include/linux/fscache-cache.h

   1 /* General filesystem caching backing cache 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/backend-api.txt
  14  *
  15  * for a description of the cache backend interface declared here.
  16  */
  17
  18 #ifndef _LINUX_FSCACHE_CACHE_H
  19 #define _LINUX_FSCACHE_CACHE_H
  20
  21 #include <linux/fscache.h>
  22 #include <linux/sched.h>
  23 #include <linux/workqueue.h>
  24
  25 #define NR_MAXCACHES BITS_PER_LONG
  26
  27 struct fscache_cache;
  28 struct fscache_cache_ops;
  29 struct fscache_object;
  30 struct fscache_operation;
  31
  32 /*
  33  * cache tag definition
  34  */
  35 struct fscache_cache_tag {
  36         struct list_head        link;
  37         struct fscache_cache    *cache;         /* cache referred to by this tag */
  38         unsigned long           flags;
  39 #define FSCACHE_TAG_RESERVED    0               /* T if tag is reserved for a cache */
  40         atomic_t                usage;
  41         char                    name[0];        /* tag name */
  42 };
  43
  44 /*
  45  * cache definition
  46  */
  47 struct fscache_cache {
  48         const struct fscache_cache_ops *ops;
  49         struct fscache_cache_tag *tag;          /* tag representing this cache */
  50         struct kobject          *kobj;          /* system representation of this cache */
  51         struct list_head        link;           /* link in list of caches */
  52         size_t                  max_index_size; /* maximum size of index data */
  53         char                    identifier[36]; /* cache label */
  54
  55         /* node management */
  56         struct work_struct      op_gc;          /* operation garbage collector */
  57         struct list_head        object_list;    /* list of data/index objects */
  58         struct list_head        op_gc_list;     /* list of ops to be deleted */
  59         spinlock_t              object_list_lock;
  60         spinlock_t              op_gc_list_lock;
  61         atomic_t                object_count;   /* no. of live objects in this cache */
  62         struct fscache_object   *fsdef;         /* object for the fsdef index */
  63         unsigned long           flags;
  64 #define FSCACHE_IOERROR         0       /* cache stopped on I/O error */
  65 #define FSCACHE_CACHE_WITHDRAWN 1       /* cache has been withdrawn */
  66 };
  67
  68 extern wait_queue_head_t fscache_cache_cleared_wq;
  69
  70 /*
  71  * operation to be applied to a cache object
  72  * - retrieval initiation operations are done in the context of the process
  73  *   that issued them, and not in an async thread pool
  74  */
  75 typedef void (*fscache_operation_release_t)(struct fscache_operation *op);
  76 typedef void (*fscache_operation_processor_t)(struct fscache_operation *op);
  77
  78 enum fscache_operation_state {
  79         FSCACHE_OP_ST_BLANK,            /* Op is not yet submitted */
  80         FSCACHE_OP_ST_INITIALISED,      /* Op is initialised */
  81         FSCACHE_OP_ST_PENDING,          /* Op is blocked from running */
  82         FSCACHE_OP_ST_IN_PROGRESS,      /* Op is in progress */
  83         FSCACHE_OP_ST_COMPLETE,         /* Op is complete */
  84         FSCACHE_OP_ST_CANCELLED,        /* Op has been cancelled */
  85         FSCACHE_OP_ST_DEAD              /* Op is now dead */
  86 };
  87
  88 struct fscache_operation {
  89         struct work_struct      work;           /* record for async ops */
  90         struct list_head        pend_link;      /* link in object->pending_ops */
  91         struct fscache_object   *object;        /* object to be operated upon */
  92
  93         unsigned long           flags;
  94 #define FSCACHE_OP_TYPE         0x000f  /* operation type */
  95 #define FSCACHE_OP_ASYNC        0x0001  /* - async op, processor may sleep for disk */
  96 #define FSCACHE_OP_MYTHREAD     0x0002  /* - processing is done be issuing thread, not pool */
