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.gnu.org/licenses/gpl-2.0.html
 *
 * GPL HEADER END
 */
/*
 * Copyright (c) 2008, 2010, Oracle and/or its affiliates. All rights reserved.
 * Use is subject to license terms.
 *
 * Copyright (c) 2011, 2015, 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>
 *   Author: Jinshan Xiong <jinshan.xiong@intel.com>
 */

#define DEBUG_SUBSYSTEM S_CLASS

#include "../include/obd_class.h"
#include "../include/obd_support.h"
#include "../include/lustre_fid.h"
#include <linux/list.h>
#include <linux/sched.h>
#include "../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;
}

/**
 * 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));
}

/**
 * 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));

	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)
			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:
		break;
	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();
	}
}
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));

	io->ci_type = iot;
	INIT_LIST_HEAD(&io->ci_lockset.cls_todo);
	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) {
			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)
		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);

	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);

	LU_OBJECT_HEADER(D_VFSTRACE, env, &io->ci_obj->co_lu,
			 "io range: %u [%llu, %llu) %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 int cl_lock_descr_sort(const struct cl_lock_descr *d0,
			      const struct cl_lock_descr *d1)
{
	return lu_fid_cmp(lu_object_fid(&d0->cld_obj->co_lu),
			  lu_object_fid(&d1->cld_obj->co_lu));
}

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

	/* 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) {
				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);
}

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;
}

static int cl_lockset_merge(const struct cl_lockset *set,
			    const struct cl_lock_descr *need)
{
	struct cl_io_lock_link *scan;

	list_for_each_entry(scan, &set->cls_todo, cill_linkage) {
		if (!cl_object_same(scan->cill_descr.cld_obj, need->cld_obj))
			continue;

		/* Merge locks for the same object because ldlm lock server
		 * may expand the lock extent, otherwise there is a deadlock
		 * case if two conflicted locks are queueud for the same object
		 * and lock server expands one lock to overlap the another.
		 * The side effect is that it can generate a multi-stripe lock
		 * that may cause casacading problem
		 */
		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_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;
	int result;

	result = 0;
	list_for_each_entry_safe(link, temp, &set->cls_todo, cill_linkage) {
		result = cl_lock_request(env, io, &link->cill_lock);
		if (result < 0)
			break;

		list_move(&link->cill_linkage, &set->cls_done);
	}
	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));

	cl_io_for_each(scan, io) {
		if (!scan->cis_iop->op[io->ci_type].cio_lock)
			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));

	set = &io->ci_lockset;

	list_for_each_entry_safe(link, temp, &set->cls_todo, cill_linkage) {
		list_del_init(&link->cill_linkage);
		if (link->cill_fini)
			link->cill_fini(env, link);
	}

	list_for_each_entry_safe(link, temp, &set->cls_done, cill_linkage) {
		list_del_init(&link->cill_linkage);
		cl_lock_release(env, &link->cill_lock);
		if (link->cill_fini)
			link->cill_fini(env, link);
	}

	cl_io_for_each_reverse(scan, io) {
		if (scan->cis_iop->op[io->ci_type].cio_unlock)
			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);
}
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));

	result = 0;
	cl_io_for_each(scan, io) {
		if (!scan->cis_iop->op[io->ci_type].cio_iter_init)
			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));

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

/**
 * Records that read or write io progressed \a nob bytes forward.
 */
static 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));

	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)
			scan->cis_iop->op[io->ci_type].cio_advance(env, scan,
								   nob);
	}
}

/**
 * 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;

	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)
{
	kfree(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;

	link = kzalloc(sizeof(*link), GFP_NOFS);
	if (link) {
		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));

	io->ci_state = CIS_IO_GOING;
	cl_io_for_each(scan, io) {
		if (!scan->cis_iop->op[io->ci_type].cio_start)
			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));

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

/**
 * 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_io_invariant(io));

	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) {
			const struct cl_page_slice *slice;

			slice = cl_io_slice_page(scan, page);
			LINVRNT(slice);
			result = scan->cis_iop->cio_read_page(env, scan, slice);
			if (result != 0)
				break;
		}
	}
	if (result == 0 && queue->c2_qin.pl_nr > 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);

