/*
 * GPL HEADER START
 *
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 only,
 * as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License version 2 for more details (a copy is included
 * in the LICENSE file that accompanied this code).
 *
 * You should have received a copy of the GNU General Public License
 * version 2 along with this program; If not, see
 * http://www.sun.com/software/products/lustre/docs/GPLv2.pdf
 *
 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
 * CA 95054 USA or visit www.sun.com if you need additional information or
 * have any questions.
 *
 * GPL HEADER END
 */
/*
 * Copyright (c) 2008, 2010, Oracle and/or its affiliates. All rights reserved.
 * Use is subject to license terms.
 *
 * Copyright (c) 2011, 2012, Intel Corporation.
 */
/*
 * This file is part of Lustre, http://www.lustre.org/
 * Lustre is a trademark of Sun Microsystems, Inc.
 *
 * Client Lustre Page.
 *
 *   Author: Nikita Danilov <nikita.danilov@sun.com>
 */

#define DEBUG_SUBSYSTEM S_CLASS

#include "../../include/linux/libcfs/libcfs.h"
#include "../include/obd_class.h"
#include "../include/obd_support.h"
#include <linux/list.h>

#include "../include/cl_object.h"
#include "cl_internal.h"

static void cl_page_delete0(const struct lu_env *env, struct cl_page *pg,
                            int radix);

# define PASSERT(env, page, expr)                                          \
        do {                                                               \
                if (unlikely(!(expr))) {                                   \
                        CL_PAGE_DEBUG(D_ERROR, (env), (page), #expr "\n"); \
                        LASSERT(0);                                        \
                }                                                          \
        } while (0)

# define PINVRNT(env, page, exp) \
        ((void)sizeof(env), (void)sizeof(page), (void)sizeof !!(exp))

/**
 * Internal version of cl_page_top, it should be called if the page is
 * known to be not freed, says with page referenced, or radix tree lock held,
 * or page owned.
 */
static struct cl_page *cl_page_top_trusted(struct cl_page *page)
{
        while (page->cp_parent != NULL)
                page = page->cp_parent;
        return page;
}

/**
 * Internal version of cl_page_get().
 *
 * This function can be used to obtain initial reference to previously
 * unreferenced cached object. It can be called only if concurrent page
 * reclamation is somehow prevented, e.g., by locking page radix-tree
 * (cl_object_header::hdr->coh_page_guard), or by keeping a lock on a VM page,
 * associated with \a page.
 *
 * Use with care! Not exported.
 */
static void cl_page_get_trust(struct cl_page *page)
{
        LASSERT(atomic_read(&page->cp_ref) > 0);
        atomic_inc(&page->cp_ref);
}

/**
 * Returns a slice within a page, corresponding to the given layer in the
 * device stack.
 *
 * \see cl_lock_at()
 */
static const struct cl_page_slice *
cl_page_at_trusted(const struct cl_page *page,
                   const struct lu_device_type *dtype)
{
        const struct cl_page_slice *slice;

        page = cl_page_top_trusted((struct cl_page *)page);
        do {
                list_for_each_entry(slice, &page->cp_layers, cpl_linkage) {
                        if (slice->cpl_obj->co_lu.lo_dev->ld_type == dtype)
                                return slice;
                }
                page = page->cp_child;
        } while (page != NULL);
        return NULL;
}

/**
 * Returns a page with given index in the given object, or NULL if no page is
 * found. Acquires a reference on \a page.
 *
 * Locking: called under cl_object_header::coh_page_guard spin-lock.
 */
struct cl_page *cl_page_lookup(struct cl_object_header *hdr, pgoff_t index)
{
        struct cl_page *page;

        assert_spin_locked(&hdr->coh_page_guard);

        page = radix_tree_lookup(&hdr->coh_tree, index);
        if (page != NULL)
                cl_page_get_trust(page);
        return page;
}
EXPORT_SYMBOL(cl_page_lookup);

/**
 * Returns a list of pages by a given [start, end] of \a obj.
 *
 * \param resched If not NULL, then we give up before hogging CPU for too
 * long and set *resched = 1, in that case caller should implement a retry
 * logic.
 *
 * Gang tree lookup (radix_tree_gang_lookup()) optimization is absolutely
 * crucial in the face of [offset, EOF] locks.
 *
 * Return at least one page in @queue unless there is no covered page.
 */
int cl_page_gang_lookup(const struct lu_env *env, struct cl_object *obj,
                        struct cl_io *io, pgoff_t start, pgoff_t end,
                        cl_page_gang_cb_t cb, void *cbdata)
{
        struct cl_object_header *hdr;
        struct cl_page    *page;
        struct cl_page   **pvec;
        const struct cl_page_slice  *slice;
        const struct lu_device_type *dtype;
        pgoff_t           idx;
        unsigned int         nr;
        unsigned int         i;
        unsigned int         j;
        int                   res = CLP_GANG_OKAY;
        int                   tree_lock = 1;

        idx = start;
        hdr = cl_object_header(obj);
        pvec = cl_env_info(env)->clt_pvec;
        dtype = cl_object_top(obj)->co_lu.lo_dev->ld_type;
        spin_lock(&hdr->coh_page_guard);
        while ((nr = radix_tree_gang_lookup(&hdr->coh_tree, (void **)pvec,
                                            idx, CLT_PVEC_SIZE)) > 0) {
                int end_of_region = 0;

                idx = pvec[nr - 1]->cp_index + 1;
                for (i = 0, j = 0; i < nr; ++i) {
                        page = pvec[i];
                        pvec[i] = NULL;

                        LASSERT(page->cp_type == CPT_CACHEABLE);
                        if (page->cp_index > end) {
                                end_of_region = 1;
                                break;
                        }
                        if (page->cp_state == CPS_FREEING)
                                continue;

                        slice = cl_page_at_trusted(page, dtype);
                        /*
                         * Pages for lsm-less file has no underneath sub-page
                         * for osc, in case of ...
                         */
                        PASSERT(env, page, slice != NULL);

                        page = slice->cpl_page;
                        /*
                         * Can safely call cl_page_get_trust() under
                         * radix-tree spin-lock.
                         *
                         * XXX not true, because @page is from object another
                         * than @hdr and protected by different tree lock.
                         */
                        cl_page_get_trust(page);
                        lu_ref_add_atomic(&page->cp_reference,
                                          "gang_lookup", current);
                        pvec[j++] = page;
                }

