[deliverable/linux.git] / drivers / staging / lustre / lustre / obdclass / cl_io.c

/*
 * 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 IO.
 *
 *   Author: Nikita Danilov <nikita.danilov@sun.com>
 */

#define DEBUG_SUBSYSTEM S_CLASS

#include <obd_class.h>
#include <obd_support.h>
#include <lustre_fid.h>
#include <linux/list.h>
#include <cl_object.h>
#include "cl_internal.h"

/*****************************************************************************
 *
 * cl_io interface.
 *
 */

#define cl_io_for_each(slice, io) \
        list_for_each_entry((slice), &io->ci_layers, cis_linkage)
#define cl_io_for_each_reverse(slice, io)                \
        list_for_each_entry_reverse((slice), &io->ci_layers, cis_linkage)

static inline int cl_io_type_is_valid(enum cl_io_type type)
{
        return CIT_READ <= type && type < CIT_OP_NR;
}

static inline int cl_io_is_loopable(const struct cl_io *io)
{
        return cl_io_type_is_valid(io->ci_type) && io->ci_type != CIT_MISC;
}

/**
 * Returns true iff there is an IO ongoing in the given environment.
 */
int cl_io_is_going(const struct lu_env *env)
{
        return cl_env_info(env)->clt_current_io != NULL;
}
EXPORT_SYMBOL(cl_io_is_going);

/**
 * cl_io invariant that holds at all times when exported cl_io_*() functions
 * are entered and left.
 */
static int cl_io_invariant(const struct cl_io *io)
{
        struct cl_io *up;

        up = io->ci_parent;
        return
                /*
                 * io can own pages only when it is ongoing. Sub-io might
                 * still be in CIS_LOCKED state when top-io is in
                 * CIS_IO_GOING.
                 */
                ergo(io->ci_owned_nr > 0, io->ci_state == CIS_IO_GOING ||
                     (io->ci_state == CIS_LOCKED && up != NULL));
}

/**
 * Finalize \a io, by calling cl_io_operations::cio_fini() bottom-to-top.
 */
void cl_io_fini(const struct lu_env *env, struct cl_io *io)
{
        struct cl_io_slice    *slice;
        struct cl_thread_info *info;

        LINVRNT(cl_io_type_is_valid(io->ci_type));
        LINVRNT(cl_io_invariant(io));
        ENTRY;

        while (!list_empty(&io->ci_layers)) {
                slice = container_of(io->ci_layers.prev, struct cl_io_slice,
                                     cis_linkage);
                list_del_init(&slice->cis_linkage);
                if (slice->cis_iop->op[io->ci_type].cio_fini != NULL)
                        slice->cis_iop->op[io->ci_type].cio_fini(env, slice);
                /*
                 * Invalidate slice to catch use after free. This assumes that
                 * slices are allocated within session and can be touched
                 * after ->cio_fini() returns.
                 */
                slice->cis_io = NULL;
        }
        io->ci_state = CIS_FINI;
        info = cl_env_info(env);
        if (info->clt_current_io == io)
                info->clt_current_io = NULL;

        /* sanity check for layout change */
        switch(io->ci_type) {
        case CIT_READ:
        case CIT_WRITE:
                break;
        case CIT_FAULT:
        case CIT_FSYNC:
                LASSERT(!io->ci_need_restart);
                break;
        case CIT_SETATTR:
        case CIT_MISC:
                /* Check ignore layout change conf */
                LASSERT(ergo(io->ci_ignore_layout || !io->ci_verify_layout,
                                !io->ci_need_restart));
                break;
        default:
                LBUG();
        }
        EXIT;
}
EXPORT_SYMBOL(cl_io_fini);

static int cl_io_init0(const struct lu_env *env, struct cl_io *io,
                       enum cl_io_type iot, struct cl_object *obj)
{
        struct cl_object *scan;
        int result;

        LINVRNT(io->ci_state == CIS_ZERO || io->ci_state == CIS_FINI);
        LINVRNT(cl_io_type_is_valid(iot));
        LINVRNT(cl_io_invariant(io));
        ENTRY;

        io->ci_type = iot;
        INIT_LIST_HEAD(&io->ci_lockset.cls_todo);
        INIT_LIST_HEAD(&io->ci_lockset.cls_curr);
        INIT_LIST_HEAD(&io->ci_lockset.cls_done);
        INIT_LIST_HEAD(&io->ci_layers);

        result = 0;
        cl_object_for_each(scan, obj) {
                if (scan->co_ops->coo_io_init != NULL) {
                        result = scan->co_ops->coo_io_init(env, scan, io);
                        if (result != 0)
                                break;
                }
        }
        if (result == 0)
                io->ci_state = CIS_INIT;
        RETURN(result);
}

/**
 * Initialize sub-io, by calling cl_io_operations::cio_init() top-to-bottom.
 *
 * \pre obj != cl_object_top(obj)
 */
int cl_io_sub_init(const struct lu_env *env, struct cl_io *io,
                   enum cl_io_type iot, struct cl_object *obj)
{
        struct cl_thread_info *info = cl_env_info(env);

        LASSERT(obj != cl_object_top(obj));
        if (info->clt_current_io == NULL)
                info->clt_current_io = io;
        return cl_io_init0(env, io, iot, obj);
}
EXPORT_SYMBOL(cl_io_sub_init);

/**
 * Initialize \a io, by calling cl_io_operations::cio_init() top-to-bottom.
 *
 * Caller has to call cl_io_fini() after a call to cl_io_init(), no matter
 * what the latter returned.
 *
 * \pre obj == cl_object_top(obj)
 * \pre cl_io_type_is_valid(iot)
 * \post cl_io_type_is_valid(io->ci_type) && io->ci_type == iot
 */
int cl_io_init(const struct lu_env *env, struct cl_io *io,
               enum cl_io_type iot, struct cl_object *obj)
{
        struct cl_thread_info *info = cl_env_info(env);

        LASSERT(obj == cl_object_top(obj));
        LASSERT(info->clt_current_io == NULL);

        info->clt_current_io = io;
        return cl_io_init0(env, io, iot, obj);
}
EXPORT_SYMBOL(cl_io_init);

/**
 * Initialize read or write io.
 *
 * \pre iot == CIT_READ || iot == CIT_WRITE
 */
int cl_io_rw_init(const struct lu_env *env, struct cl_io *io,
                  enum cl_io_type iot, loff_t pos, size_t count)
{
        LINVRNT(iot == CIT_READ || iot == CIT_WRITE);
        LINVRNT(io->ci_obj != NULL);
        ENTRY;

