include/linux/fscache.h

   1 /* General filesystem caching interface
   2  *
   3  * Copyright (C) 2004-2007 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  * NOTE!!! See:
  12  *
  13  *      Documentation/filesystems/caching/netfs-api.txt
  14  *
  15  * for a description of the network filesystem interface declared here.
  16  */
  17
  18 #ifndef _LINUX_FSCACHE_H
  19 #define _LINUX_FSCACHE_H
  20
  21 #include <linux/fs.h>
  22 #include <linux/list.h>
  23 #include <linux/pagemap.h>
  24 #include <linux/pagevec.h>
  25
  26 #if defined(CONFIG_FSCACHE) || defined(CONFIG_FSCACHE_MODULE)
  27 #define fscache_available() (1)
  28 #define fscache_cookie_valid(cookie) (cookie)
  29 #else
  30 #define fscache_available() (0)
  31 #define fscache_cookie_valid(cookie) (0)
  32 #endif
  33
  34
  35 /*
  36  * overload PG_private_2 to give us PG_fscache - this is used to indicate that
  37  * a page is currently backed by a local disk cache
  38  */
  39 #define PageFsCache(page)               PagePrivate2((page))
  40 #define SetPageFsCache(page)            SetPagePrivate2((page))
  41 #define ClearPageFsCache(page)          ClearPagePrivate2((page))
  42 #define TestSetPageFsCache(page)        TestSetPagePrivate2((page))
  43 #define TestClearPageFsCache(page)      TestClearPagePrivate2((page))
  44
  45 /* pattern used to fill dead space in an index entry */
  46 #define FSCACHE_INDEX_DEADFILL_PATTERN 0x79
  47
  48 struct pagevec;
  49 struct fscache_cache_tag;
  50 struct fscache_cookie;
  51 struct fscache_netfs;
  52
  53 typedef void (*fscache_rw_complete_t)(struct page *page,
  54                                       void *context,
  55                                       int error);
  56
  57 /* result of index entry consultation */
  58 enum fscache_checkaux {
  59         FSCACHE_CHECKAUX_OKAY,          /* entry okay as is */
  60         FSCACHE_CHECKAUX_NEEDS_UPDATE,  /* entry requires update */
  61         FSCACHE_CHECKAUX_OBSOLETE,      /* entry requires deletion */
  62 };
  63
  64 /*
  65  * fscache cookie definition
  66  */
  67 struct fscache_cookie_def {
  68         /* name of cookie type */
  69         char name[16];
  70
  71         /* cookie type */
  72         uint8_t type;
  73 #define FSCACHE_COOKIE_TYPE_INDEX       0
  74 #define FSCACHE_COOKIE_TYPE_DATAFILE    1
  75
  76         /* select the cache into which to insert an entry in this index
  77          * - optional
  78          * - should return a cache identifier or NULL to cause the cache to be
  79          *   inherited from the parent if possible or the first cache picked
  80          *   for a non-index file if not
  81          */
  82         struct fscache_cache_tag *(*select_cache)(
  83                 const void *parent_netfs_data,
  84                 const void *cookie_netfs_data);
  85
  86         /* get an index key
  87          * - should store the key data in the buffer
  88          * - should return the amount of data stored
  89          * - not permitted to return an error
  90          * - the netfs data from the cookie being used as the source is
  91          *   presented
  92          */
  93         uint16_t (*get_key)(const void *cookie_netfs_data,
  94                             void *buffer,
  95                             uint16_t bufmax);
  96
  97         /* get certain file attributes from the netfs data
  98          * - this function can be absent for an index
  99          * - not permitted to return an error
 100          * - the netfs data from the cookie being used as the source is
 101          *   presented
 102          */
 103         void (*get_attr)(const void *cookie_netfs_data, uint64_t *size);
 104
 105         /* get the auxiliary data from netfs data
 106          * - this function can be absent if the index carries no state data
 107          * - should store the auxiliary data in the buffer
 108          * - should return the amount of amount stored
 109          * - not permitted to return an error
 110          * - the netfs data from the cookie being used as the source is
 111          *   presented
 112          */
 113         uint16_t (*get_aux)(const void *cookie_netfs_data,
 114                             void *buffer,
 115                             uint16_t bufmax);
 116
 117         /* consult the netfs about the state of an object
 118          * - this function can be absent if the index carries no state data
 119          * - the netfs data from the cookie being used as the target is
 120          *   presented, as is the auxiliary data
 121          */
 122         enum fscache_checkaux (*check_aux)(void *cookie_netfs_data,
