5917 User-mode SMB server

[unleashed.git] / usr / src / uts / common / fs / smbsrv / smb_lock.c

/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (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 (c) 2007, 2010, Oracle and/or its affiliates. All rights reserved.
 * Copyright 2013 Nexenta Systems, Inc.  All rights reserved.
 */

/*
 * This module provides range lock functionality for CIFS/SMB clients.
 * Lock range service functions process SMB lock and and unlock
 * requests for a file by applying lock rules and marks file range
 * as locked if the lock is successful otherwise return proper
 * error code.
 */

#include <smbsrv/smb_kproto.h>
#include <smbsrv/smb_fsops.h>
#include <sys/nbmlock.h>
#include <sys/param.h>

extern caller_context_t smb_ct;

static void smb_lock_posix_unlock(smb_node_t *, smb_lock_t *, cred_t *);
static boolean_t smb_is_range_unlocked(uint64_t, uint64_t, uint32_t,
    smb_llist_t *, uint64_t *);
static int smb_lock_range_overlap(smb_lock_t *, uint64_t, uint64_t);
static uint32_t smb_lock_range_lckrules(smb_request_t *, smb_ofile_t *,
    smb_node_t *, smb_lock_t *, smb_lock_t **);
static clock_t smb_lock_wait(smb_request_t *, smb_lock_t *, smb_lock_t *);
static uint32_t smb_lock_range_ulckrules(smb_request_t *, smb_node_t *,
    uint64_t, uint64_t, smb_lock_t **nodelock);
static smb_lock_t *smb_lock_create(smb_request_t *, uint64_t, uint64_t,
    uint32_t, uint32_t);
static void smb_lock_destroy(smb_lock_t *);
static void smb_lock_free(smb_lock_t *);

/*
 * Return the number of range locks on the specified ofile.
 */
uint32_t
smb_lock_get_lock_count(smb_node_t *node, smb_ofile_t *of)
{
        smb_lock_t      *lock;
        smb_llist_t     *llist;
        uint32_t        count = 0;

        SMB_NODE_VALID(node);
        SMB_OFILE_VALID(of);

        llist = &node->n_lock_list;

        smb_llist_enter(llist, RW_READER);
        for (lock = smb_llist_head(llist);
            lock != NULL;
            lock = smb_llist_next(llist, lock)) {
                if (lock->l_file == of)
                        ++count;
        }
        smb_llist_exit(llist);

        return (count);
}

/*
 * smb_unlock_range
 *
 * locates lock range performed for corresponding to unlock request.
 *
 * NT_STATUS_SUCCESS - Lock range performed successfully.
 * !NT_STATUS_SUCCESS - Error in unlock range operation.
 */
uint32_t
smb_unlock_range(
    smb_request_t       *sr,
    smb_node_t          *node,
    uint64_t            start,
    uint64_t            length)
{
        smb_lock_t      *lock = NULL;
        uint32_t        status;

        /* Apply unlocking rules */
        smb_llist_enter(&node->n_lock_list, RW_WRITER);
        status = smb_lock_range_ulckrules(sr, node, start, length, &lock);
        if (status != NT_STATUS_SUCCESS) {
                /*
                 * If lock range is not matching in the list
                 * return error.
                 */
                ASSERT(lock == NULL);
                smb_llist_exit(&node->n_lock_list);
                return (status);
        }

        smb_llist_remove(&node->n_lock_list, lock);
        smb_lock_posix_unlock(node, lock, sr->user_cr);
        smb_llist_exit(&node->n_lock_list);
        smb_lock_destroy(lock);

        return (status);
}

/*
 * smb_lock_range
 *
 * Checks for integrity of file lock operation for the given range of file data.
 * This is performed by applying lock rules with all the elements of the node
 * lock list.
 *
 * Break shared (levelII) oplocks. If there is an exclusive oplock, it is
 * owned by this ofile and therefore should not be broken.
 *
 * The function returns with new lock added if lock request is non-conflicting
 * with existing range lock for the file. Otherwise smb request is filed
 * without returning.
 *
 * NT_STATUS_SUCCESS - Lock range performed successfully.
 * !NT_STATUS_SUCCESS - Error in lock range operation.
 */
uint32_t
smb_lock_range(
    smb_request_t       *sr,
    uint64_t            start,
    uint64_t            length,
    uint32_t            timeout,
    uint32_t            locktype)
{
        smb_ofile_t     *file = sr->fid_ofile;
        smb_node_t      *node = file->f_node;
        smb_lock_t      *lock;
        smb_lock_t      *clock = NULL;
        uint32_t        result = NT_STATUS_SUCCESS;
        boolean_t       lock_has_timeout = (timeout != 0);