        LU_OBJECT_HEADER(D_VFSTRACE, env, &io->ci_obj->co_lu,
                         "io range: %u ["LPU64", "LPU64") %u %u\n",
                         iot, (__u64)pos, (__u64)pos + count,
                         io->u.ci_rw.crw_nonblock, io->u.ci_wr.wr_append);
        io->u.ci_rw.crw_pos    = pos;
        io->u.ci_rw.crw_count  = count;
        RETURN(cl_io_init(env, io, iot, io->ci_obj));
}
EXPORT_SYMBOL(cl_io_rw_init);

static inline const struct lu_fid *
cl_lock_descr_fid(const struct cl_lock_descr *descr)
{
        return lu_object_fid(&descr->cld_obj->co_lu);
}

static int cl_lock_descr_sort(const struct cl_lock_descr *d0,
                              const struct cl_lock_descr *d1)
{
        return lu_fid_cmp(cl_lock_descr_fid(d0), cl_lock_descr_fid(d1)) ?:
                __diff_normalize(d0->cld_start, d1->cld_start);
}

static int cl_lock_descr_cmp(const struct cl_lock_descr *d0,
                             const struct cl_lock_descr *d1)
{
        int ret;

        ret = lu_fid_cmp(cl_lock_descr_fid(d0), cl_lock_descr_fid(d1));
        if (ret)
                return ret;
        if (d0->cld_end < d1->cld_start)
                return -1;
        if (d0->cld_start > d0->cld_end)
                return 1;
        return 0;
}

static void cl_lock_descr_merge(struct cl_lock_descr *d0,
                                const struct cl_lock_descr *d1)
{
        d0->cld_start = min(d0->cld_start, d1->cld_start);
        d0->cld_end = max(d0->cld_end, d1->cld_end);

        if (d1->cld_mode == CLM_WRITE && d0->cld_mode != CLM_WRITE)
                d0->cld_mode = CLM_WRITE;

        if (d1->cld_mode == CLM_GROUP && d0->cld_mode != CLM_GROUP)
                d0->cld_mode = CLM_GROUP;
}

/*
 * Sort locks in lexicographical order of their (fid, start-offset) pairs.
 */
static void cl_io_locks_sort(struct cl_io *io)
{
        int done = 0;

        ENTRY;
        /* hidden treasure: bubble sort for now. */
        do {
                struct cl_io_lock_link *curr;
                struct cl_io_lock_link *prev;
                struct cl_io_lock_link *temp;

                done = 1;
                prev = NULL;

                list_for_each_entry_safe(curr, temp,
                                             &io->ci_lockset.cls_todo,
                                             cill_linkage) {
                        if (prev != NULL) {
                                switch (cl_lock_descr_sort(&prev->cill_descr,
                                                          &curr->cill_descr)) {
                                case 0:
                                        /*
                                         * IMPOSSIBLE: Identical locks are
                                         *           already removed at
                                         *           this point.
                                         */
                                default:
                                        LBUG();
                                case +1:
                                        list_move_tail(&curr->cill_linkage,
                                                           &prev->cill_linkage);
                                        done = 0;
                                        continue; /* don't change prev: it's
                                                   * still "previous" */
                                case -1: /* already in order */
                                        break;
                                }
                        }
                        prev = curr;
                }
        } while (!done);
        EXIT;
}

/**
 * Check whether \a queue contains locks matching \a need.
 *
 * \retval +ve there is a matching lock in the \a queue
 * \retval   0 there are no matching locks in the \a queue
 */
int cl_queue_match(const struct list_head *queue,
                   const struct cl_lock_descr *need)
{
       struct cl_io_lock_link *scan;

       ENTRY;
       list_for_each_entry(scan, queue, cill_linkage) {
               if (cl_lock_descr_match(&scan->cill_descr, need))
                       RETURN(+1);
       }
       RETURN(0);
}
EXPORT_SYMBOL(cl_queue_match);

static int cl_queue_merge(const struct list_head *queue,
                          const struct cl_lock_descr *need)
{
       struct cl_io_lock_link *scan;

       ENTRY;
       list_for_each_entry(scan, queue, cill_linkage) {
               if (cl_lock_descr_cmp(&scan->cill_descr, need))
                       continue;
               cl_lock_descr_merge(&scan->cill_descr, need);
               CDEBUG(D_VFSTRACE, "lock: %d: [%lu, %lu]\n",
                      scan->cill_descr.cld_mode, scan->cill_descr.cld_start,
                      scan->cill_descr.cld_end);
               RETURN(+1);
       }
       RETURN(0);

}

static int cl_lockset_match(const struct cl_lockset *set,
                            const struct cl_lock_descr *need)
{
        return cl_queue_match(&set->cls_curr, need) ||
               cl_queue_match(&set->cls_done, need);
}

static int cl_lockset_merge(const struct cl_lockset *set,
                            const struct cl_lock_descr *need)
{
        return cl_queue_merge(&set->cls_todo, need) ||
               cl_lockset_match(set, need);
}

static int cl_lockset_lock_one(const struct lu_env *env,
                               struct cl_io *io, struct cl_lockset *set,
                               struct cl_io_lock_link *link)
{
        struct cl_lock *lock;
        int          result;

        ENTRY;

        lock = cl_lock_request(env, io, &link->cill_descr, "io", io);

        if (!IS_ERR(lock)) {
                link->cill_lock = lock;
                list_move(&link->cill_linkage, &set->cls_curr);
                if (!(link->cill_descr.cld_enq_flags & CEF_ASYNC)) {
                        result = cl_wait(env, lock);
                        if (result == 0)
                                list_move(&link->cill_linkage,
                                              &set->cls_done);
                } else
                        result = 0;
        } else
                result = PTR_ERR(lock);
        RETURN(result);
}

static void cl_lock_link_fini(const struct lu_env *env, struct cl_io *io,
                              struct cl_io_lock_link *link)
{
        struct cl_lock *lock = link->cill_lock;

        ENTRY;
        list_del_init(&link->cill_linkage);
        if (lock != NULL) {
                cl_lock_release(env, lock, "io", io);
                link->cill_lock = NULL;
        }
        if (link->cill_fini != NULL)
                link->cill_fini(env, link);
        EXIT;
}

static int cl_lockset_lock(const struct lu_env *env, struct cl_io *io,
                           struct cl_lockset *set)
{
        struct cl_io_lock_link *link;
        struct cl_io_lock_link *temp;
        struct cl_lock   *lock;
        int result;

        ENTRY;
        result = 0;
        list_for_each_entry_safe(link, temp, &set->cls_todo, cill_linkage) {
                if (!cl_lockset_match(set, &link->cill_descr)) {
                        /* XXX some locking to guarantee that locks aren't
                         * expanded in between. */
                        result = cl_lockset_lock_one(env, io, set, link);
                        if (result != 0)
                                break;
                } else
                        cl_lock_link_fini(env, io, link);
        }
        if (result == 0) {
                list_for_each_entry_safe(link, temp,
                                             &set->cls_curr, cill_linkage) {
                        lock = link->cill_lock;
                        result = cl_wait(env, lock);
                        if (result == 0)
                                list_move(&link->cill_linkage,
                                              &set->cls_done);
                        else
                                break;
                }
        }
        RETURN(result);
}

