/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License, Version 1.0 only
 * (the "License").  You may not use this file except in compliance
 * with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */
/*
 * Copyright 2005 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

/*
 * Copyright (c) 2013, Joyent, Inc.  All rights reserved.
 */

#include <sys/rwstlock.h>
#include <sys/errno.h>
#include <sys/debug.h>
#include <sys/lockstat.h>
#include <sys/sysmacros.h>
#include <sys/condvar_impl.h>

/*
 * Alternate rwlock that is interruptible and can be released by a thread
 * other than the one that acquired the lock.
 *
 * There is no priority inheritance mechanism for these locks.
 * For RW_READER, writers have priority over readers, so reader starvation
 * is possible; as with rwlocks, this behavior may be overridden by
 * specifying RW_READER_STARVEWRITER.
 */

/*
 * Common code to grab a lock.  There are three cases:
 *
 * (1) If RWST_TRYENTER is set, we try the lock without blocking.
 *     In this case we return 1 on success, 0 on failure.
 *
 * (2) If RWST_SIG is set, we block interruptibly until we get the lock.
 *     In this case we return 0 on success, EINTR if we're interrupted.
 *
 * (3) If neither flag is set, we block uninterruptibly until we get the lock.
 *     In this case we return 0 (we always succeed).
 */
static int
rwst_enter_common(rwstlock_t *l, krw_t rw, int flags)
{
        hrtime_t sleep_time;
        int writer;
        intptr_t readers;

        mutex_enter(&l->rwst_lock);
        if (rw == RW_READER || rw == RW_READER_STARVEWRITER) {
                while (RWST_WRITE_HELD(l) ||
                    (rw != RW_READER_STARVEWRITER && RWST_WRITE_WANTED(l))) {

                        if (flags & RWST_TRYENTER) {
                                mutex_exit(&l->rwst_lock);
                                return (0);
                        }
                        if (panicstr)
                                return (0);

                        if (RWST_WRITE_HELD(l)) {
                                writer = 1;
                                readers = 0;
                        } else {
                                writer = 0;
                                readers = l->rwst_count;
                        }
                        sleep_time = -gethrtime();
                        if (!RWST_READ_WAIT(l, flags)) {
                                mutex_exit(&l->rwst_lock);
                                return (EINTR);
                        }
                        sleep_time += gethrtime();
                        LOCKSTAT_RECORD4(LS_RW_ENTER_BLOCK, l, sleep_time, rw,
                            writer, readers);
                }
                RWST_READ_ENTER(l);
                LOCKSTAT_RECORD(LS_RW_ENTER_ACQUIRE, l, rw);
        } else {
                ASSERT(rw == RW_WRITER);
                while (RWST_HELD(l)) {
                        if (flags & RWST_TRYENTER) {
                                mutex_exit(&l->rwst_lock);
                                return (0);
                        }
                        if (panicstr)
                                return (0);
                        if (RWST_WRITE_HELD(l)) {
                                writer = 1;
                                readers = 0;
                        } else {
                                writer = 0;
                                readers = l->rwst_count;
                        }
                        sleep_time = -gethrtime();
                        if (!RWST_WRITE_WAIT(l, flags)) {
                                if (!RWST_WRITE_HELD(l) &&
                                    !RWST_WRITE_WANTED(l))
                                        RWST_READ_WAKE_ALL(l);
                                mutex_exit(&l->rwst_lock);
                                return (EINTR);
                        }
                        sleep_time += gethrtime();
                        LOCKSTAT_RECORD4(LS_RW_ENTER_BLOCK, l, sleep_time, rw,
                            writer, readers);
                }
                RWST_WRITE_ENTER(l);
                LOCKSTAT_RECORD(LS_RW_ENTER_ACQUIRE, l, rw);
        }
        mutex_exit(&l->rwst_lock);
        return (flags & RWST_TRYENTER);
}

void
rwst_exit(rwstlock_t *l)
{
        mutex_enter(&l->rwst_lock);
        if (RWST_WRITE_HELD(l)) {
                LOCKSTAT_RECORD(LS_RW_EXIT_RELEASE, l, RW_WRITER);
                RWST_WRITE_EXIT(l);
        } else {
                ASSERT(RWST_READ_HELD(l));
                LOCKSTAT_RECORD(LS_RW_EXIT_RELEASE, l, RW_READER);
                RWST_READ_EXIT(l);
        }
        if (!RWST_WRITE_WANTED(l))
                RWST_READ_WAKE_ALL(l);
        else if (!RWST_HELD(l))
                RWST_WRITE_WAKE_ONE(l);
        mutex_exit(&l->rwst_lock);
}

void
rwst_enter(rwstlock_t *l, krw_t rw)
{
        (void) rwst_enter_common(l, rw, 0);
}

int
rwst_enter_sig(rwstlock_t *l, krw_t rw)
{
        return (rwst_enter_common(l, rw, RWST_SIG));
}

int
rwst_tryenter(rwstlock_t *l, krw_t rw)
{
        return (rwst_enter_common(l, rw, RWST_TRYENTER));
}

int
rwst_lock_held(rwstlock_t *l, krw_t rw)
{
        if (rw != RW_WRITER)
                return (RWST_READ_HELD(l));
        ASSERT(rw == RW_WRITER);
        return (RWST_WRITE_OWNER(l));
}

/*ARGSUSED*/
void
rwst_init(rwstlock_t *l, char *name, krw_type_t krw_t, void *arg)
{
        l->rwst_count = 0;
        mutex_init(&l->rwst_lock, NULL, MUTEX_DEFAULT, NULL);
        cv_init(&l->rwst_rcv, NULL, CV_DEFAULT, NULL);
        cv_init(&l->rwst_wcv, NULL, CV_DEFAULT, NULL);
}

void
rwst_destroy(rwstlock_t *l)
{
        ASSERT(l->rwst_count == 0);
        mutex_destroy(&l->rwst_lock);
        cv_destroy(&l->rwst_rcv);
        cv_destroy(&l->rwst_wcv);
}

struct _kthread *
rwst_owner(rwstlock_t *l)
{
        return (RWST_OWNER(l));
}