py/security: Add test for dom_sid.split.

[Samba/fernandojvsilva.git] / source3 / smbd / blocking.c

/* 
   Unix SMB/CIFS implementation.
   Blocking Locking functions
   Copyright (C) Jeremy Allison 1998-2003

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.

   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 for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

#include "includes.h"
#include "smbd/globals.h"

#undef DBGC_CLASS
#define DBGC_CLASS DBGC_LOCKING

/****************************************************************************
 Determine if this is a secondary element of a chained SMB.
  **************************************************************************/

static void received_unlock_msg(struct messaging_context *msg,
                                void *private_data,
                                uint32_t msg_type,
                                struct server_id server_id,
                                DATA_BLOB *data);

static void brl_timeout_fn(struct event_context *event_ctx,
                           struct timed_event *te,
                           struct timeval now,
                           void *private_data)
{
        SMB_ASSERT(brl_timeout == te);
        TALLOC_FREE(brl_timeout);

        change_to_root_user();  /* TODO: Possibly run all timed events as
                                 * root */

        process_blocking_lock_queue();
}

/****************************************************************************
 We need a version of timeval_min that treats zero timval as infinite.
****************************************************************************/

static struct timeval timeval_brl_min(const struct timeval *tv1,
                                        const struct timeval *tv2)
{
        if (timeval_is_zero(tv1)) {
                return *tv2;
        }
        if (timeval_is_zero(tv2)) {
                return *tv1;
        }
        return timeval_min(tv1, tv2);
}

/****************************************************************************
 After a change to blocking_lock_queue, recalculate the timed_event for the
 next processing.
****************************************************************************/

static bool recalc_brl_timeout(void)
{
        struct blocking_lock_record *blr;
        struct timeval next_timeout;

        TALLOC_FREE(brl_timeout);

        next_timeout = timeval_zero();  

        for (blr = blocking_lock_queue; blr; blr = blr->next) {
                if (timeval_is_zero(&blr->expire_time)) {
                        /*
                         * If we're blocked on pid 0xFFFFFFFF this is
                         * a POSIX lock, so calculate a timeout of
                         * 10 seconds into the future.
                         */
                        if (blr->blocking_pid == 0xFFFFFFFF) {
                                struct timeval psx_to = timeval_current_ofs(10, 0);
                                next_timeout = timeval_brl_min(&next_timeout, &psx_to);
                        }

                        continue;
                }

                next_timeout = timeval_brl_min(&next_timeout, &blr->expire_time);
        }

        if (timeval_is_zero(&next_timeout)) {
                DEBUG(10, ("Next timeout = Infinite.\n"));
                return True;
        }

        if (DEBUGLVL(10)) {
                struct timeval cur, from_now;

                cur = timeval_current();
                from_now = timeval_until(&cur, &next_timeout);
                DEBUG(10, ("Next timeout = %d.%d seconds from now.\n",
                    (int)from_now.tv_sec, (int)from_now.tv_usec));
        }

        if (!(brl_timeout = event_add_timed(smbd_event_context(), NULL,
                                            next_timeout,
                                            brl_timeout_fn, NULL))) {
                return False;
        }

        return True;
}


/****************************************************************************
 Function to push a blocking lock request onto the lock queue.
****************************************************************************/

bool push_blocking_lock_request( struct byte_range_lock *br_lck,
                struct smb_request *req,
                files_struct *fsp,
                int lock_timeout,
                int lock_num,
                uint32_t lock_pid,
                enum brl_type lock_type,
                enum brl_flavour lock_flav,
                uint64_t offset,
                uint64_t count,
                uint32_t blocking_pid)
{
        struct blocking_lock_record *blr;
        NTSTATUS status;

        if(req_is_in_chain(req)) {
                DEBUG(0,("push_blocking_lock_request: cannot queue a chained request (currently).\n"));
                return False;
        }

        /*
         * Now queue an entry on the blocking lock queue. We setup
         * the expiration time here.
         */

        blr = talloc(NULL, struct blocking_lock_record);
        if (blr == NULL) {
                DEBUG(0,("push_blocking_lock_request: Malloc fail !\n" ));
                return False;
        }

        blr->next = NULL;
        blr->prev = NULL;

        blr->fsp = fsp;
        if (lock_timeout == -1) {
                blr->expire_time.tv_sec = 0;
                blr->expire_time.tv_usec = 0; /* Never expire. */
        } else {
                blr->expire_time = timeval_current_ofs(lock_timeout/1000,
                                        (lock_timeout % 1000) * 1000);
        }
        blr->lock_num = lock_num;
        blr->lock_pid = lock_pid;
        blr->blocking_pid = blocking_pid;
        blr->lock_flav = lock_flav;
        blr->lock_type = lock_type;
        blr->offset = offset;
        blr->count = count;
      
