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Linux/include/linux/fscache-cache.h

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  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 extern struct fscache_cookie fscache_fsdef_index;
312 
313 /*
314  * Event list for fscache_object::{event_mask,events}
315  */
316 enum {
317         FSCACHE_OBJECT_EV_NEW_CHILD,    /* T if object has a new child */
318         FSCACHE_OBJECT_EV_PARENT_READY, /* T if object's parent is ready */
319         FSCACHE_OBJECT_EV_UPDATE,       /* T if object should be updated */
320         FSCACHE_OBJECT_EV_INVALIDATE,   /* T if cache requested object invalidation */
321         FSCACHE_OBJECT_EV_CLEARED,      /* T if accessors all gone */
322         FSCACHE_OBJECT_EV_ERROR,        /* T if fatal error occurred during processing */
323         FSCACHE_OBJECT_EV_KILL,         /* T if netfs relinquished or cache withdrew object */
324         NR_FSCACHE_OBJECT_EVENTS
325 };
326 
327 #define FSCACHE_OBJECT_EVENTS_MASK ((1UL << NR_FSCACHE_OBJECT_EVENTS) - 1)
328 
329 /*
330  * States for object state machine.
331  */
332 struct fscache_transition {
333         unsigned long events;
334         const struct fscache_state *transit_to;
335 };
336 
337 struct fscache_state {
338         char name[24];
339         char short_name[8];
340         const struct fscache_state *(*work)(struct fscache_object *object,
341                                             int event);
342         const struct fscache_transition transitions[];
343 };
344 
345 /*
346  * on-disk cache file or index handle
347  */
348 struct fscache_object {
349         const struct fscache_state *state;      /* Object state machine state */
350         const struct fscache_transition *oob_table; /* OOB state transition table */
351         int                     debug_id;       /* debugging ID */
352         int                     n_children;     /* number of child objects */
353         int                     n_ops;          /* number of extant ops on object */
354         int                     n_obj_ops;      /* number of object ops outstanding on object */
355         int                     n_in_progress;  /* number of ops in progress */
356         int                     n_exclusive;    /* number of exclusive ops queued or in progress */
357         atomic_t                n_reads;        /* number of read ops in progress */
358         spinlock_t              lock;           /* state and operations lock */
359 
360         unsigned long           lookup_jif;     /* time at which lookup started */
361         unsigned long           oob_event_mask; /* OOB events this object is interested in */
362         unsigned long           event_mask;     /* events this object is interested in */
363         unsigned long           events;         /* events to be processed by this object
364                                                  * (order is important - using fls) */
365 
366         unsigned long           flags;
367 #define FSCACHE_OBJECT_LOCK             0       /* T if object is busy being processed */
368 #define FSCACHE_OBJECT_PENDING_WRITE    1       /* T if object has pending write */
369 #define FSCACHE_OBJECT_WAITING          2       /* T if object is waiting on its parent */
370 #define FSCACHE_OBJECT_IS_LIVE          3       /* T if object is not withdrawn or relinquished */
371 #define FSCACHE_OBJECT_IS_LOOKED_UP     4       /* T if object has been looked up */
372 #define FSCACHE_OBJECT_IS_AVAILABLE     5       /* T if object has become active */
373 #define FSCACHE_OBJECT_RETIRED          6       /* T if object was retired on relinquishment */
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 
391 extern void fscache_object_init(struct fscache_object *, struct fscache_cookie *,
392                                 struct fscache_cache *);
393 extern void fscache_object_destroy(struct fscache_object *);
394 
395 extern void fscache_object_lookup_negative(struct fscache_object *object);
396 extern void fscache_obtained_object(struct fscache_object *object);
397 
398 static inline bool fscache_object_is_live(struct fscache_object *object)
399 {
400         return test_bit(FSCACHE_OBJECT_IS_LIVE, &object->flags);
401 }
402 
403 static inline bool fscache_object_is_dying(struct fscache_object *object)
404 {
405         return !fscache_object_is_live(object);
406 }
407 
408 static inline bool fscache_object_is_available(struct fscache_object *object)
409 {
410         return test_bit(FSCACHE_OBJECT_IS_AVAILABLE, &object->flags);
411 }
412 
413 static inline bool fscache_object_is_active(struct fscache_object *object)
414 {
415         return fscache_object_is_available(object) &&
416                 fscache_object_is_live(object) &&
417                 !test_bit(FSCACHE_IOERROR, &object->cache->flags);
418 }
419 
420 static inline bool fscache_object_is_dead(struct fscache_object *object)
421 {
422         return fscache_object_is_dying(object) &&
423                 test_bit(FSCACHE_IOERROR, &object->cache->flags);
424 }
425 
426 /**
427  * fscache_object_destroyed - Note destruction of an object in a cache
428  * @cache: The cache from which the object came
429  *
430  * Note the destruction and deallocation of an object record in a cache.
