/*
 * 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, 2013, Intel Corporation.
 */
/*
 * This file is part of Lustre, http://www.lustre.org/
 * Lustre is a trademark of Sun Microsystems, Inc.
 */

#include <linux/fs.h>
#include <linux/sched.h>
#include <linux/mm.h>
#include <linux/highmem.h>
#include <linux/pagemap.h>

#define DEBUG_SUBSYSTEM S_LLITE

#include <obd_support.h>
#include <lustre_dlm.h>
#include "llite_internal.h"

#define SA_OMITTED_ENTRY_MAX 8ULL

typedef enum {
	/** negative values are for error cases */
	SA_ENTRY_INIT = 0,      /** init entry */
	SA_ENTRY_SUCC = 1,      /** stat succeed */
	SA_ENTRY_INVA = 2,      /** invalid entry */
} se_state_t;

/* sa_entry is not refcounted: statahead thread allocates it and do async stat,
 * and in async stat callback ll_statahead_interpret() will add it into
 * sai_cb_entries, later statahead thread will call sa_handle_callback() to
 * instantiate entry and move it into sai_entries, and then only scanner process
 * can access and free it. */
struct sa_entry {
	/* link into sai_cb_entries or sai_entries */
	struct list_head	se_list;
	/* link into sai hash table locally */
	struct list_head	se_hash;
	/* entry index in the sai */
	__u64			se_index;
	/* low layer ldlm lock handle */
	__u64			se_handle;
	/* entry status */
	se_state_t		se_state;
	/* entry size, contains name */
	int			se_size;
	/* pointer to async getattr enqueue info */
	struct md_enqueue_info *se_minfo;
	/* pointer to the async getattr request */
	struct ptlrpc_request  *se_req;
	/* pointer to the target inode */
	struct inode	       *se_inode;
	/* entry name */
	struct qstr		se_qstr;
};

static unsigned int sai_generation = 0;
static DEFINE_SPINLOCK(sai_generation_lock);

static inline int sa_unhashed(struct sa_entry *entry)
{
	return list_empty(&entry->se_hash);
}

/*
 * The entry only can be released by the caller, it is necessary to hold lock.
 */
static inline int sa_ready(struct sa_entry *entry)
{
	smp_rmb();
	return (entry->se_state != SA_ENTRY_INIT);
}

static inline int sa_hash(int val)
{
	return val & LL_SA_CACHE_MASK;
}

/*
 * Insert entry to hash SA table.
 */
static inline void
sa_rehash(struct ll_statahead_info *sai, struct sa_entry *entry)
{
	int i = sa_hash(entry->se_qstr.hash);

	spin_lock(&sai->sai_cache_lock[i]);
	list_add_tail(&entry->se_hash, &sai->sai_cache[i]);
	spin_unlock(&sai->sai_cache_lock[i]);
}

/*
 * Remove entry from SA table.
 */
static inline void
sa_unhash(struct ll_statahead_info *sai, struct sa_entry *entry)
{
	int i = sa_hash(entry->se_qstr.hash);

	spin_lock(&sai->sai_cache_lock[i]);
	list_del_init(&entry->se_hash);
	spin_unlock(&sai->sai_cache_lock[i]);
}

static inline int agl_should_run(struct ll_statahead_info *sai,
                                 struct inode *inode)
{
	return (inode != NULL && S_ISREG(inode->i_mode) && sai->sai_agl_valid);
}

static inline struct ll_inode_info *
agl_first_entry(struct ll_statahead_info *sai)
{
	return list_entry(sai->sai_agls.next, struct ll_inode_info,
			  lli_agl_list);
}

static inline int sa_sent_full(struct ll_statahead_info *sai)
{
	return atomic_read(&sai->sai_cache_count) >= sai->sai_max;
}

static inline int sa_has_callback(struct ll_statahead_info *sai)
{
	return !list_empty(&sai->sai_interim_entries);
}

static inline int agl_list_empty(struct ll_statahead_info *sai)
{
	return list_empty(&sai->sai_agls);
}

/**
 * (1) hit ratio less than 80%
 * or
 * (2) consecutive miss more than 8
 * then means low hit.
 */
static inline int sa_low_hit(struct ll_statahead_info *sai)
{
        return ((sai->sai_hit > 7 && sai->sai_hit < 4 * sai->sai_miss) ||
                (sai->sai_consecutive_miss > 8));
}

/*
 * If the given index is behind of statahead window more than
 * SA_OMITTED_ENTRY_MAX, then it is old.
 */
static inline int is_omitted_entry(struct ll_statahead_info *sai, __u64 index)
{
        return ((__u64)sai->sai_max + index + SA_OMITTED_ENTRY_MAX <
                 sai->sai_index);
}

/* allocate sa_entry and add it into hash to let scanner process to find it */
static struct sa_entry *
sa_alloc(struct ll_statahead_info *sai, __u64 index, const char *name, int len)
{
	struct ll_inode_info *lli;
	struct sa_entry *entry;
	int entry_size;
	char *dname;
	ENTRY;

	entry_size = sizeof(struct sa_entry) + (len & ~3) + 4;
	OBD_ALLOC(entry, entry_size);
	if (unlikely(entry == NULL))
		RETURN(ERR_PTR(-ENOMEM));

	CDEBUG(D_READA, "alloc sa entry %.*s(%p) index "LPU64"\n",
	       len, name, entry, index);

	entry->se_index = index;

	entry->se_state = SA_ENTRY_INIT;
	entry->se_size = entry_size;
	dname = (char *)entry + sizeof(struct sa_entry);
	memcpy(dname, name, len);
	dname[len] = 0;
	entry->se_qstr.hash = full_name_hash(name, len);
	entry->se_qstr.len = len;
	entry->se_qstr.name = dname;

	lli = ll_i2info(sai->sai_inode);
	spin_lock(&lli->lli_sa_lock);
	INIT_LIST_HEAD(&entry->se_list);
	sa_rehash(sai, entry);
	spin_unlock(&lli->lli_sa_lock);

	atomic_inc(&sai->sai_cache_count);

	RETURN(entry);
}

/* free sa_entry which should have been unhashed and not in any list */
static void sa_free(struct ll_statahead_info *sai, struct sa_entry *entry)
{
	CDEBUG(D_READA, "free sa entry %.*s(%p) index "LPU64"\n",
	       entry->se_qstr.len, entry->se_qstr.name, entry,
	       entry->se_index);

	LASSERT(list_empty(&entry->se_list));
	LASSERT(sa_unhashed(entry));

