linux/include/linux/fscache-cache.h
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   1/* SPDX-License-Identifier: GPL-2.0-or-later */
   2/* General filesystem caching backing cache interface
   3 *
   4 * Copyright (C) 2004-2007 Red Hat, Inc. All Rights Reserved.
   5 * Written by David Howells (dhowells@redhat.com)
   6 *
   7 * NOTE!!! See:
   8 *
   9 *      Documentation/filesystems/caching/backend-api.txt
  10 *
  11 * for a description of the cache backend interface declared here.
  12 */
  13
  14#ifndef _LINUX_FSCACHE_CACHE_H
  15#define _LINUX_FSCACHE_CACHE_H
  16
  17#include <linux/fscache.h>
  18#include <linux/sched.h>
  19#include <linux/workqueue.h>
  20
  21#define NR_MAXCACHES BITS_PER_LONG
  22
  23struct fscache_cache;
  24struct fscache_cache_ops;
  25struct fscache_object;
  26struct fscache_operation;
  27
  28enum fscache_obj_ref_trace {
  29        fscache_obj_get_add_to_deps,
  30        fscache_obj_get_queue,
  31        fscache_obj_put_alloc_fail,
  32        fscache_obj_put_attach_fail,
  33        fscache_obj_put_drop_obj,
  34        fscache_obj_put_enq_dep,
  35        fscache_obj_put_queue,
  36        fscache_obj_put_work,
  37        fscache_obj_ref__nr_traces
  38};
  39
  40/*
  41 * cache tag definition
  42 */
  43struct fscache_cache_tag {
  44        struct list_head        link;
  45        struct fscache_cache    *cache;         /* cache referred to by this tag */
  46        unsigned long           flags;
  47#define FSCACHE_TAG_RESERVED    0               /* T if tag is reserved for a cache */
  48        atomic_t                usage;
  49        char                    name[0];        /* tag name */
  50};
  51
  52/*
  53 * cache definition
  54 */
  55struct fscache_cache {
  56        const struct fscache_cache_ops *ops;
  57        struct fscache_cache_tag *tag;          /* tag representing this cache */
  58        struct kobject          *kobj;          /* system representation of this cache */
  59        struct list_head        link;           /* link in list of caches */
  60        size_t                  max_index_size; /* maximum size of index data */
  61        char                    identifier[36]; /* cache label */
  62
  63        /* node management */
  64        struct work_struct      op_gc;          /* operation garbage collector */
  65        struct list_head        object_list;    /* list of data/index objects */
  66        struct list_head        op_gc_list;     /* list of ops to be deleted */
  67        spinlock_t              object_list_lock;
  68        spinlock_t              op_gc_list_lock;
  69        atomic_t                object_count;   /* no. of live objects in this cache */
  70        struct fscache_object   *fsdef;         /* object for the fsdef index */
  71        unsigned long           flags;
  72#define FSCACHE_IOERROR         0       /* cache stopped on I/O error */
  73#define FSCACHE_CACHE_WITHDRAWN 1       /* cache has been withdrawn */
  74};
  75
  76extern wait_queue_head_t fscache_cache_cleared_wq;
  77
  78/*
  79 * operation to be applied to a cache object
  80 * - retrieval initiation operations are done in the context of the process
  81 *   that issued them, and not in an async thread pool
  82 */
  83typedef void (*fscache_operation_release_t)(struct fscache_operation *op);
  84typedef void (*fscache_operation_processor_t)(struct fscache_operation *op);
  85typedef void (*fscache_operation_cancel_t)(struct fscache_operation *op);
  86
  87enum fscache_operation_state {
  88        FSCACHE_OP_ST_BLANK,            /* Op is not yet submitted */
  89        FSCACHE_OP_ST_INITIALISED,      /* Op is initialised */
  90        FSCACHE_OP_ST_PENDING,          /* Op is blocked from running */
  91        FSCACHE_OP_ST_IN_PROGRESS,      /* Op is in progress */
  92        FSCACHE_OP_ST_COMPLETE,         /* Op is complete */
  93        FSCACHE_OP_ST_CANCELLED,        /* Op has been cancelled */
  94        FSCACHE_OP_ST_DEAD              /* Op is now dead */
  95};
  96
  97struct fscache_operation {