  97 #define FSCACHE_OP_WAITING      4       /* cleared when op is woken */
  98 #define FSCACHE_OP_EXCLUSIVE    5       /* exclusive op, other ops must wait */
  99 #define FSCACHE_OP_DEC_READ_CNT 6       /* decrement object->n_reads on destruction */
 100 #define FSCACHE_OP_UNUSE_COOKIE 7       /* call fscache_unuse_cookie() on completion */
 101 #define FSCACHE_OP_KEEP_FLAGS   0x00f0  /* flags to keep when repurposing an op */
 102
 103         enum fscache_operation_state state;
 104         atomic_t                usage;
 105         unsigned                debug_id;       /* debugging ID */
 106
 107         /* operation processor callback
 108          * - can be NULL if FSCACHE_OP_WAITING is going to be used to perform
 109          *   the op in a non-pool thread */
 110         fscache_operation_processor_t processor;
 111
 112         /* operation releaser */
 113         fscache_operation_release_t release;
 114 };
 115
 116 extern atomic_t fscache_op_debug_id;
 117 extern void fscache_op_work_func(struct work_struct *work);
 118
 119 extern void fscache_enqueue_operation(struct fscache_operation *);
 120 extern void fscache_op_complete(struct fscache_operation *, bool);
 121 extern void fscache_put_operation(struct fscache_operation *);
 122
 123 /**
 124  * fscache_operation_init - Do basic initialisation of an operation
 125  * @op: The operation to initialise
 126  * @release: The release function to assign
 127  *
 128  * Do basic initialisation of an operation.  The caller must still set flags,
 129  * object and processor if needed.
 130  */
 131 static inline void fscache_operation_init(struct fscache_operation *op,
 132                                         fscache_operation_processor_t processor,
 133                                         fscache_operation_release_t release)
 134 {
 135         INIT_WORK(&op->work, fscache_op_work_func);
 136         atomic_set(&op->usage, 1);
 137         op->state = FSCACHE_OP_ST_INITIALISED;
 138         op->debug_id = atomic_inc_return(&fscache_op_debug_id);
 139         op->processor = processor;
 140         op->release = release;
 141         INIT_LIST_HEAD(&op->pend_link);
 142 }
 143
 144 /*
 145  * data read operation
 146  */
 147 struct fscache_retrieval {
 148         struct fscache_operation op;
 149         struct address_space    *mapping;       /* netfs pages */
 150         fscache_rw_complete_t   end_io_func;    /* function to call on I/O completion */
 151         void                    *context;       /* netfs read context (pinned) */
 152         struct list_head        to_do;          /* list of things to be done by the backend */
 153         unsigned long           start_time;     /* time at which retrieval started */
 154         atomic_t                n_pages;        /* number of pages to be retrieved */
 155 };
 156
 157 typedef int (*fscache_page_retrieval_func_t)(struct fscache_retrieval *op,
 158                                              struct page *page,
 159                                              gfp_t gfp);
 160
 161 typedef int (*fscache_pages_retrieval_func_t)(struct fscache_retrieval *op,
 162                                               struct list_head *pages,
 163                                               unsigned *nr_pages,
 164                                               gfp_t gfp);
 165
 166 /**
 167  * fscache_get_retrieval - Get an extra reference on a retrieval operation
 168  * @op: The retrieval operation to get a reference on
 169  *
 170  * Get an extra reference on a retrieval operation.
 171  */
 172 static inline
 173 struct fscache_retrieval *fscache_get_retrieval(struct fscache_retrieval *op)
 174 {
 175         atomic_inc(&op->op.usage);
 176         return op;
 177 }
 178
 179 /**
 180  * fscache_enqueue_retrieval - Enqueue a retrieval operation for processing
 181  * @op: The retrieval operation affected
 182  *
 183  * Enqueue a retrieval operation for processing by the FS-Cache thread pool.