	OBD_FREE(entry, entry->se_size);
	atomic_dec(&sai->sai_cache_count);
}

/* find sa_entry by name, used by directory scanner, lock is not needed because
 * only scanner can remove the entry from hash.
 */
static struct sa_entry *
sa_get(struct ll_statahead_info *sai, const struct qstr *qstr)
{
	struct sa_entry *entry;
	int i = sa_hash(qstr->hash);

	list_for_each_entry(entry, &sai->sai_cache[i], se_hash) {
		if (entry->se_qstr.hash == qstr->hash &&
		    entry->se_qstr.len == qstr->len &&
		    memcmp(entry->se_qstr.name, qstr->name, qstr->len) == 0)
			return entry;
	}
	return NULL;
}

static inline void
sa_kill(struct ll_statahead_info *sai, struct sa_entry *entry)
{
	struct ll_inode_info *lli = ll_i2info(sai->sai_inode);

	LASSERT(!sa_unhashed(entry));
	LASSERT(!list_empty(&entry->se_list));
	LASSERT(sa_ready(entry));

	sa_unhash(sai, entry);

	spin_lock(&lli->lli_sa_lock);
	list_del_init(&entry->se_list);
	spin_unlock(&lli->lli_sa_lock);

	if (entry->se_inode != NULL)
		iput(entry->se_inode);

	sa_free(sai, entry);
}

/* called by scanner after use, sa_entry will be killed */
static void
sa_put(struct ll_statahead_info *sai, struct sa_entry *entry)
{
	struct sa_entry *tmp, *next;

	if (entry != NULL && entry->se_state == SA_ENTRY_SUCC) {
		struct ll_sb_info *sbi = ll_i2sbi(sai->sai_inode);

		sai->sai_hit++;
		sai->sai_consecutive_miss = 0;
		sai->sai_max = min(2 * sai->sai_max, sbi->ll_sa_max);
	} else {
		sai->sai_miss++;
		sai->sai_consecutive_miss++;
	}

	if (entry != NULL)
		sa_kill(sai, entry);

	/* kill old completed entries, only scanner process does this, no need
	 * to lock */
	list_for_each_entry_safe(tmp, next, &sai->sai_entries, se_list) {
		if (!is_omitted_entry(sai, tmp->se_index))
			break;
		sa_kill(sai, tmp);
	}

	wake_up(&sai->sai_thread.t_ctl_waitq);
}

/* update state and sort add entry to sai_entries by index, return true if
 * scanner is waiting on this entry. */
static bool
__sa_make_ready(struct ll_statahead_info *sai, struct sa_entry *entry, int ret)
{
	struct sa_entry *se;
	struct list_head *pos = &sai->sai_entries;

	LASSERT(!sa_ready(entry));
	LASSERT(list_empty(&entry->se_list));

	entry->se_state = ret < 0 ? SA_ENTRY_INVA : SA_ENTRY_SUCC;

	list_for_each_entry_reverse(se, &sai->sai_entries, se_list) {
		if (se->se_index < entry->se_index) {
			pos = &se->se_list;
			break;
		}
	}
	list_add(&entry->se_list, pos);

	return (entry->se_index == sai->sai_index_wait);
}

/* release resources used in async stat RPC, complete entry information and
 * wakeup if necessary */
static void
sa_make_ready(struct ll_statahead_info *sai, struct sa_entry *entry, int ret)
{
	struct ll_inode_info *lli = ll_i2info(sai->sai_inode);
	struct md_enqueue_info *minfo = entry->se_minfo;
	struct ptlrpc_request *req = entry->se_req;
	bool wakeup;

	/* release resources used in RPC */
	if (minfo) {
		entry->se_minfo = NULL;
		ll_intent_release(&minfo->mi_it);
		iput(minfo->mi_dir);
		OBD_FREE_PTR(minfo);
	}

	if (req) {
		entry->se_req = NULL;
		ptlrpc_req_finished(req);
	}

	spin_lock(&lli->lli_sa_lock);
	wakeup = __sa_make_ready(sai, entry, ret);
	spin_unlock(&lli->lli_sa_lock);

	if (wakeup)
		wake_up(&sai->sai_waitq);
}

/*
 * Insert inode into the list of sai_agls.
 */
static void ll_agl_add(struct ll_statahead_info *sai,
                       struct inode *inode, int index)
{
	struct ll_inode_info *child  = ll_i2info(inode);
	struct ll_inode_info *parent = ll_i2info(sai->sai_inode);
	int                   added  = 0;

	spin_lock(&child->lli_agl_lock);
	if (child->lli_agl_index == 0) {
		child->lli_agl_index = index;
		spin_unlock(&child->lli_agl_lock);

		LASSERT(list_empty(&child->lli_agl_list));

		igrab(inode);
		spin_lock(&parent->lli_agl_lock);
		if (agl_list_empty(sai))
			added = 1;
		list_add_tail(&child->lli_agl_list, &sai->sai_agls);
		spin_unlock(&parent->lli_agl_lock);
	} else {
		spin_unlock(&child->lli_agl_lock);
	}

	if (added > 0)
		wake_up(&sai->sai_agl_thread.t_ctl_waitq);
}

static struct ll_statahead_info *ll_sai_alloc(void)
{
	struct ll_statahead_info *sai;
	int                       i;
	ENTRY;

	OBD_ALLOC_PTR(sai);
	if (!sai)
		RETURN(NULL);

	atomic_set(&sai->sai_refcount, 1);

	spin_lock(&sai_generation_lock);
	sai->sai_generation = ++sai_generation;
	if (unlikely(sai_generation == 0))
		sai->sai_generation = ++sai_generation;
	spin_unlock(&sai_generation_lock);

	sai->sai_max = LL_SA_RPC_MIN;
	sai->sai_index = 1;
	init_waitqueue_head(&sai->sai_waitq);
	init_waitqueue_head(&sai->sai_thread.t_ctl_waitq);
	init_waitqueue_head(&sai->sai_agl_thread.t_ctl_waitq);

	INIT_LIST_HEAD(&sai->sai_interim_entries);
	INIT_LIST_HEAD(&sai->sai_entries);
	INIT_LIST_HEAD(&sai->sai_agls);

	for (i = 0; i < LL_SA_CACHE_SIZE; i++) {
		INIT_LIST_HEAD(&sai->sai_cache[i]);
		spin_lock_init(&sai->sai_cache_lock[i]);
	}
	atomic_set(&sai->sai_cache_count, 0);

	RETURN(sai);
}

static inline struct ll_statahead_info *ll_sai_get(struct inode *dir)
{
	struct ll_inode_info *lli = ll_i2info(dir);
	struct ll_statahead_info *sai = NULL;

	spin_lock(&lli->lli_sa_lock);
	sai = lli->lli_sai;
	if (sai != NULL)
		atomic_inc(&sai->sai_refcount);
	spin_unlock(&lli->lli_sa_lock);

	return sai;
}

static void ll_sai_put(struct ll_statahead_info *sai)
{
	struct ll_inode_info *lli = ll_i2info(sai->sai_inode);

	if (atomic_dec_and_lock(&sai->sai_refcount, &lli->lli_sa_lock)) {
		struct sa_entry *entry, *next;
		struct ll_sb_info *sbi = ll_i2sbi(sai->sai_inode);

		lli->lli_sai = NULL;
		spin_unlock(&lli->lli_sa_lock);