        lock = smb_lock_create(sr, start, length, locktype, timeout);

        smb_llist_enter(&node->n_lock_list, RW_WRITER);
        for (;;) {
                clock_t rc;

                /* Apply locking rules */
                result = smb_lock_range_lckrules(sr, file, node, lock, &clock);

                if ((result == NT_STATUS_CANCELLED) ||
                    (result == NT_STATUS_SUCCESS) ||
                    (result == NT_STATUS_RANGE_NOT_LOCKED)) {
                        ASSERT(clock == NULL);
                        break;
                } else if (timeout == 0) {
                        break;
                }

                ASSERT(result == NT_STATUS_LOCK_NOT_GRANTED);
                ASSERT(clock);
                /*
                 * Call smb_lock_wait holding write lock for
                 * node lock list.  smb_lock_wait will release
                 * this lock if it blocks.
                 */
                ASSERT(node == clock->l_file->f_node);

                rc = smb_lock_wait(sr, lock, clock);
                if (rc == 0) {
                        result = NT_STATUS_CANCELLED;
                        break;
                }
                if (rc == -1)
                        timeout = 0;

                clock = NULL;
        }

        lock->l_blocked_by = NULL;

        if (result != NT_STATUS_SUCCESS) {
                /*
                 * Under certain conditions NT_STATUS_FILE_LOCK_CONFLICT
                 * should be returned instead of NT_STATUS_LOCK_NOT_GRANTED.
                 */
                if (result == NT_STATUS_LOCK_NOT_GRANTED) {
                        /*
                         * Locks with timeouts always return
                         * NT_STATUS_FILE_LOCK_CONFLICT
                         */
                        if (lock_has_timeout)
                                result = NT_STATUS_FILE_LOCK_CONFLICT;

                        /*
                         * Locks starting higher than 0xef000000 that do not
                         * have the MSB set always return
                         * NT_STATUS_FILE_LOCK_CONFLICT
                         */
                        if ((lock->l_start >= 0xef000000) &&
                            !(lock->l_start & (1ULL << 63))) {
                                result = NT_STATUS_FILE_LOCK_CONFLICT;
                        }

                        /*
                         * If the last lock attempt to fail on this file handle
                         * started at the same offset as this one then return
                         * NT_STATUS_FILE_LOCK_CONFLICT
                         */
                        mutex_enter(&file->f_mutex);
                        if ((file->f_flags & SMB_OFLAGS_LLF_POS_VALID) &&
                            (lock->l_start == file->f_llf_pos)) {
                                result = NT_STATUS_FILE_LOCK_CONFLICT;
                        }
                        mutex_exit(&file->f_mutex);
                }

                /* Update last lock failed offset */
                mutex_enter(&file->f_mutex);
                file->f_llf_pos = lock->l_start;
                file->f_flags |= SMB_OFLAGS_LLF_POS_VALID;
                mutex_exit(&file->f_mutex);

                smb_lock_free(lock);
        } else {
                /*
                 * don't insert into the CIFS lock list unless the
                 * posix lock worked
                 */
                if (smb_fsop_frlock(node, lock, B_FALSE, sr->user_cr))
                        result = NT_STATUS_FILE_LOCK_CONFLICT;
                else
                        smb_llist_insert_tail(&node->n_lock_list, lock);
        }
        smb_llist_exit(&node->n_lock_list);

        if (result == NT_STATUS_SUCCESS)
                smb_oplock_break_levelII(node);