  98        struct work_struct      work;           /* record for async ops */
  99        struct list_head        pend_link;      /* link in object->pending_ops */
 100        struct fscache_object   *object;        /* object to be operated upon */
 101
 102        unsigned long           flags;
 103#define FSCACHE_OP_TYPE         0x000f  /* operation type */
 104#define FSCACHE_OP_ASYNC        0x0001  /* - async op, processor may sleep for disk */
 105#define FSCACHE_OP_MYTHREAD     0x0002  /* - processing is done be issuing thread, not pool */
 106#define FSCACHE_OP_WAITING      4       /* cleared when op is woken */
 107#define FSCACHE_OP_EXCLUSIVE    5       /* exclusive op, other ops must wait */
 108#define FSCACHE_OP_DEC_READ_CNT 6       /* decrement object->n_reads on destruction */
 109#define FSCACHE_OP_UNUSE_COOKIE 7       /* call fscache_unuse_cookie() on completion */
 110#define FSCACHE_OP_KEEP_FLAGS   0x00f0  /* flags to keep when repurposing an op */
 111
 112        enum fscache_operation_state state;
 113        atomic_t                usage;
 114        unsigned                debug_id;       /* debugging ID */
 115
 116        /* operation processor callback
 117         * - can be NULL if FSCACHE_OP_WAITING is going to be used to perform
 118         *   the op in a non-pool thread */
 119        fscache_operation_processor_t processor;
 120
 121        /* Operation cancellation cleanup (optional) */
 122        fscache_operation_cancel_t cancel;
 123
 124        /* operation releaser */
 125        fscache_operation_release_t release;
 126};
 127
 128extern atomic_t fscache_op_debug_id;
 129extern void fscache_op_work_func(struct work_struct *work);
 130
 131extern void fscache_enqueue_operation(struct fscache_operation *);
 132extern void fscache_op_complete(struct fscache_operation *, bool);
 133extern void fscache_put_operation(struct fscache_operation *);
 134extern void fscache_operation_init(struct fscache_cookie *,
 135                                   struct fscache_operation *,
 136                                   fscache_operation_processor_t,
 137                                   fscache_operation_cancel_t,
 138                                   fscache_operation_release_t);
 139
 140/*
 141 * data read operation
 142 */
 143struct fscache_retrieval {
 144        struct fscache_operation op;
 145        struct fscache_cookie   *cookie;        /* The netfs cookie */
 146        struct address_space    *mapping;       /* netfs pages */
 147        fscache_rw_complete_t   end_io_func;    /* function to call on I/O completion */
 148        void                    *context;       /* netfs read context (pinned) */
 149        struct list_head        to_do;          /* list of things to be done by the backend */
 150        unsigned long           start_time;     /* time at which retrieval started */
 151        atomic_t                n_pages;        /* number of pages to be retrieved */
 152};
 153
 154typedef int (*fscache_page_retrieval_func_t)(struct fscache_retrieval *op,
 155                                             struct page *page,
 156                                             gfp_t gfp);
 157
 158typedef int (*fscache_pages_retrieval_func_t)(struct fscache_retrieval *op,
 159                                              struct list_head *pages,
 160                                              unsigned *nr_pages,
 161                                              gfp_t gfp);
 162
 163/**
 164 * fscache_get_retrieval - Get an extra reference on a retrieval operation
 165 * @op: The retrieval operation to get a reference on
 166 *
 167 * Get an extra reference on a retrieval operation.
 168 */
 169static inline
 170struct fscache_retrieval *fscache_get_retrieval(struct fscache_retrieval *op)
 171{
 172        atomic_inc(&op->op.usage);
 173        return op;
 174}
 175
 176/**
 177 * fscache_enqueue_retrieval - Enqueue a retrieval operation for processing
 178 * @op: The retrieval operation affected
 179 *
 180 * Enqueue a retrieval operation for processing by the FS-Cache thread pool.