431  */
432 static inline void fscache_object_destroyed(struct fscache_cache *cache)
433 {
434         if (atomic_dec_and_test(&cache->object_count))
435                 wake_up_all(&fscache_cache_cleared_wq);
436 }
437 
438 /**
439  * fscache_object_lookup_error - Note an object encountered an error
440  * @object: The object on which the error was encountered
441  *
442  * Note that an object encountered a fatal error (usually an I/O error) and
443  * that it should be withdrawn as soon as possible.
444  */
445 static inline void fscache_object_lookup_error(struct fscache_object *object)
446 {
447         set_bit(FSCACHE_OBJECT_EV_ERROR, &object->events);
448 }
449 
450 /**
451  * fscache_set_store_limit - Set the maximum size to be stored in an object
452  * @object: The object to set the maximum on
453  * @i_size: The limit to set in bytes
454  *
455  * Set the maximum size an object is permitted to reach, implying the highest
456  * byte that may be written.  Intended to be called by the attr_changed() op.
457  *
458  * See Documentation/filesystems/caching/backend-api.txt for a complete
459  * description.
460  */
461 static inline
462 void fscache_set_store_limit(struct fscache_object *object, loff_t i_size)
463 {
464         object->store_limit_l = i_size;
465         object->store_limit = i_size >> PAGE_SHIFT;
466         if (i_size & ~PAGE_MASK)
467                 object->store_limit++;
468 }
469 
470 /**
471  * fscache_end_io - End a retrieval operation on a page
472  * @op: The FS-Cache operation covering the retrieval
473  * @page: The page that was to be fetched
474  * @error: The error code (0 if successful)
475  *
476  * Note the end of an operation to retrieve a page, as covered by a particular
477  * operation record.
478  */
479 static inline void fscache_end_io(struct fscache_retrieval *op,
480                                   struct page *page, int error)
481 {
482         op->end_io_func(page, op->context, error);
483 }
484 
485 static inline void __fscache_use_cookie(struct fscache_cookie *cookie)
486 {
487         atomic_inc(&cookie->n_active);
488 }
489 
490 /**
491  * fscache_use_cookie - Request usage of cookie attached to an object
492  * @object: Object description
493  * 
494  * Request usage of the cookie attached to an object.  NULL is returned if the
495  * relinquishment had reduced the cookie usage count to 0.
496  */
497 static inline bool fscache_use_cookie(struct fscache_object *object)
498 {
499         struct fscache_cookie *cookie = object->cookie;
500         return atomic_inc_not_zero(&cookie->n_active) != 0;
501 }
502 
503 static inline bool __fscache_unuse_cookie(struct fscache_cookie *cookie)
504 {
505         return atomic_dec_and_test(&cookie->n_active);
506 }
507 
508 static inline void __fscache_wake_unused_cookie(struct fscache_cookie *cookie)
509 {
510         wake_up_atomic_t(&cookie->n_active);
511 }
512 
513 /**
514  * fscache_unuse_cookie - Cease usage of cookie attached to an object
515  * @object: Object description
516  * 
517  * Cease usage of the cookie attached to an object.  When the users count
518  * reaches zero then the cookie relinquishment will be permitted to proceed.
519  */
520 static inline void fscache_unuse_cookie(struct fscache_object *object)
521 {
522         struct fscache_cookie *cookie = object->cookie;
523         if (__fscache_unuse_cookie(cookie))
524                 __fscache_wake_unused_cookie(cookie);
525 }
526 
527 /*
528  * out-of-line cache backend functions
529  */
530 extern __printf(3, 4)
531 void fscache_init_cache(struct fscache_cache *cache,
532                         const struct fscache_cache_ops *ops,
533                         const char *idfmt, ...);
534 
535 extern int fscache_add_cache(struct fscache_cache *cache,
536                              struct fscache_object *fsdef,
537                              const char *tagname);
538 extern void fscache_withdraw_cache(struct fscache_cache *cache);
539 
540 extern void fscache_io_error(struct fscache_cache *cache);
541 
542 extern void fscache_mark_page_cached(struct fscache_retrieval *op,
543                                      struct page *page);
544 
545 extern void fscache_mark_pages_cached(struct fscache_retrieval *op,
546                                       struct pagevec *pagevec);
547 
548 extern bool fscache_object_sleep_till_congested(signed long *timeoutp);
549 
550 extern enum fscache_checkaux fscache_check_aux(struct fscache_object *object,
551                                                const void *data,
552                                                uint16_t datalen);
553 
554 #endif /* _LINUX_FSCACHE_CACHE_H */
555 

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