        return (result);
}


/*
 * smb_lock_range_access
 *
 * scans node lock list
 * to check if there is any overlapping lock. Overlapping
 * lock is allowed only under same session and client pid.
 *
 * Return values
 *      NT_STATUS_SUCCESS               lock access granted.
 *      NT_STATUS_FILE_LOCK_CONFLICT    access denied due to lock conflict.
 */
int
smb_lock_range_access(
    smb_request_t       *sr,
    smb_node_t          *node,
    uint64_t            start,
    uint64_t            length,  /* zero means to EoF */
    boolean_t           will_write)
{
        smb_lock_t      *lock;
        smb_llist_t     *llist;
        int             status = NT_STATUS_SUCCESS;

        llist = &node->n_lock_list;
        smb_llist_enter(llist, RW_READER);
        /* Search for any applicable lock */
        for (lock = smb_llist_head(llist);
            lock != NULL;
            lock = smb_llist_next(llist, lock)) {

                if (!smb_lock_range_overlap(lock, start, length))
                        /* Lock does not overlap */
                        continue;

                if (lock->l_type == SMB_LOCK_TYPE_READONLY && !will_write)
                        continue;

                if (lock->l_type == SMB_LOCK_TYPE_READWRITE &&
                    lock->l_session_kid == sr->session->s_kid &&
                    lock->l_pid == sr->smb_pid)
                        continue;

                status = NT_STATUS_FILE_LOCK_CONFLICT;
                break;
        }
        smb_llist_exit(llist);
        return (status);
}

void
smb_node_destroy_lock_by_ofile(smb_node_t *node, smb_ofile_t *file)
{
        smb_lock_t      *lock;
        smb_lock_t      *nxtl;
        list_t          destroy_list;

        SMB_NODE_VALID(node);
        ASSERT(node->n_refcnt);

        /*
         * Move locks matching the specified file from the node->n_lock_list
         * to a temporary list (holding the lock the entire time) then
         * destroy all the matching locks.  We can't call smb_lock_destroy
         * while we are holding the lock for node->n_lock_list because we will
         * deadlock and we can't drop the lock because the list contents might
         * change (for example nxtl might get removed on another thread).
         */
        list_create(&destroy_list, sizeof (smb_lock_t),
            offsetof(smb_lock_t, l_lnd));

        smb_llist_enter(&node->n_lock_list, RW_WRITER);
        lock = smb_llist_head(&node->n_lock_list);
        while (lock) {
                nxtl = smb_llist_next(&node->n_lock_list, lock);
                if (lock->l_file == file) {
                        smb_llist_remove(&node->n_lock_list, lock);
                        smb_lock_posix_unlock(node, lock, file->f_user->u_cred);
                        list_insert_tail(&destroy_list, lock);
                }
                lock = nxtl;
        }
        smb_llist_exit(&node->n_lock_list);

        lock = list_head(&destroy_list);
        while (lock) {
                nxtl = list_next(&destroy_list, lock);
                list_remove(&destroy_list, lock);
                smb_lock_destroy(lock);
                lock = nxtl;
        }

        list_destroy(&destroy_list);
}

void
smb_lock_range_error(smb_request_t *sr, uint32_t status32)
{
        uint16_t errcode;

        if (status32 == NT_STATUS_CANCELLED)
                errcode = ERROR_OPERATION_ABORTED;
        else
                errcode = ERRlock;

        smbsr_error(sr, status32, ERRDOS, errcode);
}

/*
 * An SMB variant of nbl_conflict().
 *
 * SMB prevents remove or rename when conflicting locks exist
 * (unlike NFS, which is why we can't just use nbl_conflict).
 *
 * Returns:
 *      NT_STATUS_SHARING_VIOLATION - nbl_share_conflict
 *      NT_STATUS_FILE_LOCK_CONFLICT - nbl_lock_conflict
 *      NT_STATUS_SUCCESS - operation can proceed
 *
 * NB: This function used to also check the list of ofiles,
 * via: smb_lock_range_access() but we _can't_ do that here
 * due to lock order constraints between node->n_lock_list
 * and node->vp->vnbllock (taken via nvl_start_crit).
 * They must be taken in that order, and in here, we
 * already hold vp->vnbllock.
 */
DWORD
smb_nbl_conflict(smb_node_t *node, uint64_t off, uint64_t len, nbl_op_t op)
{
        int svmand;