 181 */
 182static inline void fscache_enqueue_retrieval(struct fscache_retrieval *op)
 183{
 184        fscache_enqueue_operation(&op->op);
 185}
 186
 187/**
 188 * fscache_retrieval_complete - Record (partial) completion of a retrieval
 189 * @op: The retrieval operation affected
 190 * @n_pages: The number of pages to account for
 191 */
 192static inline void fscache_retrieval_complete(struct fscache_retrieval *op,
 193                                              int n_pages)
 194{
 195        if (atomic_sub_return_relaxed(n_pages, &op->n_pages) <= 0)
 196                fscache_op_complete(&op->op, false);
 197}
 198
 199/**
 200 * fscache_put_retrieval - Drop a reference to a retrieval operation
 201 * @op: The retrieval operation affected
 202 *
 203 * Drop a reference to a retrieval operation.
 204 */
 205static inline void fscache_put_retrieval(struct fscache_retrieval *op)
 206{
 207        fscache_put_operation(&op->op);
 208}
 209
 210/*
 211 * cached page storage work item
 212 * - used to do three things:
 213 *   - batch writes to the cache
 214 *   - do cache writes asynchronously
 215 *   - defer writes until cache object lookup completion
 216 */
 217struct fscache_storage {
 218        struct fscache_operation op;
 219        pgoff_t                 store_limit;    /* don't write more than this */
 220};
 221
 222/*
 223 * cache operations
 224 */
 225struct fscache_cache_ops {
 226        /* name of cache provider */
 227        const char *name;
 228
 229        /* allocate an object record for a cookie */
 230        struct fscache_object *(*alloc_object)(struct fscache_cache *cache,
 231                                               struct fscache_cookie *cookie);
 232
 233        /* look up the object for a cookie
 234         * - return -ETIMEDOUT to be requeued
 235         */
 236        int (*lookup_object)(struct fscache_object *object);
 237
 238        /* finished looking up */
 239        void (*lookup_complete)(struct fscache_object *object);
 240
 241        /* increment the usage count on this object (may fail if unmounting) */
 242        struct fscache_object *(*grab_object)(struct fscache_object *object,
 243                                              enum fscache_obj_ref_trace why);
 244
 245        /* pin an object in the cache */
 246        int (*pin_object)(struct fscache_object *object);
 247
 248        /* unpin an object in the cache */
 249        void (*unpin_object)(struct fscache_object *object);
 250
 251        /* check the consistency between the backing cache and the FS-Cache
 252         * cookie */
 253        int (*check_consistency)(struct fscache_operation *op);
 254
 255        /* store the updated auxiliary data on an object */
 256        void (*update_object)(struct fscache_object *object);
 257
 258        /* Invalidate an object */
 259        void (*invalidate_object)(struct fscache_operation *op);
 260
 261        /* discard the resources pinned by an object and effect retirement if
 262         * necessary */
 263        void (*drop_object)(struct fscache_object *object);
 264
 265        /* dispose of a reference to an object */
 266        void (*put_object)(struct fscache_object *object,
 267                           enum fscache_obj_ref_trace why);
 268
 269        /* sync a cache */
 270        void (*sync_cache)(struct fscache_cache *cache);
 271
 272        /* notification that the attributes of a non-index object (such as
 273         * i_size) have changed */
 274        int (*attr_changed)(struct fscache_object *object);
 275
 276        /* reserve space for an object's data and associated metadata */
 277        int (*reserve_space)(struct fscache_object *object, loff_t i_size);
 278
 279        /* request a backing block for a page be read or allocated in the
 280         * cache */
 281        fscache_page_retrieval_func_t read_or_alloc_page;
 282
 283        /* request backing blocks for a list of pages be read or allocated in
 284         * the cache */
 285        fscache_pages_retrieval_func_t read_or_alloc_pages;
 286
 287        /* request a backing block for a page be allocated in the cache so that
