/* SPDX-License-Identifier: GPL-2.0-or-later */
/* General filesystem caching backing cache interface
 *
 * Copyright (C) 2004-2007 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 *
 * NOTE!!! See:
 *
 *      Documentation/filesystems/caching/backend-api.rst
 *
 * 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;

enum fscache_obj_ref_trace {
        fscache_obj_get_add_to_deps,
        fscache_obj_get_queue,
        fscache_obj_put_alloc_fail,
        fscache_obj_put_attach_fail,
        fscache_obj_put_drop_obj,
        fscache_obj_put_enq_dep,
        fscache_obj_put_queue,
        fscache_obj_put_work,
        fscache_obj_ref__nr_traces
};

/*
 * 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[]; /* 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);
typedef void (*fscache_operation_cancel_t)(struct fscache_operation *op);

enum fscache_operation_state {
        FSCACHE_OP_ST_BLANK,            /* Op is not yet submitted */
        FSCACHE_OP_ST_INITIALISED,      /* Op is initialised */
        FSCACHE_OP_ST_PENDING,          /* Op is blocked from running */
        FSCACHE_OP_ST_IN_PROGRESS,      /* Op is in progress */
        FSCACHE_OP_ST_COMPLETE,         /* Op is complete */
        FSCACHE_OP_ST_CANCELLED,        /* Op has been cancelled */
        FSCACHE_OP_ST_DEAD              /* Op is now dead */
};

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_DEC_READ_CNT 6       /* decrement object->n_reads on destruction */
#define FSCACHE_OP_UNUSE_COOKIE 7       /* call fscache_unuse_cookie() on completion */
#define FSCACHE_OP_KEEP_FLAGS   0x00f0  /* flags to keep when repurposing an op */

        enum fscache_operation_state state;
        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 cancellation cleanup (optional) */
        fscache_operation_cancel_t cancel;

        /* 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_op_complete(struct fscache_operation *, bool);
extern void fscache_put_operation(struct fscache_operation *);
extern void fscache_operation_init(struct fscache_cookie *,
                                   struct fscache_operation *,
                                   fscache_operation_processor_t,
                                   fscache_operation_cancel_t,
                                   fscache_operation_release_t);

/*
 * data read operation
 */
struct fscache_retrieval {
        struct fscache_operation op;
        struct fscache_cookie   *cookie;        /* The netfs cookie */
        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 */
        atomic_t                n_pages;        /* number of pages to be retrieved */
};

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);

/**
 * fscache_get_retrieval - Get an extra reference on a retrieval operation
 * @op: The retrieval operation to get a reference on
 *
 * Get an extra reference on a retrieval operation.
 */
static inline
struct fscache_retrieval *fscache_get_retrieval(struct fscache_retrieval *op)
{
        atomic_inc(&op->op.usage);
        return op;
}

/**
 * fscache_enqueue_retrieval - Enqueue a retrieval operation for processing
 * @op: The retrieval operation affected
 *
 * Enqueue a retrieval operation for processing by the FS-Cache thread pool.
 */
static inline void fscache_enqueue_retrieval(struct fscache_retrieval *op)
{
        fscache_enqueue_operation(&op->op);
}

/**
 * fscache_retrieval_complete - Record (partial) completion of a retrieval
 * @op: The retrieval operation affected
 * @n_pages: The number of pages to account for
 */
static inline void fscache_retrieval_complete(struct fscache_retrieval *op,
                                              int n_pages)
{
        if (atomic_sub_return_relaxed(n_pages, &op->n_pages) <= 0)
                fscache_op_complete(&op->op, false);
}

/**
 * fscache_put_retrieval - Drop a reference to a retrieval operation
 * @op: The retrieval operation affected
 *
 * Drop a reference to a retrieval operation.
 */
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,
                                              enum fscache_obj_ref_trace why);

        /* 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);

        /* check the consistency between the backing cache and the FS-Cache
         * cookie */
        int (*check_consistency)(struct fscache_operation *op);

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

        /* Invalidate an object */
        void (*invalidate_object)(struct fscache_operation *op);

        /* 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,
                           enum fscache_obj_ref_trace why);

        /* 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);

        /* Begin a read operation for the netfs lib */
        int (*begin_read_operation)(struct netfs_read_request *rreq,
                                    struct fscache_retrieval *op);
};

extern struct fscache_cookie fscache_fsdef_index;

/*
 * Event list for fscache_object::{event_mask,events}
 */
enum {
        FSCACHE_OBJECT_EV_NEW_CHILD,    /* T if object has a new child */
        FSCACHE_OBJECT_EV_PARENT_READY, /* T if object's parent is ready */
        FSCACHE_OBJECT_EV_UPDATE,       /* T if object should be updated */
        FSCACHE_OBJECT_EV_INVALIDATE,   /* T if cache requested object invalidation */
        FSCACHE_OBJECT_EV_CLEARED,      /* T if accessors all gone */
        FSCACHE_OBJECT_EV_ERROR,        /* T if fatal error occurred during processing */
        FSCACHE_OBJECT_EV_KILL,         /* T if netfs relinquished or cache withdrew object */
        NR_FSCACHE_OBJECT_EVENTS
};

#define FSCACHE_OBJECT_EVENTS_MASK ((1UL << NR_FSCACHE_OBJECT_EVENTS) - 1)

/*
 * States for object state machine.
 */
struct fscache_transition {
        unsigned long events;
        const struct fscache_state *transit_to;
};

struct fscache_state {
        char name[24];
        char short_name[8];
        const struct fscache_state *(*work)(struct fscache_object *object,
                                            int event);
        const struct fscache_transition transitions[];
};