		LASSERT(thread_is_stopped(&sai->sai_thread));
		LASSERT(thread_is_stopped(&sai->sai_agl_thread));
		LASSERT(sai->sai_sent == sai->sai_replied);
		LASSERT(!sa_has_callback(sai));

		list_for_each_entry_safe(entry, next, &sai->sai_entries,
					 se_list)
			sa_kill(sai, entry);

		LASSERT(atomic_read(&sai->sai_cache_count) == 0);
		LASSERT(agl_list_empty(sai));

		iput(sai->sai_inode);
		OBD_FREE_PTR(sai);
		atomic_dec(&sbi->ll_sa_running);
	}
}

/* Do NOT forget to drop inode refcount when into sai_agls. */
static void ll_agl_trigger(struct inode *inode, struct ll_statahead_info *sai)
{
	struct ll_inode_info *lli = ll_i2info(inode);
	__u64 index = lli->lli_agl_index;
	int rc;
	ENTRY;

	LASSERT(list_empty(&lli->lli_agl_list));

        /* AGL maybe fall behind statahead with one entry */
        if (is_omitted_entry(sai, index + 1)) {
                lli->lli_agl_index = 0;
                iput(inode);
                RETURN_EXIT;
        }

        /* Someone is in glimpse (sync or async), do nothing. */
	rc = down_write_trylock(&lli->lli_glimpse_sem);
        if (rc == 0) {
                lli->lli_agl_index = 0;
                iput(inode);
                RETURN_EXIT;
        }

        /*
         * Someone triggered glimpse within 1 sec before.
         * 1) The former glimpse succeeded with glimpse lock granted by OST, and
         *    if the lock is still cached on client, AGL needs to do nothing. If
         *    it is cancelled by other client, AGL maybe cannot obtaion new lock
         *    for no glimpse callback triggered by AGL.
         * 2) The former glimpse succeeded, but OST did not grant glimpse lock.
         *    Under such case, it is quite possible that the OST will not grant
         *    glimpse lock for AGL also.
         * 3) The former glimpse failed, compared with other two cases, it is
         *    relative rare. AGL can ignore such case, and it will not muchly
         *    affect the performance.
         */
        if (lli->lli_glimpse_time != 0 &&
            cfs_time_before(cfs_time_shift(-1), lli->lli_glimpse_time)) {
		up_write(&lli->lli_glimpse_sem);
                lli->lli_agl_index = 0;
                iput(inode);
                RETURN_EXIT;
        }

        CDEBUG(D_READA, "Handling (init) async glimpse: inode = "
               DFID", idx = "LPU64"\n", PFID(&lli->lli_fid), index);

        cl_agl(inode);
        lli->lli_agl_index = 0;
        lli->lli_glimpse_time = cfs_time_current();
	up_write(&lli->lli_glimpse_sem);

        CDEBUG(D_READA, "Handled (init) async glimpse: inode= "
               DFID", idx = "LPU64", rc = %d\n",
               PFID(&lli->lli_fid), index, rc);

        iput(inode);

        EXIT;
}

/* prepare inode for sa entry, add it into agl list, now sa_entry is ready
 * to be used by scanner process. */
static void sa_instantiate(struct ll_statahead_info *sai,
				 struct sa_entry *entry)
{
	struct inode *dir = sai->sai_inode;
	struct inode *child;
	struct md_enqueue_info *minfo;
	struct lookup_intent *it;
	struct ptlrpc_request *req;
	struct mdt_body *body;
	int rc = 0;
	ENTRY;

        LASSERT(entry->se_handle != 0);

        minfo = entry->se_minfo;
        it = &minfo->mi_it;
        req = entry->se_req;
        body = req_capsule_server_get(&req->rq_pill, &RMF_MDT_BODY);
        if (body == NULL)
                GOTO(out, rc = -EFAULT);

        child = entry->se_inode;
        if (child == NULL) {
                /*
                 * lookup.
                 */
                LASSERT(fid_is_zero(&minfo->mi_data.op_fid2));

                /* XXX: No fid in reply, this is probaly cross-ref case.
                 * SA can't handle it yet. */
		if (body->mbo_valid & OBD_MD_MDS)
			GOTO(out, rc = -EAGAIN);
	} else {
		/*
		 * revalidate.
		 */
		/* unlinked and re-created with the same name */
		if (unlikely(!lu_fid_eq(&minfo->mi_data.op_fid2,
					&body->mbo_fid1))) {
                        entry->se_inode = NULL;
                        iput(child);
                        child = NULL;
                }
        }

        it->d.lustre.it_lock_handle = entry->se_handle;
	rc = md_revalidate_lock(ll_i2mdexp(dir), it, ll_inode2fid(dir), NULL);
        if (rc != 1)
                GOTO(out, rc = -EAGAIN);

        rc = ll_prep_inode(&child, req, dir->i_sb, it);
        if (rc)
                GOTO(out, rc);

	CDEBUG(D_READA, "%s: setting %.*s"DFID" l_data to inode %p\n",
	       ll_get_fsname(child->i_sb, NULL, 0),
	       entry->se_qstr.len, entry->se_qstr.name,
	       PFID(ll_inode2fid(child)), child);
        ll_set_lock_data(ll_i2sbi(dir)->ll_md_exp, child, it, NULL);

        entry->se_inode = child;

        if (agl_should_run(sai, child))
                ll_agl_add(sai, child, entry->se_index);

        EXIT;

out:
	/* sa_make_ready() will drop ldlm ibits lock refcount by calling
	 * ll_intent_drop_lock() in spite of failures. Do not worry about
	 * calling ll_intent_drop_lock() more than once. */
	sa_make_ready(sai, entry, rc);
}