 184  */
 185 static inline void fscache_enqueue_retrieval(struct fscache_retrieval *op)
 186 {
 187         fscache_enqueue_operation(&op->op);
 188 }
 189
 190 /**
 191  * fscache_retrieval_complete - Record (partial) completion of a retrieval
 192  * @op: The retrieval operation affected
 193  * @n_pages: The number of pages to account for
 194  */
 195 static inline void fscache_retrieval_complete(struct fscache_retrieval *op,
 196                                               int n_pages)
 197 {
 198         atomic_sub(n_pages, &op->n_pages);
 199         if (atomic_read(&op->n_pages) <= 0)
 200                 fscache_op_complete(&op->op, true);
 201 }
 202
 203 /**
 204  * fscache_put_retrieval - Drop a reference to a retrieval operation
 205  * @op: The retrieval operation affected
 206  *
 207  * Drop a reference to a retrieval operation.
 208  */
 209 static inline void fscache_put_retrieval(struct fscache_retrieval *op)
 210 {
 211         fscache_put_operation(&op->op);
 212 }
 213
 214 /*
 215  * cached page storage work item
 216  * - used to do three things:
 217  *   - batch writes to the cache
 218  *   - do cache writes asynchronously
 219  *   - defer writes until cache object lookup completion
 220  */
 221 struct fscache_storage {
 222         struct fscache_operation op;
 223         pgoff_t                 store_limit;    /* don't write more than this */
 224 };
 225
 226 /*
 227  * cache operations
 228  */
 229 struct fscache_cache_ops {
 230         /* name of cache provider */
 231         const char *name;
 232
 233         /* allocate an object record for a cookie */
 234         struct fscache_object *(*alloc_object)(struct fscache_cache *cache,
 235                                                struct fscache_cookie *cookie);
 236
 237         /* look up the object for a cookie
 238          * - return -ETIMEDOUT to be requeued
 239          */
 240         int (*lookup_object)(struct fscache_object *object);
 241
 242         /* finished looking up */
 243         void (*lookup_complete)(struct fscache_object *object);
 244
 245         /* increment the usage count on this object (may fail if unmounting) */
 246         struct fscache_object *(*grab_object)(struct fscache_object *object);
 247
 248         /* pin an object in the cache */
 249         int (*pin_object)(struct fscache_object *object);
 250
 251         /* unpin an object in the cache */
 252         void (*unpin_object)(struct fscache_object *object);
 253
 254         /* check the consistency between the backing cache and the FS-Cache
 255          * cookie */
 256         bool (*check_consistency)(struct fscache_operation *op);
 257
 258         /* store the updated auxiliary data on an object */
 259         void (*update_object)(struct fscache_object *object);
 260
 261         /* Invalidate an object */
 262         void (*invalidate_object)(struct fscache_operation *op);
 263
 264         /* discard the resources pinned by an object and effect retirement if
 265          * necessary */
 266         void (*drop_object)(struct fscache_object *object);
 267
 268         /* dispose of a reference to an object */
 269         void (*put_object)(struct fscache_object *object);
 270
 271         /* sync a cache */
 272         void (*sync_cache)(struct fscache_cache *cache);
 273
 274         /* notification that the attributes of a non-index object (such as
 275          * i_size) have changed */
 276         int (*attr_changed)(struct fscache_object *object);
 277
 278         /* reserve space for an object's data and associated metadata */
 279         int (*reserve_space)(struct fscache_object *object, loff_t i_size);
 280
 281         /* request a backing block for a page be read or allocated in the
 282          * cache */
 283         fscache_page_retrieval_func_t read_or_alloc_page;
 284
 285         /* request backing blocks for a list of pages be read or allocated in
 286          * the cache */