/**
 * Commit a list of contiguous pages into writeback cache.
 *
 * \returns 0 if all pages committed, or errcode if error occurred.
 * \see cl_io_operations::cio_commit_async()
 */
int cl_io_commit_async(const struct lu_env *env, struct cl_io *io,
		       struct cl_page_list *queue, int from, int to,
		       cl_commit_cbt cb)
{
	const struct cl_io_slice *scan;
	int result = 0;

	cl_io_for_each(scan, io) {
		if (!scan->cis_iop->cio_commit_async)
			continue;
		result = scan->cis_iop->cio_commit_async(env, scan, queue,
							 from, to, cb);
		if (result != 0)
			break;
	}
	return result;
}
EXPORT_SYMBOL(cl_io_commit_async);

/**
 * 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;

	cl_io_for_each(scan, io) {
		if (!scan->cis_iop->cio_submit)
			continue;
		result = scan->cis_iop->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);

static void cl_page_list_assume(const struct lu_env *env,
				struct cl_io *io, struct cl_page_list *plist);

/**
 * 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);
		pg->cp_sync_io = anchor;
	}

	cl_sync_io_init(anchor, queue->c2_qin.pl_nr, &cl_sync_io_end);
	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(env, anchor, 1);
		}

		/* wait for the IO to be finished. */
		rc = cl_sync_io_wait(env, anchor, timeout);
		cl_page_list_assume(env, io, &queue->c2_qout);
	} 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);

/**
 * 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));

	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 && !linkage->next) ||
		list_empty(linkage));

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

/**
 * Initializes page list.
 */
void cl_page_list_init(struct cl_page_list *plist)
{
	plist->pl_nr = 0;
	INIT_LIST_HEAD(&plist->pl_pages);
	plist->pl_owner = current;
}
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)
{
	/* it would be better to check that page is owned by "current" io, but
	 * it is not passed here.
	 */
	LASSERT(page->cp_owner);
	LINVRNT(plist->pl_owner == current);

	LASSERT(list_empty(&page->cp_batch));
	list_add_tail(&page->cp_batch, &plist->pl_pages);
	++plist->pl_nr;
	lu_ref_add_at(&page->cp_reference, &page->cp_queue_ref, "queue", plist);
	cl_page_get(page);
}
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);
	LASSERT(cl_page_is_vmlocked(env, page));
	LINVRNT(plist->pl_owner == current);

	list_del_init(&page->cp_batch);
	--plist->pl_nr;
	lu_ref_del_at(&page->cp_reference, &page->cp_queue_ref, "queue", plist);
	cl_page_put(env, page);
}
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);

	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);
}
EXPORT_SYMBOL(cl_page_list_move);

/**
 * Moves a page from one page list to the head of another list.
 */
void cl_page_list_move_head(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);

	list_move(&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);
}
EXPORT_SYMBOL(cl_page_list_move_head);

/**
 * 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);

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


/**
 * 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);

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

		list_del_init(&page->cp_batch);
		--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_at(&page->cp_reference, &page->cp_queue_ref, "queue",
			      plist);
		cl_page_put(env, page);
	}
}
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);

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

/**
 * Assumes all pages in a queue.
 */
static 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);
}

/**
 * Discards all pages in a queue.
 */
static 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);
	cl_page_list_for_each(page, plist)
		cl_page_discard(env, io, page);
}

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

/**
 * 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)
{
	cl_page_list_disown(env, io, &queue->c2_qin);
	cl_page_list_disown(env, io, &queue->c2_qout);
}
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)
{
	cl_page_list_discard(env, io, &queue->c2_qin);
	cl_page_list_discard(env, io, &queue->c2_qout);
}
EXPORT_SYMBOL(cl_2queue_discard);

/**
 * Finalize both page lists of a 2-queue.
 */
void cl_2queue_fini(const struct lu_env *env, struct cl_2queue *queue)
{
	cl_page_list_fini(env, &queue->c2_qout);
	cl_page_list_fini(env, &queue->c2_qin);
}
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)
{
	cl_2queue_init(queue);
	/*
	 * Add a page to the incoming page list of 2-queue.
	 */
	cl_page_list_add(&queue->c2_qin, page);
}
EXPORT_SYMBOL(cl_2queue_init_page);

/**
 * Returns top-level io.
 *
 * \see cl_object_top()
 */
struct cl_io *cl_io_top(struct cl_io *io)
{
	while (io->ci_parent)
		io = io->ci_parent;
	return io;
}
EXPORT_SYMBOL(cl_io_top);