        /* Specific brl_lock() implementations can fill this in. */
        blr->blr_private = NULL;

        /* Add a pending lock record for this. */
        status = brl_lock(smbd_messaging_context(),
                        br_lck,
                        lock_pid,
                        procid_self(),
                        offset,
                        count,
                        lock_type == READ_LOCK ? PENDING_READ_LOCK : PENDING_WRITE_LOCK,
                        blr->lock_flav,
                        lock_timeout ? True : False, /* blocking_lock. */
                        NULL,
                        blr);

        if (!NT_STATUS_IS_OK(status)) {
                DEBUG(0,("push_blocking_lock_request: failed to add PENDING_LOCK record.\n"));
                TALLOC_FREE(blr);
                return False;
        }

        SMB_PERFCOUNT_DEFER_OP(&req->pcd, &req->pcd);
        blr->req = talloc_move(blr, &req);

        DLIST_ADD_END(blocking_lock_queue, blr, struct blocking_lock_record *);
        recalc_brl_timeout();

        /* Ensure we'll receive messages when this is unlocked. */
        if (!blocking_lock_unlock_state) {
                messaging_register(smbd_messaging_context(), NULL,
                                   MSG_SMB_UNLOCK, received_unlock_msg);
                blocking_lock_unlock_state = true;
        }

        DEBUG(3,("push_blocking_lock_request: lock request blocked with "
                "expiry time (%u sec. %u usec) (+%d msec) for fnum = %d, name = %s\n",
                (unsigned int)blr->expire_time.tv_sec,
                (unsigned int)blr->expire_time.tv_usec, lock_timeout,
                blr->fsp->fnum, fsp_str_dbg(blr->fsp)));

        return True;
}

/****************************************************************************
 Return a lockingX success SMB.
*****************************************************************************/

static void reply_lockingX_success(struct blocking_lock_record *blr)
{
        reply_outbuf(blr->req, 2, 0);

        /*
         * As this message is a lockingX call we must handle
         * any following chained message correctly.
         * This is normally handled in construct_reply(),
         * but as that calls switch_message, we can't use
         * that here and must set up the chain info manually.
         */

        chain_reply(blr->req);
        TALLOC_FREE(blr->req->outbuf);
}

/****************************************************************************
 Return a generic lock fail error blocking call.
*****************************************************************************/

static void generic_blocking_lock_error(struct blocking_lock_record *blr, NTSTATUS status)
{
        /* whenever a timeout is given w2k maps LOCK_NOT_GRANTED to
           FILE_LOCK_CONFLICT! (tridge) */
        if (NT_STATUS_EQUAL(status, NT_STATUS_LOCK_NOT_GRANTED)) {
                status = NT_STATUS_FILE_LOCK_CONFLICT;
        }

        if (NT_STATUS_EQUAL(status, NT_STATUS_FILE_LOCK_CONFLICT)) {
                /* Store the last lock error. */
                files_struct *fsp = blr->fsp;

                if (fsp) {
                        fsp->last_lock_failure.context.smbpid = blr->lock_pid;
                        fsp->last_lock_failure.context.tid = fsp->conn->cnum;
                        fsp->last_lock_failure.context.pid = procid_self();
                        fsp->last_lock_failure.start = blr->offset;
                        fsp->last_lock_failure.size = blr->count;
                        fsp->last_lock_failure.fnum = fsp->fnum;
                        fsp->last_lock_failure.lock_type = READ_LOCK; /* Don't care. */
                        fsp->last_lock_failure.lock_flav = blr->lock_flav;
                }
        }

        reply_nterror(blr->req, status);
        if (!srv_send_smb(smbd_server_fd(), (char *)blr->req->outbuf,
                          true, blr->req->seqnum+1,
                          blr->req->encrypted, NULL)) {
                exit_server_cleanly("generic_blocking_lock_error: srv_send_smb failed.");
        }
        TALLOC_FREE(blr->req->outbuf);
}