 287         fscache_pages_retrieval_func_t read_or_alloc_pages;
 288
 289         /* request a backing block for a page be allocated in the cache so that
 290          * it can be written directly */
 291         fscache_page_retrieval_func_t allocate_page;
 292
 293         /* request backing blocks for pages be allocated in the cache so that
 294          * they can be written directly */
 295         fscache_pages_retrieval_func_t allocate_pages;
 296
 297         /* write a page to its backing block in the cache */
 298         int (*write_page)(struct fscache_storage *op, struct page *page);
 299
 300         /* detach backing block from a page (optional)
 301          * - must release the cookie lock before returning
 302          * - may sleep
 303          */
 304         void (*uncache_page)(struct fscache_object *object,
 305                              struct page *page);
 306
 307         /* dissociate a cache from all the pages it was backing */
 308         void (*dissociate_pages)(struct fscache_cache *cache);
 309 };
 310
 311 /*
 312  * data file or index object cookie
 313  * - a file will only appear in one cache
 314  * - a request to cache a file may or may not be honoured, subject to
 315  *   constraints such as disk space
 316  * - indices are created on disk just-in-time
 317  */
 318 struct fscache_cookie {
 319         atomic_t                        usage;          /* number of users of this cookie */
 320         atomic_t                        n_children;     /* number of children of this cookie */
 321         atomic_t                        n_active;       /* number of active users of netfs ptrs */
 322         spinlock_t                      lock;
 323         spinlock_t                      stores_lock;    /* lock on page store tree */
 324         struct hlist_head               backing_objects; /* object(s) backing this file/index */
 325         const struct fscache_cookie_def *def;           /* definition */
 326         struct fscache_cookie           *parent;        /* parent of this entry */
 327         void                            *netfs_data;    /* back pointer to netfs */
 328         struct radix_tree_root          stores;         /* pages to be stored on this cookie */
 329 #define FSCACHE_COOKIE_PENDING_TAG      0               /* pages tag: pending write to cache */
 330 #define FSCACHE_COOKIE_STORING_TAG      1               /* pages tag: writing to cache */
 331
 332         unsigned long                   flags;
 333 #define FSCACHE_COOKIE_LOOKING_UP       0       /* T if non-index cookie being looked up still */
 334 #define FSCACHE_COOKIE_NO_DATA_YET      1       /* T if new object with no cached data yet */
 335 #define FSCACHE_COOKIE_UNAVAILABLE      2       /* T if cookie is unavailable (error, etc) */
 336 #define FSCACHE_COOKIE_INVALIDATING     3       /* T if cookie is being invalidated */
 337 #define FSCACHE_COOKIE_RELINQUISHED     4       /* T if cookie has been relinquished */
 338 #define FSCACHE_COOKIE_RETIRED          5       /* T if cookie was retired */
 339 };
 340
 341 extern struct fscache_cookie fscache_fsdef_index;
 342
 343 /*
 344  * Event list for fscache_object::{event_mask,events}
 345  */
 346 enum {
 347         FSCACHE_OBJECT_EV_NEW_CHILD,    /* T if object has a new child */
 348         FSCACHE_OBJECT_EV_PARENT_READY, /* T if object's parent is ready */
 349         FSCACHE_OBJECT_EV_UPDATE,       /* T if object should be updated */
 350         FSCACHE_OBJECT_EV_INVALIDATE,   /* T if cache requested object invalidation */
 351         FSCACHE_OBJECT_EV_CLEARED,      /* T if accessors all gone */
 352         FSCACHE_OBJECT_EV_ERROR,        /* T if fatal error occurred during processing */
 353         FSCACHE_OBJECT_EV_KILL,         /* T if netfs relinquished or cache withdrew object */
 354         NR_FSCACHE_OBJECT_EVENTS
 355 };
 356
 357 #define FSCACHE_OBJECT_EVENTS_MASK ((1UL << NR_FSCACHE_OBJECT_EVENTS) - 1)
 358
 359 /*
 360  * States for object state machine.