/**
 * Takes locks necessary for the current iteration of io.
 *
 * Calls cl_io_operations::cio_lock() top-to-bottom to collect locks required
 * by layers for the current iteration. Then sort locks (to avoid dead-locks),
 * and acquire them.
 */
int cl_io_lock(const struct lu_env *env, struct cl_io *io)
{
        const struct cl_io_slice *scan;
        int result = 0;

        LINVRNT(cl_io_is_loopable(io));
        LINVRNT(io->ci_state == CIS_IT_STARTED);
        LINVRNT(cl_io_invariant(io));

        ENTRY;
        cl_io_for_each(scan, io) {
                if (scan->cis_iop->op[io->ci_type].cio_lock == NULL)
                        continue;
                result = scan->cis_iop->op[io->ci_type].cio_lock(env, scan);
                if (result != 0)
                        break;
        }
        if (result == 0) {
                cl_io_locks_sort(io);
                result = cl_lockset_lock(env, io, &io->ci_lockset);
        }
        if (result != 0)
                cl_io_unlock(env, io);
        else
                io->ci_state = CIS_LOCKED;
        RETURN(result);
}
EXPORT_SYMBOL(cl_io_lock);

/**
 * Release locks takes by io.
 */
void cl_io_unlock(const struct lu_env *env, struct cl_io *io)
{
        struct cl_lockset       *set;
        struct cl_io_lock_link   *link;
        struct cl_io_lock_link   *temp;
        const struct cl_io_slice *scan;

        LASSERT(cl_io_is_loopable(io));
        LASSERT(CIS_IT_STARTED <= io->ci_state && io->ci_state < CIS_UNLOCKED);
        LINVRNT(cl_io_invariant(io));

        ENTRY;
        set = &io->ci_lockset;

        list_for_each_entry_safe(link, temp, &set->cls_todo, cill_linkage)
                cl_lock_link_fini(env, io, link);

        list_for_each_entry_safe(link, temp, &set->cls_curr, cill_linkage)
                cl_lock_link_fini(env, io, link);

        list_for_each_entry_safe(link, temp, &set->cls_done, cill_linkage) {
                cl_unuse(env, link->cill_lock);
                cl_lock_link_fini(env, io, link);
        }
        cl_io_for_each_reverse(scan, io) {
                if (scan->cis_iop->op[io->ci_type].cio_unlock != NULL)
                        scan->cis_iop->op[io->ci_type].cio_unlock(env, scan);
        }
        io->ci_state = CIS_UNLOCKED;
        LASSERT(!cl_env_info(env)->clt_counters[CNL_TOP].ctc_nr_locks_acquired);
        EXIT;
}
EXPORT_SYMBOL(cl_io_unlock);

/**
 * Prepares next iteration of io.
 *
 * Calls cl_io_operations::cio_iter_init() top-to-bottom. This exists to give
 * layers a chance to modify io parameters, e.g., so that lov can restrict io
 * to a single stripe.
 */
int cl_io_iter_init(const struct lu_env *env, struct cl_io *io)
{
        const struct cl_io_slice *scan;
        int result;

        LINVRNT(cl_io_is_loopable(io));
        LINVRNT(io->ci_state == CIS_INIT || io->ci_state == CIS_IT_ENDED);
        LINVRNT(cl_io_invariant(io));

        ENTRY;
        result = 0;
        cl_io_for_each(scan, io) {
                if (scan->cis_iop->op[io->ci_type].cio_iter_init == NULL)
                        continue;
                result = scan->cis_iop->op[io->ci_type].cio_iter_init(env,
                                                                      scan);
                if (result != 0)
                        break;
        }
        if (result == 0)
                io->ci_state = CIS_IT_STARTED;
        RETURN(result);
}
EXPORT_SYMBOL(cl_io_iter_init);

/**
 * Finalizes io iteration.
 *
 * Calls cl_io_operations::cio_iter_fini() bottom-to-top.
 */
void cl_io_iter_fini(const struct lu_env *env, struct cl_io *io)
{
        const struct cl_io_slice *scan;

        LINVRNT(cl_io_is_loopable(io));
        LINVRNT(io->ci_state == CIS_UNLOCKED);
        LINVRNT(cl_io_invariant(io));

        ENTRY;
        cl_io_for_each_reverse(scan, io) {
                if (scan->cis_iop->op[io->ci_type].cio_iter_fini != NULL)
                        scan->cis_iop->op[io->ci_type].cio_iter_fini(env, scan);
        }
        io->ci_state = CIS_IT_ENDED;
        EXIT;
}
EXPORT_SYMBOL(cl_io_iter_fini);

/**
 * Records that read or write io progressed \a nob bytes forward.
 */
void cl_io_rw_advance(const struct lu_env *env, struct cl_io *io, size_t nob)
{
        const struct cl_io_slice *scan;

        LINVRNT(io->ci_type == CIT_READ || io->ci_type == CIT_WRITE ||
                nob == 0);
        LINVRNT(cl_io_is_loopable(io));
        LINVRNT(cl_io_invariant(io));

        ENTRY;

        io->u.ci_rw.crw_pos   += nob;
        io->u.ci_rw.crw_count -= nob;

        /* layers have to be notified. */
        cl_io_for_each_reverse(scan, io) {
                if (scan->cis_iop->op[io->ci_type].cio_advance != NULL)
                        scan->cis_iop->op[io->ci_type].cio_advance(env, scan,
                                                                   nob);
        }
        EXIT;
}
EXPORT_SYMBOL(cl_io_rw_advance);

/**
 * Adds a lock to a lockset.
 */
int cl_io_lock_add(const struct lu_env *env, struct cl_io *io,
                   struct cl_io_lock_link *link)
{
        int result;

        ENTRY;
        if (cl_lockset_merge(&io->ci_lockset, &link->cill_descr))
                result = +1;
        else {
                list_add(&link->cill_linkage, &io->ci_lockset.cls_todo);
                result = 0;
        }
        RETURN(result);
}
EXPORT_SYMBOL(cl_io_lock_add);

static void cl_free_io_lock_link(const struct lu_env *env,
                                 struct cl_io_lock_link *link)
{
        OBD_FREE_PTR(link);
}

/**
 * Allocates new lock link, and uses it to add a lock to a lockset.
 */
int cl_io_lock_alloc_add(const struct lu_env *env, struct cl_io *io,
                         struct cl_lock_descr *descr)
{
        struct cl_io_lock_link *link;
        int result;

        ENTRY;
        OBD_ALLOC_PTR(link);
        if (link != NULL) {
                link->cill_descr     = *descr;
                link->cill_fini      = cl_free_io_lock_link;
                result = cl_io_lock_add(env, io, link);
                if (result) /* lock match */
                        link->cill_fini(env, link);
        } else
                result = -ENOMEM;

        RETURN(result);
}
EXPORT_SYMBOL(cl_io_lock_alloc_add);

