fscache.h

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/* General filesystem caching 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/netfs-api.txt
 *
 * for a description of the network filesystem interface declared here.
 */

#ifndef _LINUX_FSCACHE_H
#define _LINUX_FSCACHE_H

#include <linux/fs.h>
#include <linux/list.h>
#include <linux/pagemap.h>
#include <linux/pagevec.h>

#if defined(CONFIG_FSCACHE) || defined(CONFIG_FSCACHE_MODULE)
#define fscache_available() (1)
#define fscache_cookie_valid(cookie) (cookie)
#else
#define fscache_available() (0)
#define fscache_cookie_valid(cookie) (0)
#endif


/*
 * overload PG_private_2 to give us PG_fscache - this is used to indicate that
 * a page is currently backed by a local disk cache
 */
#define PageFsCache(page)       PagePrivate2((page))
#define SetPageFsCache(page)        SetPagePrivate2((page))
#define ClearPageFsCache(page)      ClearPagePrivate2((page))
#define TestSetPageFsCache(page)    TestSetPagePrivate2((page))
#define TestClearPageFsCache(page)  TestClearPagePrivate2((page))

/* pattern used to fill dead space in an index entry */
#define FSCACHE_INDEX_DEADFILL_PATTERN 0x79

struct pagevec;
struct fscache_cache_tag;
struct fscache_cookie;
struct fscache_netfs;

typedef void (*fscache_rw_complete_t)(struct page *page,
                      void *context,
                      int error);

/* result of index entry consultation */
enum fscache_checkaux {
    FSCACHE_CHECKAUX_OKAY,      /* entry okay as is */
    FSCACHE_CHECKAUX_NEEDS_UPDATE,  /* entry requires update */
    FSCACHE_CHECKAUX_OBSOLETE,  /* entry requires deletion */
};

/*
 * fscache cookie definition
 */
struct fscache_cookie_def {
    /* name of cookie type */
    char name[16];

    /* cookie type */
    uint8_t type;
#define FSCACHE_COOKIE_TYPE_INDEX   0
#define FSCACHE_COOKIE_TYPE_DATAFILE    1

    /* select the cache into which to insert an entry in this index
     * - optional
     * - should return a cache identifier or NULL to cause the cache to be
     *   inherited from the parent if possible or the first cache picked
     *   for a non-index file if not
     */
    struct fscache_cache_tag *(*select_cache)(
        const void *parent_netfs_data,
        const void *cookie_netfs_data);

    /* get an index key
     * - should store the key data in the buffer
     * - should return the amount of data stored
     * - not permitted to return an error
     * - the netfs data from the cookie being used as the source is
     *   presented
     */
    uint16_t (*get_key)(const void *cookie_netfs_data,
                void *buffer,
                uint16_t bufmax);

    /* get certain file attributes from the netfs data
     * - this function can be absent for an index
     * - not permitted to return an error
     * - the netfs data from the cookie being used as the source is
     *   presented
     */
    void (*get_attr)(const void *cookie_netfs_data, uint64_t *size);

    /* get the auxiliary data from netfs data
     * - this function can be absent if the index carries no state data
     * - should store the auxiliary data in the buffer
     * - should return the amount of amount stored
     * - not permitted to return an error
     * - the netfs data from the cookie being used as the source is
     *   presented
     */
    uint16_t (*get_aux)(const void *cookie_netfs_data,
                void *buffer,
                uint16_t bufmax);

    /* consult the netfs about the state of an object
     * - this function can be absent if the index carries no state data
     * - the netfs data from the cookie being used as the target is
     *   presented, as is the auxiliary data
     */
    enum fscache_checkaux (*check_aux)(void *cookie_netfs_data,
                       const void *data,
                       uint16_t datalen);

    /* get an extra reference on a read context
     * - this function can be absent if the completion function doesn't
     *   require a context
     */
    void (*get_context)(void *cookie_netfs_data, void *context);