 361  */
 362 struct fscache_transition {
 363         unsigned long events;
 364         const struct fscache_state *transit_to;
 365 };
 366
 367 struct fscache_state {
 368         char name[24];
 369         char short_name[8];
 370         const struct fscache_state *(*work)(struct fscache_object *object,
 371                                             int event);
 372         const struct fscache_transition transitions[];
 373 };
 374
 375 /*
 376  * on-disk cache file or index handle
 377  */
 378 struct fscache_object {
 379         const struct fscache_state *state;      /* Object state machine state */
 380         const struct fscache_transition *oob_table; /* OOB state transition table */
 381         int                     debug_id;       /* debugging ID */
 382         int                     n_children;     /* number of child objects */
 383         int                     n_ops;          /* number of extant ops on object */
 384         int                     n_obj_ops;      /* number of object ops outstanding on object */
 385         int                     n_in_progress;  /* number of ops in progress */
 386         int                     n_exclusive;    /* number of exclusive ops queued or in progress */
 387         atomic_t                n_reads;        /* number of read ops in progress */
 388         spinlock_t              lock;           /* state and operations lock */
 389
 390         unsigned long           lookup_jif;     /* time at which lookup started */
 391         unsigned long           oob_event_mask; /* OOB events this object is interested in */
 392         unsigned long           event_mask;     /* events this object is interested in */
 393         unsigned long           events;         /* events to be processed by this object
 394                                                  * (order is important - using fls) */
 395
 396         unsigned long           flags;
 397 #define FSCACHE_OBJECT_LOCK             0       /* T if object is busy being processed */
 398 #define FSCACHE_OBJECT_PENDING_WRITE    1       /* T if object has pending write */
 399 #define FSCACHE_OBJECT_WAITING          2       /* T if object is waiting on its parent */
 400 #define FSCACHE_OBJECT_IS_LIVE          3       /* T if object is not withdrawn or relinquished */
 401 #define FSCACHE_OBJECT_IS_LOOKED_UP     4       /* T if object has been looked up */
 402 #define FSCACHE_OBJECT_IS_AVAILABLE     5       /* T if object has become active */
 403
 404         struct list_head        cache_link;     /* link in cache->object_list */
 405         struct hlist_node       cookie_link;    /* link in cookie->backing_objects */
 406         struct fscache_cache    *cache;         /* cache that supplied this object */
 407         struct fscache_cookie   *cookie;        /* netfs's file/index object */
 408         struct fscache_object   *parent;        /* parent object */
 409         struct work_struct      work;           /* attention scheduling record */
 410         struct list_head        dependents;     /* FIFO of dependent objects */
 411         struct list_head        dep_link;       /* link in parent's dependents list */
 412         struct list_head        pending_ops;    /* unstarted operations on this object */
 413 #ifdef CONFIG_FSCACHE_OBJECT_LIST
 414         struct rb_node          objlist_link;   /* link in global object list */
 415 #endif
 416         pgoff_t                 store_limit;    /* current storage limit */
 417         loff_t                  store_limit_l;  /* current storage limit */
 418 };
 419
 420 extern void fscache_object_init(struct fscache_object *, struct fscache_cookie *,
 421                                 struct fscache_cache *);
 422 extern void fscache_object_destroy(struct fscache_object *);
 423
 424 extern void fscache_object_lookup_negative(struct fscache_object *object);
 425 extern void fscache_obtained_object(struct fscache_object *object);
 426
 427 static inline bool fscache_object_is_live(struct fscache_object *object)
 428 {
 429         return test_bit(FSCACHE_OBJECT_IS_LIVE, &object->flags);
 430 }
 431
 432 static inline bool fscache_object_is_dying(struct fscache_object *object)
 433 {
 434         return !fscache_object_is_live(object);
 435 }
 436
 437 static inline bool fscache_object_is_available(struct fscache_object *object)
 438 {
 439         return test_bit(FSCACHE_OBJECT_IS_AVAILABLE, &object->flags);
 440 }
 441
 442 static inline bool fscache_object_is_active(struct fscache_object *object)
 443 {
 444         return fscache_object_is_available(object) &&
 445                 fscache_object_is_live(object) &&
 446                 !test_bit(FSCACHE_IOERROR, &object->cache->flags);
 447 }
 448
 449 static inline bool fscache_object_is_dead(struct fscache_object *object)
 450 {
 451         return fscache_object_is_dying(object) &&
 452                 test_bit(FSCACHE_IOERROR, &object->cache->flags);
 453 }
 454
 455 /**
 456  * fscache_object_destroyed - Note destruction of an object in a cache
 457  * @cache: The cache from which the object came
 458  *
 459  * Note the destruction and deallocation of an object record in a cache.
