mm/cleancache.c

   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_register_ops to contain the pointers
  23  * to the cleancache "backend" implementation functions.
  24  */
  25 static 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  */
  32 static u64 cleancache_succ_gets;
  33 static u64 cleancache_failed_gets;
  34 static u64 cleancache_puts;
  35 static u64 cleancache_invalidates;
  36
  37 static 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  */
  52 int 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 }
 111 EXPORT_SYMBOL(cleancache_register_ops);
 112
 113 /* Called by a cleancache-enabled filesystem at time of mount */
 114 void __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 }
 125 EXPORT_SYMBOL(__cleancache_init_fs);
 126
 127 /* Called by a cleancache-enabled clustered filesystem at time of mount */
 128 void __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 }
 139 EXPORT_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  */
 145 static 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  */
 177 int __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++;
 201 out:
 202         return ret;
 203 }
 204 EXPORT_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  */
 216 void __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 }
 234 EXPORT_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  */
 244 void __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 }
 263 EXPORT_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  */
 274 void __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 }
 285 EXPORT_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  */
 292 void __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 }
 302 EXPORT_SYMBOL(__cleancache_invalidate_fs);
 303
 304 static 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", S_IRUGO, root, &cleancache_succ_gets);
 311         debugfs_create_u64("failed_gets", S_IRUGO,
 312                                 root, &cleancache_failed_gets);
 313         debugfs_create_u64("puts", S_IRUGO, root, &cleancache_puts);
 314         debugfs_create_u64("invalidates", S_IRUGO,
 315                                 root, &cleancache_invalidates);
 316 #endif
 317         return 0;
 318 }
 319 module_init(init_cleancache)