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<concept id="GUID-2341CFE1-1CDF-537A-99FB-78C59FFA30CE" xml:lang="en"><title>Requesting
Data Notification Tutorial</title><shortdesc>Explains how to use the kernel trace tool API to request data notification.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>
<section id="GUID-2E72FF91-A53A-4EB0-92F7-9C99E68304BD"><title>Purpose</title> <p>Trace data is written to kernel side chunks.
The kernel trace tool API can request notification that data has been written
and requires further processing. </p> </section>
<section id="GUID-138D29CE-49C5-4FB4-9B50-07C1F8A8D7E4"><title>Intended audience</title> <p>This document is intended for
application developers writing a trace tool using the kernel trace tool component. </p></section>
<section id="GUID-F72D33B1-3B5B-40DF-AF95-866A72093E96"><title>Required background</title> <p>The trace filters defined in <codeph>EUser</codeph>.
The kernel trace tool component in general. </p> </section>
<section id="GUID-F0FE2BBC-0F1D-49D1-B9AD-E1F7BD9C13D0"><title>Introduction</title> <p>Requesting data notification is a
short task which is performed in combination with related tasks as explained
in <xref href="GUID-55C05441-33B5-5057-971D-4200345E941E.dita">Kernel Trace Tool
Tutorial</xref>. </p></section>
<section id="GUID-F6454A4A-9EF4-4794-9FD1-A359CBDD8768"><title>Using Kernel Trace tool to request data notification </title> <p>The
Following tasks will be covered in this tutorial: </p> <ul>
<li id="GUID-0D02154B-B044-595D-AB52-B1D3B9BBA95C"><p>Requesting data notification. </p> </li>
</ul> </section>
<section id="GUID-267174B1-47E0-4E56-AD67-57F3CC55CD9B"><title>Basic procedure</title> <p>The high level steps to requesting
data notification are shown here: </p> <ol id="GUID-22FAE4C1-02B0-53C1-817D-B7724B3CE44F">
<li id="GUID-6016B39C-1AF7-5D46-B81B-96C815576AF7"><p>Request data notification,
specifying the minimum number of bytes to return. </p> </li>
</ol> </section>
<section id="GUID-3CD1668E-C2AF-498A-9C2F-09C3729B15B8"><title>Using the API</title> <p>These are the function calls required
to </p> <ol id="GUID-4B5319BA-F739-5A6D-93D5-9F25F985A2C3">
<li id="GUID-9719F661-FD82-5616-BB85-E2E434DEC46E"><p>Call the <xref href="GUID-30D4103B-85D3-313A-B695-6CC7DF320E8F.dita"><apiname>RequestData()</apiname></xref> function
of the <xref href="GUID-9E859841-E8A3-37D5-9A19-BCAA3C700922.dita"><apiname>RBTrace</apiname></xref> object. This function has two arguments: </p> <ul>
<li id="GUID-D91274F9-5BA7-50E2-BA5D-7F57B2E8A842"><p>a <xref href="GUID-E0B34F3E-D4C4-3232-B8B1-7DB35B454646.dita"><apiname>TRequestStatus</apiname></xref> object
which takes the value KErrNone when data becomes available, and </p> </li>
<li id="GUID-ADF0D1E8-186D-540C-AA54-ECAF62780CBB"><p>a <xref href="GUID-7A2A43EC-6125-3BFE-834B-23C37F7B40D5.dita"><apiname>TInt</apiname></xref> specifying
the minimum number of bytes to return. </p> </li>
</ul> <p>The <xref href="GUID-E0B34F3E-D4C4-3232-B8B1-7DB35B454646.dita"><apiname>TRequestStatus</apiname></xref> object is intended for use
in the test statement of a loop in which the function call is embedded. </p> </li>
</ol> </section>
</conbody><related-links>
<link href="GUID-F27F49B3-4AC1-5517-AF3A-1ADBA1E87A0B.dita"><linktext>Kernel Trace
Tool Overview</linktext></link>
<link href="GUID-9E0957A1-0691-5741-ABCA-3EA61B4AC0CD.dita"><linktext>Kernel Trace
Tool Tutorial</linktext></link>
</related-links></concept>