<?xml version="1.0" encoding="utf-8"?>
<!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. -->
<!-- This component and the accompanying materials are made available under the terms of the License 
"Eclipse Public License v1.0" which accompanies this distribution, 
and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". -->
<!-- Initial Contributors:
    Nokia Corporation - initial contribution.
Contributors: 
-->
<!DOCTYPE concept
  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
<concept id="GUID-3102F778-DD2F-4C87-A0DF-7FA44C9709D8" xml:lang="en"><title>Multiple
Client Support</title><shortdesc>This document describes how multiple clients can access a driver
over a single logical channel.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>
<p>A single channel has a single handle which is shared by driver users. A
driver can allow or prevent the sharing of a handle to a logical channel between
multiple users. This policy is implemented by the <xref href="GUID-A3CC1D95-4681-3349-A67C-F113A614041D.dita#GUID-A3CC1D95-4681-3349-A67C-F113A614041D/GUID-9E23019E-7383-371E-B63C-85500F6B653D"><apiname>DLogicalChannel::RequestUserHandle()</apiname></xref> function.
The default implementation does not restrict sharing of the channel, but a
driver can override the function to change this. </p>
<p>In the following example, the driver ensures that only the intended clients
can get the handle and access the driver. Any other client that tries to share
the handle gets a <codeph>KErrAccessDenied</codeph> error. </p>
<codeblock id="GUID-2FEB04B3-ABD3-58E4-BFDB-0AD947BA6E16" xml:space="preserve">TInt DExDriverLogicalChannel::RequestUserHandle(DThread* aThread,
        TOwnerType aType)
    {
    // Handle should be provided only to the intended client. Any 
    // other clients that try to get a handle to the driver should get an access 
    // denied error.
    if ( aType!=EOwnerThread || aThread!=iClient)
        return KErrAccessDenied;
    return KErrNone;
    }</codeblock>
<p> <xref href="GUID-A3CC1D95-4681-3349-A67C-F113A614041D.dita#GUID-A3CC1D95-4681-3349-A67C-F113A614041D/GUID-9E23019E-7383-371E-B63C-85500F6B653D"><apiname>DLogicalChannel::RequestUserHandle()</apiname></xref> only restricts
the user from sharing or duplicating an existing channel. It does not restrict
another process from opening its own separate channel on the same device. </p>
<p> <note> More than one user can access the driver at the same time. It is
up to the driver to manage and provide correct and secure access to the driver. </note></p>
</conbody></concept>