/****************************************************************************
 Return a lock fail error for a lockingX call. Undo all the locks we have 
 obtained first.
*****************************************************************************/

static void reply_lockingX_error(struct blocking_lock_record *blr, NTSTATUS status)
{
        files_struct *fsp = blr->fsp;
        uint16 num_ulocks = SVAL(blr->req->vwv+6, 0);
        uint64_t count = (uint64_t)0, offset = (uint64_t) 0;
        uint32 lock_pid;
        unsigned char locktype = CVAL(blr->req->vwv+3, 0);
        bool large_file_format = (locktype & LOCKING_ANDX_LARGE_FILES);
        uint8_t *data;
        int i;

        data = (uint8_t *)blr->req->buf
                + ((large_file_format ? 20 : 10)*num_ulocks);

        /* 
         * Data now points at the beginning of the list
         * of smb_lkrng structs.
         */

        /*
         * Ensure we don't do a remove on the lock that just failed,
         * as under POSIX rules, if we have a lock already there, we
         * will delete it (and we shouldn't) .....
         */

        for(i = blr->lock_num - 1; i >= 0; i--) {
                bool err;

                lock_pid = get_lock_pid( data, i, large_file_format);
                count = get_lock_count( data, i, large_file_format);
                offset = get_lock_offset( data, i, large_file_format, &err);

                /*
                 * We know err cannot be set as if it was the lock
                 * request would never have been queued. JRA.
                 */

                do_unlock(smbd_messaging_context(),
                        fsp,
                        lock_pid,
                        count,
                        offset,
                        WINDOWS_LOCK);
        }

        generic_blocking_lock_error(blr, status);
}

/****************************************************************************
 Return a lock fail error.
*****************************************************************************/

static void blocking_lock_reply_error(struct blocking_lock_record *blr, NTSTATUS status)
{
        DEBUG(10, ("Replying with error=%s. BLR = %p\n", nt_errstr(status), blr));

        switch(blr->req->cmd) {
        case SMBlockingX:
                reply_lockingX_error(blr, status);
                break;
        case SMBtrans2:
        case SMBtranss2:
                reply_nterror(blr->req, status);

                /*
                 * construct_reply_common has done us the favor to pre-fill
                 * the command field with SMBtranss2 which is wrong :-)
                 */
                SCVAL(blr->req->outbuf,smb_com,SMBtrans2);

                if (!srv_send_smb(smbd_server_fd(),
                                  (char *)blr->req->outbuf,
                                  true, blr->req->seqnum+1,
                                  IS_CONN_ENCRYPTED(blr->fsp->conn),
                                  NULL)) {
                        exit_server_cleanly("blocking_lock_reply_error: "
                                            "srv_send_smb failed.");
                }
                TALLOC_FREE(blr->req->outbuf);
                break;
        default:
                DEBUG(0,("blocking_lock_reply_error: PANIC - unknown type on blocking lock queue - exiting.!\n"));
                exit_server("PANIC - unknown type on blocking lock queue");
        }
}

/****************************************************************************
 Attempt to finish off getting all pending blocking locks for a lockingX call.
 Returns True if we want to be removed from the list.
*****************************************************************************/

static bool process_lockingX(struct blocking_lock_record *blr)
{
        unsigned char locktype = CVAL(blr->req->vwv+3, 0);
        files_struct *fsp = blr->fsp;
        uint16 num_ulocks = SVAL(blr->req->vwv+6, 0);
        uint16 num_locks = SVAL(blr->req->vwv+7, 0);
        uint64_t count = (uint64_t)0, offset = (uint64_t)0;
        uint32 lock_pid;
        bool large_file_format = (locktype & LOCKING_ANDX_LARGE_FILES);
        uint8_t *data;
        NTSTATUS status = NT_STATUS_OK;

        data = (uint8_t *)blr->req->buf
                + ((large_file_format ? 20 : 10)*num_ulocks);

        /* 
         * Data now points at the beginning of the list
         * of smb_lkrng structs.
         */

        for(; blr->lock_num < num_locks; blr->lock_num++) {
                struct byte_range_lock *br_lck = NULL;
                bool err;

                lock_pid = get_lock_pid( data, blr->lock_num, large_file_format);
                count = get_lock_count( data, blr->lock_num, large_file_format);
                offset = get_lock_offset( data, blr->lock_num, large_file_format, &err);

                /*
                 * We know err cannot be set as if it was the lock
                 * request would never have been queued. JRA.
                 */
                errno = 0;
                br_lck = do_lock(smbd_messaging_context(),
                                fsp,
                                lock_pid,
                                count,
                                offset, 
                                ((locktype & LOCKING_ANDX_SHARED_LOCK) ?
                                        READ_LOCK : WRITE_LOCK),
                                WINDOWS_LOCK,
                                True,
                                &status,
                                &blr->blocking_pid,
                                blr);