 460  */
 461 static inline void fscache_object_destroyed(struct fscache_cache *cache)
 462 {
 463         if (atomic_dec_and_test(&cache->object_count))
 464                 wake_up_all(&fscache_cache_cleared_wq);
 465 }
 466
 467 /**
 468  * fscache_object_lookup_error - Note an object encountered an error
 469  * @object: The object on which the error was encountered
 470  *
 471  * Note that an object encountered a fatal error (usually an I/O error) and
 472  * that it should be withdrawn as soon as possible.
 473  */
 474 static inline void fscache_object_lookup_error(struct fscache_object *object)
 475 {
 476         set_bit(FSCACHE_OBJECT_EV_ERROR, &object->events);
 477 }
 478
 479 /**
 480  * fscache_set_store_limit - Set the maximum size to be stored in an object
 481  * @object: The object to set the maximum on
 482  * @i_size: The limit to set in bytes
 483  *
 484  * Set the maximum size an object is permitted to reach, implying the highest
 485  * byte that may be written.  Intended to be called by the attr_changed() op.
 486  *
 487  * See Documentation/filesystems/caching/backend-api.txt for a complete
 488  * description.
 489  */
 490 static inline
 491 void fscache_set_store_limit(struct fscache_object *object, loff_t i_size)
 492 {
 493         object->store_limit_l = i_size;
 494         object->store_limit = i_size >> PAGE_SHIFT;
 495         if (i_size & ~PAGE_MASK)
 496                 object->store_limit++;
 497 }
 498
 499 /**
 500  * fscache_end_io - End a retrieval operation on a page
 501  * @op: The FS-Cache operation covering the retrieval
 502  * @page: The page that was to be fetched
 503  * @error: The error code (0 if successful)
 504  *
 505  * Note the end of an operation to retrieve a page, as covered by a particular
 506  * operation record.
 507  */
 508 static inline void fscache_end_io(struct fscache_retrieval *op,
 509                                   struct page *page, int error)
 510 {
 511         op->end_io_func(page, op->context, error);
 512 }
 513
 514 /**
 515  * fscache_use_cookie - Request usage of cookie attached to an object
 516  * @object: Object description
 517  *
 518  * Request usage of the cookie attached to an object.  NULL is returned if the
 519  * relinquishment had reduced the cookie usage count to 0.
 520  */
 521 static inline bool fscache_use_cookie(struct fscache_object *object)
 522 {
 523         struct fscache_cookie *cookie = object->cookie;
 524         return atomic_inc_not_zero(&cookie->n_active) != 0;
 525 }
 526
 527 /**
 528  * fscache_unuse_cookie - Cease usage of cookie attached to an object
 529  * @object: Object description
 530  *
 531  * Cease usage of the cookie attached to an object.  When the users count
 532  * reaches zero then the cookie relinquishment will be permitted to proceed.
 533  */
 534 static inline void fscache_unuse_cookie(struct fscache_object *object)
 535 {
 536         struct fscache_cookie *cookie = object->cookie;
 537         if (atomic_dec_and_test(&cookie->n_active))
 538                 wake_up_atomic_t(&cookie->n_active);
 539 }
 540
 541 /*
 542  * out-of-line cache backend functions
 543  */
 544 extern __printf(3, 4)
 545 void fscache_init_cache(struct fscache_cache *cache,
 546                         const struct fscache_cache_ops *ops,
 547                         const char *idfmt, ...);
 548
 549 extern int fscache_add_cache(struct fscache_cache *cache,
 550                              struct fscache_object *fsdef,
 551                              const char *tagname);
 552 extern void fscache_withdraw_cache(struct fscache_cache *cache);
 553
 554 extern void fscache_io_error(struct fscache_cache *cache);
 555
 556 extern void fscache_mark_page_cached(struct fscache_retrieval *op,
 557                                      struct page *page);
 558
 559 extern void fscache_mark_pages_cached(struct fscache_retrieval *op,
 560                                       struct pagevec *pagevec);
 561
 562 extern bool fscache_object_sleep_till_congested(signed long *timeoutp);
 563
 564 extern enum fscache_checkaux fscache_check_aux(struct fscache_object *object,
 565                                                const void *data,
 566                                                uint16_t datalen);
 567
 568 #endif /* _LINUX_FSCACHE_CACHE_H */