        SMB_NODE_VALID(node);
        ASSERT(smb_node_in_crit(node));
        ASSERT(op == NBL_READ || op == NBL_WRITE || op == NBL_READWRITE ||
            op == NBL_REMOVE || op == NBL_RENAME);

        if (smb_node_is_dir(node))
                return (NT_STATUS_SUCCESS);

        if (nbl_share_conflict(node->vp, op, &smb_ct))
                return (NT_STATUS_SHARING_VIOLATION);

        /*
         * When checking for lock conflicts, rename and remove
         * are not allowed, so treat those as read/write.
         */
        if (op == NBL_RENAME || op == NBL_REMOVE)
                op = NBL_READWRITE;

        if (nbl_svmand(node->vp, zone_kcred(), &svmand))
                svmand = 1;

        if (nbl_lock_conflict(node->vp, op, off, len, svmand, &smb_ct))
                return (NT_STATUS_FILE_LOCK_CONFLICT);

        return (NT_STATUS_SUCCESS);
}

/*
 * smb_lock_posix_unlock
 *
 * checks if the current unlock request is in another lock and repeatedly calls
 * smb_is_range_unlocked on a sliding basis to unlock all bits of the lock
 * that are not in other locks
 *
 */
static void
smb_lock_posix_unlock(smb_node_t *node, smb_lock_t *lock, cred_t *cr)
{
        uint64_t        new_mark;
        uint64_t        unlock_start;
        uint64_t        unlock_end;
        smb_lock_t      new_unlock;
        smb_llist_t     *llist;
        boolean_t       can_unlock;

        new_mark = 0;
        unlock_start = lock->l_start;
        unlock_end = unlock_start + lock->l_length;
        llist = &node->n_lock_list;

        for (;;) {
                can_unlock = smb_is_range_unlocked(unlock_start, unlock_end,
                    lock->l_file->f_uniqid, llist, &new_mark);
                if (can_unlock) {
                        if (new_mark) {
                                new_unlock = *lock;
                                new_unlock.l_start = unlock_start;
                                new_unlock.l_length = new_mark - unlock_start;
                                (void) smb_fsop_frlock(node, &new_unlock,
                                    B_TRUE, cr);
                                unlock_start = new_mark;
                        } else {
                                new_unlock = *lock;
                                new_unlock.l_start = unlock_start;
                                new_unlock.l_length = unlock_end - unlock_start;
                                (void) smb_fsop_frlock(node, &new_unlock,
                                    B_TRUE, cr);
                                break;
                        }
                } else if (new_mark) {
                        unlock_start = new_mark;
                } else {
                        break;
                }
        }
}

/*
 * smb_lock_range_overlap
 *
 * Checks if lock range(start, length) overlaps range in lock structure.
 *
 * Zero-length byte range locks actually affect no single byte of the stream,
 * meaning they can still be accessed even with such locks in place. However,
 * they do conflict with other ranges in the following manner:
 *  conflict will only exist if the positive-length range contains the
 *  zero-length range's offset but doesn't start at it
 *
 * return values:
 *      0 - Lock range doesn't overlap
 *      1 - Lock range overlaps.
 */

#define RANGE_NO_OVERLAP        0
#define RANGE_OVERLAP           1

static int
smb_lock_range_overlap(struct smb_lock *lock, uint64_t start, uint64_t length)
{
        if (length == 0) {
                if ((lock->l_start < start) &&
                    ((lock->l_start + lock->l_length) > start))
                        return (RANGE_OVERLAP);

                return (RANGE_NO_OVERLAP);
        }

        /* The following test is intended to catch roll over locks. */
        if ((start == lock->l_start) && (length == lock->l_length))
                return (RANGE_OVERLAP);

        if (start < lock->l_start) {
                if (start + length > lock->l_start)
                        return (RANGE_OVERLAP);
        } else if (start < lock->l_start + lock->l_length)
                return (RANGE_OVERLAP);