                /*
                 * Here a delicate locking dance is performed. Current thread
                 * holds a reference to a page, but has to own it before it
                 * can be placed into queue. Owning implies waiting, so
                 * radix-tree lock is to be released. After a wait one has to
                 * check that pages weren't truncated (cl_page_own() returns
                 * error in the latter case).
                 */
                spin_unlock(&hdr->coh_page_guard);
                tree_lock = 0;

                for (i = 0; i < j; ++i) {
                        page = pvec[i];
                        if (res == CLP_GANG_OKAY)
                                res = (*cb)(env, io, page, cbdata);
                        lu_ref_del(&page->cp_reference,
                                   "gang_lookup", current);
                        cl_page_put(env, page);
                }
                if (nr < CLT_PVEC_SIZE || end_of_region)
                        break;

                if (res == CLP_GANG_OKAY && need_resched())
                        res = CLP_GANG_RESCHED;
                if (res != CLP_GANG_OKAY)
                        break;

                spin_lock(&hdr->coh_page_guard);
                tree_lock = 1;
        }
        if (tree_lock)
                spin_unlock(&hdr->coh_page_guard);
        return res;
}
EXPORT_SYMBOL(cl_page_gang_lookup);

static void cl_page_free(const struct lu_env *env, struct cl_page *page)
{
        struct cl_object *obj  = page->cp_obj;

        PASSERT(env, page, list_empty(&page->cp_batch));
        PASSERT(env, page, page->cp_owner == NULL);
        PASSERT(env, page, page->cp_req == NULL);
        PASSERT(env, page, page->cp_parent == NULL);
        PASSERT(env, page, page->cp_state == CPS_FREEING);

        might_sleep();
        while (!list_empty(&page->cp_layers)) {
                struct cl_page_slice *slice;

                slice = list_entry(page->cp_layers.next,
                                       struct cl_page_slice, cpl_linkage);
                list_del_init(page->cp_layers.next);
                slice->cpl_ops->cpo_fini(env, slice);
        }
        lu_object_ref_del_at(&obj->co_lu, &page->cp_obj_ref, "cl_page", page);
        cl_object_put(env, obj);
        lu_ref_fini(&page->cp_reference);
        kfree(page);
}

/**
 * Helper function updating page state. This is the only place in the code
 * where cl_page::cp_state field is mutated.
 */
static inline void cl_page_state_set_trust(struct cl_page *page,
                                           enum cl_page_state state)
{
        /* bypass const. */
        *(enum cl_page_state *)&page->cp_state = state;
}

static struct cl_page *cl_page_alloc(const struct lu_env *env,
                struct cl_object *o, pgoff_t ind, struct page *vmpage,
                enum cl_page_type type)
{
        struct cl_page    *page;
        struct lu_object_header *head;

        OBD_ALLOC_GFP(page, cl_object_header(o)->coh_page_bufsize,
                        GFP_NOFS);
        if (page != NULL) {
                int result = 0;

                atomic_set(&page->cp_ref, 1);
                if (type == CPT_CACHEABLE) /* for radix tree */
                        atomic_inc(&page->cp_ref);
                page->cp_obj = o;
                cl_object_get(o);
                lu_object_ref_add_at(&o->co_lu, &page->cp_obj_ref, "cl_page",
                                     page);
                page->cp_index = ind;
                cl_page_state_set_trust(page, CPS_CACHED);
                page->cp_type = type;
                INIT_LIST_HEAD(&page->cp_layers);
                INIT_LIST_HEAD(&page->cp_batch);
                INIT_LIST_HEAD(&page->cp_flight);
                mutex_init(&page->cp_mutex);
                lu_ref_init(&page->cp_reference);
                head = o->co_lu.lo_header;
                list_for_each_entry(o, &head->loh_layers,
                                        co_lu.lo_linkage) {
                        if (o->co_ops->coo_page_init != NULL) {
                                result = o->co_ops->coo_page_init(env, o,
                                                                  page, vmpage);
                                if (result != 0) {
                                        cl_page_delete0(env, page, 0);
                                        cl_page_free(env, page);
                                        page = ERR_PTR(result);
                                        break;
                                }
                        }
                }
        } else {
                page = ERR_PTR(-ENOMEM);
        }
        return page;
}

/**
 * Returns a cl_page with index \a idx at the object \a o, and associated with
 * the VM page \a vmpage.
 *
 * This is the main entry point into the cl_page caching interface. First, a
 * cache (implemented as a per-object radix tree) is consulted. If page is
 * found there, it is returned immediately. Otherwise new page is allocated
 * and returned. In any case, additional reference to page is acquired.
 *
 * \see cl_object_find(), cl_lock_find()
 */
static struct cl_page *cl_page_find0(const struct lu_env *env,
                                     struct cl_object *o,
                                     pgoff_t idx, struct page *vmpage,
                                     enum cl_page_type type,
                                     struct cl_page *parent)
{
        struct cl_page    *page = NULL;
        struct cl_page    *ghost = NULL;
        struct cl_object_header *hdr;
        int err;

        LASSERT(type == CPT_CACHEABLE || type == CPT_TRANSIENT);
        might_sleep();

        hdr = cl_object_header(o);

        CDEBUG(D_PAGE, "%lu@"DFID" %p %lx %d\n",
               idx, PFID(&hdr->coh_lu.loh_fid), vmpage, vmpage->private, type);
        /* fast path. */
        if (type == CPT_CACHEABLE) {
                /*
                 * vmpage lock is used to protect the child/parent
                 * relationship
                 */
                KLASSERT(PageLocked(vmpage));
                /*
                 * cl_vmpage_page() can be called here without any locks as
                 *
                 *     - "vmpage" is locked (which prevents ->private from
                 *       concurrent updates), and
                 *
                 *     - "o" cannot be destroyed while current thread holds a
                 *       reference on it.
                 */
                page = cl_vmpage_page(vmpage, o);
                PINVRNT(env, page,
                        ergo(page != NULL,
                             cl_page_vmpage(env, page) == vmpage &&
                             (void *)radix_tree_lookup(&hdr->coh_tree,
                                                       idx) == page));
        }

        if (page != NULL)
                return page;

        /* allocate and initialize cl_page */
        page = cl_page_alloc(env, o, idx, vmpage, type);
        if (IS_ERR(page))
                return page;

        if (type == CPT_TRANSIENT) {
                if (parent) {
                        LASSERT(page->cp_parent == NULL);
                        page->cp_parent = parent;
                        parent->cp_child = page;
                }
                return page;
        }

