fscache-cache.h

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/* General filesystem caching backing cache interface
 *
 * Copyright (C) 2004-2007 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells ([email protected])
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version
 * 2 of the License, or (at your option) any later version.
 *
 * NOTE!!! See:
 *
 *  Documentation/filesystems/caching/backend-api.txt
 *
 * for a description of the cache backend interface declared here.
 */

#ifndef _LINUX_FSCACHE_CACHE_H
#define _LINUX_FSCACHE_CACHE_H

#include <linux/fscache.h>
#include <linux/sched.h>
#include <linux/workqueue.h>

#define NR_MAXCACHES BITS_PER_LONG

struct fscache_cache;
struct fscache_cache_ops;
struct fscache_object;
struct fscache_operation;

/*
 * cache tag definition
 */
struct fscache_cache_tag {
    struct list_head    link;
    struct fscache_cache    *cache;     /* cache referred to by this tag */
    unsigned long       flags;
#define FSCACHE_TAG_RESERVED    0       /* T if tag is reserved for a cache */
    atomic_t        usage;
    char            name[0];    /* tag name */
};

/*
 * cache definition
 */
struct fscache_cache {
    const struct fscache_cache_ops *ops;
    struct fscache_cache_tag *tag;      /* tag representing this cache */
    struct kobject      *kobj;      /* system representation of this cache */
    struct list_head    link;       /* link in list of caches */
    size_t          max_index_size; /* maximum size of index data */
    char            identifier[36]; /* cache label */

    /* node management */
    struct work_struct  op_gc;      /* operation garbage collector */
    struct list_head    object_list;    /* list of data/index objects */
    struct list_head    op_gc_list; /* list of ops to be deleted */
    spinlock_t      object_list_lock;
    spinlock_t      op_gc_list_lock;
    atomic_t        object_count;   /* no. of live objects in this cache */
    struct fscache_object   *fsdef;     /* object for the fsdef index */
    unsigned long       flags;
#define FSCACHE_IOERROR     0   /* cache stopped on I/O error */
#define FSCACHE_CACHE_WITHDRAWN 1   /* cache has been withdrawn */
};

extern wait_queue_head_t fscache_cache_cleared_wq;

/*
 * operation to be applied to a cache object
 * - retrieval initiation operations are done in the context of the process
 *   that issued them, and not in an async thread pool
 */
typedef void (*fscache_operation_release_t)(struct fscache_operation *op);
typedef void (*fscache_operation_processor_t)(struct fscache_operation *op);

struct fscache_operation {
    struct work_struct  work;       /* record for async ops */
    struct list_head    pend_link;  /* link in object->pending_ops */
    struct fscache_object   *object;    /* object to be operated upon */

    unsigned long       flags;
#define FSCACHE_OP_TYPE     0x000f  /* operation type */
#define FSCACHE_OP_ASYNC    0x0001  /* - async op, processor may sleep for disk */
#define FSCACHE_OP_MYTHREAD 0x0002  /* - processing is done be issuing thread, not pool */
#define FSCACHE_OP_WAITING  4   /* cleared when op is woken */
#define FSCACHE_OP_EXCLUSIVE    5   /* exclusive op, other ops must wait */
#define FSCACHE_OP_DEAD     6   /* op is now dead */
#define FSCACHE_OP_DEC_READ_CNT 7   /* decrement object->n_reads on destruction */
#define FSCACHE_OP_KEEP_FLAGS   0xc0    /* flags to keep when repurposing an op */

    atomic_t        usage;
    unsigned        debug_id;   /* debugging ID */

    /* operation processor callback
     * - can be NULL if FSCACHE_OP_WAITING is going to be used to perform
     *   the op in a non-pool thread */
    fscache_operation_processor_t processor;

    /* operation releaser */
    fscache_operation_release_t release;
};

extern atomic_t fscache_op_debug_id;
extern void fscache_op_work_func(struct work_struct *work);

extern void fscache_enqueue_operation(struct fscache_operation *);
extern void fscache_put_operation(struct fscache_operation *);

static inline void fscache_operation_init(struct fscache_operation *op,
                    fscache_operation_processor_t processor,
                    fscache_operation_release_t release)
{
    INIT_WORK(&op->work, fscache_op_work_func);
    atomic_set(&op->usage, 1);
    op->debug_id = atomic_inc_return(&fscache_op_debug_id);
    op->processor = processor;
    op->release = release;
    INIT_LIST_HEAD(&op->pend_link);
}