 123                                            const void *data,
 124                                            uint16_t datalen);
 125
 126         /* get an extra reference on a read context
 127          * - this function can be absent if the completion function doesn't
 128          *   require a context
 129          */
 130         void (*get_context)(void *cookie_netfs_data, void *context);
 131
 132         /* release an extra reference on a read context
 133          * - this function can be absent if the completion function doesn't
 134          *   require a context
 135          */
 136         void (*put_context)(void *cookie_netfs_data, void *context);
 137
 138         /* indicate pages that now have cache metadata retained
 139          * - this function should mark the specified pages as now being cached
 140          * - the pages will have been marked with PG_fscache before this is
 141          *   called, so this is optional
 142          */
 143         void (*mark_pages_cached)(void *cookie_netfs_data,
 144                                   struct address_space *mapping,
 145                                   struct pagevec *cached_pvec);
 146
 147         /* indicate the cookie is no longer cached
 148          * - this function is called when the backing store currently caching
 149          *   a cookie is removed
 150          * - the netfs should use this to clean up any markers indicating
 151          *   cached pages
 152          * - this is mandatory for any object that may have data
 153          */
 154         void (*now_uncached)(void *cookie_netfs_data);
 155 };
 156
 157 /*
 158  * fscache cached network filesystem type
 159  * - name, version and ops must be filled in before registration
 160  * - all other fields will be set during registration
 161  */
 162 struct fscache_netfs {
 163         uint32_t                        version;        /* indexing version */
 164         const char                      *name;          /* filesystem name */
 165         struct fscache_cookie           *primary_index;
 166         struct list_head                link;           /* internal link */
 167 };
 168
 169 /*
 170  * slow-path functions for when there is actually caching available, and the
 171  * netfs does actually have a valid token
 172  * - these are not to be called directly
 173  * - these are undefined symbols when FS-Cache is not configured and the
 174  *   optimiser takes care of not using them
 175  */
 176 extern int __fscache_register_netfs(struct fscache_netfs *);
 177 extern void __fscache_unregister_netfs(struct fscache_netfs *);
 178 extern struct fscache_cache_tag *__fscache_lookup_cache_tag(const char *);
 179 extern void __fscache_release_cache_tag(struct fscache_cache_tag *);
 180
 181 extern struct fscache_cookie *__fscache_acquire_cookie(
 182         struct fscache_cookie *,
 183         const struct fscache_cookie_def *,
 184         void *);
 185 extern void __fscache_relinquish_cookie(struct fscache_cookie *, int);
 186 extern void __fscache_update_cookie(struct fscache_cookie *);
 187 extern int __fscache_attr_changed(struct fscache_cookie *);
 188 extern int __fscache_read_or_alloc_page(struct fscache_cookie *,
 189                                         struct page *,
 190                                         fscache_rw_complete_t,
 191                                         void *,
 192                                         gfp_t);
 193 extern int __fscache_read_or_alloc_pages(struct fscache_cookie *,
 194                                          struct address_space *,
 195                                          struct list_head *,
 196                                          unsigned *,
 197                                          fscache_rw_complete_t,
 198                                          void *,
 199                                          gfp_t);
 200 extern int __fscache_alloc_page(struct fscache_cookie *, struct page *, gfp_t);
 201 extern int __fscache_write_page(struct fscache_cookie *, struct page *, gfp_t);
 202 extern void __fscache_uncache_page(struct fscache_cookie *, struct page *);
 203 extern bool __fscache_check_page_write(struct fscache_cookie *, struct page *);
 204 extern void __fscache_wait_on_page_write(struct fscache_cookie *, struct page *);
 205 extern bool __fscache_maybe_release_page(struct fscache_cookie *, struct page *,
 206                                          gfp_t);
 207
 208 /**
 209  * fscache_register_netfs - Register a filesystem as desiring caching services
 210  * @netfs: The description of the filesystem
 211  *
 212  * Register a filesystem as desiring caching services if they're available.
