/* SPDX-License-Identifier: GPL-2.0-or-later */
/* General filesystem caching backing cache interface
 *
 * Copyright (C) 2021 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>

enum fscache_cache_trace;
enum fscache_cookie_trace;
enum fscache_access_trace;
enum fscache_volume_trace;

enum fscache_cache_state {
        FSCACHE_CACHE_IS_NOT_PRESENT,   /* No cache is present for this name */
        FSCACHE_CACHE_IS_PREPARING,     /* A cache is preparing to come live */
        FSCACHE_CACHE_IS_ACTIVE,        /* Attached cache is active and can be used */
        FSCACHE_CACHE_GOT_IOERROR,      /* Attached cache stopped on I/O error */
        FSCACHE_CACHE_IS_WITHDRAWN,     /* Attached cache is being withdrawn */
#define NR__FSCACHE_CACHE_STATE (FSCACHE_CACHE_IS_WITHDRAWN + 1)
};

/*
 * Cache cookie.
 */
struct fscache_cache {
        const struct fscache_cache_ops *ops;
        struct list_head        cache_link;     /* Link in cache list */
        void                    *cache_priv;    /* Private cache data (or NULL) */
        refcount_t              ref;
        atomic_t                n_volumes;      /* Number of active volumes; */
        atomic_t                n_accesses;     /* Number of in-progress accesses on the cache */
        atomic_t                object_count;   /* no. of live objects in this cache */
        unsigned int            debug_id;
        enum fscache_cache_state state;
        char                    *name;
};

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

        /* Acquire a volume */
        void (*acquire_volume)(struct fscache_volume *volume);

        /* Free the cache's data attached to a volume */
        void (*free_volume)(struct fscache_volume *volume);

        /* Look up a cookie in the cache */
        bool (*lookup_cookie)(struct fscache_cookie *cookie);

        /* Withdraw an object without any cookie access counts held */
        void (*withdraw_cookie)(struct fscache_cookie *cookie);

        /* Change the size of a data object */
        void (*resize_cookie)(struct netfs_cache_resources *cres,
                              loff_t new_size);

        /* Invalidate an object */
        bool (*invalidate_cookie)(struct fscache_cookie *cookie);

        /* Begin an operation for the netfs lib */
        bool (*begin_operation)(struct netfs_cache_resources *cres,
                                enum fscache_want_state want_state);

        /* Prepare to write to a live cache object */
        void (*prepare_to_write)(struct fscache_cookie *cookie);
};

extern struct workqueue_struct *fscache_wq;
extern wait_queue_head_t fscache_clearance_waiters;

/*
 * out-of-line cache backend functions
 */
extern struct rw_semaphore fscache_addremove_sem;
extern struct fscache_cache *fscache_acquire_cache(const char *name);
extern void fscache_relinquish_cache(struct fscache_cache *cache);
extern int fscache_add_cache(struct fscache_cache *cache,
                             const struct fscache_cache_ops *ops,
                             void *cache_priv);
extern void fscache_withdraw_cache(struct fscache_cache *cache);
extern void fscache_withdraw_volume(struct fscache_volume *volume);
extern void fscache_withdraw_cookie(struct fscache_cookie *cookie);

extern void fscache_io_error(struct fscache_cache *cache);

extern struct fscache_volume *
fscache_try_get_volume(struct fscache_volume *volume,
                       enum fscache_volume_trace where);
extern void fscache_put_volume(struct fscache_volume *volume,
                               enum fscache_volume_trace where);
extern void fscache_end_volume_access(struct fscache_volume *volume,
                                      struct fscache_cookie *cookie,
                                      enum fscache_access_trace why);

extern struct fscache_cookie *fscache_get_cookie(struct fscache_cookie *cookie,
                                                 enum fscache_cookie_trace where);
extern void fscache_put_cookie(struct fscache_cookie *cookie,
                               enum fscache_cookie_trace where);
extern void fscache_end_cookie_access(struct fscache_cookie *cookie,
                                      enum fscache_access_trace why);
extern void fscache_cookie_lookup_negative(struct fscache_cookie *cookie);
extern void fscache_resume_after_invalidation(struct fscache_cookie *cookie);
extern void fscache_caching_failed(struct fscache_cookie *cookie);
extern bool fscache_wait_for_operation(struct netfs_cache_resources *cred,
                                       enum fscache_want_state state);

/**
 * fscache_cookie_state - Read the state of a cookie
 * @cookie: The cookie to query
 *
 * Get the state of a cookie, imposing an ordering between the cookie contents
 * and the state value.  Paired with fscache_set_cookie_state().
 */
static inline
enum fscache_cookie_state fscache_cookie_state(struct fscache_cookie *cookie)
{
        return smp_load_acquire(&cookie->state);
}

/**
 * fscache_get_key - Get a pointer to the cookie key
 * @cookie: The cookie to query
 *
 * Return a pointer to the where a cookie's key is stored.
 */
static inline void *fscache_get_key(struct fscache_cookie *cookie)
{
        if (cookie->key_len <= sizeof(cookie->inline_key))
                return cookie->inline_key;
        else
                return cookie->key;
}

static inline struct fscache_cookie *fscache_cres_cookie(struct netfs_cache_resources *cres)
{
        return cres->cache_priv;
}

/**
 * fscache_count_object - Tell fscache that an object has been added
 * @cache: The cache to account to
 *
 * Tell fscache that an object has been added to the cache.  This prevents the
 * cache from tearing down the cache structure until the object is uncounted.
 */
static inline void fscache_count_object(struct fscache_cache *cache)
{
        atomic_inc(&cache->object_count);
}

/**
 * fscache_uncount_object - Tell fscache that an object has been removed
 * @cache: The cache to account to
 *
 * Tell fscache that an object has been removed from the cache and will no
 * longer be accessed.  After this point, the cache cookie may be destroyed.
 */
static inline void fscache_uncount_object(struct fscache_cache *cache)
{
        if (atomic_dec_and_test(&cache->object_count))
                wake_up_all(&fscache_clearance_waiters);
}

/**
 * fscache_wait_for_objects - Wait for all objects to be withdrawn
 * @cache: The cache to query
 *
 * Wait for all extant objects in a cache to finish being withdrawn
 * and go away.
 */
static inline void fscache_wait_for_objects(struct fscache_cache *cache)
{
        wait_event(fscache_clearance_waiters,
                   atomic_read(&cache->object_count) == 0);
}

#ifdef CONFIG_FSCACHE_STATS
extern atomic_t fscache_n_read;
extern atomic_t fscache_n_write;
extern atomic_t fscache_n_no_write_space;
extern atomic_t fscache_n_no_create_space;
extern atomic_t fscache_n_culled;
extern atomic_t fscache_n_dio_misfit;
#define fscache_count_read() atomic_inc(&fscache_n_read)
#define fscache_count_write() atomic_inc(&fscache_n_write)
#define fscache_count_no_write_space() atomic_inc(&fscache_n_no_write_space)
#define fscache_count_no_create_space() atomic_inc(&fscache_n_no_create_space)
#define fscache_count_culled() atomic_inc(&fscache_n_culled)
#define fscache_count_dio_misfit() atomic_inc(&fscache_n_dio_misfit)
#else
#define fscache_count_read() do {} while(0)
#define fscache_count_write() do {} while(0)
#define fscache_count_no_write_space() do {} while(0)
#define fscache_count_no_create_space() do {} while(0)
#define fscache_count_culled() do {} while(0)
#define fscache_count_dio_misfit() do {} while(0)
#endif

#endif /* _LINUX_FSCACHE_CACHE_H */