
 163        return 0;
 164}
 165
 166/*
 167 * "Get" data from cleancache associated with the poolid/inode/index
 168 * that were specified when the data was put to cleanache and, if
 169 * successful, use it to fill the specified page with data and return 0.
 170 * The pageframe is unchanged and returns -1 if the get fails.
 171 * Page must be locked by caller.
 172 *
 173 * The function has two checks before any action is taken - whether
 174 * a backend is registered and whether the sb->cleancache_poolid
 175 * is correct.
 176 */
 177int __cleancache_get_page(struct page *page)
 178{
 179        int ret = -1;
 180        int pool_id;
 181        struct cleancache_filekey key = { .u.key = { 0 } };
 182
 183        if (!cleancache_ops) {
 184                cleancache_failed_gets++;
 185                goto out;
 186        }
 187
 188        VM_BUG_ON_PAGE(!PageLocked(page), page);
 189        pool_id = page->mapping->host->i_sb->cleancache_poolid;
 190        if (pool_id < 0)
 191                goto out;
 192
 193        if (cleancache_get_key(page->mapping->host, &key) < 0)
 194                goto out;
 195
 196        ret = cleancache_ops->get_page(pool_id, key, page->index, page);
 197        if (ret == 0)
 198                cleancache_succ_gets++;
 199        else
 200                cleancache_failed_gets++;
 201out:
 202        return ret;
 203}
 204EXPORT_SYMBOL(__cleancache_get_page);
 205
 206/*
 207 * "Put" data from a page to cleancache and associate it with the
 208 * (previously-obtained per-filesystem) poolid and the page's,
 209 * inode and page index.  Page must be locked.  Note that a put_page
 210 * always "succeeds", though a subsequent get_page may succeed or fail.
 211 *
 212 * The function has two checks before any action is taken - whether
 213 * a backend is registered and whether the sb->cleancache_poolid
 214 * is correct.
 215 */
 216void __cleancache_put_page(struct page *page)
 217{
 218        int pool_id;
 219        struct cleancache_filekey key = { .u.key = { 0 } };
 220
 221        if (!cleancache_ops) {
 222                cleancache_puts++;
 223                return;
 224        }
 225
 226        VM_BUG_ON_PAGE(!PageLocked(page), page);
 227        pool_id = page->mapping->host->i_sb->cleancache_poolid;
 228        if (pool_id >= 0 &&
 229                cleancache_get_key(page->mapping->host, &key) >= 0) {
 230                cleancache_ops->put_page(pool_id, key, page->index, page);
 231                cleancache_puts++;
 232        }
 233}
 234EXPORT_SYMBOL(__cleancache_put_page);
 235
 236/*
 237 * Invalidate any data from cleancache associated with the poolid and the
 238 * page's inode and page index so that a subsequent "get" will fail.
 239 *
 240 * The function has two checks before any action is taken - whether
 241 * a backend is registered and whether the sb->cleancache_poolid
 242 * is correct.
 243 */
 244void __cleancache_invalidate_page(struct address_space *mapping,
 245                                        struct page *page)
 246{
 247        /* careful... page->mapping is NULL sometimes when this is called */
 248        int pool_id = mapping->host->i_sb->cleancache_poolid;
 249        struct cleancache_filekey key = { .u.key = { 0 } };
 250
 251        if (!cleancache_ops)
 252                return;
 253
 254        if (pool_id >= 0) {
 255                VM_BUG_ON_PAGE(!PageLocked(page), page);
 256                if (cleancache_get_key(mapping->host, &key) >= 0) {
 257                        cleancache_ops->invalidate_page(pool_id,
 258                                        key, page->index);
 259                        cleancache_invalidates++;
 260                }
 261        }
 262}
 263EXPORT_SYMBOL(__cleancache_invalidate_page);
 264
 265/*
 266 * Invalidate all data from cleancache associated with the poolid and the
 267 * mappings's inode so that all subsequent gets to this poolid/inode
 268 * will fail.
 269 *
 270 * The function has two checks before any action is taken - whether
 271 * a backend is registered and whether the sb->cleancache_poolid
 272 * is correct.
 273 */
 274void __cleancache_invalidate_inode(struct address_space *mapping)
 275{
 276        int pool_id = mapping->host->i_sb->cleancache_poolid;
 277        struct cleancache_filekey key = { .u.key = { 0 } };
 278
 279        if (!cleancache_ops)
 280                return;
 281
 282        if (pool_id >= 0 && cleancache_get_key(mapping->host, &key) >= 0)
 283                cleancache_ops->invalidate_inode(pool_id, key);
 284}
 285EXPORT_SYMBOL(__cleancache_invalidate_inode);
 286
 287/*
 288 * Called by any cleancache-enabled filesystem at time of unmount;
 289 * note that pool_id is surrendered and may be returned by a subsequent
 290 * cleancache_init_fs or cleancache_init_shared_fs.
 291 */
 292void __cleancache_invalidate_fs(struct super_block *sb)
 293{
 294        int pool_id;
 295
 296        pool_id = sb->cleancache_poolid;
 297        sb->cleancache_poolid = CLEANCACHE_NO_POOL;
 298
 299        if (cleancache_ops && pool_id >= 0)
 300                cleancache_ops->invalidate_fs(pool_id);
 301}
 302EXPORT_SYMBOL(__cleancache_invalidate_fs);
 303
 304static int __init init_cleancache(void)
 305{
 306#ifdef CONFIG_DEBUG_FS
 307        struct dentry *root = debugfs_create_dir("cleancache", NULL);
 308        if (root == NULL)
 309                return -ENXIO;
 310        debugfs_create_u64("succ_gets", 0444, root, &cleancache_succ_gets);
 311        debugfs_create_u64("failed_gets", 0444, root, &cleancache_failed_gets);
 312        debugfs_create_u64("puts", 0444, root, &cleancache_puts);
 313        debugfs_create_u64("invalidates", 0444, root, &cleancache_invalidates);
 314#endif
 315        return 0;
 316}
 317module_init(init_cleancache)
 318