 213  *
 214  * See Documentation/filesystems/caching/netfs-api.txt for a complete
 215  * description.
 216  */
 217 static inline
 218 int fscache_register_netfs(struct fscache_netfs *netfs)
 219 {
 220         if (fscache_available())
 221                 return __fscache_register_netfs(netfs);
 222         else
 223                 return 0;
 224 }
 225
 226 /**
 227  * fscache_unregister_netfs - Indicate that a filesystem no longer desires
 228  * caching services
 229  * @netfs: The description of the filesystem
 230  *
 231  * Indicate that a filesystem no longer desires caching services for the
 232  * moment.
 233  *
 234  * See Documentation/filesystems/caching/netfs-api.txt for a complete
 235  * description.
 236  */
 237 static inline
 238 void fscache_unregister_netfs(struct fscache_netfs *netfs)
 239 {
 240         if (fscache_available())
 241                 __fscache_unregister_netfs(netfs);
 242 }
 243
 244 /**
 245  * fscache_lookup_cache_tag - Look up a cache tag
 246  * @name: The name of the tag to search for
 247  *
 248  * Acquire a specific cache referral tag that can be used to select a specific
 249  * cache in which to cache an index.
 250  *
 251  * See Documentation/filesystems/caching/netfs-api.txt for a complete
 252  * description.
 253  */
 254 static inline
 255 struct fscache_cache_tag *fscache_lookup_cache_tag(const char *name)
 256 {
 257         if (fscache_available())
 258                 return __fscache_lookup_cache_tag(name);
 259         else
 260                 return NULL;
 261 }
 262
 263 /**
 264  * fscache_release_cache_tag - Release a cache tag
 265  * @tag: The tag to release
 266  *
 267  * Release a reference to a cache referral tag previously looked up.
 268  *
 269  * See Documentation/filesystems/caching/netfs-api.txt for a complete
 270  * description.
 271  */
 272 static inline
 273 void fscache_release_cache_tag(struct fscache_cache_tag *tag)
 274 {
 275         if (fscache_available())
 276                 __fscache_release_cache_tag(tag);
 277 }
 278
 279 /**
 280  * fscache_acquire_cookie - Acquire a cookie to represent a cache object
 281  * @parent: The cookie that's to be the parent of this one
 282  * @def: A description of the cache object, including callback operations
 283  * @netfs_data: An arbitrary piece of data to be kept in the cookie to
 284  * represent the cache object to the netfs
 285  *
 286  * This function is used to inform FS-Cache about part of an index hierarchy
 287  * that can be used to locate files.  This is done by requesting a cookie for
 288  * each index in the path to the file.
 289  *
 290  * See Documentation/filesystems/caching/netfs-api.txt for a complete
 291  * description.
 292  */
 293 static inline
 294 struct fscache_cookie *fscache_acquire_cookie(
 295         struct fscache_cookie *parent,
 296         const struct fscache_cookie_def *def,
 297         void *netfs_data)
 298 {
 299         if (fscache_cookie_valid(parent))
 300                 return __fscache_acquire_cookie(parent, def, netfs_data);
 301         else
 302                 return NULL;
 303 }
 304
 305 /**
 306  * fscache_relinquish_cookie - Return the cookie to the cache, maybe discarding
 307  * it
 308  * @cookie: The cookie being returned
 309  * @retire: True if the cache object the cookie represents is to be discarded
 310  *
 311  * This function returns a cookie to the cache, forcibly discarding the
 312  * associated cache object if retire is set to true.
 313  *
 314  * See Documentation/filesystems/caching/netfs-api.txt for a complete
 315  * description.
 316  */
 317 static inline
 318 void fscache_relinquish_cookie(struct fscache_cookie *cookie, int retire)
 319 {
 320         if (fscache_cookie_valid(cookie))
 321                 __fscache_relinquish_cookie(cookie, retire);
 322 }
 323
 324 /**
 325  * fscache_update_cookie - Request that a cache object be updated
 326  * @cookie: The cookie representing the cache object
 327  *
 328  * Request an update of the index data for the cache object associated with the
 329  * cookie.