/* once there are async stat replies, instantiate sa_entry */
static void sa_handle_callback(struct ll_statahead_info *sai)
{
	struct ll_inode_info *lli;

	lli = ll_i2info(sai->sai_inode);

	while (sa_has_callback(sai)) {
		struct sa_entry *entry;

		spin_lock(&lli->lli_sa_lock);
		if (unlikely(!sa_has_callback(sai))) {
			spin_unlock(&lli->lli_sa_lock);
			break;
		}
		entry = list_entry(sai->sai_interim_entries.next,
				   struct sa_entry, se_list);
		list_del_init(&entry->se_list);
		spin_unlock(&lli->lli_sa_lock);

		sa_instantiate(sai, entry);
	}

	spin_lock(&lli->lli_agl_lock);
	while (!agl_list_empty(sai)) {
		struct ll_inode_info *clli;

		clli = agl_first_entry(sai);
		list_del_init(&clli->lli_agl_list);
		spin_unlock(&lli->lli_agl_lock);

		ll_agl_trigger(&clli->lli_vfs_inode, sai);

		spin_lock(&lli->lli_agl_lock);
	}
	spin_unlock(&lli->lli_agl_lock);
}

/* callback for async stat, because this is called in ptlrpcd context, we only
 * put sa_entry in sai_cb_entries list, and let sa_handle_callback() to really
 * prepare inode and instantiate sa_entry later. */
static int ll_statahead_interpret(struct ptlrpc_request *req,
				  struct md_enqueue_info *minfo, int rc)
{
	struct lookup_intent *it = &minfo->mi_it;
	struct inode *dir = minfo->mi_dir;
	struct ll_inode_info *lli = ll_i2info(dir);
	struct ll_statahead_info *sai = lli->lli_sai;
	struct sa_entry *entry = (struct sa_entry *)minfo->mi_cbdata;
	__u64 handle = 0;
	bool wakeup;
	ENTRY;

	if (it_disposition(it, DISP_LOOKUP_NEG))
		rc = -ENOENT;

	/* because statahead thread will wait for all inflight RPC to finish,
	 * sai should be always valid, no need to refcount */
	LASSERT(sai != NULL);
	LASSERT(!thread_is_stopped(&sai->sai_thread));
	LASSERT(entry != NULL);

	CDEBUG(D_READA, "sa_entry %.*s rc %d\n",
	       entry->se_qstr.len, entry->se_qstr.name, rc);

	if (rc != 0) {
		ll_intent_release(it);
		iput(dir);
		OBD_FREE_PTR(minfo);
	} else {
		/* release ibits lock ASAP to avoid deadlock when statahead
		 * thread enqueues lock on parent in readdir and another
		 * process enqueues lock on child with parent lock held, eg.
		 * unlink. */
		handle = it->d.lustre.it_lock_handle;
		ll_intent_drop_lock(it);
	}

	spin_lock(&lli->lli_sa_lock);
	if (rc != 0) {
		wakeup = __sa_make_ready(sai, entry, rc);
	} else {
		entry->se_minfo = minfo;
		entry->se_req = ptlrpc_request_addref(req);
		/* Release the async ibits lock ASAP to avoid deadlock
		 * when statahead thread tries to enqueue lock on parent
		 * for readpage and other tries to enqueue lock on child
		 * with parent's lock held, for example: unlink. */
		entry->se_handle = handle;
		wakeup = !sa_has_callback(sai);
		list_add_tail(&entry->se_list, &sai->sai_interim_entries);
	}
	sai->sai_replied++;
	if (wakeup)
		wake_up(&sai->sai_thread.t_ctl_waitq);
	spin_unlock(&lli->lli_sa_lock);

	RETURN(rc);
}

static void sa_fini_data(struct md_enqueue_info *minfo,
                         struct ldlm_enqueue_info *einfo)
{
        LASSERT(minfo && einfo);
        iput(minfo->mi_dir);
        capa_put(minfo->mi_data.op_capa1);
        capa_put(minfo->mi_data.op_capa2);
        OBD_FREE_PTR(minfo);
        OBD_FREE_PTR(einfo);
}

/**
 * There is race condition between "capa_put" and "ll_statahead_interpret" for
 * accessing "op_data.op_capa[1,2]" as following:
 * "capa_put" releases "op_data.op_capa[1,2]"'s reference count after calling
 * "md_intent_getattr_async". But "ll_statahead_interpret" maybe run first, and
 * fill "op_data.op_capa[1,2]" as POISON, then cause "capa_put" access invalid
 * "ocapa". So here reserve "op_data.op_capa[1,2]" in "pcapa" before calling
 * "md_intent_getattr_async".
 */
static int sa_prep_data(struct inode *dir, struct inode *child,
			struct sa_entry *entry, struct md_enqueue_info **pmi,
			struct ldlm_enqueue_info **pei,
			struct obd_capa **pcapa)
{
        struct qstr              *qstr = &entry->se_qstr;
        struct md_enqueue_info   *minfo;
        struct ldlm_enqueue_info *einfo;
        struct md_op_data        *op_data;

        OBD_ALLOC_PTR(einfo);
        if (einfo == NULL)
                return -ENOMEM;

        OBD_ALLOC_PTR(minfo);
        if (minfo == NULL) {
                OBD_FREE_PTR(einfo);
                return -ENOMEM;
        }

        op_data = ll_prep_md_op_data(&minfo->mi_data, dir, child, qstr->name,
                                     qstr->len, 0, LUSTRE_OPC_ANY, NULL);
        if (IS_ERR(op_data)) {
                OBD_FREE_PTR(einfo);
                OBD_FREE_PTR(minfo);
                return PTR_ERR(op_data);
        }

	minfo->mi_it.it_op = IT_GETATTR;
	minfo->mi_dir = igrab(dir);
	minfo->mi_cb = ll_statahead_interpret;
	minfo->mi_cbdata = entry;

        einfo->ei_type   = LDLM_IBITS;
        einfo->ei_mode   = it_to_lock_mode(&minfo->mi_it);
        einfo->ei_cb_bl  = ll_md_blocking_ast;
        einfo->ei_cb_cp  = ldlm_completion_ast;
        einfo->ei_cb_gl  = NULL;
        einfo->ei_cbdata = NULL;

        *pmi = minfo;
        *pei = einfo;
        pcapa[0] = op_data->op_capa1;
        pcapa[1] = op_data->op_capa2;

        return 0;
}

static int sa_lookup(struct inode *dir, struct sa_entry *entry)
{
	struct md_enqueue_info   *minfo;
	struct ldlm_enqueue_info *einfo;
	struct obd_capa          *capas[2];
	int                       rc;
	ENTRY;

	rc = sa_prep_data(dir, NULL, entry, &minfo, &einfo, capas);
	if (rc)
		RETURN(rc);

	rc = md_intent_getattr_async(ll_i2mdexp(dir), minfo, einfo);
	if (!rc) {
		capa_put(capas[0]);
		capa_put(capas[1]);
	} else {
		sa_fini_data(minfo, einfo);
	}