        /*
         * XXX optimization: use radix_tree_preload() here, and change tree
         * gfp mask to GFP_KERNEL in cl_object_header_init().
         */
        spin_lock(&hdr->coh_page_guard);
        err = radix_tree_insert(&hdr->coh_tree, idx, page);
        if (err != 0) {
                ghost = page;
                /*
                 * Noted by Jay: a lock on \a vmpage protects cl_page_find()
                 * from this race, but
                 *
                 *     0. it's better to have cl_page interface "locally
                 *     consistent" so that its correctness can be reasoned
                 *     about without appealing to the (obscure world of) VM
                 *     locking.
                 *
                 *     1. handling this race allows ->coh_tree to remain
                 *     consistent even when VM locking is somehow busted,
                 *     which is very useful during diagnosing and debugging.
                 */
                page = ERR_PTR(err);
                CL_PAGE_DEBUG(D_ERROR, env, ghost,
                              "fail to insert into radix tree: %d\n", err);
        } else {
                if (parent) {
                        LASSERT(page->cp_parent == NULL);
                        page->cp_parent = parent;
                        parent->cp_child = page;
                }
                hdr->coh_pages++;
        }
        spin_unlock(&hdr->coh_page_guard);

        if (unlikely(ghost != NULL)) {
                cl_page_delete0(env, ghost, 0);
                cl_page_free(env, ghost);
        }
        return page;
}

struct cl_page *cl_page_find(const struct lu_env *env, struct cl_object *o,
                             pgoff_t idx, struct page *vmpage,
                             enum cl_page_type type)
{
        return cl_page_find0(env, o, idx, vmpage, type, NULL);
}
EXPORT_SYMBOL(cl_page_find);


struct cl_page *cl_page_find_sub(const struct lu_env *env, struct cl_object *o,
                                 pgoff_t idx, struct page *vmpage,
                                 struct cl_page *parent)
{
        return cl_page_find0(env, o, idx, vmpage, parent->cp_type, parent);
}
EXPORT_SYMBOL(cl_page_find_sub);

static inline int cl_page_invariant(const struct cl_page *pg)
{
        struct cl_object_header *header;
        struct cl_page    *parent;
        struct cl_page    *child;
        struct cl_io        *owner;

        /*
         * Page invariant is protected by a VM lock.
         */
        LINVRNT(cl_page_is_vmlocked(NULL, pg));

        header = cl_object_header(pg->cp_obj);
        parent = pg->cp_parent;
        child  = pg->cp_child;
        owner  = pg->cp_owner;

        return cl_page_in_use(pg) &&
                ergo(parent != NULL, parent->cp_child == pg) &&
                ergo(child != NULL, child->cp_parent == pg) &&
                ergo(child != NULL, pg->cp_obj != child->cp_obj) &&
                ergo(parent != NULL, pg->cp_obj != parent->cp_obj) &&
                ergo(owner != NULL && parent != NULL,
                     parent->cp_owner == pg->cp_owner->ci_parent) &&
                ergo(owner != NULL && child != NULL,
                     child->cp_owner->ci_parent == owner) &&
                /*
                 * Either page is early in initialization (has neither child
                 * nor parent yet), or it is in the object radix tree.
                 */
                ergo(pg->cp_state < CPS_FREEING && pg->cp_type == CPT_CACHEABLE,
                     (void *)radix_tree_lookup(&header->coh_tree,
                                               pg->cp_index) == pg ||
                     (child == NULL && parent == NULL));
}

static void cl_page_state_set0(const struct lu_env *env,
                               struct cl_page *page, enum cl_page_state state)
{
        enum cl_page_state old;

        /*
         * Matrix of allowed state transitions [old][new], for sanity
         * checking.
         */
        static const int allowed_transitions[CPS_NR][CPS_NR] = {
                [CPS_CACHED] = {
                        [CPS_CACHED]  = 0,
                        [CPS_OWNED]   = 1, /* io finds existing cached page */
                        [CPS_PAGEIN]  = 0,
                        [CPS_PAGEOUT] = 1, /* write-out from the cache */
                        [CPS_FREEING] = 1, /* eviction on the memory pressure */
                },
                [CPS_OWNED] = {
                        [CPS_CACHED]  = 1, /* release to the cache */
                        [CPS_OWNED]   = 0,
                        [CPS_PAGEIN]  = 1, /* start read immediately */
                        [CPS_PAGEOUT] = 1, /* start write immediately */
                        [CPS_FREEING] = 1, /* lock invalidation or truncate */
                },
                [CPS_PAGEIN] = {
                        [CPS_CACHED]  = 1, /* io completion */
                        [CPS_OWNED]   = 0,
                        [CPS_PAGEIN]  = 0,
                        [CPS_PAGEOUT] = 0,
                        [CPS_FREEING] = 0,
                },
                [CPS_PAGEOUT] = {
                        [CPS_CACHED]  = 1, /* io completion */
                        [CPS_OWNED]   = 0,
                        [CPS_PAGEIN]  = 0,
                        [CPS_PAGEOUT] = 0,
                        [CPS_FREEING] = 0,
                },
                [CPS_FREEING] = {
                        [CPS_CACHED]  = 0,
                        [CPS_OWNED]   = 0,
                        [CPS_PAGEIN]  = 0,
                        [CPS_PAGEOUT] = 0,
                        [CPS_FREEING] = 0,
                }
        };

        old = page->cp_state;
        PASSERT(env, page, allowed_transitions[old][state]);
        CL_PAGE_HEADER(D_TRACE, env, page, "%d -> %d\n", old, state);
        for (; page != NULL; page = page->cp_child) {
                PASSERT(env, page, page->cp_state == old);
                PASSERT(env, page,
                        equi(state == CPS_OWNED, page->cp_owner != NULL));

                cl_page_state_set_trust(page, state);
        }
}

static void cl_page_state_set(const struct lu_env *env,
                              struct cl_page *page, enum cl_page_state state)
{
        cl_page_state_set0(env, page, state);
}

/**
 * Acquires an additional reference to a page.
 *
 * This can be called only by caller already possessing a reference to \a
 * page.
 *
 * \see cl_object_get(), cl_lock_get().
 */
void cl_page_get(struct cl_page *page)
{
        cl_page_get_trust(page);
}
EXPORT_SYMBOL(cl_page_get);

/**
 * Releases a reference to a page.
 *
 * When last reference is released, page is returned to the cache, unless it
 * is in cl_page_state::CPS_FREEING state, in which case it is immediately
 * destroyed.
 *
 * \see cl_object_put(), cl_lock_put().
 */
void cl_page_put(const struct lu_env *env, struct cl_page *page)
{
        PASSERT(env, page, atomic_read(&page->cp_ref) > !!page->cp_parent);

        CL_PAGE_HEADER(D_TRACE, env, page, "%d\n",
                       atomic_read(&page->cp_ref));

        if (atomic_dec_and_test(&page->cp_ref)) {
                LASSERT(page->cp_state == CPS_FREEING);