/**
 * Starts io by calling cl_io_operations::cio_start() top-to-bottom.
 */
int cl_io_start(const struct lu_env *env, struct cl_io *io)
{
        const struct cl_io_slice *scan;
        int result = 0;

        LINVRNT(cl_io_is_loopable(io));
        LINVRNT(io->ci_state == CIS_LOCKED);
        LINVRNT(cl_io_invariant(io));
        ENTRY;

        io->ci_state = CIS_IO_GOING;
        cl_io_for_each(scan, io) {
                if (scan->cis_iop->op[io->ci_type].cio_start == NULL)
                        continue;
                result = scan->cis_iop->op[io->ci_type].cio_start(env, scan);
                if (result != 0)
                        break;
        }
        if (result >= 0)
                result = 0;
        RETURN(result);
}
EXPORT_SYMBOL(cl_io_start);

/**
 * Wait until current io iteration is finished by calling
 * cl_io_operations::cio_end() bottom-to-top.
 */
void cl_io_end(const struct lu_env *env, struct cl_io *io)
{
        const struct cl_io_slice *scan;

        LINVRNT(cl_io_is_loopable(io));
        LINVRNT(io->ci_state == CIS_IO_GOING);
        LINVRNT(cl_io_invariant(io));
        ENTRY;

        cl_io_for_each_reverse(scan, io) {
                if (scan->cis_iop->op[io->ci_type].cio_end != NULL)
                        scan->cis_iop->op[io->ci_type].cio_end(env, scan);
                /* TODO: error handling. */
        }
        io->ci_state = CIS_IO_FINISHED;
        EXIT;
}
EXPORT_SYMBOL(cl_io_end);

static const struct cl_page_slice *
cl_io_slice_page(const struct cl_io_slice *ios, struct cl_page *page)
{
        const struct cl_page_slice *slice;

        slice = cl_page_at(page, ios->cis_obj->co_lu.lo_dev->ld_type);
        LINVRNT(slice != NULL);
        return slice;
}

/**
 * True iff \a page is within \a io range.
 */
static int cl_page_in_io(const struct cl_page *page, const struct cl_io *io)
{
        int     result = 1;
        loff_t  start;
        loff_t  end;
        pgoff_t idx;

        idx = page->cp_index;
        switch (io->ci_type) {
        case CIT_READ:
        case CIT_WRITE:
                /*
                 * check that [start, end) and [pos, pos + count) extents
                 * overlap.
                 */
                if (!cl_io_is_append(io)) {
                        const struct cl_io_rw_common *crw = &(io->u.ci_rw);
                        start = cl_offset(page->cp_obj, idx);
                        end   = cl_offset(page->cp_obj, idx + 1);
                        result = crw->crw_pos < end &&
                                 start < crw->crw_pos + crw->crw_count;
                }
                break;
        case CIT_FAULT:
                result = io->u.ci_fault.ft_index == idx;
                break;
        default:
                LBUG();
        }
        return result;
}

/**
 * Called by read io, when page has to be read from the server.
 *
 * \see cl_io_operations::cio_read_page()
 */
int cl_io_read_page(const struct lu_env *env, struct cl_io *io,
                    struct cl_page *page)
{
        const struct cl_io_slice *scan;
        struct cl_2queue         *queue;
        int                    result = 0;

        LINVRNT(io->ci_type == CIT_READ || io->ci_type == CIT_FAULT);
        LINVRNT(cl_page_is_owned(page, io));
        LINVRNT(io->ci_state == CIS_IO_GOING || io->ci_state == CIS_LOCKED);
        LINVRNT(cl_page_in_io(page, io));
        LINVRNT(cl_io_invariant(io));
        ENTRY;

        queue = &io->ci_queue;

        cl_2queue_init(queue);
        /*
         * ->cio_read_page() methods called in the loop below are supposed to
         * never block waiting for network (the only subtle point is the
         * creation of new pages for read-ahead that might result in cache
         * shrinking, but currently only clean pages are shrunk and this
         * requires no network io).
         *
         * Should this ever starts blocking, retry loop would be needed for
         * "parallel io" (see CLO_REPEAT loops in cl_lock.c).
         */
        cl_io_for_each(scan, io) {
                if (scan->cis_iop->cio_read_page != NULL) {
                        const struct cl_page_slice *slice;

                        slice = cl_io_slice_page(scan, page);
                        LINVRNT(slice != NULL);
                        result = scan->cis_iop->cio_read_page(env, scan, slice);
                        if (result != 0)
                                break;
                }
        }
        if (result == 0)
                result = cl_io_submit_rw(env, io, CRT_READ, queue);
        /*
         * Unlock unsent pages in case of error.
         */
        cl_page_list_disown(env, io, &queue->c2_qin);
        cl_2queue_fini(env, queue);
        RETURN(result);
}
EXPORT_SYMBOL(cl_io_read_page);

/**
 * Called by write io to prepare page to receive data from user buffer.
 *
 * \see cl_io_operations::cio_prepare_write()
 */
int cl_io_prepare_write(const struct lu_env *env, struct cl_io *io,
                        struct cl_page *page, unsigned from, unsigned to)
{
        const struct cl_io_slice *scan;
        int result = 0;

        LINVRNT(io->ci_type == CIT_WRITE);
        LINVRNT(cl_page_is_owned(page, io));
        LINVRNT(io->ci_state == CIS_IO_GOING || io->ci_state == CIS_LOCKED);
        LINVRNT(cl_io_invariant(io));
        LASSERT(cl_page_in_io(page, io));
        ENTRY;

        cl_io_for_each_reverse(scan, io) {
                if (scan->cis_iop->cio_prepare_write != NULL) {
                        const struct cl_page_slice *slice;

                        slice = cl_io_slice_page(scan, page);
                        result = scan->cis_iop->cio_prepare_write(env, scan,
                                                                  slice,
                                                                  from, to);
                        if (result != 0)
                                break;
                }
        }
        RETURN(result);
}
EXPORT_SYMBOL(cl_io_prepare_write);

/**
 * Called by write io after user data were copied into a page.
 *
 * \see cl_io_operations::cio_commit_write()
 */
int cl_io_commit_write(const struct lu_env *env, struct cl_io *io,
                       struct cl_page *page, unsigned from, unsigned to)
{
        const struct cl_io_slice *scan;
        int result = 0;

        LINVRNT(io->ci_type == CIT_WRITE);
        LINVRNT(io->ci_state == CIS_IO_GOING || io->ci_state == CIS_LOCKED);
        LINVRNT(cl_io_invariant(io));
        /*
         * XXX Uh... not nice. Top level cl_io_commit_write() call (vvp->lov)
         * already called cl_page_cache_add(), moving page into CPS_CACHED
         * state. Better (and more general) way of dealing with such situation
         * is needed.
         */
        LASSERT(cl_page_is_owned(page, io) || page->cp_parent != NULL);
        LASSERT(cl_page_in_io(page, io));
        ENTRY;

        cl_io_for_each(scan, io) {
                if (scan->cis_iop->cio_commit_write != NULL) {
                        const struct cl_page_slice *slice;