	RETURN(rc);
}

/**
 * similar to ll_revalidate_it().
 * \retval      1 -- dentry valid
 * \retval      0 -- will send stat-ahead request
 * \retval others -- prepare stat-ahead request failed
 */
static int sa_revalidate(struct inode *dir, struct sa_entry *entry,
			 struct dentry *dentry)
{
	struct inode *inode = dentry->d_inode;
	struct lookup_intent it = { .it_op = IT_GETATTR,
				    .d.lustre.it_lock_handle = 0 };
	struct md_enqueue_info *minfo;
	struct ldlm_enqueue_info *einfo;
	struct obd_capa *capas[2];
	int rc;
	ENTRY;

	if (unlikely(inode == NULL))
		RETURN(1);

	if (d_mountpoint(dentry))
		RETURN(1);

	entry->se_inode = igrab(inode);
	rc = md_revalidate_lock(ll_i2mdexp(dir), &it, ll_inode2fid(inode),
				NULL);
	if (rc == 1) {
		entry->se_handle = it.d.lustre.it_lock_handle;
		ll_intent_release(&it);
		RETURN(1);
	}

	rc = sa_prep_data(dir, inode, entry, &minfo, &einfo, capas);
	if (rc) {
		entry->se_inode = NULL;
		iput(inode);
		RETURN(rc);
	}

	rc = md_intent_getattr_async(ll_i2mdexp(dir), minfo, einfo);
	if (!rc) {
		capa_put(capas[0]);
		capa_put(capas[1]);
	} else {
		entry->se_inode = NULL;
		iput(inode);
		sa_fini_data(minfo, einfo);
	}

	RETURN(rc);
}

static void sa_statahead(struct dentry *parent, const char *name, int len)
{
	struct inode *dir = parent->d_inode;
	struct ll_inode_info *lli = ll_i2info(dir);
	struct ll_statahead_info *sai = lli->lli_sai;
	struct dentry *dentry = NULL;
	struct sa_entry *entry;
	int rc;
	ENTRY;

	entry = sa_alloc(sai, sai->sai_index, name, len);
	if (IS_ERR(entry))
		RETURN_EXIT;

	dentry = d_lookup(parent, &entry->se_qstr);
	if (!dentry) {
		rc = sa_lookup(dir, entry);
	} else {
		rc = sa_revalidate(dir, entry, dentry);
		if (rc == 1 && agl_should_run(sai, dentry->d_inode))
			ll_agl_add(sai, dentry->d_inode, entry->se_index);
	}

	if (dentry != NULL)
		dput(dentry);

	if (rc != 0)
		sa_make_ready(sai, entry, rc);
	else
		sai->sai_sent++;

	sai->sai_index++;

	EXIT;
}

static int ll_agl_thread(void *arg)
{
	struct dentry *parent = (struct dentry *)arg;
	struct inode *dir = parent->d_inode;
	struct ll_inode_info *plli = ll_i2info(dir);
	struct ll_inode_info *clli;
	struct ll_sb_info *sbi = ll_i2sbi(dir);
	struct ll_statahead_info *sai;
	struct ptlrpc_thread *thread;
	struct l_wait_info lwi = { 0 };
	ENTRY;


	sai = ll_sai_get(dir);
	thread = &sai->sai_agl_thread;
	thread->t_pid = current_pid();
	CDEBUG(D_READA, "agl thread started: sai %p, parent %.*s\n",
	       sai, parent->d_name.len, parent->d_name.name);

	atomic_inc(&sbi->ll_agl_total);
	spin_lock(&plli->lli_agl_lock);
	sai->sai_agl_valid = 1;
	if (thread_is_init(thread))
		/* If someone else has changed the thread state
		 * (e.g. already changed to SVC_STOPPING), we can't just
		 * blindly overwrite that setting. */
		thread_set_flags(thread, SVC_RUNNING);
	spin_unlock(&plli->lli_agl_lock);
	wake_up(&thread->t_ctl_waitq);

        while (1) {
                l_wait_event(thread->t_ctl_waitq,
                             !agl_list_empty(sai) ||
                             !thread_is_running(thread),
                             &lwi);

                if (!thread_is_running(thread))
                        break;

		spin_lock(&plli->lli_agl_lock);
		/* The statahead thread maybe help to process AGL entries,
		 * so check whether list empty again. */
		if (!agl_list_empty(sai)) {
			clli = agl_first_entry(sai);
			list_del_init(&clli->lli_agl_list);
			spin_unlock(&plli->lli_agl_lock);
			ll_agl_trigger(&clli->lli_vfs_inode, sai);
		} else {
			spin_unlock(&plli->lli_agl_lock);
		}
	}

	spin_lock(&plli->lli_agl_lock);
	sai->sai_agl_valid = 0;
	while (!agl_list_empty(sai)) {
		clli = agl_first_entry(sai);
		list_del_init(&clli->lli_agl_list);
		spin_unlock(&plli->lli_agl_lock);
		clli->lli_agl_index = 0;
		iput(&clli->lli_vfs_inode);
		spin_lock(&plli->lli_agl_lock);
	}
	thread_set_flags(thread, SVC_STOPPED);
	spin_unlock(&plli->lli_agl_lock);
	wake_up(&thread->t_ctl_waitq);
	ll_sai_put(sai);
	CDEBUG(D_READA, "agl thread stopped: sai %p, parent %.*s\n",
	       sai, parent->d_name.len, parent->d_name.name);
	RETURN(0);
}

static void ll_start_agl(struct dentry *parent, struct ll_statahead_info *sai)
{
	struct ptlrpc_thread *thread = &sai->sai_agl_thread;
	struct l_wait_info    lwi    = { 0 };
	struct ll_inode_info  *plli;
	struct task_struct	      *task;
	ENTRY;

	CDEBUG(D_READA, "start agl thread: sai %p, parent %.*s\n",
	       sai, parent->d_name.len, parent->d_name.name);

	plli = ll_i2info(parent->d_inode);
	task = kthread_run(ll_agl_thread, parent,
			       "ll_agl_%u", plli->lli_opendir_pid);
	if (IS_ERR(task)) {
		CERROR("can't start ll_agl thread, rc: %ld\n", PTR_ERR(task));
		thread_set_flags(thread, SVC_STOPPED);
		RETURN_EXIT;
	}

	l_wait_event(thread->t_ctl_waitq,
		     thread_is_running(thread) || thread_is_stopped(thread),
		     &lwi);
	EXIT;
}

static int ll_statahead_thread(void *arg)
{
	struct dentry *parent = (struct dentry *)arg;
	struct inode *dir = parent->d_inode;
	struct ll_inode_info *lli = ll_i2info(dir);
	struct ll_sb_info *sbi = ll_i2sbi(dir);
	struct ll_statahead_info *sai;
	struct ptlrpc_thread *thread;
	struct ptlrpc_thread *agl_thread;
	int first = 0;
	struct md_op_data *op_data;
	struct ll_dir_chain chain;
	struct l_wait_info lwi = { 0 };
	struct page *page = NULL;
	__u64 pos = 0;
	int rc = 0;
	ENTRY;