                LASSERT(atomic_read(&page->cp_ref) == 0);
                PASSERT(env, page, page->cp_owner == NULL);
                PASSERT(env, page, list_empty(&page->cp_batch));
                /*
                 * Page is no longer reachable by other threads. Tear
                 * it down.
                 */
                cl_page_free(env, page);
        }
}
EXPORT_SYMBOL(cl_page_put);

/**
 * Returns a VM page associated with a given cl_page.
 */
struct page *cl_page_vmpage(const struct lu_env *env, struct cl_page *page)
{
        const struct cl_page_slice *slice;

        /*
         * Find uppermost layer with ->cpo_vmpage() method, and return its
         * result.
         */
        page = cl_page_top(page);
        do {
                list_for_each_entry(slice, &page->cp_layers, cpl_linkage) {
                        if (slice->cpl_ops->cpo_vmpage != NULL)
                                return slice->cpl_ops->cpo_vmpage(env, slice);
                }
                page = page->cp_child;
        } while (page != NULL);
        LBUG(); /* ->cpo_vmpage() has to be defined somewhere in the stack */
}
EXPORT_SYMBOL(cl_page_vmpage);

/**
 * Returns a cl_page associated with a VM page, and given cl_object.
 */
struct cl_page *cl_vmpage_page(struct page *vmpage, struct cl_object *obj)
{
        struct cl_page *top;
        struct cl_page *page;

        KLASSERT(PageLocked(vmpage));

        /*
         * NOTE: absence of races and liveness of data are guaranteed by page
         *       lock on a "vmpage". That works because object destruction has
         *       bottom-to-top pass.
         */

        /*
         * This loop assumes that ->private points to the top-most page. This
         * can be rectified easily.
         */
        top = (struct cl_page *)vmpage->private;
        if (top == NULL)
                return NULL;

        for (page = top; page != NULL; page = page->cp_child) {
                if (cl_object_same(page->cp_obj, obj)) {
                        cl_page_get_trust(page);
                        break;
                }
        }
        LASSERT(ergo(page, page->cp_type == CPT_CACHEABLE));
        return page;
}
EXPORT_SYMBOL(cl_vmpage_page);

/**
 * Returns the top-page for a given page.
 *
 * \see cl_object_top(), cl_io_top()
 */
struct cl_page *cl_page_top(struct cl_page *page)
{
        return cl_page_top_trusted(page);
}
EXPORT_SYMBOL(cl_page_top);

const struct cl_page_slice *cl_page_at(const struct cl_page *page,
                                       const struct lu_device_type *dtype)
{
        return cl_page_at_trusted(page, dtype);
}
EXPORT_SYMBOL(cl_page_at);

#define CL_PAGE_OP(opname) offsetof(struct cl_page_operations, opname)

#define CL_PAGE_INVOKE(_env, _page, _op, _proto, ...)              \
({                                                                    \
        const struct lu_env     *__env  = (_env);                   \
        struct cl_page       *__page = (_page);            \
        const struct cl_page_slice *__scan;                          \
        int                      __result;                         \
        ptrdiff_t                  __op   = (_op);                   \
        int                    (*__method)_proto;                   \
                                                                        \
        __result = 0;                                              \
        __page = cl_page_top(__page);                              \
        do {                                                        \
                list_for_each_entry(__scan, &__page->cp_layers,     \
                                        cpl_linkage) {            \
                        __method = *(void **)((char *)__scan->cpl_ops + \
                                              __op);                \
                        if (__method != NULL) {                  \
                                __result = (*__method)(__env, __scan,   \
                                                       ## __VA_ARGS__); \
                                if (__result != 0)                    \
                                        break;                    \
                        }                                              \
                }                                                      \
                __page = __page->cp_child;                            \
        } while (__page != NULL && __result == 0);                    \
        if (__result > 0)                                              \
                __result = 0;                                      \
        __result;                                                      \
})

#define CL_PAGE_INVOID(_env, _page, _op, _proto, ...)              \
do {                                                                \
        const struct lu_env     *__env  = (_env);                   \
        struct cl_page       *__page = (_page);            \
        const struct cl_page_slice *__scan;                          \
        ptrdiff_t                  __op   = (_op);                   \
        void                  (*__method)_proto;                    \
                                                                        \
        __page = cl_page_top(__page);                              \
        do {                                                        \
                list_for_each_entry(__scan, &__page->cp_layers,     \
                                        cpl_linkage) {            \
                        __method = *(void **)((char *)__scan->cpl_ops + \
                                              __op);                \
                        if (__method != NULL)                      \
                                (*__method)(__env, __scan,            \
                                            ## __VA_ARGS__);        \
                }                                                      \
                __page = __page->cp_child;                            \
        } while (__page != NULL);                                      \
} while (0)

#define CL_PAGE_INVOID_REVERSE(_env, _page, _op, _proto, ...)          \
do {                                                                    \
        const struct lu_env     *__env  = (_env);                       \
        struct cl_page       *__page = (_page);                \
        const struct cl_page_slice *__scan;                              \
        ptrdiff_t                  __op   = (_op);                       \
        void                  (*__method)_proto;                        \
                                                                            \
        /* get to the bottom page. */                                  \
        while (__page->cp_child != NULL)                                    \
                __page = __page->cp_child;                                \
        do {                                                            \
                list_for_each_entry_reverse(__scan, &__page->cp_layers, \
                                                cpl_linkage) {        \
                        __method = *(void **)((char *)__scan->cpl_ops +     \
                                              __op);                    \
                        if (__method != NULL)                          \
                                (*__method)(__env, __scan,                \
                                            ## __VA_ARGS__);            \
                }                                                          \
                __page = __page->cp_parent;                              \
        } while (__page != NULL);                                          \
} while (0)

static int cl_page_invoke(const struct lu_env *env,
                          struct cl_io *io, struct cl_page *page, ptrdiff_t op)

{
        PINVRNT(env, page, cl_object_same(page->cp_obj, io->ci_obj));
        return CL_PAGE_INVOKE(env, page, op,
                              (const struct lu_env *,
                               const struct cl_page_slice *, struct cl_io *),
                              io);
}

static void cl_page_invoid(const struct lu_env *env,
                           struct cl_io *io, struct cl_page *page, ptrdiff_t op)