    /* release an extra reference on a read context
     * - this function can be absent if the completion function doesn't
     *   require a context
     */
    void (*put_context)(void *cookie_netfs_data, void *context);

    /* indicate pages that now have cache metadata retained
     * - this function should mark the specified pages as now being cached
     * - the pages will have been marked with PG_fscache before this is
     *   called, so this is optional
     */
    void (*mark_pages_cached)(void *cookie_netfs_data,
                  struct address_space *mapping,
                  struct pagevec *cached_pvec);

    /* indicate the cookie is no longer cached
     * - this function is called when the backing store currently caching
     *   a cookie is removed
     * - the netfs should use this to clean up any markers indicating
     *   cached pages
     * - this is mandatory for any object that may have data
     */
    void (*now_uncached)(void *cookie_netfs_data);
};

/*
 * fscache cached network filesystem type
 * - name, version and ops must be filled in before registration
 * - all other fields will be set during registration
 */
struct fscache_netfs {
    uint32_t            version;    /* indexing version */
    const char          *name;      /* filesystem name */
    struct fscache_cookie       *primary_index;
    struct list_head        link;       /* internal link */
};

/*
 * slow-path functions for when there is actually caching available, and the
 * netfs does actually have a valid token
 * - these are not to be called directly
 * - these are undefined symbols when FS-Cache is not configured and the
 *   optimiser takes care of not using them
 */
extern int __fscache_register_netfs(struct fscache_netfs *);
extern void __fscache_unregister_netfs(struct fscache_netfs *);
extern struct fscache_cache_tag *__fscache_lookup_cache_tag(const char *);
extern void __fscache_release_cache_tag(struct fscache_cache_tag *);

extern struct fscache_cookie *__fscache_acquire_cookie(
    struct fscache_cookie *,
    const struct fscache_cookie_def *,
    void *);
extern void __fscache_relinquish_cookie(struct fscache_cookie *, int);
extern void __fscache_update_cookie(struct fscache_cookie *);
extern int __fscache_attr_changed(struct fscache_cookie *);
extern int __fscache_read_or_alloc_page(struct fscache_cookie *,
                    struct page *,
                    fscache_rw_complete_t,
                    void *,
                    gfp_t);
extern int __fscache_read_or_alloc_pages(struct fscache_cookie *,
                     struct address_space *,
                     struct list_head *,
                     unsigned *,
                     fscache_rw_complete_t,
                     void *,
                     gfp_t);
extern int __fscache_alloc_page(struct fscache_cookie *, struct page *, gfp_t);
extern int __fscache_write_page(struct fscache_cookie *, struct page *, gfp_t);
extern void __fscache_uncache_page(struct fscache_cookie *, struct page *);
extern bool __fscache_check_page_write(struct fscache_cookie *, struct page *);
extern void __fscache_wait_on_page_write(struct fscache_cookie *, struct page *);
extern bool __fscache_maybe_release_page(struct fscache_cookie *, struct page *,
                     gfp_t);
extern void __fscache_uncache_all_inode_pages(struct fscache_cookie *,
                          struct inode *);

static inline
int fscache_register_netfs(struct fscache_netfs *netfs)
{
    if (fscache_available())
        return __fscache_register_netfs(netfs);
    else
        return 0;
}

static inline
void fscache_unregister_netfs(struct fscache_netfs *netfs)
{
    if (fscache_available())
        __fscache_unregister_netfs(netfs);
}

static inline
struct fscache_cache_tag *fscache_lookup_cache_tag(const char *name)
{
    if (fscache_available())
        return __fscache_lookup_cache_tag(name);
    else
        return NULL;
}

static inline
void fscache_release_cache_tag(struct fscache_cache_tag *tag)
{
    if (fscache_available())
        __fscache_release_cache_tag(tag);
}

