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<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>