/*
 * data read operation
 */
struct fscache_retrieval {
    struct fscache_operation op;
    struct address_space    *mapping;   /* netfs pages */
    fscache_rw_complete_t   end_io_func;    /* function to call on I/O completion */
    void            *context;   /* netfs read context (pinned) */
    struct list_head    to_do;      /* list of things to be done by the backend */
    unsigned long       start_time; /* time at which retrieval started */
};

typedef int (*fscache_page_retrieval_func_t)(struct fscache_retrieval *op,
                         struct page *page,
                         gfp_t gfp);

typedef int (*fscache_pages_retrieval_func_t)(struct fscache_retrieval *op,
                          struct list_head *pages,
                          unsigned *nr_pages,
                          gfp_t gfp);

static inline
struct fscache_retrieval *fscache_get_retrieval(struct fscache_retrieval *op)
{
    atomic_inc(&op->op.usage);
    return op;
}

static inline void fscache_enqueue_retrieval(struct fscache_retrieval *op)
{
    fscache_enqueue_operation(&op->op);
}

static inline void fscache_put_retrieval(struct fscache_retrieval *op)
{
    fscache_put_operation(&op->op);
}

/*
 * cached page storage work item
 * - used to do three things:
 *   - batch writes to the cache
 *   - do cache writes asynchronously
 *   - defer writes until cache object lookup completion
 */
struct fscache_storage {
    struct fscache_operation op;
    pgoff_t         store_limit;    /* don't write more than this */
};

/*
 * cache operations
 */
struct fscache_cache_ops {
    /* name of cache provider */
    const char *name;

    /* allocate an object record for a cookie */
    struct fscache_object *(*alloc_object)(struct fscache_cache *cache,
                           struct fscache_cookie *cookie);

    /* look up the object for a cookie
     * - return -ETIMEDOUT to be requeued
     */
    int (*lookup_object)(struct fscache_object *object);

    /* finished looking up */
    void (*lookup_complete)(struct fscache_object *object);

    /* increment the usage count on this object (may fail if unmounting) */
    struct fscache_object *(*grab_object)(struct fscache_object *object);

    /* pin an object in the cache */
    int (*pin_object)(struct fscache_object *object);

    /* unpin an object in the cache */
    void (*unpin_object)(struct fscache_object *object);

    /* store the updated auxiliary data on an object */
    void (*update_object)(struct fscache_object *object);

    /* discard the resources pinned by an object and effect retirement if
     * necessary */
    void (*drop_object)(struct fscache_object *object);

    /* dispose of a reference to an object */
    void (*put_object)(struct fscache_object *object);

    /* sync a cache */
    void (*sync_cache)(struct fscache_cache *cache);

    /* notification that the attributes of a non-index object (such as
     * i_size) have changed */
    int (*attr_changed)(struct fscache_object *object);

    /* reserve space for an object's data and associated metadata */
    int (*reserve_space)(struct fscache_object *object, loff_t i_size);

    /* request a backing block for a page be read or allocated in the
     * cache */
    fscache_page_retrieval_func_t read_or_alloc_page;

    /* request backing blocks for a list of pages be read or allocated in
     * the cache */
    fscache_pages_retrieval_func_t read_or_alloc_pages;

    /* request a backing block for a page be allocated in the cache so that
     * it can be written directly */
    fscache_page_retrieval_func_t allocate_page;

    /* request backing blocks for pages be allocated in the cache so that
     * they can be written directly */
    fscache_pages_retrieval_func_t allocate_pages;

    /* write a page to its backing block in the cache */
    int (*write_page)(struct fscache_storage *op, struct page *page);

    /* detach backing block from a page (optional)
     * - must release the cookie lock before returning
     * - may sleep
     */
    void (*uncache_page)(struct fscache_object *object,
                 struct page *page);

    /* dissociate a cache from all the pages it was backing */
    void (*dissociate_pages)(struct fscache_cache *cache);
};

