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     7     Nokia Corporation - initial contribution.

     8 Contributors: 

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    10 <!DOCTYPE concept

    11   PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">

    12 <concept id="GUID-3102F778-DD2F-4C87-A0DF-7FA44C9709D8" xml:lang="en"><title>Multiple

    13 Client Support</title><shortdesc>This document describes how multiple clients can access a driver

    14 over a single logical channel.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

    15 <p>A single channel has a single handle which is shared by driver users. A

    16 driver can allow or prevent the sharing of a handle to a logical channel between

    17 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.

    18 The default implementation does not restrict sharing of the channel, but a

    19 driver can override the function to change this. </p>

    20 <p>In the following example, the driver ensures that only the intended clients

    21 can get the handle and access the driver. Any other client that tries to share

    22 the handle gets a <codeph>KErrAccessDenied</codeph> error. </p>

    23 <codeblock id="GUID-2FEB04B3-ABD3-58E4-BFDB-0AD947BA6E16" xml:space="preserve">TInt DExDriverLogicalChannel::RequestUserHandle(DThread* aThread,

    24         TOwnerType aType)

    25     {

    26     // Handle should be provided only to the intended client. Any 

    27     // other clients that try to get a handle to the driver should get an access 

    28     // denied error.

    29     if ( aType!=EOwnerThread || aThread!=iClient)

    30         return KErrAccessDenied;

    31     return KErrNone;

    32     }</codeblock>

    33 <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

    34 the user from sharing or duplicating an existing channel. It does not restrict

    35 another process from opening its own separate channel on the same device. </p>

    36 <p> <note> More than one user can access the driver at the same time. It is

    37 up to the driver to manage and provide correct and secure access to the driver. </note></p>

    38 </conbody></concept>