static inline
struct fscache_cookie *fscache_acquire_cookie(
    struct fscache_cookie *parent,
    const struct fscache_cookie_def *def,
    void *netfs_data)
{
    if (fscache_cookie_valid(parent))
        return __fscache_acquire_cookie(parent, def, netfs_data);
    else
        return NULL;
}

static inline
void fscache_relinquish_cookie(struct fscache_cookie *cookie, int retire)
{
    if (fscache_cookie_valid(cookie))
        __fscache_relinquish_cookie(cookie, retire);
}

static inline
void fscache_update_cookie(struct fscache_cookie *cookie)
{
    if (fscache_cookie_valid(cookie))
        __fscache_update_cookie(cookie);
}

static inline
int fscache_pin_cookie(struct fscache_cookie *cookie)
{
    return -ENOBUFS;
}

static inline
void fscache_unpin_cookie(struct fscache_cookie *cookie)
{
}

static inline
int fscache_attr_changed(struct fscache_cookie *cookie)
{
    if (fscache_cookie_valid(cookie))
        return __fscache_attr_changed(cookie);
    else
        return -ENOBUFS;
}

static inline
int fscache_reserve_space(struct fscache_cookie *cookie, loff_t size)
{
    return -ENOBUFS;
}

static inline
int fscache_read_or_alloc_page(struct fscache_cookie *cookie,
                   struct page *page,
                   fscache_rw_complete_t end_io_func,
                   void *context,
                   gfp_t gfp)
{
    if (fscache_cookie_valid(cookie))
        return __fscache_read_or_alloc_page(cookie, page, end_io_func,
                            context, gfp);
    else
        return -ENOBUFS;
}

static inline
int fscache_read_or_alloc_pages(struct fscache_cookie *cookie,
                struct address_space *mapping,
                struct list_head *pages,
                unsigned *nr_pages,
                fscache_rw_complete_t end_io_func,
                void *context,
                gfp_t gfp)
{
    if (fscache_cookie_valid(cookie))
        return __fscache_read_or_alloc_pages(cookie, mapping, pages,
                             nr_pages, end_io_func,
                             context, gfp);
    else
        return -ENOBUFS;
}

static inline
int fscache_alloc_page(struct fscache_cookie *cookie,
               struct page *page,
               gfp_t gfp)
{
    if (fscache_cookie_valid(cookie))
        return __fscache_alloc_page(cookie, page, gfp);
    else
        return -ENOBUFS;
}

static inline
int fscache_write_page(struct fscache_cookie *cookie,
               struct page *page,
               gfp_t gfp)
{
    if (fscache_cookie_valid(cookie))
        return __fscache_write_page(cookie, page, gfp);
    else
        return -ENOBUFS;
}

static inline
void fscache_uncache_page(struct fscache_cookie *cookie,
              struct page *page)
{
    if (fscache_cookie_valid(cookie))
        __fscache_uncache_page(cookie, page);
}

static inline
bool fscache_check_page_write(struct fscache_cookie *cookie,
                  struct page *page)
{
    if (fscache_cookie_valid(cookie))
        return __fscache_check_page_write(cookie, page);
    return false;
}

static inline
void fscache_wait_on_page_write(struct fscache_cookie *cookie,
                struct page *page)
{
    if (fscache_cookie_valid(cookie))
        __fscache_wait_on_page_write(cookie, page);
}

static inline
bool fscache_maybe_release_page(struct fscache_cookie *cookie,
                struct page *page,
                gfp_t gfp)
{
    if (fscache_cookie_valid(cookie) && PageFsCache(page))
        return __fscache_maybe_release_page(cookie, page, gfp);
    return false;
}

static inline
void fscache_uncache_all_inode_pages(struct fscache_cookie *cookie,
                     struct inode *inode)
{
    if (fscache_cookie_valid(cookie))
        __fscache_uncache_all_inode_pages(cookie, inode);
}

#endif /* _LINUX_FSCACHE_H */