 330  *
 331  * See Documentation/filesystems/caching/netfs-api.txt for a complete
 332  * description.
 333  */
 334 static inline
 335 void fscache_update_cookie(struct fscache_cookie *cookie)
 336 {
 337         if (fscache_cookie_valid(cookie))
 338                 __fscache_update_cookie(cookie);
 339 }
 340
 341 /**
 342  * fscache_pin_cookie - Pin a data-storage cache object in its cache
 343  * @cookie: The cookie representing the cache object
 344  *
 345  * Permit data-storage cache objects to be pinned in the cache.
 346  *
 347  * See Documentation/filesystems/caching/netfs-api.txt for a complete
 348  * description.
 349  */
 350 static inline
 351 int fscache_pin_cookie(struct fscache_cookie *cookie)
 352 {
 353         return -ENOBUFS;
 354 }
 355
 356 /**
 357  * fscache_pin_cookie - Unpin a data-storage cache object in its cache
 358  * @cookie: The cookie representing the cache object
 359  *
 360  * Permit data-storage cache objects to be unpinned from the cache.
 361  *
 362  * See Documentation/filesystems/caching/netfs-api.txt for a complete
 363  * description.
 364  */
 365 static inline
 366 void fscache_unpin_cookie(struct fscache_cookie *cookie)
 367 {
 368 }
 369
 370 /**
 371  * fscache_attr_changed - Notify cache that an object's attributes changed
 372  * @cookie: The cookie representing the cache object
 373  *
 374  * Send a notification to the cache indicating that an object's attributes have
 375  * changed.  This includes the data size.  These attributes will be obtained
 376  * through the get_attr() cookie definition op.
 377  *
 378  * See Documentation/filesystems/caching/netfs-api.txt for a complete
 379  * description.
 380  */
 381 static inline
 382 int fscache_attr_changed(struct fscache_cookie *cookie)
 383 {
 384         if (fscache_cookie_valid(cookie))
 385                 return __fscache_attr_changed(cookie);
 386         else
 387                 return -ENOBUFS;
 388 }
 389
 390 /**
 391  * fscache_reserve_space - Reserve data space for a cached object
 392  * @cookie: The cookie representing the cache object
 393  * @i_size: The amount of space to be reserved
 394  *
 395  * Reserve an amount of space in the cache for the cache object attached to a
 396  * cookie so that a write to that object within the space can always be
 397  * honoured.
 398  *
 399  * See Documentation/filesystems/caching/netfs-api.txt for a complete
 400  * description.
 401  */
 402 static inline
 403 int fscache_reserve_space(struct fscache_cookie *cookie, loff_t size)
 404 {
 405         return -ENOBUFS;
 406 }
 407
 408 /**
 409  * fscache_read_or_alloc_page - Read a page from the cache or allocate a block
 410  * in which to store it
 411  * @cookie: The cookie representing the cache object
 412  * @page: The netfs page to fill if possible
 413  * @end_io_func: The callback to invoke when and if the page is filled
 414  * @context: An arbitrary piece of data to pass on to end_io_func()
 415  * @gfp: The conditions under which memory allocation should be made
 416  *
 417  * Read a page from the cache, or if that's not possible make a potential
 418  * one-block reservation in the cache into which the page may be stored once
 419  * fetched from the server.
 420  *
 421  * If the page is not backed by the cache object, or if it there's some reason
 422  * it can't be, -ENOBUFS will be returned and nothing more will be done for
 423  * that page.
 424  *
 425  * Else, if that page is backed by the cache, a read will be initiated directly
 426  * to the netfs's page and 0 will be returned by this function.  The
 427  * end_io_func() callback will be invoked when the operation terminates on a
 428  * completion or failure.  Note that the callback may be invoked before the
 429  * return.
 430  *
 431  * Else, if the page is unbacked, -ENODATA is returned and a block may have
 432  * been allocated in the cache.
 433  *
 434  * See Documentation/filesystems/caching/netfs-api.txt for a complete
 435  * description.