 288         * it can be written directly */
 289        fscache_page_retrieval_func_t allocate_page;
 290
 291        /* request backing blocks for pages be allocated in the cache so that
 292         * they can be written directly */
 293        fscache_pages_retrieval_func_t allocate_pages;
 294
 295        /* write a page to its backing block in the cache */
 296        int (*write_page)(struct fscache_storage *op, struct page *page);
 297
 298        /* detach backing block from a page (optional)
 299         * - must release the cookie lock before returning
 300         * - may sleep
 301         */
 302        void (*uncache_page)(struct fscache_object *object,
 303                             struct page *page);
 304
 305        /* dissociate a cache from all the pages it was backing */
 306        void (*dissociate_pages)(struct fscache_cache *cache);
 307};
 308
 309extern struct fscache_cookie fscache_fsdef_index;
 310
 311/*
 312 * Event list for fscache_object::{event_mask,events}
 313 */
 314enum {
 315        FSCACHE_OBJECT_EV_NEW_CHILD,    /* T if object has a new child */
 316        FSCACHE_OBJECT_EV_PARENT_READY, /* T if object's parent is ready */
 317        FSCACHE_OBJECT_EV_UPDATE,       /* T if object should be updated */
 318        FSCACHE_OBJECT_EV_INVALIDATE,   /* T if cache requested object invalidation */
 319        FSCACHE_OBJECT_EV_CLEARED,      /* T if accessors all gone */
 320        FSCACHE_OBJECT_EV_ERROR,        /* T if fatal error occurred during processing */
 321        FSCACHE_OBJECT_EV_KILL,         /* T if netfs relinquished or cache withdrew object */
 322        NR_FSCACHE_OBJECT_EVENTS
 323};
 324
 325#define FSCACHE_OBJECT_EVENTS_MASK ((1UL << NR_FSCACHE_OBJECT_EVENTS) - 1)
 326
 327/*
 328 * States for object state machine.
 329 */
 330struct fscache_transition {
 331        unsigned long events;
 332        const struct fscache_state *transit_to;
 333};
 334
 335struct fscache_state {
 336        char name[24];
 337        char short_name[8];
 338        const struct fscache_state *(*work)(struct fscache_object *object,
 339                                            int event);
 340        const struct fscache_transition transitions[];
 341};
 342
 343/*
 344 * on-disk cache file or index handle
 345 */
 346struct fscache_object {
 347        const struct fscache_state *state;      /* Object state machine state */
 348        const struct fscache_transition *oob_table; /* OOB state transition table */
 349        int                     debug_id;       /* debugging ID */
 350        int                     n_children;     /* number of child objects */
 351        int                     n_ops;          /* number of extant ops on object */
 352        int                     n_obj_ops;      /* number of object ops outstanding on object */
 353        int                     n_in_progress;  /* number of ops in progress */
 354        int                     n_exclusive;    /* number of exclusive ops queued or in progress */
 355        atomic_t                n_reads;        /* number of read ops in progress */
 356        spinlock_t              lock;           /* state and operations lock */
 357
 358        unsigned long           lookup_jif;     /* time at which lookup started */
 359        unsigned long           oob_event_mask; /* OOB events this object is interested in */
 360        unsigned long           event_mask;     /* events this object is interested in */
 361        unsigned long           events;         /* events to be processed by this object
 362                                                 * (order is important - using fls) */
 363
 364        unsigned long           flags;
 365#define FSCACHE_OBJECT_LOCK             0       /* T if object is busy being processed */
 366#define FSCACHE_OBJECT_PENDING_WRITE    1       /* T if object has pending write */
 367#define FSCACHE_OBJECT_WAITING          2       /* T if object is waiting on its parent */
 368#define FSCACHE_OBJECT_IS_LIVE          3       /* T if object is not withdrawn or relinquished */