                TALLOC_FREE(br_lck);

                if (NT_STATUS_IS_ERR(status)) {
                        break;
                }
        }

        if(blr->lock_num == num_locks) {
                /*
                 * Success - we got all the locks.
                 */

                DEBUG(3,("process_lockingX file = %s, fnum=%d type=%d "
                         "num_locks=%d\n", fsp_str_dbg(fsp), fsp->fnum,
                         (unsigned int)locktype, num_locks));

                reply_lockingX_success(blr);
                return True;
        }

        if (!NT_STATUS_EQUAL(status,NT_STATUS_LOCK_NOT_GRANTED) &&
            !NT_STATUS_EQUAL(status,NT_STATUS_FILE_LOCK_CONFLICT)) {
                /*
                 * We have other than a "can't get lock"
                 * error. Free any locks we had and return an error.
                 * Return True so we get dequeued.
                 */
                blocking_lock_reply_error(blr, status);
                return True;
        }

        /*
         * Still can't get all the locks - keep waiting.
         */

        DEBUG(10,("process_lockingX: only got %d locks of %d needed for file %s, fnum = %d. \
Waiting....\n", 
                 blr->lock_num, num_locks, fsp_str_dbg(fsp), fsp->fnum));

        return False;
}

/****************************************************************************
 Attempt to get the posix lock request from a SMBtrans2 call.
 Returns True if we want to be removed from the list.
*****************************************************************************/

static bool process_trans2(struct blocking_lock_record *blr)
{
        char params[2];
        NTSTATUS status;
        struct byte_range_lock *br_lck = do_lock(smbd_messaging_context(),
                                                blr->fsp,
                                                blr->lock_pid,
                                                blr->count,
                                                blr->offset,
                                                blr->lock_type,
                                                blr->lock_flav,
                                                True,
                                                &status,
                                                &blr->blocking_pid,
                                                blr);
        TALLOC_FREE(br_lck);

        if (!NT_STATUS_IS_OK(status)) {
                if (ERROR_WAS_LOCK_DENIED(status)) {
                        /* Still can't get the lock, just keep waiting. */
                        return False;
                }       
                /*
                 * We have other than a "can't get lock"
                 * error. Send an error and return True so we get dequeued.
                 */
                blocking_lock_reply_error(blr, status);
                return True;
        }

        /* We finally got the lock, return success. */

        SSVAL(params,0,0);
        /* Fake up max_data_bytes here - we know it fits. */
        send_trans2_replies(blr->fsp->conn, blr->req, params, 2, NULL, 0, 0xffff);
        return True;
}


/****************************************************************************
 Process a blocking lock SMB.
 Returns True if we want to be removed from the list.
*****************************************************************************/

static bool blocking_lock_record_process(struct blocking_lock_record *blr)
{
        switch(blr->req->cmd) {
                case SMBlockingX:
                        return process_lockingX(blr);
                case SMBtrans2:
                case SMBtranss2:
                        return process_trans2(blr);
                default:
                        DEBUG(0,("blocking_lock_record_process: PANIC - unknown type on blocking lock queue - exiting.!\n"));
                        exit_server("PANIC - unknown type on blocking lock queue");
        }
        return False; /* Keep compiler happy. */
}

/****************************************************************************
 Cancel entries by fnum from the blocking lock pending queue.
*****************************************************************************/

void cancel_pending_lock_requests_by_fid(files_struct *fsp, struct byte_range_lock *br_lck)
{
        struct blocking_lock_record *blr, *blr_cancelled, *next = NULL;

        for(blr = blocking_lock_queue; blr; blr = next) {
                unsigned char locktype = 0;

                next = blr->next;
                if (blr->fsp->fnum != fsp->fnum) {
                        continue;
                }

                if (blr->req->cmd == SMBlockingX) {
                        locktype = CVAL(blr->req->vwv+3, 0);
                }

                DEBUG(10, ("remove_pending_lock_requests_by_fid - removing "
                           "request type %d for file %s fnum = %d\n",
                           blr->req->cmd, fsp_str_dbg(fsp), fsp->fnum));

                blr_cancelled = blocking_lock_cancel(fsp,
                                     blr->lock_pid,
                                     blr->offset,
                                     blr->count,
                                     blr->lock_flav,
                                     locktype,
                                     NT_STATUS_RANGE_NOT_LOCKED);