	sai = ll_sai_get(dir);
	thread = &sai->sai_thread;
	agl_thread = &sai->sai_agl_thread;
	thread->t_pid = current_pid();
	CDEBUG(D_READA, "statahead thread starting: sai %p, parent %.*s\n",
	       sai, parent->d_name.len, parent->d_name.name);

	op_data = ll_prep_md_op_data(NULL, dir, dir, NULL, 0, 0,
				     LUSTRE_OPC_ANY, dir);
	if (IS_ERR(op_data))
		GOTO(out, rc = PTR_ERR(op_data));

	op_data->op_max_pages = ll_i2sbi(dir)->ll_md_brw_pages;

	if (sbi->ll_flags & LL_SBI_AGL_ENABLED)
		ll_start_agl(parent, sai);

	atomic_inc(&sbi->ll_sa_total);
	spin_lock(&lli->lli_sa_lock);
	if (thread_is_init(thread))
		/* If someone else has changed the thread state
		 * (e.g. already changed to SVC_STOPPING), we can't just
		 * blindly overwrite that setting. */
		thread_set_flags(thread, SVC_RUNNING);
	spin_unlock(&lli->lli_sa_lock);
	wake_up(&thread->t_ctl_waitq);

	ll_dir_chain_init(&chain);
	while (pos != MDS_DIR_END_OFF && thread_is_running(thread)) {
		struct lu_dirpage *dp;
		struct lu_dirent  *ent;

		sai->sai_in_readpage = 1;
		page = ll_get_dir_page(dir, op_data, pos, &chain);
		sai->sai_in_readpage = 0;
		if (IS_ERR(page)) {
			rc = PTR_ERR(page);
			CDEBUG(D_READA, "error reading dir "DFID" at "LPU64
			       "/"LPU64" opendir_pid = %u: rc = %d\n",
			       PFID(ll_inode2fid(dir)), pos, sai->sai_index,
			       lli->lli_opendir_pid, rc);
			break;
		}

		dp = page_address(page);
		for (ent = lu_dirent_start(dp);
		     ent != NULL && thread_is_running(thread) &&
		     !sa_low_hit(sai);
		     ent = lu_dirent_next(ent)) {
			__u64 hash;
			int namelen;
			char *name;

			hash = le64_to_cpu(ent->lde_hash);
			if (unlikely(hash < pos))
				/*
				 * Skip until we find target hash value.
				 */
				continue;

			namelen = le16_to_cpu(ent->lde_namelen);
			if (unlikely(namelen == 0))
				/*
				 * Skip dummy record.
				 */
				continue;

			name = ent->lde_name;
			if (name[0] == '.') {
				if (namelen == 1) {
					/*
					 * skip "."
					 */
					continue;
				} else if (name[1] == '.' && namelen == 2) {
					/*
					 * skip ".."
					 */
					continue;
				} else if (!sai->sai_ls_all) {
					/*
					 * skip hidden files.
					 */
					sai->sai_skip_hidden++;
					continue;
				}
			}

			/*
			 * don't stat-ahead first entry.
			 */
			if (unlikely(++first == 1))
				continue;

			/* wait for spare statahead window */
			do {
				l_wait_event(thread->t_ctl_waitq,
					     !sa_sent_full(sai) ||
					     sa_has_callback(sai) ||
					     !agl_list_empty(sai) ||
					     !thread_is_running(thread),
					     &lwi);

				sa_handle_callback(sai);
			} while (sa_sent_full(sai) &&
				 thread_is_running(thread));

			sa_statahead(parent, name, namelen);
		}

		pos = le64_to_cpu(dp->ldp_hash_end);
		ll_release_page(dir, page,
				le32_to_cpu(dp->ldp_flags) & LDF_COLLIDE);

		if (sa_low_hit(sai)) {
			rc = -EFAULT;
			atomic_inc(&sbi->ll_sa_wrong);
			CDEBUG(D_READA, "Statahead for dir "DFID" hit "
			       "ratio too low: hit/miss "LPU64"/"LPU64
			       ", sent/replied "LPU64"/"LPU64", stopping "
			       "statahead thread: pid %d\n",
			       PFID(&lli->lli_fid), sai->sai_hit,
			       sai->sai_miss, sai->sai_sent,
			       sai->sai_replied, current_pid());
			break;
		}
	}
	ll_dir_chain_fini(&chain);
	ll_finish_md_op_data(op_data);

	if (rc < 0) {
		spin_lock(&lli->lli_sa_lock);
		thread_set_flags(thread, SVC_STOPPING);
		lli->lli_sa_enabled = 0;
		spin_unlock(&lli->lli_sa_lock);
	}

	/* statahead is finished, but statahead entries need to be cached, wait
	 * for file release to stop me. */
	while (thread_is_running(thread)) {
		l_wait_event(thread->t_ctl_waitq,
			     sa_has_callback(sai) ||
			     !agl_list_empty(sai) ||
			     !thread_is_running(thread),
			     &lwi);

		sa_handle_callback(sai);
	}

	EXIT;
out:
	if (sai->sai_agl_valid) {
		spin_lock(&lli->lli_agl_lock);
		thread_set_flags(agl_thread, SVC_STOPPING);
		spin_unlock(&lli->lli_agl_lock);
		wake_up(&agl_thread->t_ctl_waitq);

		CDEBUG(D_READA, "stop agl thread: sai %p pid %u\n",
		       sai, (unsigned int)agl_thread->t_pid);
		l_wait_event(agl_thread->t_ctl_waitq,
			     thread_is_stopped(agl_thread),
			     &lwi);
	} else {
		/* Set agl_thread flags anyway. */
		thread_set_flags(agl_thread, SVC_STOPPED);
	}

	/* wait for inflight statahead RPCs to finish, and then we can free sai
	 * safely because statahead RPC will access sai data */
	while (sai->sai_sent != sai->sai_replied) {
		/* in case we're not woken up, timeout wait */
		lwi = LWI_TIMEOUT(HZ >> 3, NULL, NULL);
		l_wait_event(thread->t_ctl_waitq,
			sai->sai_sent == sai->sai_replied, &lwi);
	}

	/* release resources held by statahead RPCs */
	sa_handle_callback(sai);

	spin_lock(&lli->lli_sa_lock);
	thread_set_flags(thread, SVC_STOPPED);
	spin_unlock(&lli->lli_sa_lock);

	wake_up(&sai->sai_waitq);
	wake_up(&thread->t_ctl_waitq);
        ll_sai_put(sai);
	CDEBUG(D_READA, "statahead thread stopped: sai %p, parent %.*s\n",
	       sai, parent->d_name.len, parent->d_name.name);
	dput(parent);
	return rc;
}