 436  */
 437 static inline
 438 int fscache_read_or_alloc_page(struct fscache_cookie *cookie,
 439                                struct page *page,
 440                                fscache_rw_complete_t end_io_func,
 441                                void *context,
 442                                gfp_t gfp)
 443 {
 444         if (fscache_cookie_valid(cookie))
 445                 return __fscache_read_or_alloc_page(cookie, page, end_io_func,
 446                                                     context, gfp);
 447         else
 448                 return -ENOBUFS;
 449 }
 450
 451 /**
 452  * fscache_read_or_alloc_pages - Read pages from the cache and/or allocate
 453  * blocks in which to store them
 454  * @cookie: The cookie representing the cache object
 455  * @mapping: The netfs inode mapping to which the pages will be attached
 456  * @pages: A list of potential netfs pages to be filled
 457  * @nr_pages: Number of pages to be read and/or allocated
 458  * @end_io_func: The callback to invoke when and if each page is filled
 459  * @context: An arbitrary piece of data to pass on to end_io_func()
 460  * @gfp: The conditions under which memory allocation should be made
 461  *
 462  * Read a set of pages from the cache, or if that's not possible, attempt to
 463  * make a potential one-block reservation for each page in the cache into which
 464  * that page may be stored once fetched from the server.
 465  *
 466  * If some pages are not backed by the cache object, or if it there's some
 467  * reason they can't be, -ENOBUFS will be returned and nothing more will be
 468  * done for that pages.
 469  *
 470  * Else, if some of the pages are backed by the cache, a read will be initiated
 471  * directly to the netfs's page and 0 will be returned by this function.  The
 472  * end_io_func() callback will be invoked when the operation terminates on a
 473  * completion or failure.  Note that the callback may be invoked before the
 474  * return.
 475  *
 476  * Else, if a page is unbacked, -ENODATA is returned and a block may have
 477  * been allocated in the cache.
 478  *
 479  * Because the function may want to return all of -ENOBUFS, -ENODATA and 0 in
 480  * regard to different pages, the return values are prioritised in that order.
 481  * Any pages submitted for reading are removed from the pages list.
 482  *
 483  * See Documentation/filesystems/caching/netfs-api.txt for a complete
 484  * description.
 485  */
 486 static inline
 487 int fscache_read_or_alloc_pages(struct fscache_cookie *cookie,
 488                                 struct address_space *mapping,
 489                                 struct list_head *pages,
 490                                 unsigned *nr_pages,
 491                                 fscache_rw_complete_t end_io_func,
 492                                 void *context,
 493                                 gfp_t gfp)
 494 {
 495         if (fscache_cookie_valid(cookie))
 496                 return __fscache_read_or_alloc_pages(cookie, mapping, pages,
 497                                                      nr_pages, end_io_func,
 498                                                      context, gfp);
 499         else
 500                 return -ENOBUFS;
 501 }
 502
 503 /**
 504  * fscache_alloc_page - Allocate a block in which to store a page
 505  * @cookie: The cookie representing the cache object
 506  * @page: The netfs page to allocate a page for
 507  * @gfp: The conditions under which memory allocation should be made
 508  *
 509  * Request Allocation a block in the cache in which to store a netfs page
 510  * without retrieving any contents from the cache.
 511  *
 512  * If the page is not backed by a file then -ENOBUFS will be returned and
 513  * nothing more will be done, and no reservation will be made.
 514  *
 515  * Else, a block will be allocated if one wasn't already, and 0 will be
 516  * returned
 517  *
 518  * See Documentation/filesystems/caching/netfs-api.txt for a complete
 519  * description.
 520  */
 521 static inline
 522 int fscache_alloc_page(struct fscache_cookie *cookie,
 523                        struct page *page,
 524                        gfp_t gfp)
 525 {
 526         if (fscache_cookie_valid(cookie))
 527                 return __fscache_alloc_page(cookie, page, gfp);
 528         else
 529                 return -ENOBUFS;
 530 }
 531
 532 /**
 533  * fscache_write_page - Request storage of a page in the cache
 534  * @cookie: The cookie representing the cache object
 535  * @page: The netfs page to store
 536  * @gfp: The conditions under which memory allocation should be made
 537  *
 538  * Request the contents of the netfs page be written into the cache.  This
 539  * request may be ignored if no cache block is currently allocated, in which
 540  * case it will return -ENOBUFS.