                SMB_ASSERT(blr_cancelled == blr);

                brl_lock_cancel(br_lck,
                                blr->lock_pid,
                                procid_self(),
                                blr->offset,
                                blr->count,
                                blr->lock_flav,
                                blr);

                /* We're closing the file fsp here, so ensure
                 * we don't have a dangling pointer. */
                blr->fsp = NULL;
        }
}

/****************************************************************************
 Delete entries by mid from the blocking lock pending queue. Always send reply.
*****************************************************************************/

void remove_pending_lock_requests_by_mid(int mid)
{
        struct blocking_lock_record *blr, *next = NULL;

        for(blr = blocking_lock_queue; blr; blr = next) {
                files_struct *fsp;
                struct byte_range_lock *br_lck;

                next = blr->next;

                if (blr->req->mid != mid) {
                        continue;
                }

                fsp = blr->fsp;
                br_lck = brl_get_locks(talloc_tos(), fsp);

                if (br_lck) {
                        DEBUG(10, ("remove_pending_lock_requests_by_mid - "
                                   "removing request type %d for file %s fnum "
                                   "= %d\n", blr->req->cmd, fsp_str_dbg(fsp),
                                   fsp->fnum ));

                        brl_lock_cancel(br_lck,
                                        blr->lock_pid,
                                        procid_self(),
                                        blr->offset,
                                        blr->count,
                                        blr->lock_flav,
                                        blr);
                        TALLOC_FREE(br_lck);
                }

                blocking_lock_reply_error(blr,NT_STATUS_FILE_LOCK_CONFLICT);
                DLIST_REMOVE(blocking_lock_queue, blr);
                TALLOC_FREE(blr);
        }
}

/****************************************************************************
 Is this mid a blocking lock request on the queue ?
*****************************************************************************/

bool blocking_lock_was_deferred(int mid)
{
        struct blocking_lock_record *blr, *next = NULL;

        for(blr = blocking_lock_queue; blr; blr = next) {
                next = blr->next;
                if(blr->req->mid == mid) {
                        return True;
                }
        }
        return False;
}

/****************************************************************************
  Set a flag as an unlock request affects one of our pending locks.
*****************************************************************************/

static void received_unlock_msg(struct messaging_context *msg,
                                void *private_data,
                                uint32_t msg_type,
                                struct server_id server_id,
                                DATA_BLOB *data)
{
        DEBUG(10,("received_unlock_msg\n"));
        process_blocking_lock_queue();
}

/****************************************************************************
 Process the blocking lock queue. Note that this is only called as root.
*****************************************************************************/

void process_blocking_lock_queue(void)
{
        struct timeval tv_curr = timeval_current();
        struct blocking_lock_record *blr, *next = NULL;

        /*
         * Go through the queue and see if we can get any of the locks.
         */

        for (blr = blocking_lock_queue; blr; blr = next) {

                next = blr->next;

                /*
                 * Go through the remaining locks and try and obtain them.
                 * The call returns True if all locks were obtained successfully
                 * and False if we still need to wait.
                 */

                DEBUG(10, ("Processing BLR = %p\n", blr));

                /* We use set_current_service so connections with
                 * pending locks are not marked as idle.
                 */

                set_current_service(blr->fsp->conn,
                                SVAL(blr->req->inbuf,smb_flg),
                                false);

                if(blocking_lock_record_process(blr)) {
                        struct byte_range_lock *br_lck = brl_get_locks(
                                talloc_tos(), blr->fsp);

                        DEBUG(10, ("BLR_process returned true: cancelling and "
                            "removing lock. BLR = %p\n", blr));

                        if (br_lck) {
                                brl_lock_cancel(br_lck,
                                        blr->lock_pid,
                                        procid_self(),
                                        blr->offset,
                                        blr->count,
                                        blr->lock_flav,
                                        blr);
                                TALLOC_FREE(br_lck);
                        }

                        DLIST_REMOVE(blocking_lock_queue, blr);
                        TALLOC_FREE(blr);
                        continue;
                }

                /*
                 * We couldn't get the locks for this record on the list.
                 * If the time has expired, return a lock error.
                 */

                if (!timeval_is_zero(&blr->expire_time) && timeval_compare(&blr->expire_time, &tv_curr) <= 0) {
                        struct byte_range_lock *br_lck = brl_get_locks(
                                talloc_tos(), blr->fsp);