 369#define FSCACHE_OBJECT_IS_LOOKED_UP     4       /* T if object has been looked up */
 370#define FSCACHE_OBJECT_IS_AVAILABLE     5       /* T if object has become active */
 371#define FSCACHE_OBJECT_RETIRED          6       /* T if object was retired on relinquishment */
 372#define FSCACHE_OBJECT_KILLED_BY_CACHE  7       /* T if object was killed by the cache */
 373#define FSCACHE_OBJECT_RUN_AFTER_DEAD   8       /* T if object has been dispatched after death */
 374
 375        struct list_head        cache_link;     /* link in cache->object_list */
 376        struct hlist_node       cookie_link;    /* link in cookie->backing_objects */
 377        struct fscache_cache    *cache;         /* cache that supplied this object */
 378        struct fscache_cookie   *cookie;        /* netfs's file/index object */
 379        struct fscache_object   *parent;        /* parent object */
 380        struct work_struct      work;           /* attention scheduling record */
 381        struct list_head        dependents;     /* FIFO of dependent objects */
 382        struct list_head        dep_link;       /* link in parent's dependents list */
 383        struct list_head        pending_ops;    /* unstarted operations on this object */
 384#ifdef CONFIG_FSCACHE_OBJECT_LIST
 385        struct rb_node          objlist_link;   /* link in global object list */
 386#endif
 387        pgoff_t                 store_limit;    /* current storage limit */
 388        loff_t                  store_limit_l;  /* current storage limit */
 389};
 390
 391extern void fscache_object_init(struct fscache_object *, struct fscache_cookie *,
 392                                struct fscache_cache *);
 393extern void fscache_object_destroy(struct fscache_object *);
 394
 395extern void fscache_object_lookup_negative(struct fscache_object *object);
 396extern void fscache_obtained_object(struct fscache_object *object);
 397
 398static inline bool fscache_object_is_live(struct fscache_object *object)
 399{
 400        return test_bit(FSCACHE_OBJECT_IS_LIVE, &object->flags);
 401}
 402
 403static inline bool fscache_object_is_dying(struct fscache_object *object)
 404{
 405        return !fscache_object_is_live(object);
 406}
 407
 408static inline bool fscache_object_is_available(struct fscache_object *object)
 409{
 410        return test_bit(FSCACHE_OBJECT_IS_AVAILABLE, &object->flags);
 411}
 412
 413static inline bool fscache_cache_is_broken(struct fscache_object *object)
 414{
 415        return test_bit(FSCACHE_IOERROR, &object->cache->flags);
 416}
 417
 418static inline bool fscache_object_is_active(struct fscache_object *object)
 419{
 420        return fscache_object_is_available(object) &&
 421                fscache_object_is_live(object) &&
 422                !fscache_cache_is_broken(object);
 423}
 424
 425/**
 426 * fscache_object_destroyed - Note destruction of an object in a cache
 427 * @cache: The cache from which the object came
 428 *
 429 * Note the destruction and deallocation of an object record in a cache.
 430 */
 431static inline void fscache_object_destroyed(struct fscache_cache *cache)
 432{
 433        if (atomic_dec_and_test(&cache->object_count))
 434                wake_up_all(&fscache_cache_cleared_wq);
 435}
 436
 437/**
 438 * fscache_object_lookup_error - Note an object encountered an error
 439 * @object: The object on which the error was encountered
 440 *
 441 * Note that an object encountered a fatal error (usually an I/O error) and
 442 * that it should be withdrawn as soon as possible.
 443 */
 444static inline void fscache_object_lookup_error(struct fscache_object *object)
 445{
 446        set_bit(FSCACHE_OBJECT_EV_ERROR, &object->events);
 447}
 448
 449/**
 450 * fscache_set_store_limit - Set the maximum size to be stored in an object
 451 * @object: The object to set the maximum on
 452 * @i_size: The limit to set in bytes
 453 *
 454 * Set the maximum size an object is permitted to reach, implying the highest
 455 * byte that may be written.  Intended to be called by the attr_changed() op.
 456 *
 457 * See Documentation/filesystems/caching/backend-api.txt for a complete
 458 * description.