{
        PINVRNT(env, page, cl_object_same(page->cp_obj, io->ci_obj));
        CL_PAGE_INVOID(env, page, op,
                       (const struct lu_env *,
                        const struct cl_page_slice *, struct cl_io *), io);
}

static void cl_page_owner_clear(struct cl_page *page)
{
        for (page = cl_page_top(page); page != NULL; page = page->cp_child) {
                if (page->cp_owner != NULL) {
                        LASSERT(page->cp_owner->ci_owned_nr > 0);
                        page->cp_owner->ci_owned_nr--;
                        page->cp_owner = NULL;
                        page->cp_task = NULL;
                }
        }
}

static void cl_page_owner_set(struct cl_page *page)
{
        for (page = cl_page_top(page); page != NULL; page = page->cp_child) {
                LASSERT(page->cp_owner != NULL);
                page->cp_owner->ci_owned_nr++;
        }
}

void cl_page_disown0(const struct lu_env *env,
                     struct cl_io *io, struct cl_page *pg)
{
        enum cl_page_state state;

        state = pg->cp_state;
        PINVRNT(env, pg, state == CPS_OWNED || state == CPS_FREEING);
        PINVRNT(env, pg, cl_page_invariant(pg));
        cl_page_owner_clear(pg);

        if (state == CPS_OWNED)
                cl_page_state_set(env, pg, CPS_CACHED);
        /*
         * Completion call-backs are executed in the bottom-up order, so that
         * uppermost layer (llite), responsible for VFS/VM interaction runs
         * last and can release locks safely.
         */
        CL_PAGE_INVOID_REVERSE(env, pg, CL_PAGE_OP(cpo_disown),
                               (const struct lu_env *,
                                const struct cl_page_slice *, struct cl_io *),
                               io);
}

/**
 * returns true, iff page is owned by the given io.
 */
int cl_page_is_owned(const struct cl_page *pg, const struct cl_io *io)
{
        LINVRNT(cl_object_same(pg->cp_obj, io->ci_obj));
        return pg->cp_state == CPS_OWNED && pg->cp_owner == io;
}
EXPORT_SYMBOL(cl_page_is_owned);

/**
 * Try to own a page by IO.
 *
 * Waits until page is in cl_page_state::CPS_CACHED state, and then switch it
 * into cl_page_state::CPS_OWNED state.
 *
 * \pre  !cl_page_is_owned(pg, io)
 * \post result == 0 iff cl_page_is_owned(pg, io)
 *
 * \retval 0   success
 *
 * \retval -ve failure, e.g., page was destroyed (and landed in
 *           cl_page_state::CPS_FREEING instead of cl_page_state::CPS_CACHED).
 *           or, page was owned by another thread, or in IO.
 *
 * \see cl_page_disown()
 * \see cl_page_operations::cpo_own()
 * \see cl_page_own_try()
 * \see cl_page_own
 */
static int cl_page_own0(const struct lu_env *env, struct cl_io *io,
                        struct cl_page *pg, int nonblock)
{
        int result;

        PINVRNT(env, pg, !cl_page_is_owned(pg, io));

        pg = cl_page_top(pg);
        io = cl_io_top(io);

        if (pg->cp_state == CPS_FREEING) {
                result = -ENOENT;
        } else {
                result = CL_PAGE_INVOKE(env, pg, CL_PAGE_OP(cpo_own),
                                        (const struct lu_env *,
                                         const struct cl_page_slice *,
                                         struct cl_io *, int),
                                        io, nonblock);
                if (result == 0) {
                        PASSERT(env, pg, pg->cp_owner == NULL);
                        PASSERT(env, pg, pg->cp_req == NULL);
                        pg->cp_owner = io;
                        pg->cp_task  = current;
                        cl_page_owner_set(pg);
                        if (pg->cp_state != CPS_FREEING) {
                                cl_page_state_set(env, pg, CPS_OWNED);
                        } else {
                                cl_page_disown0(env, io, pg);
                                result = -ENOENT;
                        }
                }
        }
        PINVRNT(env, pg, ergo(result == 0, cl_page_invariant(pg)));
        return result;
}

/**
 * Own a page, might be blocked.
 *
 * \see cl_page_own0()
 */
int cl_page_own(const struct lu_env *env, struct cl_io *io, struct cl_page *pg)
{
        return cl_page_own0(env, io, pg, 0);
}
EXPORT_SYMBOL(cl_page_own);

/**
 * Nonblock version of cl_page_own().
 *
 * \see cl_page_own0()
 */
int cl_page_own_try(const struct lu_env *env, struct cl_io *io,
                    struct cl_page *pg)
{
        return cl_page_own0(env, io, pg, 1);
}
EXPORT_SYMBOL(cl_page_own_try);


/**
 * Assume page ownership.
 *
 * Called when page is already locked by the hosting VM.
 *
 * \pre !cl_page_is_owned(pg, io)
 * \post cl_page_is_owned(pg, io)
 *
 * \see cl_page_operations::cpo_assume()
 */
void cl_page_assume(const struct lu_env *env,
                    struct cl_io *io, struct cl_page *pg)
{
        PINVRNT(env, pg, cl_object_same(pg->cp_obj, io->ci_obj));

        pg = cl_page_top(pg);
        io = cl_io_top(io);

        cl_page_invoid(env, io, pg, CL_PAGE_OP(cpo_assume));
        PASSERT(env, pg, pg->cp_owner == NULL);
        pg->cp_owner = io;
        pg->cp_task = current;
        cl_page_owner_set(pg);
        cl_page_state_set(env, pg, CPS_OWNED);
}
EXPORT_SYMBOL(cl_page_assume);

/**
 * Releases page ownership without unlocking the page.
 *
 * Moves page into cl_page_state::CPS_CACHED without releasing a lock on the
 * underlying VM page (as VM is supposed to do this itself).
 *
 * \pre   cl_page_is_owned(pg, io)
 * \post !cl_page_is_owned(pg, io)
 *
 * \see cl_page_assume()
 */
void cl_page_unassume(const struct lu_env *env,
                      struct cl_io *io, struct cl_page *pg)
{
        PINVRNT(env, pg, cl_page_is_owned(pg, io));
        PINVRNT(env, pg, cl_page_invariant(pg));

        pg = cl_page_top(pg);
        io = cl_io_top(io);
        cl_page_owner_clear(pg);
        cl_page_state_set(env, pg, CPS_CACHED);
        CL_PAGE_INVOID_REVERSE(env, pg, CL_PAGE_OP(cpo_unassume),
                               (const struct lu_env *,
                                const struct cl_page_slice *, struct cl_io *),
                               io);
}
EXPORT_SYMBOL(cl_page_unassume);

/**
 * Releases page ownership.
 *
 * Moves page into cl_page_state::CPS_CACHED.
 *
 * \pre   cl_page_is_owned(pg, io)
 * \post !cl_page_is_owned(pg, io)
 *
 * \see cl_page_own()
 * \see cl_page_operations::cpo_disown()
 */
void cl_page_disown(const struct lu_env *env,
                    struct cl_io *io, struct cl_page *pg)
{
        PINVRNT(env, pg, cl_page_is_owned(pg, io));

        pg = cl_page_top(pg);
        io = cl_io_top(io);
        cl_page_disown0(env, io, pg);
}
EXPORT_SYMBOL(cl_page_disown);