                        slice = cl_io_slice_page(scan, page);
                        result = scan->cis_iop->cio_commit_write(env, scan,
                                                                 slice,
                                                                 from, to);
                        if (result != 0)
                                break;
                }
        }
        LINVRNT(result <= 0);
        RETURN(result);
}
EXPORT_SYMBOL(cl_io_commit_write);

/**
 * Submits a list of pages for immediate io.
 *
 * After the function gets returned, The submitted pages are moved to
 * queue->c2_qout queue, and queue->c2_qin contain both the pages don't need
 * to be submitted, and the pages are errant to submit.
 *
 * \returns 0 if at least one page was submitted, error code otherwise.
 * \see cl_io_operations::cio_submit()
 */
int cl_io_submit_rw(const struct lu_env *env, struct cl_io *io,
                    enum cl_req_type crt, struct cl_2queue *queue)
{
        const struct cl_io_slice *scan;
        int result = 0;

        LINVRNT(crt < ARRAY_SIZE(scan->cis_iop->req_op));
        ENTRY;

        cl_io_for_each(scan, io) {
                if (scan->cis_iop->req_op[crt].cio_submit == NULL)
                        continue;
                result = scan->cis_iop->req_op[crt].cio_submit(env, scan, crt,
                                                               queue);
                if (result != 0)
                        break;
        }
        /*
         * If ->cio_submit() failed, no pages were sent.
         */
        LASSERT(ergo(result != 0, list_empty(&queue->c2_qout.pl_pages)));
        RETURN(result);
}
EXPORT_SYMBOL(cl_io_submit_rw);

/**
 * Submit a sync_io and wait for the IO to be finished, or error happens.
 * If \a timeout is zero, it means to wait for the IO unconditionally.
 */
int cl_io_submit_sync(const struct lu_env *env, struct cl_io *io,
                      enum cl_req_type iot, struct cl_2queue *queue,
                      long timeout)
{
        struct cl_sync_io *anchor = &cl_env_info(env)->clt_anchor;
        struct cl_page *pg;
        int rc;

        cl_page_list_for_each(pg, &queue->c2_qin) {
                LASSERT(pg->cp_sync_io == NULL);
                pg->cp_sync_io = anchor;
        }

        cl_sync_io_init(anchor, queue->c2_qin.pl_nr);
        rc = cl_io_submit_rw(env, io, iot, queue);
        if (rc == 0) {
                /*
                 * If some pages weren't sent for any reason (e.g.,
                 * read found up-to-date pages in the cache, or write found
                 * clean pages), count them as completed to avoid infinite
                 * wait.
                 */
                 cl_page_list_for_each(pg, &queue->c2_qin) {
                        pg->cp_sync_io = NULL;
                        cl_sync_io_note(anchor, +1);
                 }

                 /* wait for the IO to be finished. */
                 rc = cl_sync_io_wait(env, io, &queue->c2_qout,
                                      anchor, timeout);
        } else {
                LASSERT(list_empty(&queue->c2_qout.pl_pages));
                cl_page_list_for_each(pg, &queue->c2_qin)
                        pg->cp_sync_io = NULL;
        }
        return rc;
}
EXPORT_SYMBOL(cl_io_submit_sync);

/**
 * Cancel an IO which has been submitted by cl_io_submit_rw.
 */
int cl_io_cancel(const struct lu_env *env, struct cl_io *io,
                 struct cl_page_list *queue)
{
        struct cl_page *page;
        int result = 0;

        CERROR("Canceling ongoing page trasmission\n");
        cl_page_list_for_each(page, queue) {
                int rc;

                LINVRNT(cl_page_in_io(page, io));
                rc = cl_page_cancel(env, page);
                result = result ?: rc;
        }
        return result;
}
EXPORT_SYMBOL(cl_io_cancel);

/**
 * Main io loop.
 *
 * Pumps io through iterations calling
 *
 *    - cl_io_iter_init()
 *
 *    - cl_io_lock()
 *
 *    - cl_io_start()
 *
 *    - cl_io_end()
 *
 *    - cl_io_unlock()
 *
 *    - cl_io_iter_fini()
 *
 * repeatedly until there is no more io to do.
 */
int cl_io_loop(const struct lu_env *env, struct cl_io *io)
{
        int result   = 0;

        LINVRNT(cl_io_is_loopable(io));
        ENTRY;

        do {
                size_t nob;

                io->ci_continue = 0;
                result = cl_io_iter_init(env, io);
                if (result == 0) {
                        nob    = io->ci_nob;
                        result = cl_io_lock(env, io);
                        if (result == 0) {
                                /*
                                 * Notify layers that locks has been taken,
                                 * and do actual i/o.
                                 *
                                 *   - llite: kms, short read;
                                 *   - llite: generic_file_read();
                                 */
                                result = cl_io_start(env, io);
                                /*
                                 * Send any remaining pending
                                 * io, etc.
                                 *
                                 *   - llite: ll_rw_stats_tally.
                                 */
                                cl_io_end(env, io);
                                cl_io_unlock(env, io);
                                cl_io_rw_advance(env, io, io->ci_nob - nob);
                        }
                }
                cl_io_iter_fini(env, io);
        } while (result == 0 && io->ci_continue);
        if (result == 0)
                result = io->ci_result;
        RETURN(result < 0 ? result : 0);
}
EXPORT_SYMBOL(cl_io_loop);

/**
 * Adds io slice to the cl_io.
 *
 * This is called by cl_object_operations::coo_io_init() methods to add a
 * per-layer state to the io. New state is added at the end of
 * cl_io::ci_layers list, that is, it is at the bottom of the stack.
 *
 * \see cl_lock_slice_add(), cl_req_slice_add(), cl_page_slice_add()
 */
void cl_io_slice_add(struct cl_io *io, struct cl_io_slice *slice,
                     struct cl_object *obj,
                     const struct cl_io_operations *ops)
{
        struct list_head *linkage = &slice->cis_linkage;

        LASSERT((linkage->prev == NULL && linkage->next == NULL) ||
                list_empty(linkage));
        ENTRY;

        list_add_tail(linkage, &io->ci_layers);
        slice->cis_io  = io;
        slice->cis_obj = obj;
        slice->cis_iop = ops;
        EXIT;
}
EXPORT_SYMBOL(cl_io_slice_add);


/**
 * Initializes page list.
 */
void cl_page_list_init(struct cl_page_list *plist)
{
        ENTRY;
        plist->pl_nr = 0;
        INIT_LIST_HEAD(&plist->pl_pages);
        plist->pl_owner = current;
        EXIT;
}
EXPORT_SYMBOL(cl_page_list_init);