/*
 * data file or index object cookie
 * - a file will only appear in one cache
 * - a request to cache a file may or may not be honoured, subject to
 *   constraints such as disk space
 * - indices are created on disk just-in-time
 */
struct fscache_cookie {
    atomic_t            usage;      /* number of users of this cookie */
    atomic_t            n_children; /* number of children of this cookie */
    spinlock_t          lock;
    spinlock_t          stores_lock;    /* lock on page store tree */
    struct hlist_head       backing_objects; /* object(s) backing this file/index */
    const struct fscache_cookie_def *def;       /* definition */
    struct fscache_cookie       *parent;    /* parent of this entry */
    void                *netfs_data;    /* back pointer to netfs */
    struct radix_tree_root      stores;     /* pages to be stored on this cookie */
#define FSCACHE_COOKIE_PENDING_TAG  0       /* pages tag: pending write to cache */
#define FSCACHE_COOKIE_STORING_TAG  1       /* pages tag: writing to cache */

    unsigned long           flags;
#define FSCACHE_COOKIE_LOOKING_UP   0   /* T if non-index cookie being looked up still */
#define FSCACHE_COOKIE_CREATING     1   /* T if non-index object being created still */
#define FSCACHE_COOKIE_NO_DATA_YET  2   /* T if new object with no cached data yet */
#define FSCACHE_COOKIE_PENDING_FILL 3   /* T if pending initial fill on object */
#define FSCACHE_COOKIE_FILLING      4   /* T if filling object incrementally */
#define FSCACHE_COOKIE_UNAVAILABLE  5   /* T if cookie is unavailable (error, etc) */
};

extern struct fscache_cookie fscache_fsdef_index;

/*
 * on-disk cache file or index handle
 */
struct fscache_object {
    enum fscache_object_state {
        FSCACHE_OBJECT_INIT,        /* object in initial unbound state */
        FSCACHE_OBJECT_LOOKING_UP,  /* looking up object */
        FSCACHE_OBJECT_CREATING,    /* creating object */

        /* active states */
        FSCACHE_OBJECT_AVAILABLE,   /* cleaning up object after creation */
        FSCACHE_OBJECT_ACTIVE,      /* object is usable */
        FSCACHE_OBJECT_UPDATING,    /* object is updating */

        /* terminal states */
        FSCACHE_OBJECT_DYING,       /* object waiting for accessors to finish */
        FSCACHE_OBJECT_LC_DYING,    /* object cleaning up after lookup/create */
        FSCACHE_OBJECT_ABORT_INIT,  /* abort the init state */
        FSCACHE_OBJECT_RELEASING,   /* releasing object */
        FSCACHE_OBJECT_RECYCLING,   /* retiring object */
        FSCACHE_OBJECT_WITHDRAWING, /* withdrawing object */
        FSCACHE_OBJECT_DEAD,        /* object is now dead */
        FSCACHE_OBJECT__NSTATES
    } state;

    int         debug_id;   /* debugging ID */
    int         n_children; /* number of child objects */
    int         n_ops;      /* number of ops outstanding on object */
    int         n_obj_ops;  /* number of object ops outstanding on object */
    int         n_in_progress;  /* number of ops in progress */
    int         n_exclusive;    /* number of exclusive ops queued */
    atomic_t        n_reads;    /* number of read ops in progress */
    spinlock_t      lock;       /* state and operations lock */

    unsigned long       lookup_jif; /* time at which lookup started */
    unsigned long       event_mask; /* events this object is interested in */
    unsigned long       events;     /* events to be processed by this object
                         * (order is important - using fls) */
#define FSCACHE_OBJECT_EV_REQUEUE   0   /* T if object should be requeued */
#define FSCACHE_OBJECT_EV_UPDATE    1   /* T if object should be updated */
#define FSCACHE_OBJECT_EV_CLEARED   2   /* T if accessors all gone */
#define FSCACHE_OBJECT_EV_ERROR     3   /* T if fatal error occurred during processing */
#define FSCACHE_OBJECT_EV_RELEASE   4   /* T if netfs requested object release */
#define FSCACHE_OBJECT_EV_RETIRE    5   /* T if netfs requested object retirement */
#define FSCACHE_OBJECT_EV_WITHDRAW  6   /* T if cache requested object withdrawal */
#define FSCACHE_OBJECT_EVENTS_MASK  0x7f    /* mask of all events*/

    unsigned long       flags;
#define FSCACHE_OBJECT_LOCK     0   /* T if object is busy being processed */
#define FSCACHE_OBJECT_PENDING_WRITE    1   /* T if object has pending write */
#define FSCACHE_OBJECT_WAITING      2   /* T if object is waiting on its parent */