                        DEBUG(10, ("Lock timed out! BLR = %p\n", blr));

                        /*
                         * Lock expired - throw away all previously
                         * obtained locks and return lock error.
                         */

                        if (br_lck) {
                                DEBUG(5,("process_blocking_lock_queue: "
                                         "pending lock fnum = %d for file %s "
                                         "timed out.\n", blr->fsp->fnum,
                                         fsp_str_dbg(blr->fsp)));

                                brl_lock_cancel(br_lck,
                                        blr->lock_pid,
                                        procid_self(),
                                        blr->offset,
                                        blr->count,
                                        blr->lock_flav,
                                        blr);
                                TALLOC_FREE(br_lck);
                        }

                        blocking_lock_reply_error(blr,NT_STATUS_FILE_LOCK_CONFLICT);
                        DLIST_REMOVE(blocking_lock_queue, blr);
                        TALLOC_FREE(blr);
                }
        }

        recalc_brl_timeout();
}

/****************************************************************************
 Handle a cancel message. Lock already moved onto the cancel queue.
*****************************************************************************/

#define MSG_BLOCKING_LOCK_CANCEL_SIZE (sizeof(struct blocking_lock_record *) + sizeof(NTSTATUS))

static void process_blocking_lock_cancel_message(struct messaging_context *ctx,
                                                 void *private_data,
                                                 uint32_t msg_type,
                                                 struct server_id server_id,
                                                 DATA_BLOB *data)
{
        NTSTATUS err;
        const char *msg = (const char *)data->data;
        struct blocking_lock_record *blr;

        if (data->data == NULL) {
                smb_panic("process_blocking_lock_cancel_message: null msg");
        }

        if (data->length != MSG_BLOCKING_LOCK_CANCEL_SIZE) {
                DEBUG(0, ("process_blocking_lock_cancel_message: "
                          "Got invalid msg len %d\n", (int)data->length));
                smb_panic("process_blocking_lock_cancel_message: bad msg");
        }

        memcpy(&blr, msg, sizeof(blr));
        memcpy(&err, &msg[sizeof(blr)], sizeof(NTSTATUS));

        DEBUG(10,("process_blocking_lock_cancel_message: returning error %s\n",
                nt_errstr(err) ));

        blocking_lock_reply_error(blr, err);
        DLIST_REMOVE(blocking_lock_cancelled_queue, blr);
        TALLOC_FREE(blr);
}

/****************************************************************************
 Send ourselves a blocking lock cancelled message. Handled asynchronously above.
 Returns the blocking_lock_record that is being cancelled.
*****************************************************************************/

struct blocking_lock_record *blocking_lock_cancel(files_struct *fsp,
                        uint32 lock_pid,
                        uint64_t offset,
                        uint64_t count,
                        enum brl_flavour lock_flav,
                        unsigned char locktype,
                        NTSTATUS err)
{
        char msg[MSG_BLOCKING_LOCK_CANCEL_SIZE];
        struct blocking_lock_record *blr;

        if (!blocking_lock_cancel_state) {
                /* Register our message. */
                messaging_register(smbd_messaging_context(), NULL,
                                   MSG_SMB_BLOCKING_LOCK_CANCEL,
                                   process_blocking_lock_cancel_message);

                blocking_lock_cancel_state = True;
        }

        for (blr = blocking_lock_queue; blr; blr = blr->next) {
                if (fsp == blr->fsp &&
                                lock_pid == blr->lock_pid &&
                                offset == blr->offset &&
                                count == blr->count &&
                                lock_flav == blr->lock_flav) {
                        break;
                }
        }

        if (!blr) {
                return NULL;
        }

        /* Check the flags are right. */
        if (blr->req->cmd == SMBlockingX &&
                (locktype & LOCKING_ANDX_LARGE_FILES) !=
                        (CVAL(blr->req->vwv+3, 0) & LOCKING_ANDX_LARGE_FILES)) {
                return NULL;
        }

        /* Move to cancelled queue. */
        DLIST_REMOVE(blocking_lock_queue, blr);
        DLIST_ADD(blocking_lock_cancelled_queue, blr);

        /* Create the message. */
        memcpy(msg, &blr, sizeof(blr));
        memcpy(&msg[sizeof(blr)], &err, sizeof(NTSTATUS));

        messaging_send_buf(smbd_messaging_context(), procid_self(),
                           MSG_SMB_BLOCKING_LOCK_CANCEL,
                           (uint8 *)&msg, sizeof(msg));

        return blr;
}