/**
 * Adds a page to a page list.
 */
void cl_page_list_add(struct cl_page_list *plist, struct cl_page *page)
{
        ENTRY;
        /* it would be better to check that page is owned by "current" io, but
         * it is not passed here. */
        LASSERT(page->cp_owner != NULL);
        LINVRNT(plist->pl_owner == current);

        lockdep_off();
        mutex_lock(&page->cp_mutex);
        lockdep_on();
        LASSERT(list_empty(&page->cp_batch));
        list_add_tail(&page->cp_batch, &plist->pl_pages);
        ++plist->pl_nr;
        page->cp_queue_ref = lu_ref_add(&page->cp_reference, "queue", plist);
        cl_page_get(page);
        EXIT;
}
EXPORT_SYMBOL(cl_page_list_add);

/**
 * Removes a page from a page list.
 */
void cl_page_list_del(const struct lu_env *env,
                      struct cl_page_list *plist, struct cl_page *page)
{
        LASSERT(plist->pl_nr > 0);
        LINVRNT(plist->pl_owner == current);

        ENTRY;
        list_del_init(&page->cp_batch);
        lockdep_off();
        mutex_unlock(&page->cp_mutex);
        lockdep_on();
        --plist->pl_nr;
        lu_ref_del_at(&page->cp_reference, page->cp_queue_ref, "queue", plist);
        cl_page_put(env, page);
        EXIT;
}
EXPORT_SYMBOL(cl_page_list_del);

/**
 * Moves a page from one page list to another.
 */
void cl_page_list_move(struct cl_page_list *dst, struct cl_page_list *src,
                       struct cl_page *page)
{
        LASSERT(src->pl_nr > 0);
        LINVRNT(dst->pl_owner == current);
        LINVRNT(src->pl_owner == current);

        ENTRY;
        list_move_tail(&page->cp_batch, &dst->pl_pages);
        --src->pl_nr;
        ++dst->pl_nr;
        lu_ref_set_at(&page->cp_reference,
                      page->cp_queue_ref, "queue", src, dst);
        EXIT;
}
EXPORT_SYMBOL(cl_page_list_move);

/**
 * splice the cl_page_list, just as list head does
 */
void cl_page_list_splice(struct cl_page_list *list, struct cl_page_list *head)
{
        struct cl_page *page;
        struct cl_page *tmp;

        LINVRNT(list->pl_owner == current);
        LINVRNT(head->pl_owner == current);

        ENTRY;
        cl_page_list_for_each_safe(page, tmp, list)
                cl_page_list_move(head, list, page);
        EXIT;
}
EXPORT_SYMBOL(cl_page_list_splice);

void cl_page_disown0(const struct lu_env *env,
                     struct cl_io *io, struct cl_page *pg);

/**
 * Disowns pages in a queue.
 */
void cl_page_list_disown(const struct lu_env *env,
                         struct cl_io *io, struct cl_page_list *plist)
{
        struct cl_page *page;
        struct cl_page *temp;

        LINVRNT(plist->pl_owner == current);

        ENTRY;
        cl_page_list_for_each_safe(page, temp, plist) {
                LASSERT(plist->pl_nr > 0);

                list_del_init(&page->cp_batch);
                lockdep_off();
                mutex_unlock(&page->cp_mutex);
                lockdep_on();
                --plist->pl_nr;
                /*
                 * cl_page_disown0 rather than usual cl_page_disown() is used,
                 * because pages are possibly in CPS_FREEING state already due
                 * to the call to cl_page_list_discard().
                 */
                /*
                 * XXX cl_page_disown0() will fail if page is not locked.
                 */
                cl_page_disown0(env, io, page);
                lu_ref_del(&page->cp_reference, "queue", plist);
                cl_page_put(env, page);
        }
        EXIT;
}
EXPORT_SYMBOL(cl_page_list_disown);

/**
 * Releases pages from queue.
 */
void cl_page_list_fini(const struct lu_env *env, struct cl_page_list *plist)
{
        struct cl_page *page;
        struct cl_page *temp;

        LINVRNT(plist->pl_owner == current);

        ENTRY;
        cl_page_list_for_each_safe(page, temp, plist)
                cl_page_list_del(env, plist, page);
        LASSERT(plist->pl_nr == 0);
        EXIT;
}
EXPORT_SYMBOL(cl_page_list_fini);

/**
 * Owns all pages in a queue.
 */
int cl_page_list_own(const struct lu_env *env,
                     struct cl_io *io, struct cl_page_list *plist)
{
        struct cl_page *page;
        struct cl_page *temp;
        pgoff_t index = 0;
        int result;

        LINVRNT(plist->pl_owner == current);

        ENTRY;
        result = 0;
        cl_page_list_for_each_safe(page, temp, plist) {
                LASSERT(index <= page->cp_index);
                index = page->cp_index;
                if (cl_page_own(env, io, page) == 0)
                        result = result ?: page->cp_error;
                else
                        cl_page_list_del(env, plist, page);
        }
        RETURN(result);
}
EXPORT_SYMBOL(cl_page_list_own);

/**
 * Assumes all pages in a queue.
 */
void cl_page_list_assume(const struct lu_env *env,
                         struct cl_io *io, struct cl_page_list *plist)
{
        struct cl_page *page;

        LINVRNT(plist->pl_owner == current);

        cl_page_list_for_each(page, plist)
                cl_page_assume(env, io, page);
}
EXPORT_SYMBOL(cl_page_list_assume);

/**
 * Discards all pages in a queue.
 */
void cl_page_list_discard(const struct lu_env *env, struct cl_io *io,
                          struct cl_page_list *plist)
{
        struct cl_page *page;

        LINVRNT(plist->pl_owner == current);
        ENTRY;
        cl_page_list_for_each(page, plist)
                cl_page_discard(env, io, page);
        EXIT;
}
EXPORT_SYMBOL(cl_page_list_discard);

/**
 * Unmaps all pages in a queue from user virtual memory.
 */
int cl_page_list_unmap(const struct lu_env *env, struct cl_io *io,
                        struct cl_page_list *plist)
{
        struct cl_page *page;
        int result;

        LINVRNT(plist->pl_owner == current);
        ENTRY;
        result = 0;
        cl_page_list_for_each(page, plist) {
                result = cl_page_unmap(env, io, page);
                if (result != 0)
                        break;
        }
        RETURN(result);
}
EXPORT_SYMBOL(cl_page_list_unmap);

/**
 * Initialize dual page queue.
 */
void cl_2queue_init(struct cl_2queue *queue)
{
        ENTRY;
        cl_page_list_init(&queue->c2_qin);
        cl_page_list_init(&queue->c2_qout);
        EXIT;
}
EXPORT_SYMBOL(cl_2queue_init);

/**
 * Add a page to the incoming page list of 2-queue.
 */
void cl_2queue_add(struct cl_2queue *queue, struct cl_page *page)
{
        ENTRY;
        cl_page_list_add(&queue->c2_qin, page);
        EXIT;
}
EXPORT_SYMBOL(cl_2queue_add);