/**
 * Called when page is to be removed from the object, e.g., as a result of
 * truncate.
 *
 * Calls cl_page_operations::cpo_discard() top-to-bottom.
 *
 * \pre cl_page_is_owned(pg, io)
 *
 * \see cl_page_operations::cpo_discard()
 */
void cl_page_discard(const struct lu_env *env,
                     struct cl_io *io, struct cl_page *pg)
{
        PINVRNT(env, pg, cl_page_is_owned(pg, io));
        PINVRNT(env, pg, cl_page_invariant(pg));

        cl_page_invoid(env, io, pg, CL_PAGE_OP(cpo_discard));
}
EXPORT_SYMBOL(cl_page_discard);

/**
 * Version of cl_page_delete() that can be called for not fully constructed
 * pages, e.g,. in a error handling cl_page_find()->cl_page_delete0()
 * path. Doesn't check page invariant.
 */
static void cl_page_delete0(const struct lu_env *env, struct cl_page *pg,
                            int radix)
{
        struct cl_page *tmp = pg;

        PASSERT(env, pg, pg == cl_page_top(pg));
        PASSERT(env, pg, pg->cp_state != CPS_FREEING);

        /*
         * Severe all ways to obtain new pointers to @pg.
         */
        cl_page_owner_clear(pg);

        /*
         * unexport the page firstly before freeing it so that
         * the page content is considered to be invalid.
         * We have to do this because a CPS_FREEING cl_page may
         * be NOT under the protection of a cl_lock.
         * Afterwards, if this page is found by other threads, then this
         * page will be forced to reread.
         */
        cl_page_export(env, pg, 0);
        cl_page_state_set0(env, pg, CPS_FREEING);

        CL_PAGE_INVOID(env, pg, CL_PAGE_OP(cpo_delete),
                       (const struct lu_env *, const struct cl_page_slice *));

        if (tmp->cp_type == CPT_CACHEABLE) {
                if (!radix)
                        /* !radix means that @pg is not yet in the radix tree,
                         * skip removing it.
                         */
                        tmp = pg->cp_child;
                for (; tmp != NULL; tmp = tmp->cp_child) {
                        void                *value;
                        struct cl_object_header *hdr;

                        hdr = cl_object_header(tmp->cp_obj);
                        spin_lock(&hdr->coh_page_guard);
                        value = radix_tree_delete(&hdr->coh_tree,
                                                  tmp->cp_index);
                        PASSERT(env, tmp, value == tmp);
                        PASSERT(env, tmp, hdr->coh_pages > 0);
                        hdr->coh_pages--;
                        spin_unlock(&hdr->coh_page_guard);
                        cl_page_put(env, tmp);
                }
        }
}

/**
 * Called when a decision is made to throw page out of memory.
 *
 * Notifies all layers about page destruction by calling
 * cl_page_operations::cpo_delete() method top-to-bottom.
 *
 * Moves page into cl_page_state::CPS_FREEING state (this is the only place
 * where transition to this state happens).
 *
 * Eliminates all venues through which new references to the page can be
 * obtained:
 *
 *     - removes page from the radix trees,
 *
 *     - breaks linkage from VM page to cl_page.
 *
 * Once page reaches cl_page_state::CPS_FREEING, all remaining references will
 * drain after some time, at which point page will be recycled.
 *
 * \pre  pg == cl_page_top(pg)
 * \pre  VM page is locked
 * \post pg->cp_state == CPS_FREEING
 *
 * \see cl_page_operations::cpo_delete()
 */
void cl_page_delete(const struct lu_env *env, struct cl_page *pg)
{
        PINVRNT(env, pg, cl_page_invariant(pg));
        cl_page_delete0(env, pg, 1);
}
EXPORT_SYMBOL(cl_page_delete);

/**
 * Unmaps page from user virtual memory.
 *
 * Calls cl_page_operations::cpo_unmap() through all layers top-to-bottom. The
 * layer responsible for VM interaction has to unmap page from user space
 * virtual memory.
 *
 * \see cl_page_operations::cpo_unmap()
 */
int cl_page_unmap(const struct lu_env *env,
                  struct cl_io *io, struct cl_page *pg)
{
        PINVRNT(env, pg, cl_page_is_owned(pg, io));
        PINVRNT(env, pg, cl_page_invariant(pg));

        return cl_page_invoke(env, io, pg, CL_PAGE_OP(cpo_unmap));
}
EXPORT_SYMBOL(cl_page_unmap);

/**
 * Marks page up-to-date.
 *
 * Call cl_page_operations::cpo_export() through all layers top-to-bottom. The
 * layer responsible for VM interaction has to mark/clear page as up-to-date
 * by the \a uptodate argument.
 *
 * \see cl_page_operations::cpo_export()
 */
void cl_page_export(const struct lu_env *env, struct cl_page *pg, int uptodate)
{
        PINVRNT(env, pg, cl_page_invariant(pg));
        CL_PAGE_INVOID(env, pg, CL_PAGE_OP(cpo_export),
                       (const struct lu_env *,
                        const struct cl_page_slice *, int), uptodate);
}
EXPORT_SYMBOL(cl_page_export);

/**
 * Returns true, iff \a pg is VM locked in a suitable sense by the calling
 * thread.
 */
int cl_page_is_vmlocked(const struct lu_env *env, const struct cl_page *pg)
{
        int result;
        const struct cl_page_slice *slice;

        pg = cl_page_top_trusted((struct cl_page *)pg);
        slice = container_of(pg->cp_layers.next,
                             const struct cl_page_slice, cpl_linkage);
        PASSERT(env, pg, slice->cpl_ops->cpo_is_vmlocked != NULL);
        /*
         * Call ->cpo_is_vmlocked() directly instead of going through
         * CL_PAGE_INVOKE(), because cl_page_is_vmlocked() is used by
         * cl_page_invariant().
         */
        result = slice->cpl_ops->cpo_is_vmlocked(env, slice);
        PASSERT(env, pg, result == -EBUSY || result == -ENODATA);
        return result == -EBUSY;
}
EXPORT_SYMBOL(cl_page_is_vmlocked);

static enum cl_page_state cl_req_type_state(enum cl_req_type crt)
{
        return crt == CRT_WRITE ? CPS_PAGEOUT : CPS_PAGEIN;
}

static void cl_page_io_start(const struct lu_env *env,
                             struct cl_page *pg, enum cl_req_type crt)
{
        /*
         * Page is queued for IO, change its state.
         */
        cl_page_owner_clear(pg);
        cl_page_state_set(env, pg, cl_req_type_state(crt));
}