        return (RANGE_NO_OVERLAP);
}

/*
 * smb_lock_range_lckrules
 *
 * Lock range rules:
 *      1. Overlapping read locks are allowed if the
 *         current locks in the region are only read locks
 *         irrespective of pid of smb client issuing lock request.
 *
 *      2. Read lock in the overlapped region of write lock
 *         are allowed if the pervious lock is performed by the
 *         same pid and connection.
 *
 * return status:
 *      NT_STATUS_SUCCESS - Input lock range adapts to lock rules.
 *      NT_STATUS_LOCK_NOT_GRANTED - Input lock conflicts lock rules.
 *      NT_STATUS_CANCELLED - Error in processing lock rules
 */
static uint32_t
smb_lock_range_lckrules(
    smb_request_t       *sr,
    smb_ofile_t         *file,
    smb_node_t          *node,
    smb_lock_t          *dlock,
    smb_lock_t          **clockp)
{
        smb_lock_t      *lock;
        uint32_t        status = NT_STATUS_SUCCESS;

        /* Check if file is closed */
        if (!smb_ofile_is_open(file)) {
                return (NT_STATUS_RANGE_NOT_LOCKED);
        }

        /* Caller must hold lock for node->n_lock_list */
        for (lock = smb_llist_head(&node->n_lock_list);
            lock != NULL;
            lock = smb_llist_next(&node->n_lock_list, lock)) {

                if (!smb_lock_range_overlap(lock, dlock->l_start,
                    dlock->l_length))
                        continue;

                /*
                 * Check to see if lock in the overlapping record
                 * is only read lock. Current finding is read
                 * locks can overlapped irrespective of pids.
                 */
                if ((lock->l_type == SMB_LOCK_TYPE_READONLY) &&
                    (dlock->l_type == SMB_LOCK_TYPE_READONLY)) {
                        continue;
                }

                /*
                 * When the read lock overlaps write lock, check if
                 * allowed.
                 */
                if ((dlock->l_type == SMB_LOCK_TYPE_READONLY) &&
                    !(lock->l_type == SMB_LOCK_TYPE_READONLY)) {
                        if (lock->l_file == sr->fid_ofile &&
                            lock->l_session_kid == sr->session->s_kid &&
                            lock->l_pid == sr->smb_pid &&
                            lock->l_uid == sr->smb_uid) {
                                continue;
                        }
                }

                /* Conflict in overlapping lock element */
                *clockp = lock;
                status = NT_STATUS_LOCK_NOT_GRANTED;
                break;
        }

        return (status);
}

/*
 * smb_lock_wait
 *
 * Wait operation for smb overlapping lock to be released.  Caller must hold
 * write lock for node->n_lock_list so that the set of active locks can't
 * change unexpectedly.  The lock for node->n_lock_list  will be released
 * within this function during the sleep after the lock dependency has
 * been recorded.
 *
 * return value
 *
 *      0       The request was canceled.
 *      -1      The timeout was reached.
 *      >0      Condition met.
 */
static clock_t
smb_lock_wait(smb_request_t *sr, smb_lock_t *b_lock, smb_lock_t *c_lock)
{
        clock_t         rc = 0;

        ASSERT(sr->sr_awaiting == NULL);

        mutex_enter(&sr->sr_mutex);

        switch (sr->sr_state) {
        case SMB_REQ_STATE_ACTIVE:
                /*
                 * Wait up till the timeout time keeping track of actual
                 * time waited for possible retry failure.
                 */
                sr->sr_state = SMB_REQ_STATE_WAITING_LOCK;
                sr->sr_awaiting = c_lock;
                mutex_exit(&sr->sr_mutex);

                mutex_enter(&c_lock->l_mutex);
                /*
                 * The conflict list (l_conflict_list) for a lock contains
                 * all the locks that are blocked by and in conflict with
                 * that lock.  Add the new lock to the conflict list for the
                 * active lock.
                 *
                 * l_conflict_list is currently a fancy way of representing
                 * the references/dependencies on a lock.  It could be
                 * replaced with a reference count but this approach
                 * has the advantage that MDB can display the lock
                 * dependencies at any point in time.  In the future
                 * we should be able to leverage the list to implement
                 * an asynchronous locking model.
                 *
                 * l_blocked_by is the reverse of the conflict list.  It
                 * points to the lock that the new lock conflicts with.
                 * As currently implemented this value is purely for
                 * debug purposes -- there are windows of time when
                 * l_blocked_by may be non-NULL even though there is no
                 * conflict list
                 */
                b_lock->l_blocked_by = c_lock;
                smb_slist_insert_tail(&c_lock->l_conflict_list, b_lock);
                smb_llist_exit(&c_lock->l_file->f_node->n_lock_list);