/* authorize opened dir handle @key to statahead later */
void ll_authorize_statahead(struct inode *dir, void *key)
{
	struct ll_inode_info *lli = ll_i2info(dir);

	spin_lock(&lli->lli_sa_lock);
	if (lli->lli_opendir_key == NULL && lli->lli_sai == NULL) {
		/*
		 * if lli_sai is not NULL, it means previous statahead is not
		 * finished yet, we'd better not start a new statahead for now.
		 */
		LASSERT(lli->lli_opendir_pid == 0);
		lli->lli_opendir_key = key;
		lli->lli_opendir_pid = current_pid();
		lli->lli_sa_enabled = 1;
	}
	spin_unlock(&lli->lli_sa_lock);
}

/* deauthorize opened dir handle @key to statahead, but statahead thread may
 * still be running, notify it to quit. */
void ll_deauthorize_statahead(struct inode *dir, void *key)
{
	struct ll_inode_info *lli = ll_i2info(dir);
	struct ll_statahead_info *sai;

	LASSERT(lli->lli_opendir_key == key);
	LASSERT(lli->lli_opendir_pid != 0);

	CDEBUG(D_READA, "deauthorize statahead for "DFID"\n",
		PFID(&lli->lli_fid));

	spin_lock(&lli->lli_sa_lock);
	lli->lli_opendir_key = NULL;
	lli->lli_opendir_pid = 0;
	lli->lli_sa_enabled = 0;
	sai = lli->lli_sai;
	if (sai != NULL && thread_is_running(&sai->sai_thread)) {
		/*
		 * statahead thread may not quit yet because it needs to cache
		 * entries, now it's time to tell it to quit.
		 */
		thread_set_flags(&sai->sai_thread, SVC_STOPPING);
		wake_up(&sai->sai_thread.t_ctl_waitq);
	}
	spin_unlock(&lli->lli_sa_lock);
}

enum {
        /**
         * not first dirent, or is "."
         */
        LS_NONE_FIRST_DE = 0,
        /**
         * the first non-hidden dirent
         */
        LS_FIRST_DE,
        /**
         * the first hidden dirent, that is "."
         */
        LS_FIRST_DOT_DE
};

static int is_first_dirent(struct inode *dir, struct dentry *dentry)
{
	struct ll_dir_chain   chain;
	struct qstr          *target = &dentry->d_name;
	struct md_op_data    *op_data;
	int                   dot_de;
	struct page	     *page = NULL;
	int                   rc     = LS_NONE_FIRST_DE;
	__u64		      pos = 0;
	ENTRY;

	op_data = ll_prep_md_op_data(NULL, dir, dir, NULL, 0, 0,
				     LUSTRE_OPC_ANY, dir);
	if (IS_ERR(op_data))
		RETURN(PTR_ERR(op_data));
	/**
	 *FIXME choose the start offset of the readdir
	 */
	op_data->op_stripe_offset = 0;
	op_data->op_max_pages = ll_i2sbi(dir)->ll_md_brw_pages;

	ll_dir_chain_init(&chain);
	page = ll_get_dir_page(dir, op_data, 0, &chain);

	while (1) {
		struct lu_dirpage *dp;
		struct lu_dirent  *ent;

		if (IS_ERR(page)) {
			struct ll_inode_info *lli = ll_i2info(dir);

			rc = PTR_ERR(page);
			CERROR("%s: reading dir "DFID" at "LPU64
			       "opendir_pid = %u : rc = %d\n",
			       ll_get_fsname(dir->i_sb, NULL, 0),
			       PFID(ll_inode2fid(dir)), pos,
			       lli->lli_opendir_pid, rc);
			break;
		}

		dp = page_address(page);
		for (ent = lu_dirent_start(dp); ent != NULL;
		     ent = lu_dirent_next(ent)) {
			__u64 hash;
			int namelen;
			char *name;

			hash = le64_to_cpu(ent->lde_hash);
			/* The ll_get_dir_page() can return any page containing
			 * the given hash which may be not the start hash. */
			if (unlikely(hash < pos))
				continue;

			namelen = le16_to_cpu(ent->lde_namelen);
			if (unlikely(namelen == 0))
				/*
				 * skip dummy record.
				 */
				continue;

			name = ent->lde_name;
			if (name[0] == '.') {
				if (namelen == 1)
					/*
					 * skip "."
					 */
					continue;
				else if (name[1] == '.' && namelen == 2)
					/*
					 * skip ".."
					 */
					continue;
				else
					dot_de = 1;
			} else {
				dot_de = 0;
			}

			if (dot_de && target->name[0] != '.') {
				CDEBUG(D_READA, "%.*s skip hidden file %.*s\n",
				       target->len, target->name,
				       namelen, name);
				continue;
			}

			if (target->len != namelen ||
			    memcmp(target->name, name, namelen) != 0)
				rc = LS_NONE_FIRST_DE;
			else if (!dot_de)
				rc = LS_FIRST_DE;
			else
				rc = LS_FIRST_DOT_DE;

			ll_release_page(dir, page, false);
			GOTO(out, rc);
		}
		pos = le64_to_cpu(dp->ldp_hash_end);
		if (pos == MDS_DIR_END_OFF) {
			/*
			 * End of directory reached.
			 */
			ll_release_page(dir, page, false);
			GOTO(out, rc);
		} else {
			/*
			 * chain is exhausted
			 * Normal case: continue to the next page.
			 */
			ll_release_page(dir, page, le32_to_cpu(dp->ldp_flags) &
					      LDF_COLLIDE);
			page = ll_get_dir_page(dir, op_data, pos, &chain);
		}
	}
	EXIT;
out:
	ll_dir_chain_fini(&chain);
	ll_finish_md_op_data(op_data);
        return rc;
}

static int revalidate_statahead_dentry(struct inode *dir,
					struct ll_statahead_info *sai,
					struct dentry **dentryp,
					int only_unplug)
{
	struct sa_entry *entry = NULL;
	struct l_wait_info lwi = { 0 };
	int rc = 0;
	ENTRY;

	if ((*dentryp)->d_name.name[0] == '.') {
		if (sai->sai_ls_all ||
		    sai->sai_miss_hidden >= sai->sai_skip_hidden) {
			/*
			 * Hidden dentry is the first one, or statahead
			 * thread does not skip so many hidden dentries
			 * before "sai_ls_all" enabled as below.
			 */
		} else {
			if (!sai->sai_ls_all)
				/*
				 * It maybe because hidden dentry is not
				 * the first one, "sai_ls_all" was not
				 * set, then "ls -al" missed. Enable
				 * "sai_ls_all" for such case.
				 */
				sai->sai_ls_all = 1;

			/*
			 * Such "getattr" has been skipped before
			 * "sai_ls_all" enabled as above.
			 */
			sai->sai_miss_hidden++;
			RETURN(-EAGAIN);
		}
	}

	entry = sa_get(sai, &(*dentryp)->d_name);
	if (entry == NULL || only_unplug) {
		sa_put(sai, entry);
		RETURN(entry ? 1 : -EAGAIN);
	}