/**
 * Prepares page for immediate transfer. cl_page_operations::cpo_prep() is
 * called top-to-bottom. Every layer either agrees to submit this page (by
 * returning 0), or requests to omit this page (by returning -EALREADY). Layer
 * handling interactions with the VM also has to inform VM that page is under
 * transfer now.
 */
int cl_page_prep(const struct lu_env *env, struct cl_io *io,
                 struct cl_page *pg, enum cl_req_type crt)
{
        int result;

        PINVRNT(env, pg, cl_page_is_owned(pg, io));
        PINVRNT(env, pg, cl_page_invariant(pg));
        PINVRNT(env, pg, crt < CRT_NR);

        /*
         * XXX this has to be called bottom-to-top, so that llite can set up
         * PG_writeback without risking other layers deciding to skip this
         * page.
         */
        if (crt >= CRT_NR)
                return -EINVAL;
        result = cl_page_invoke(env, io, pg, CL_PAGE_OP(io[crt].cpo_prep));
        if (result == 0)
                cl_page_io_start(env, pg, crt);

        CL_PAGE_HEADER(D_TRACE, env, pg, "%d %d\n", crt, result);
        return result;
}
EXPORT_SYMBOL(cl_page_prep);

/**
 * Notify layers about transfer completion.
 *
 * Invoked by transfer sub-system (which is a part of osc) to notify layers
 * that a transfer, of which this page is a part of has completed.
 *
 * Completion call-backs are executed in the bottom-up order, so that
 * uppermost layer (llite), responsible for the VFS/VM interaction runs last
 * and can release locks safely.
 *
 * \pre  pg->cp_state == CPS_PAGEIN || pg->cp_state == CPS_PAGEOUT
 * \post pg->cp_state == CPS_CACHED
 *
 * \see cl_page_operations::cpo_completion()
 */
void cl_page_completion(const struct lu_env *env,
                        struct cl_page *pg, enum cl_req_type crt, int ioret)
{
        struct cl_sync_io *anchor = pg->cp_sync_io;

        PASSERT(env, pg, crt < CRT_NR);
        /* cl_page::cp_req already cleared by the caller (osc_completion()) */
        PASSERT(env, pg, pg->cp_req == NULL);
        PASSERT(env, pg, pg->cp_state == cl_req_type_state(crt));

        CL_PAGE_HEADER(D_TRACE, env, pg, "%d %d\n", crt, ioret);
        if (crt == CRT_READ && ioret == 0) {
                PASSERT(env, pg, !(pg->cp_flags & CPF_READ_COMPLETED));
                pg->cp_flags |= CPF_READ_COMPLETED;
        }

        cl_page_state_set(env, pg, CPS_CACHED);
        if (crt >= CRT_NR)
                return;
        CL_PAGE_INVOID_REVERSE(env, pg, CL_PAGE_OP(io[crt].cpo_completion),
                               (const struct lu_env *,
                                const struct cl_page_slice *, int), ioret);
        if (anchor) {
                LASSERT(cl_page_is_vmlocked(env, pg));
                LASSERT(pg->cp_sync_io == anchor);
                pg->cp_sync_io = NULL;
        }
        /*
         * As page->cp_obj is pinned by a reference from page->cp_req, it is
         * safe to call cl_page_put() without risking object destruction in a
         * non-blocking context.
         */
        cl_page_put(env, pg);

        if (anchor)
                cl_sync_io_note(anchor, ioret);
}
EXPORT_SYMBOL(cl_page_completion);

/**
 * Notify layers that transfer formation engine decided to yank this page from
 * the cache and to make it a part of a transfer.
 *
 * \pre  pg->cp_state == CPS_CACHED
 * \post pg->cp_state == CPS_PAGEIN || pg->cp_state == CPS_PAGEOUT
 *
 * \see cl_page_operations::cpo_make_ready()
 */
int cl_page_make_ready(const struct lu_env *env, struct cl_page *pg,
                       enum cl_req_type crt)
{
        int result;

        PINVRNT(env, pg, crt < CRT_NR);

        if (crt >= CRT_NR)
                return -EINVAL;
        result = CL_PAGE_INVOKE(env, pg, CL_PAGE_OP(io[crt].cpo_make_ready),
                                (const struct lu_env *,
                                 const struct cl_page_slice *));
        if (result == 0) {
                PASSERT(env, pg, pg->cp_state == CPS_CACHED);
                cl_page_io_start(env, pg, crt);
        }
        CL_PAGE_HEADER(D_TRACE, env, pg, "%d %d\n", crt, result);
        return result;
}
EXPORT_SYMBOL(cl_page_make_ready);

/**
 * Notify layers that high level io decided to place this page into a cache
 * for future transfer.
 *
 * The layer implementing transfer engine (osc) has to register this page in
 * its queues.
 *
 * \pre  cl_page_is_owned(pg, io)
 * \post cl_page_is_owned(pg, io)
 *
 * \see cl_page_operations::cpo_cache_add()
 */
int cl_page_cache_add(const struct lu_env *env, struct cl_io *io,
                      struct cl_page *pg, enum cl_req_type crt)
{
        const struct cl_page_slice *scan;
        int result = 0;

        PINVRNT(env, pg, crt < CRT_NR);
        PINVRNT(env, pg, cl_page_is_owned(pg, io));
        PINVRNT(env, pg, cl_page_invariant(pg));

        if (crt >= CRT_NR)
                return -EINVAL;

        list_for_each_entry(scan, &pg->cp_layers, cpl_linkage) {
                if (scan->cpl_ops->io[crt].cpo_cache_add == NULL)
                        continue;

                result = scan->cpl_ops->io[crt].cpo_cache_add(env, scan, io);
                if (result != 0)
                        break;
        }
        CL_PAGE_HEADER(D_TRACE, env, pg, "%d %d\n", crt, result);
        return result;
}
EXPORT_SYMBOL(cl_page_cache_add);

/**
 * Called if a pge is being written back by kernel's intention.
 *
 * \pre  cl_page_is_owned(pg, io)
 * \post ergo(result == 0, pg->cp_state == CPS_PAGEOUT)
 *
 * \see cl_page_operations::cpo_flush()
 */
int cl_page_flush(const struct lu_env *env, struct cl_io *io,
                  struct cl_page *pg)
{
        int result;