                if (SMB_LOCK_INDEFINITE_WAIT(b_lock)) {
                        cv_wait(&c_lock->l_cv, &c_lock->l_mutex);
                } else {
                        rc = cv_timedwait(&c_lock->l_cv,
                            &c_lock->l_mutex, b_lock->l_end_time);
                }

                mutex_exit(&c_lock->l_mutex);

                smb_llist_enter(&c_lock->l_file->f_node->n_lock_list,
                    RW_WRITER);
                smb_slist_remove(&c_lock->l_conflict_list, b_lock);

                mutex_enter(&sr->sr_mutex);
                sr->sr_awaiting = NULL;
                if (sr->sr_state == SMB_REQ_STATE_CANCELED) {
                        rc = 0;
                } else {
                        sr->sr_state = SMB_REQ_STATE_ACTIVE;
                }
                break;

        default:
                ASSERT(sr->sr_state == SMB_REQ_STATE_CANCELED);
                rc = 0;
                break;
        }
        mutex_exit(&sr->sr_mutex);

        return (rc);
}

/*
 * smb_lock_range_ulckrules
 *
 *      1. Unlock should be performed at exactly matching ends.
 *         This has been changed because overlapping ends is
 *         allowed and there is no other precise way of locating
 *         lock entity in node lock list.
 *
 *      2. Unlock is failed if there is no corresponding lock exists.
 *
 * Return values
 *
 *      NT_STATUS_SUCCESS               Unlock request matches lock record
 *                                      pointed by 'nodelock' lock structure.
 *
 *      NT_STATUS_RANGE_NOT_LOCKED      Unlock request doen't match any
 *                                      of lock record in node lock request or
 *                                      error in unlock range processing.
 */
static uint32_t
smb_lock_range_ulckrules(
    smb_request_t       *sr,
    smb_node_t          *node,
    uint64_t            start,
    uint64_t            length,
    smb_lock_t          **nodelock)
{
        smb_lock_t      *lock;
        uint32_t        status = NT_STATUS_RANGE_NOT_LOCKED;

        /* Caller must hold lock for node->n_lock_list */
        for (lock = smb_llist_head(&node->n_lock_list);
            lock != NULL;
            lock = smb_llist_next(&node->n_lock_list, lock)) {

                if ((start == lock->l_start) &&
                    (length == lock->l_length) &&
                    lock->l_file == sr->fid_ofile &&
                    lock->l_session_kid == sr->session->s_kid &&
                    lock->l_pid == sr->smb_pid &&
                    lock->l_uid == sr->smb_uid) {
                        *nodelock = lock;
                        status = NT_STATUS_SUCCESS;
                        break;
                }
        }

        return (status);
}

static smb_lock_t *
smb_lock_create(
    smb_request_t *sr,
    uint64_t start,
    uint64_t length,
    uint32_t locktype,
    uint32_t timeout)
{
        smb_lock_t *lock;

        ASSERT(locktype == SMB_LOCK_TYPE_READWRITE ||
            locktype == SMB_LOCK_TYPE_READONLY);

        lock = kmem_zalloc(sizeof (smb_lock_t), KM_SLEEP);
        lock->l_magic = SMB_LOCK_MAGIC;
        lock->l_sr = sr; /* Invalid after lock is active */
        lock->l_session_kid = sr->session->s_kid;
        lock->l_session = sr->session;
        lock->l_file = sr->fid_ofile;
        lock->l_uid = sr->smb_uid;
        lock->l_pid = sr->smb_pid;
        lock->l_type = locktype;
        lock->l_start = start;
        lock->l_length = length;
        /*
         * Calculate the absolute end time so that we can use it
         * in cv_timedwait.
         */
        lock->l_end_time = ddi_get_lbolt() + MSEC_TO_TICK(timeout);
        if (timeout == UINT_MAX)
                lock->l_flags |= SMB_LOCK_FLAG_INDEFINITE;