	/* if statahead is busy in readdir, help it do post-work */
	if (!sa_ready(entry) && sai->sai_in_readpage)
		sa_handle_callback(sai);

	if (!sa_ready(entry)) {
		sai->sai_index_wait = entry->se_index;
		lwi = LWI_TIMEOUT_INTR(cfs_time_seconds(30), NULL,
					LWI_ON_SIGNAL_NOOP, NULL);
		rc = l_wait_event(sai->sai_waitq,
				sa_ready(entry) ||
				thread_is_stopped(&sai->sai_thread),
				&lwi);
		if (rc < 0) {
			sa_put(sai, entry);
			RETURN(-EAGAIN);
		}
	}

	if (entry->se_state == SA_ENTRY_SUCC && entry->se_inode != NULL) {
		struct inode *inode = entry->se_inode;
		struct lookup_intent it = { .it_op = IT_GETATTR,
					    .d.lustre.it_lock_handle =
						entry->se_handle };
		__u64 bits;

		rc = md_revalidate_lock(ll_i2mdexp(dir), &it,
					ll_inode2fid(inode), &bits);
		if (rc == 1) {
			if ((*dentryp)->d_inode == NULL) {
				struct dentry *alias;

				alias = ll_splice_alias(inode, *dentryp);
				if (IS_ERR(alias)) {
					sa_put(sai, entry);
					RETURN(PTR_ERR(alias));
				}
				*dentryp = alias;
			} else if ((*dentryp)->d_inode != inode) {
				/* revalidate, but inode is recreated */
				CDEBUG(D_READA,
					"%s: stale dentry %.*s inode "
					DFID", statahead inode "DFID
					"\n",
					ll_get_fsname((*dentryp)->d_inode->i_sb,
						      NULL, 0),
					(*dentryp)->d_name.len,
					(*dentryp)->d_name.name,
					PFID(ll_inode2fid((*dentryp)->d_inode)),
					PFID(ll_inode2fid(inode)));
				sa_put(sai, entry);
				RETURN(-ESTALE);
			} else {
				iput(inode);
			}
			entry->se_inode = NULL;

			if ((bits & MDS_INODELOCK_LOOKUP) &&
			    d_lustre_invalid(*dentryp))
				d_lustre_revalidate(*dentryp);
			ll_intent_release(&it);
		}
	}

	sa_put(sai, entry);
	RETURN(rc);
}

static int start_statahead_thread(struct inode *dir, struct dentry *dentry)
{
	struct ll_inode_info *lli = ll_i2info(dir);
	struct ll_statahead_info *sai = NULL;
	struct dentry *parent;
	struct ptlrpc_thread *thread;
	struct l_wait_info lwi = { 0 };
	struct task_struct *task;
	int rc;
	ENTRY;

	/* I am the "lli_opendir_pid" owner, only me can set "lli_sai". */
	rc = is_first_dirent(dir, dentry);
	if (rc == LS_NONE_FIRST_DE)
		/* It is not "ls -{a}l" operation, no need statahead for it. */
		GOTO(out, rc = -EAGAIN);

	sai = ll_sai_alloc();
	if (sai == NULL)
		GOTO(out, rc = -ENOMEM);

	sai->sai_ls_all = (rc == LS_FIRST_DOT_DE);
	sai->sai_inode = igrab(dir);
	if (unlikely(sai->sai_inode == NULL)) {
		CWARN("Do not start stat ahead on dying inode "DFID"\n",
			PFID(&lli->lli_fid));
		GOTO(out, rc = -ESTALE);
	}

	/* get parent reference count here, and put it in ll_statahead_thread */
	parent = dget(dentry->d_parent);
	if (unlikely(sai->sai_inode != parent->d_inode)) {
		struct ll_inode_info *nlli = ll_i2info(parent->d_inode);

		CWARN("Race condition, someone changed %.*s just now: "
			"old parent "DFID", new parent "DFID"\n",
			dentry->d_name.len, dentry->d_name.name,
			PFID(&lli->lli_fid), PFID(&nlli->lli_fid));
		dput(parent);
		iput(sai->sai_inode);
		GOTO(out, rc = -EAGAIN);
	}

	CDEBUG(D_READA, "start statahead thread: sai %p, parent %.*s\n",
	       sai, parent->d_name.len, parent->d_name.name);

        lli->lli_sai = sai;

	task = kthread_run(ll_statahead_thread, parent, "ll_sa_%u",
			   lli->lli_opendir_pid);
	thread = &sai->sai_thread;
	if (IS_ERR(task)) {
		rc = PTR_ERR(task);
		CERROR("cannot start ll_sa thread: rc = %d\n", rc);
		dput(parent);
		lli->lli_opendir_key = NULL;
		thread_set_flags(thread, SVC_STOPPED);
		thread_set_flags(&sai->sai_agl_thread, SVC_STOPPED);
		ll_sai_put(sai);
		LASSERT(lli->lli_sai == NULL);
		RETURN(-EAGAIN);
	}

	l_wait_event(thread->t_ctl_waitq,
		     thread_is_running(thread) || thread_is_stopped(thread),
		     &lwi);
	atomic_inc(&ll_i2sbi(parent->d_inode)->ll_sa_running);
	ll_sai_put(sai);

	/*
	 * We don't stat-ahead for the first dirent since we are already in
	 * lookup.
	 */
	RETURN(-EAGAIN);

out:
	if (sai != NULL)
		OBD_FREE_PTR(sai);
	spin_lock(&lli->lli_sa_lock);
	lli->lli_opendir_key = NULL;
	lli->lli_opendir_pid = 0;
	lli->lli_sa_enabled = 0;
	spin_unlock(&lli->lli_sa_lock);

	RETURN(rc);
}

/**
 * Start statahead thread if this is the first dir entry.
 * Otherwise if a thread is started already, wait it until it is ahead of me.
 * \retval 1       -- find entry with lock in cache, the caller needs to do
 *		      nothing.
 * \retval 0       -- find entry in cache, but without lock, the caller needs
 *		      refresh from MDS.
 * \retval others  -- the caller need to process as non-statahead.
 */
int do_statahead_enter(struct inode *dir, struct dentry **dentryp,
		       int only_unplug)
{
	struct ll_statahead_info *sai;

	sai = ll_sai_get(dir);
	if (sai != NULL) {
		int rc;

		rc = revalidate_statahead_dentry(dir, sai, dentryp,
						 only_unplug);
		CDEBUG(D_READA, "revalidate statahead %.*s: %d.\n",
			(*dentryp)->d_name.len, (*dentryp)->d_name.name, rc);
		ll_sai_put(sai);
		return rc;
	}

	return start_statahead_thread(dir, *dentryp);
}