/*
 * on-disk cache file or index handle
 */
struct fscache_object {
        const struct fscache_state *state;      /* Object state machine state */
        const struct fscache_transition *oob_table; /* OOB state transition table */
        int                     debug_id;       /* debugging ID */
        int                     n_children;     /* number of child objects */
        int                     n_ops;          /* number of extant ops 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 or in progress */
        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           oob_event_mask; /* OOB events this object is interested in */
        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) */

        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 */
#define FSCACHE_OBJECT_IS_LIVE          3       /* T if object is not withdrawn or relinquished */
#define FSCACHE_OBJECT_IS_LOOKED_UP     4       /* T if object has been looked up */
#define FSCACHE_OBJECT_IS_AVAILABLE     5       /* T if object has become active */
#define FSCACHE_OBJECT_RETIRED          6       /* T if object was retired on relinquishment */
#define FSCACHE_OBJECT_KILLED_BY_CACHE  7       /* T if object was killed by the cache */
#define FSCACHE_OBJECT_RUN_AFTER_DEAD   8       /* T if object has been dispatched after death */

        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 */
        pgoff_t                 store_limit;    /* current storage limit */
        loff_t                  store_limit_l;  /* current storage limit */
};

extern void fscache_object_init(struct fscache_object *, struct fscache_cookie *,
                                struct fscache_cache *);
extern void fscache_object_destroy(struct fscache_object *);

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

static inline bool fscache_object_is_live(struct fscache_object *object)
{
        return test_bit(FSCACHE_OBJECT_IS_LIVE, &object->flags);
}

static inline bool fscache_object_is_dying(struct fscache_object *object)
{
        return !fscache_object_is_live(object);
}

static inline bool fscache_object_is_available(struct fscache_object *object)
{
        return test_bit(FSCACHE_OBJECT_IS_AVAILABLE, &object->flags);
}

static inline bool fscache_cache_is_broken(struct fscache_object *object)
{
        return test_bit(FSCACHE_IOERROR, &object->cache->flags);
}

static inline bool fscache_object_is_active(struct fscache_object *object)
{
        return fscache_object_is_available(object) &&
                fscache_object_is_live(object) &&
                !fscache_cache_is_broken(object);
}

/**
 * fscache_object_destroyed - Note destruction of an object in a cache
 * @cache: The cache from which the object came
 *
 * Note the destruction and deallocation of an object record in a cache.
 */
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);
}

/**
 * fscache_object_lookup_error - Note an object encountered an error
 * @object: The object on which the error was encountered
 *
 * Note that an object encountered a fatal error (usually an I/O error) and
 * that it should be withdrawn as soon as possible.
 */
static inline void fscache_object_lookup_error(struct fscache_object *object)
{
        set_bit(FSCACHE_OBJECT_EV_ERROR, &object->events);
}

/**
 * fscache_set_store_limit - Set the maximum size to be stored in an object
 * @object: The object to set the maximum on
 * @i_size: The limit to set in bytes
 *
 * Set the maximum size an object is permitted to reach, implying the highest
 * byte that may be written.  Intended to be called by the attr_changed() op.
 *
 * See Documentation/filesystems/caching/backend-api.rst for a complete
 * description.
 */
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++;
}

/**
 * fscache_end_io - End a retrieval operation on a page
 * @op: The FS-Cache operation covering the retrieval
 * @page: The page that was to be fetched
 * @error: The error code (0 if successful)
 *
 * Note the end of an operation to retrieve a page, as covered by a particular
 * operation record.
 */
static inline void fscache_end_io(struct fscache_retrieval *op,
                                  struct page *page, int error)
{
        op->end_io_func(page, op->context, error);
}

static inline void __fscache_use_cookie(struct fscache_cookie *cookie)
{
        atomic_inc(&cookie->n_active);
}

/**
 * fscache_use_cookie - Request usage of cookie attached to an object
 * @object: Object description
 * 
 * Request usage of the cookie attached to an object.  NULL is returned if the
 * relinquishment had reduced the cookie usage count to 0.
 */
static inline bool fscache_use_cookie(struct fscache_object *object)
{
        struct fscache_cookie *cookie = object->cookie;
        return atomic_inc_not_zero(&cookie->n_active) != 0;
}

static inline bool __fscache_unuse_cookie(struct fscache_cookie *cookie)
{
        return atomic_dec_and_test(&cookie->n_active);
}

static inline void __fscache_wake_unused_cookie(struct fscache_cookie *cookie)
{
        wake_up_var(&cookie->n_active);
}

/**
 * fscache_unuse_cookie - Cease usage of cookie attached to an object
 * @object: Object description
 * 
 * Cease usage of the cookie attached to an object.  When the users count
 * reaches zero then the cookie relinquishment will be permitted to proceed.
 */
static inline void fscache_unuse_cookie(struct fscache_object *object)
{
        struct fscache_cookie *cookie = object->cookie;
        if (__fscache_unuse_cookie(cookie))
                __fscache_wake_unused_cookie(cookie);
}

/*
 * 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_page_cached(struct fscache_retrieval *op,
                                     struct page *page);

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,
                                               loff_t object_size);

extern void fscache_object_retrying_stale(struct fscache_object *object);

enum fscache_why_object_killed {
        FSCACHE_OBJECT_IS_STALE,
        FSCACHE_OBJECT_NO_SPACE,
        FSCACHE_OBJECT_WAS_RETIRED,
        FSCACHE_OBJECT_WAS_CULLED,
};
extern void fscache_object_mark_killed(struct fscache_object *object,
                                       enum fscache_why_object_killed why);

#endif /* _LINUX_FSCACHE_CACHE_H */