    struct list_head    cache_link; /* link in cache->object_list */
    struct hlist_node   cookie_link;    /* link in cookie->backing_objects */
    struct fscache_cache    *cache;     /* cache that supplied this object */
    struct fscache_cookie   *cookie;    /* netfs's file/index object */
    struct fscache_object   *parent;    /* parent object */
    struct work_struct  work;       /* attention scheduling record */
    struct list_head    dependents; /* FIFO of dependent objects */
    struct list_head    dep_link;   /* link in parent's dependents list */
    struct list_head    pending_ops;    /* unstarted operations on this object */
#ifdef CONFIG_FSCACHE_OBJECT_LIST
    struct rb_node      objlist_link;   /* link in global object list */
#endif
    pgoff_t         store_limit;    /* current storage limit */
    loff_t          store_limit_l;  /* current storage limit */
};

extern const char *fscache_object_states[];

#define fscache_object_is_active(obj)                 \
    (!test_bit(FSCACHE_IOERROR, &(obj)->cache->flags) &&  \
     (obj)->state >= FSCACHE_OBJECT_AVAILABLE &&          \
     (obj)->state < FSCACHE_OBJECT_DYING)

#define fscache_object_is_dead(obj)             \
    (test_bit(FSCACHE_IOERROR, &(obj)->cache->flags) && \
     (obj)->state >= FSCACHE_OBJECT_DYING)

extern void fscache_object_work_func(struct work_struct *work);

static inline
void fscache_object_init(struct fscache_object *object,
             struct fscache_cookie *cookie,
             struct fscache_cache *cache)
{
    atomic_inc(&cache->object_count);

    object->state = FSCACHE_OBJECT_INIT;
    spin_lock_init(&object->lock);
    INIT_LIST_HEAD(&object->cache_link);
    INIT_HLIST_NODE(&object->cookie_link);
    INIT_WORK(&object->work, fscache_object_work_func);
    INIT_LIST_HEAD(&object->dependents);
    INIT_LIST_HEAD(&object->dep_link);
    INIT_LIST_HEAD(&object->pending_ops);
    object->n_children = 0;
    object->n_ops = object->n_in_progress = object->n_exclusive = 0;
    object->events = object->event_mask = 0;
    object->flags = 0;
    object->store_limit = 0;
    object->store_limit_l = 0;
    object->cache = cache;
    object->cookie = cookie;
    object->parent = NULL;
}

extern void fscache_object_lookup_negative(struct fscache_object *object);
extern void fscache_obtained_object(struct fscache_object *object);

#ifdef CONFIG_FSCACHE_OBJECT_LIST
extern void fscache_object_destroy(struct fscache_object *object);
#else
#define fscache_object_destroy(object) do {} while(0)
#endif

static inline void fscache_object_destroyed(struct fscache_cache *cache)
{
    if (atomic_dec_and_test(&cache->object_count))
        wake_up_all(&fscache_cache_cleared_wq);
}

static inline void fscache_object_lookup_error(struct fscache_object *object)
{
    set_bit(FSCACHE_OBJECT_EV_ERROR, &object->events);
}

static inline
void fscache_set_store_limit(struct fscache_object *object, loff_t i_size)
{
    object->store_limit_l = i_size;
    object->store_limit = i_size >> PAGE_SHIFT;
    if (i_size & ~PAGE_MASK)
        object->store_limit++;
}

static inline void fscache_end_io(struct fscache_retrieval *op,
                  struct page *page, int error)
{
    op->end_io_func(page, op->context, error);
}

/*
 * out-of-line cache backend functions
 */
extern __printf(3, 4)
void fscache_init_cache(struct fscache_cache *cache,
            const struct fscache_cache_ops *ops,
            const char *idfmt, ...);

extern int fscache_add_cache(struct fscache_cache *cache,
                 struct fscache_object *fsdef,
                 const char *tagname);
extern void fscache_withdraw_cache(struct fscache_cache *cache);

extern void fscache_io_error(struct fscache_cache *cache);

extern void fscache_mark_pages_cached(struct fscache_retrieval *op,
                      struct pagevec *pagevec);

extern bool fscache_object_sleep_till_congested(signed long *timeoutp);

extern enum fscache_checkaux fscache_check_aux(struct fscache_object *object,
                           const void *data,
                           uint16_t datalen);

#endif /* _LINUX_FSCACHE_CACHE_H */