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