 459 */
 460static inline
 461void fscache_set_store_limit(struct fscache_object *object, loff_t i_size)
 462{
 463        object->store_limit_l = i_size;
 464        object->store_limit = i_size >> PAGE_SHIFT;
 465        if (i_size & ~PAGE_MASK)
 466                object->store_limit++;
 467}
 468
 469/**
 470 * fscache_end_io - End a retrieval operation on a page
 471 * @op: The FS-Cache operation covering the retrieval
 472 * @page: The page that was to be fetched
 473 * @error: The error code (0 if successful)
 474 *
 475 * Note the end of an operation to retrieve a page, as covered by a particular
 476 * operation record.
 477 */
 478static inline void fscache_end_io(struct fscache_retrieval *op,
 479                                  struct page *page, int error)
 480{
 481        op->end_io_func(page, op->context, error);
 482}
 483
 484static inline void __fscache_use_cookie(struct fscache_cookie *cookie)
 485{
 486        atomic_inc(&cookie->n_active);
 487}
 488
 489/**
 490 * fscache_use_cookie - Request usage of cookie attached to an object
 491 * @object: Object description
 492 * 
 493 * Request usage of the cookie attached to an object.  NULL is returned if the
 494 * relinquishment had reduced the cookie usage count to 0.
 495 */
 496static inline bool fscache_use_cookie(struct fscache_object *object)
 497{
 498        struct fscache_cookie *cookie = object->cookie;
 499        return atomic_inc_not_zero(&cookie->n_active) != 0;
 500}
 501
 502static inline bool __fscache_unuse_cookie(struct fscache_cookie *cookie)
 503{
 504        return atomic_dec_and_test(&cookie->n_active);
 505}
 506
 507static inline void __fscache_wake_unused_cookie(struct fscache_cookie *cookie)
 508{
 509        wake_up_var(&cookie->n_active);
 510}
 511
 512/**
 513 * fscache_unuse_cookie - Cease usage of cookie attached to an object
 514 * @object: Object description
 515 * 
 516 * Cease usage of the cookie attached to an object.  When the users count
 517 * reaches zero then the cookie relinquishment will be permitted to proceed.
 518 */
 519static inline void fscache_unuse_cookie(struct fscache_object *object)
 520{
 521        struct fscache_cookie *cookie = object->cookie;
 522        if (__fscache_unuse_cookie(cookie))
 523                __fscache_wake_unused_cookie(cookie);
 524}
 525
 526/*
 527 * out-of-line cache backend functions
 528 */
 529extern __printf(3, 4)
 530void fscache_init_cache(struct fscache_cache *cache,
 531                        const struct fscache_cache_ops *ops,
 532                        const char *idfmt, ...);
 533
 534extern int fscache_add_cache(struct fscache_cache *cache,
 535                             struct fscache_object *fsdef,
 536                             const char *tagname);
 537extern void fscache_withdraw_cache(struct fscache_cache *cache);
 538
 539extern void fscache_io_error(struct fscache_cache *cache);
 540
 541extern void fscache_mark_page_cached(struct fscache_retrieval *op,
 542                                     struct page *page);
 543
 544extern void fscache_mark_pages_cached(struct fscache_retrieval *op,
 545                                      struct pagevec *pagevec);
 546
 547extern bool fscache_object_sleep_till_congested(signed long *timeoutp);
 548
 549extern enum fscache_checkaux fscache_check_aux(struct fscache_object *object,
 550                                               const void *data,
 551                                               uint16_t datalen,
 552                                               loff_t object_size);
 553
 554extern void fscache_object_retrying_stale(struct fscache_object *object);
 555
 556enum fscache_why_object_killed {
 557        FSCACHE_OBJECT_IS_STALE,
 558        FSCACHE_OBJECT_NO_SPACE,
 559        FSCACHE_OBJECT_WAS_RETIRED,
 560        FSCACHE_OBJECT_WAS_CULLED,
 561};
 562extern void fscache_object_mark_killed(struct fscache_object *object,
 563                                       enum fscache_why_object_killed why);
 564
 565#endif /* _LINUX_FSCACHE_CACHE_H */
 566