 541  *
 542  * If a cache block was already allocated, a write will be initiated and 0 will
 543  * be returned.  The PG_fscache_write page bit is set immediately and will then
 544  * be cleared at the completion of the write to indicate the success or failure
 545  * of the operation.  Note that the completion may happen before the return.
 546  *
 547  * See Documentation/filesystems/caching/netfs-api.txt for a complete
 548  * description.
 549  */
 550 static inline
 551 int fscache_write_page(struct fscache_cookie *cookie,
 552                        struct page *page,
 553                        gfp_t gfp)
 554 {
 555         if (fscache_cookie_valid(cookie))
 556                 return __fscache_write_page(cookie, page, gfp);
 557         else
 558                 return -ENOBUFS;
 559 }
 560
 561 /**
 562  * fscache_uncache_page - Indicate that caching is no longer required on a page
 563  * @cookie: The cookie representing the cache object
 564  * @page: The netfs page that was being cached.
 565  *
 566  * Tell the cache that we no longer want a page to be cached and that it should
 567  * remove any knowledge of the netfs page it may have.
 568  *
 569  * Note that this cannot cancel any outstanding I/O operations between this
 570  * page and the cache.
 571  *
 572  * See Documentation/filesystems/caching/netfs-api.txt for a complete
 573  * description.
 574  */
 575 static inline
 576 void fscache_uncache_page(struct fscache_cookie *cookie,
 577                           struct page *page)
 578 {
 579         if (fscache_cookie_valid(cookie))
 580                 __fscache_uncache_page(cookie, page);
 581 }
 582
 583 /**
 584  * fscache_check_page_write - Ask if a page is being writing to the cache
 585  * @cookie: The cookie representing the cache object
 586  * @page: The netfs page that is being cached.
 587  *
 588  * Ask the cache if a page is being written to the cache.
 589  *
 590  * See Documentation/filesystems/caching/netfs-api.txt for a complete
 591  * description.
 592  */
 593 static inline
 594 bool fscache_check_page_write(struct fscache_cookie *cookie,
 595                               struct page *page)
 596 {
 597         if (fscache_cookie_valid(cookie))
 598                 return __fscache_check_page_write(cookie, page);
 599         return false;
 600 }
 601
 602 /**
 603  * fscache_wait_on_page_write - Wait for a page to complete writing to the cache
 604  * @cookie: The cookie representing the cache object
 605  * @page: The netfs page that is being cached.
 606  *
 607  * Ask the cache to wake us up when a page is no longer being written to the
 608  * cache.
 609  *
 610  * See Documentation/filesystems/caching/netfs-api.txt for a complete
 611  * description.
 612  */
 613 static inline
 614 void fscache_wait_on_page_write(struct fscache_cookie *cookie,
 615                                 struct page *page)
 616 {
 617         if (fscache_cookie_valid(cookie))
 618                 __fscache_wait_on_page_write(cookie, page);
 619 }
 620
 621 /**
 622  * fscache_maybe_release_page - Consider releasing a page, cancelling a store
 623  * @cookie: The cookie representing the cache object
 624  * @page: The netfs page that is being cached.
 625  * @gfp: The gfp flags passed to releasepage()
 626  *
 627  * Consider releasing a page for the vmscan algorithm, on behalf of the netfs's
 628  * releasepage() call.  A storage request on the page may cancelled if it is
 629  * not currently being processed.
 630  *
 631  * The function returns true if the page no longer has a storage request on it,
 632  * and false if a storage request is left in place.  If true is returned, the
 633  * page will have been passed to fscache_uncache_page().  If false is returned
 634  * the page cannot be freed yet.
 635  */
 636 static inline
 637 bool fscache_maybe_release_page(struct fscache_cookie *cookie,
 638                                 struct page *page,
 639                                 gfp_t gfp)
 640 {
 641         if (fscache_cookie_valid(cookie) && PageFsCache(page))
 642                 return __fscache_maybe_release_page(cookie, page, gfp);
 643         return false;
 644 }
 645
 646 #endif /* _LINUX_FSCACHE_H */