        PINVRNT(env, pg, cl_page_is_owned(pg, io));
        PINVRNT(env, pg, cl_page_invariant(pg));

        result = cl_page_invoke(env, io, pg, CL_PAGE_OP(cpo_flush));

        CL_PAGE_HEADER(D_TRACE, env, pg, "%d\n", result);
        return result;
}
EXPORT_SYMBOL(cl_page_flush);

/**
 * Checks whether page is protected by any extent lock is at least required
 * mode.
 *
 * \return the same as in cl_page_operations::cpo_is_under_lock() method.
 * \see cl_page_operations::cpo_is_under_lock()
 */
int cl_page_is_under_lock(const struct lu_env *env, struct cl_io *io,
                          struct cl_page *page)
{
        int rc;

        PINVRNT(env, page, cl_page_invariant(page));

        rc = CL_PAGE_INVOKE(env, page, CL_PAGE_OP(cpo_is_under_lock),
                            (const struct lu_env *,
                             const struct cl_page_slice *, struct cl_io *),
                            io);
        PASSERT(env, page, rc != 0);
        return rc;
}
EXPORT_SYMBOL(cl_page_is_under_lock);

static int page_prune_cb(const struct lu_env *env, struct cl_io *io,
                         struct cl_page *page, void *cbdata)
{
        cl_page_own(env, io, page);
        cl_page_unmap(env, io, page);
        cl_page_discard(env, io, page);
        cl_page_disown(env, io, page);
        return CLP_GANG_OKAY;
}

/**
 * Purges all cached pages belonging to the object \a obj.
 */
int cl_pages_prune(const struct lu_env *env, struct cl_object *clobj)
{
        struct cl_thread_info   *info;
        struct cl_object        *obj = cl_object_top(clobj);
        struct cl_io        *io;
        int                   result;

        info  = cl_env_info(env);
        io    = &info->clt_io;

        /*
         * initialize the io. This is ugly since we never do IO in this
         * function, we just make cl_page_list functions happy. -jay
         */
        io->ci_obj = obj;
        io->ci_ignore_layout = 1;
        result = cl_io_init(env, io, CIT_MISC, obj);
        if (result != 0) {
                cl_io_fini(env, io);
                return io->ci_result;
        }

        do {
                result = cl_page_gang_lookup(env, obj, io, 0, CL_PAGE_EOF,
                                             page_prune_cb, NULL);
                if (result == CLP_GANG_RESCHED)
                        cond_resched();
        } while (result != CLP_GANG_OKAY);

        cl_io_fini(env, io);
        return result;
}
EXPORT_SYMBOL(cl_pages_prune);

/**
 * Tells transfer engine that only part of a page is to be transmitted.
 *
 * \see cl_page_operations::cpo_clip()
 */
void cl_page_clip(const struct lu_env *env, struct cl_page *pg,
                  int from, int to)
{
        PINVRNT(env, pg, cl_page_invariant(pg));

        CL_PAGE_HEADER(D_TRACE, env, pg, "%d %d\n", from, to);
        CL_PAGE_INVOID(env, pg, CL_PAGE_OP(cpo_clip),
                       (const struct lu_env *,
                        const struct cl_page_slice *, int, int),
                       from, to);
}
EXPORT_SYMBOL(cl_page_clip);

/**
 * Prints human readable representation of \a pg to the \a f.
 */
void cl_page_header_print(const struct lu_env *env, void *cookie,
                          lu_printer_t printer, const struct cl_page *pg)
{
        (*printer)(env, cookie,
                   "page@%p[%d %p:%lu ^%p_%p %d %d %d %p %p %#x]\n",
                   pg, atomic_read(&pg->cp_ref), pg->cp_obj,
                   pg->cp_index, pg->cp_parent, pg->cp_child,
                   pg->cp_state, pg->cp_error, pg->cp_type,
                   pg->cp_owner, pg->cp_req, pg->cp_flags);
}
EXPORT_SYMBOL(cl_page_header_print);

/**
 * Prints human readable representation of \a pg to the \a f.
 */
void cl_page_print(const struct lu_env *env, void *cookie,
                   lu_printer_t printer, const struct cl_page *pg)
{
        struct cl_page *scan;

        for (scan = cl_page_top((struct cl_page *)pg);
             scan != NULL; scan = scan->cp_child)
                cl_page_header_print(env, cookie, printer, scan);
        CL_PAGE_INVOKE(env, (struct cl_page *)pg, CL_PAGE_OP(cpo_print),
                       (const struct lu_env *env,
                        const struct cl_page_slice *slice,
                        void *cookie, lu_printer_t p), cookie, printer);
        (*printer)(env, cookie, "end page@%p\n", pg);
}
EXPORT_SYMBOL(cl_page_print);

/**
 * Cancel a page which is still in a transfer.
 */
int cl_page_cancel(const struct lu_env *env, struct cl_page *page)
{
        return CL_PAGE_INVOKE(env, page, CL_PAGE_OP(cpo_cancel),
                              (const struct lu_env *,
                               const struct cl_page_slice *));
}
EXPORT_SYMBOL(cl_page_cancel);

/**
 * Converts a byte offset within object \a obj into a page index.
 */
loff_t cl_offset(const struct cl_object *obj, pgoff_t idx)
{
        /*
         * XXX for now.
         */
        return (loff_t)idx << PAGE_CACHE_SHIFT;
}
EXPORT_SYMBOL(cl_offset);

/**
 * Converts a page index into a byte offset within object \a obj.
 */
pgoff_t cl_index(const struct cl_object *obj, loff_t offset)
{
        /*
         * XXX for now.
         */
        return offset >> PAGE_CACHE_SHIFT;
}
EXPORT_SYMBOL(cl_index);

int cl_page_size(const struct cl_object *obj)
{
        return 1 << PAGE_CACHE_SHIFT;
}
EXPORT_SYMBOL(cl_page_size);

/**
 * Adds page slice to the compound page.
 *
 * This is called by cl_object_operations::coo_page_init() methods to add a
 * per-layer state to the page. New state is added at the end of
 * cl_page::cp_layers list, that is, it is at the bottom of the stack.
 *
 * \see cl_lock_slice_add(), cl_req_slice_add(), cl_io_slice_add()
 */
void cl_page_slice_add(struct cl_page *page, struct cl_page_slice *slice,
                       struct cl_object *obj,
                       const struct cl_page_operations *ops)
{
        list_add_tail(&slice->cpl_linkage, &page->cp_layers);
        slice->cpl_obj  = obj;
        slice->cpl_ops  = ops;
        slice->cpl_page = page;
}
EXPORT_SYMBOL(cl_page_slice_add);

int  cl_page_init(void)
{
        return 0;
}

void cl_page_fini(void)
{
}