        mutex_init(&lock->l_mutex, NULL, MUTEX_DEFAULT, NULL);
        cv_init(&lock->l_cv, NULL, CV_DEFAULT, NULL);
        smb_slist_constructor(&lock->l_conflict_list, sizeof (smb_lock_t),
            offsetof(smb_lock_t, l_conflict_lnd));

        return (lock);
}

static void
smb_lock_free(smb_lock_t *lock)
{
        smb_slist_destructor(&lock->l_conflict_list);
        cv_destroy(&lock->l_cv);
        mutex_destroy(&lock->l_mutex);

        kmem_free(lock, sizeof (smb_lock_t));
}

/*
 * smb_lock_destroy
 *
 * Caller must hold node->n_lock_list
 */
static void
smb_lock_destroy(smb_lock_t *lock)
{
        /*
         * Caller must hold node->n_lock_list lock.
         */
        mutex_enter(&lock->l_mutex);
        cv_broadcast(&lock->l_cv);
        mutex_exit(&lock->l_mutex);

        /*
         * The cv_broadcast above should wake up any locks that previous
         * had conflicts with this lock.  Wait for the locking threads
         * to remove their references to this lock.
         */
        smb_slist_wait_for_empty(&lock->l_conflict_list);

        smb_lock_free(lock);
}

/*
 * smb_is_range_unlocked
 *
 * Checks if the current unlock byte range request overlaps another lock
 * This function is used to determine where POSIX unlocks should be
 * applied.
 *
 * The return code and the value of new_mark must be interpreted as
 * follows:
 *
 * B_TRUE and (new_mark == 0):
 *   This is the last or only lock left to be unlocked
 *
 * B_TRUE and (new_mark > 0):
 *   The range from start to new_mark can be unlocked
 *
 * B_FALSE and (new_mark == 0):
 *   The unlock can't be performed and we are done
 *
 * B_FALSE and (new_mark > 0),
 *   The range from start to new_mark can't be unlocked
 *   Start should be reset to new_mark for the next pass
 */

static boolean_t
smb_is_range_unlocked(uint64_t start, uint64_t end, uint32_t uniqid,
    smb_llist_t *llist_head, uint64_t *new_mark)
{
        struct smb_lock *lk = NULL;
        uint64_t low_water_mark = MAXOFFSET_T;
        uint64_t lk_start;
        uint64_t lk_end;

        *new_mark = 0;
        lk = smb_llist_head(llist_head);
        while (lk) {
                if (lk->l_length == 0) {
                        lk = smb_llist_next(llist_head, lk);
                        continue;
                }

                if (lk->l_file->f_uniqid != uniqid) {
                        lk = smb_llist_next(llist_head, lk);
                        continue;
                }

                lk_end = lk->l_start + lk->l_length - 1;
                lk_start = lk->l_start;

                /*
                 * there is no overlap for the first 2 cases
                 * check next node
                 */
                if (lk_end < start) {
                        lk = smb_llist_next(llist_head, lk);
                        continue;
                }
                if (lk_start > end) {
                        lk = smb_llist_next(llist_head, lk);
                        continue;
                }

                /* this range is completely locked */
                if ((lk_start <= start) && (lk_end >= end)) {
                        return (B_FALSE);
                }

                /* the first part of this range is locked */
                if ((start >= lk_start) && (start <= lk_end)) {
                        if (end > lk_end)
                                *new_mark = lk_end + 1;
                        return (B_FALSE);
                }

                /* this piece is unlocked */
                if ((lk_start >= start) && (lk_start <= end)) {
                        if (low_water_mark > lk_start)
                                low_water_mark  = lk_start;
                }

                lk = smb_llist_next(llist_head, lk);
        }

        if (low_water_mark != MAXOFFSET_T) {
                *new_mark = low_water_mark;
                return (B_TRUE);
        }
        /* the range is completely unlocked */
        return (B_TRUE);
}