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    10 <!DOCTYPE concept

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

    12 <concept id="GUID-FD8634B8-E522-4AC4-8129-ED807A7754A2-GENID-1-2-1-9-1-5-1-6-1" xml:lang="en"><title>Kernel-side

    13 Implementation</title><shortdesc>This document describes kernel-side implementation of requests

    14 to device drivers.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

    15 <p>Requests from the user-side are initially handled by the driver

    16 in the context of the client user-side thread. All requests are passed to

    17 the "gateway" function: <xref href="GUID-E7550422-5121-3393-A85E-BB797969CD2A.dita#GUID-E7550422-5121-3393-A85E-BB797969CD2A/GUID-FD4DA73F-45E7-37BE-9380-1D8ED36114F7"><apiname>DLogicalChannelBase::Request()</apiname></xref>.

    18 This is defined as pure virtual in <codeph>DLogicalChannelBase</codeph>, and

    19 needs to be implemented in a derived class as part of your logical channel

    20 implementation. </p>

    21 <fig id="GUID-0DEEF003-53B6-5892-8FF2-6684BC424E27-GENID-1-2-1-9-1-5-1-6-1-3-2">

    22 <title>                 Device driver logical channel communication      

    23         </title>

    24 <image href="GUID-4A2E212E-BC1B-5965-9A62-6309CC7CAAAB_d0e61647_href.png" placement="inline"/>

    25 </fig>

    26 <p>There are two options for implementing this: </p>

    27 <ol id="GUID-F9FDC221-82F8-569E-B12A-969194137E24-GENID-1-2-1-9-1-5-1-6-1-3-4">

    28 <li id="GUID-A58B2511-6058-5DE6-8407-0ED4EB7A0112-GENID-1-2-1-9-1-5-1-6-1-3-4-1"><p>Use the ready-made framework

    29 provided by the <xref href="GUID-A3CC1D95-4681-3349-A67C-F113A614041D.dita"><apiname>DLogicalChannel</apiname></xref> class, which handles a

    30 request in the context of a single kernel-side thread. This framework uses

    31 the kernel-side messaging mechanism for queuing requests on a DFC that runs

    32 in that single kernel-side thread. </p> <p>In practice, this model makes the

    33 writing of device drivers easier because the same kernel thread can be used

    34 to process requests from (potentially multiple) user-side clients and DFCs,

    35 thus in effect serialising access to the device driver, and eliminating thread-related

    36 issues, such as the need to know about mutexes, pre-emption, etc. Several

    37 drivers can use the same request/DFC kernel thread to reduce resource usage. </p> </li>

    38 <li id="GUID-DE277962-5BDC-5CD7-9868-65FA576E11AD-GENID-1-2-1-9-1-5-1-6-1-3-4-2"><p>Derive your own logical

    39 channel class from <xref href="GUID-E7550422-5121-3393-A85E-BB797969CD2A.dita"><apiname>DLogicalChannelBase</apiname></xref> to handle requests.

    40 This allows you to build your own thread model for running DFCs to handle

    41 requests and to handle request completion. This requires that you manage inter-thread

    42 conflicts. However, your design may give you the chance to do some optimisation

    43 by handling some requests in the context of the user-side thread, minimising

    44 context-switching overhead. </p> </li>

    45 </ol>

    46 <p>Option 1 lets you get a new driver up and running quickly. Option 2 gives

    47 you greater flexibility if the requirements of your driver demand it. </p>

    48 </conbody></concept>