/**
 * Disown pages in both lists of a 2-queue.
 */
void cl_2queue_disown(const struct lu_env *env,
                      struct cl_io *io, struct cl_2queue *queue)
{
        ENTRY;
        cl_page_list_disown(env, io, &queue->c2_qin);
        cl_page_list_disown(env, io, &queue->c2_qout);
        EXIT;
}
EXPORT_SYMBOL(cl_2queue_disown);

/**
 * Discard (truncate) pages in both lists of a 2-queue.
 */
void cl_2queue_discard(const struct lu_env *env,
                       struct cl_io *io, struct cl_2queue *queue)
{
        ENTRY;
        cl_page_list_discard(env, io, &queue->c2_qin);
        cl_page_list_discard(env, io, &queue->c2_qout);
        EXIT;
}
EXPORT_SYMBOL(cl_2queue_discard);

/**
 * Assume to own the pages in cl_2queue
 */
void cl_2queue_assume(const struct lu_env *env,
                      struct cl_io *io, struct cl_2queue *queue)
{
        cl_page_list_assume(env, io, &queue->c2_qin);
        cl_page_list_assume(env, io, &queue->c2_qout);
}
EXPORT_SYMBOL(cl_2queue_assume);

/**
 * Finalize both page lists of a 2-queue.
 */
void cl_2queue_fini(const struct lu_env *env, struct cl_2queue *queue)
{
        ENTRY;
        cl_page_list_fini(env, &queue->c2_qout);
        cl_page_list_fini(env, &queue->c2_qin);
        EXIT;
}
EXPORT_SYMBOL(cl_2queue_fini);

/**
 * Initialize a 2-queue to contain \a page in its incoming page list.
 */
void cl_2queue_init_page(struct cl_2queue *queue, struct cl_page *page)
{
        ENTRY;
        cl_2queue_init(queue);
        cl_2queue_add(queue, page);
        EXIT;
}
EXPORT_SYMBOL(cl_2queue_init_page);

/**
 * Returns top-level io.
 *
 * \see cl_object_top(), cl_page_top().
 */
struct cl_io *cl_io_top(struct cl_io *io)
{
        ENTRY;
        while (io->ci_parent != NULL)
                io = io->ci_parent;
        RETURN(io);
}
EXPORT_SYMBOL(cl_io_top);

/**
 * Prints human readable representation of \a io to the \a f.
 */
void cl_io_print(const struct lu_env *env, void *cookie,
                 lu_printer_t printer, const struct cl_io *io)
{
}

/**
 * Adds request slice to the compound request.
 *
 * This is called by cl_device_operations::cdo_req_init() methods to add a
 * per-layer state to the request. New state is added at the end of
 * cl_req::crq_layers list, that is, it is at the bottom of the stack.
 *
 * \see cl_lock_slice_add(), cl_page_slice_add(), cl_io_slice_add()
 */
void cl_req_slice_add(struct cl_req *req, struct cl_req_slice *slice,
                      struct cl_device *dev,
                      const struct cl_req_operations *ops)
{
        ENTRY;
        list_add_tail(&slice->crs_linkage, &req->crq_layers);
        slice->crs_dev = dev;
        slice->crs_ops = ops;
        slice->crs_req = req;
        EXIT;
}
EXPORT_SYMBOL(cl_req_slice_add);

static void cl_req_free(const struct lu_env *env, struct cl_req *req)
{
        unsigned i;

        LASSERT(list_empty(&req->crq_pages));
        LASSERT(req->crq_nrpages == 0);
        LINVRNT(list_empty(&req->crq_layers));
        LINVRNT(equi(req->crq_nrobjs > 0, req->crq_o != NULL));
        ENTRY;

        if (req->crq_o != NULL) {
                for (i = 0; i < req->crq_nrobjs; ++i) {
                        struct cl_object *obj = req->crq_o[i].ro_obj;
                        if (obj != NULL) {
                                lu_object_ref_del_at(&obj->co_lu,
                                                     req->crq_o[i].ro_obj_ref,
                                                     "cl_req", req);
                                cl_object_put(env, obj);
                        }
                }
                OBD_FREE(req->crq_o, req->crq_nrobjs * sizeof req->crq_o[0]);
        }
        OBD_FREE_PTR(req);
        EXIT;
}

static int cl_req_init(const struct lu_env *env, struct cl_req *req,
                       struct cl_page *page)
{
        struct cl_device     *dev;
        struct cl_page_slice *slice;
        int result;

        ENTRY;
        result = 0;
        page = cl_page_top(page);
        do {
                list_for_each_entry(slice, &page->cp_layers, cpl_linkage) {
                        dev = lu2cl_dev(slice->cpl_obj->co_lu.lo_dev);
                        if (dev->cd_ops->cdo_req_init != NULL) {
                                result = dev->cd_ops->cdo_req_init(env,
                                                                   dev, req);
                                if (result != 0)
                                        break;
                        }
                }
                page = page->cp_child;
        } while (page != NULL && result == 0);
        RETURN(result);
}

/**
 * Invokes per-request transfer completion call-backs
 * (cl_req_operations::cro_completion()) bottom-to-top.
 */
void cl_req_completion(const struct lu_env *env, struct cl_req *req, int rc)
{
        struct cl_req_slice *slice;

        ENTRY;
        /*
         * for the lack of list_for_each_entry_reverse_safe()...
         */
        while (!list_empty(&req->crq_layers)) {
                slice = list_entry(req->crq_layers.prev,
                                       struct cl_req_slice, crs_linkage);
                list_del_init(&slice->crs_linkage);
                if (slice->crs_ops->cro_completion != NULL)
                        slice->crs_ops->cro_completion(env, slice, rc);
        }
        cl_req_free(env, req);
        EXIT;
}
EXPORT_SYMBOL(cl_req_completion);

/**
 * Allocates new transfer request.
 */
struct cl_req *cl_req_alloc(const struct lu_env *env, struct cl_page *page,
                            enum cl_req_type crt, int nr_objects)
{
        struct cl_req *req;

        LINVRNT(nr_objects > 0);
        ENTRY;

        OBD_ALLOC_PTR(req);
        if (req != NULL) {
                int result;

                OBD_ALLOC(req->crq_o, nr_objects * sizeof req->crq_o[0]);
                if (req->crq_o != NULL) {
                        req->crq_nrobjs = nr_objects;
                        req->crq_type = crt;
                        INIT_LIST_HEAD(&req->crq_pages);
                        INIT_LIST_HEAD(&req->crq_layers);
                        result = cl_req_init(env, req, page);
                } else
                        result = -ENOMEM;
                if (result != 0) {
                        cl_req_completion(env, req, result);
                        req = ERR_PTR(result);
                }
        } else
                req = ERR_PTR(-ENOMEM);
        RETURN(req);
}
EXPORT_SYMBOL(cl_req_alloc);