/**
 * 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)
{
	list_add_tail(&slice->crs_linkage, &req->crq_layers);
	slice->crs_dev = dev;
	slice->crs_ops = ops;
	slice->crs_req = req;
}
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));

	if (req->crq_o) {
		for (i = 0; i < req->crq_nrobjs; ++i) {
			struct cl_object *obj = req->crq_o[i].ro_obj;

			if (obj) {
				lu_object_ref_del_at(&obj->co_lu,
						     &req->crq_o[i].ro_obj_ref,
						     "cl_req", req);
				cl_object_put(env, obj);
			}
		}
		kfree(req->crq_o);
	}
	kfree(req);
}

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;

	result = 0;
	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) {
			result = dev->cd_ops->cdo_req_init(env, dev, req);
			if (result != 0)
				break;
		}
	}
	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;

	/*
	 * 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)
			slice->crs_ops->cro_completion(env, slice, rc);
	}
	cl_req_free(env, req);
}
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);

	req = kzalloc(sizeof(*req), GFP_NOFS);
	if (req) {
		int result;

		req->crq_type = crt;
		INIT_LIST_HEAD(&req->crq_pages);
		INIT_LIST_HEAD(&req->crq_layers);

		req->crq_o = kcalloc(nr_objects, sizeof(req->crq_o[0]),
				     GFP_NOFS);
		if (req->crq_o) {
			req->crq_nrobjs = nr_objects;
			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;
	unsigned int i;

	LASSERT(list_empty(&page->cp_flight));
	LASSERT(!page->cp_req);

	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) {
			rqo->ro_obj = obj;
			cl_object_get(obj);
			lu_object_ref_add_at(&obj->co_lu, &rqo->ro_obj_ref,
					     "cl_req", req);
			break;
		}
	}
	LASSERT(i < req->crq_nrobjs);
}
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;

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

	list_del_init(&page->cp_flight);
	--req->crq_nrpages;
	page->cp_req = NULL;
}
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)
{
	unsigned int i;
	int result;
	const struct cl_req_slice *slice;

	/*
	 * 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);

	result = 0;
	list_for_each_entry(slice, &req->crq_layers, crs_linkage) {
		if (slice->crs_ops->cro_prep) {
			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, u64 flags)
{
	const struct cl_req_slice *slice;
	struct cl_page	    *page;
	unsigned int i;

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

	/* 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);
			obj = scan->cpl_obj;
			if (slice->crs_ops->cro_attr_set)
				slice->crs_ops->cro_attr_set(env, slice, obj,
							     attr + i, flags);
		}
	}
}
EXPORT_SYMBOL(cl_req_attr_set);

/* cl_sync_io_callback assumes the caller must call cl_sync_io_wait() to
 * wait for the IO to finish.
 */
void cl_sync_io_end(const struct lu_env *env, struct cl_sync_io *anchor)
{
	wake_up_all(&anchor->csi_waitq);

	/* it's safe to nuke or reuse anchor now */
	atomic_set(&anchor->csi_barrier, 0);
}
EXPORT_SYMBOL(cl_sync_io_end);

/**
 * Initialize synchronous io wait anchor
 */
void cl_sync_io_init(struct cl_sync_io *anchor, int nr,
		     void (*end)(const struct lu_env *, struct cl_sync_io *))
{
	memset(anchor, 0, sizeof(*anchor));
	init_waitqueue_head(&anchor->csi_waitq);
	atomic_set(&anchor->csi_sync_nr, nr);
	atomic_set(&anchor->csi_barrier, nr > 0);
	anchor->csi_sync_rc = 0;
	anchor->csi_end_io = end;
	LASSERT(end);
}
EXPORT_SYMBOL(cl_sync_io_init);

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

	LASSERT(timeout >= 0);

	rc = l_wait_event(anchor->csi_waitq,
			  atomic_read(&anchor->csi_sync_nr) == 0,
			  &lwi);
	if (rc < 0) {
		CERROR("IO failed: %d, still wait for %d remaining entries\n",
		       rc, atomic_read(&anchor->csi_sync_nr));

		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);

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

	return rc;
}
EXPORT_SYMBOL(cl_sync_io_wait);

/**
 * Indicate that transfer of a single page completed.
 */
void cl_sync_io_note(const struct lu_env *env, struct cl_sync_io *anchor,
		     int ioret)
{
	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)) {
		LASSERT(anchor->csi_end_io);
		anchor->csi_end_io(env, anchor);
		/* Can't access anchor any more */
	}
}
EXPORT_SYMBOL(cl_sync_io_note);