/**
 * Adds a page to a request.
 */
void cl_req_page_add(const struct lu_env *env,
                     struct cl_req *req, struct cl_page *page)
{
        struct cl_object  *obj;
        struct cl_req_obj *rqo;
        int i;

        ENTRY;
        page = cl_page_top(page);

        LASSERT(list_empty(&page->cp_flight));
        LASSERT(page->cp_req == NULL);

        CL_PAGE_DEBUG(D_PAGE, env, page, "req %p, %d, %u\n",
                      req, req->crq_type, req->crq_nrpages);

        list_add_tail(&page->cp_flight, &req->crq_pages);
        ++req->crq_nrpages;
        page->cp_req = req;
        obj = cl_object_top(page->cp_obj);
        for (i = 0, rqo = req->crq_o; obj != rqo->ro_obj; ++i, ++rqo) {
                if (rqo->ro_obj == NULL) {
                        rqo->ro_obj = obj;
                        cl_object_get(obj);
                        rqo->ro_obj_ref = lu_object_ref_add(&obj->co_lu,
                                                            "cl_req", req);
                        break;
                }
        }
        LASSERT(i < req->crq_nrobjs);
        EXIT;
}
EXPORT_SYMBOL(cl_req_page_add);

/**
 * Removes a page from a request.
 */
void cl_req_page_done(const struct lu_env *env, struct cl_page *page)
{
        struct cl_req *req = page->cp_req;

        ENTRY;
        page = cl_page_top(page);

        LASSERT(!list_empty(&page->cp_flight));
        LASSERT(req->crq_nrpages > 0);

        list_del_init(&page->cp_flight);
        --req->crq_nrpages;
        page->cp_req = NULL;
        EXIT;
}
EXPORT_SYMBOL(cl_req_page_done);

/**
 * Notifies layers that request is about to depart by calling
 * cl_req_operations::cro_prep() top-to-bottom.
 */
int cl_req_prep(const struct lu_env *env, struct cl_req *req)
{
        int i;
        int result;
        const struct cl_req_slice *slice;

        ENTRY;
        /*
         * Check that the caller of cl_req_alloc() didn't lie about the number
         * of objects.
         */
        for (i = 0; i < req->crq_nrobjs; ++i)
                LASSERT(req->crq_o[i].ro_obj != NULL);

        result = 0;
        list_for_each_entry(slice, &req->crq_layers, crs_linkage) {
                if (slice->crs_ops->cro_prep != NULL) {
                        result = slice->crs_ops->cro_prep(env, slice);
                        if (result != 0)
                                break;
                }
        }
        RETURN(result);
}
EXPORT_SYMBOL(cl_req_prep);

/**
 * Fills in attributes that are passed to server together with transfer. Only
 * attributes from \a flags may be touched. This can be called multiple times
 * for the same request.
 */
void cl_req_attr_set(const struct lu_env *env, struct cl_req *req,
                     struct cl_req_attr *attr, obd_valid flags)
{
        const struct cl_req_slice *slice;
        struct cl_page      *page;
        int i;

        LASSERT(!list_empty(&req->crq_pages));
        ENTRY;

        /* Take any page to use as a model. */
        page = list_entry(req->crq_pages.next, struct cl_page, cp_flight);

        for (i = 0; i < req->crq_nrobjs; ++i) {
                list_for_each_entry(slice, &req->crq_layers, crs_linkage) {
                        const struct cl_page_slice *scan;
                        const struct cl_object     *obj;

                        scan = cl_page_at(page,
                                          slice->crs_dev->cd_lu_dev.ld_type);
                        LASSERT(scan != NULL);
                        obj = scan->cpl_obj;
                        if (slice->crs_ops->cro_attr_set != NULL)
                                slice->crs_ops->cro_attr_set(env, slice, obj,
                                                             attr + i, flags);
                }
        }
        EXIT;
}
EXPORT_SYMBOL(cl_req_attr_set);

/* XXX complete(), init_completion(), and wait_for_completion(), until they are
 * implemented in libcfs. */
# include <linux/sched.h>

/**
 * Initialize synchronous io wait anchor, for transfer of \a nrpages pages.
 */
void cl_sync_io_init(struct cl_sync_io *anchor, int nrpages)
{
        ENTRY;
        init_waitqueue_head(&anchor->csi_waitq);
        atomic_set(&anchor->csi_sync_nr, nrpages);
        atomic_set(&anchor->csi_barrier, nrpages > 0);
        anchor->csi_sync_rc = 0;
        EXIT;
}
EXPORT_SYMBOL(cl_sync_io_init);

/**
 * Wait until all transfer completes. Transfer completion routine has to call
 * cl_sync_io_note() for every page.
 */
int cl_sync_io_wait(const struct lu_env *env, struct cl_io *io,
                    struct cl_page_list *queue, struct cl_sync_io *anchor,
                    long timeout)
{
        struct l_wait_info lwi = LWI_TIMEOUT_INTR(cfs_time_seconds(timeout),
                                                  NULL, NULL, NULL);
        int rc;
        ENTRY;

        LASSERT(timeout >= 0);

        rc = l_wait_event(anchor->csi_waitq,
                          atomic_read(&anchor->csi_sync_nr) == 0,
                          &lwi);
        if (rc < 0) {
                CERROR("SYNC IO failed with error: %d, try to cancel "
                       "%d remaining pages\n",
                       rc, atomic_read(&anchor->csi_sync_nr));

                (void)cl_io_cancel(env, io, queue);

                lwi = (struct l_wait_info) { 0 };
                (void)l_wait_event(anchor->csi_waitq,
                                   atomic_read(&anchor->csi_sync_nr) == 0,
                                   &lwi);
        } else {
                rc = anchor->csi_sync_rc;
        }
        LASSERT(atomic_read(&anchor->csi_sync_nr) == 0);
        cl_page_list_assume(env, io, queue);

        /* wait until cl_sync_io_note() has done wakeup */
        while (unlikely(atomic_read(&anchor->csi_barrier) != 0)) {
                cpu_relax();
        }

        POISON(anchor, 0x5a, sizeof *anchor);
        RETURN(rc);
}
EXPORT_SYMBOL(cl_sync_io_wait);

/**
 * Indicate that transfer of a single page completed.
 */
void cl_sync_io_note(struct cl_sync_io *anchor, int ioret)
{
        ENTRY;
        if (anchor->csi_sync_rc == 0 && ioret < 0)
                anchor->csi_sync_rc = ioret;
        /*
         * Synchronous IO done without releasing page lock (e.g., as a part of
         * ->{prepare,commit}_write(). Completion is used to signal the end of
         * IO.
         */
        LASSERT(atomic_read(&anchor->csi_sync_nr) > 0);
        if (atomic_dec_and_test(&anchor->csi_sync_nr)) {
                wake_up_all(&anchor->csi_waitq);
                /* it's safe to nuke or reuse anchor now */
                atomic_set(&anchor->csi_barrier, 0);
        }
        EXIT;
}
EXPORT_SYMBOL(cl_sync_io_note);