134 lines
7.4 KiB
HTML
134 lines
7.4 KiB
HTML
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<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE html
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PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html lang="en-us" xml:lang="en-us">
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<meta name="DC.Type" content="reference" />
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<meta name="DC.Title" content="Using special attributes" />
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<meta name="abstract" content="Read about special attributes unique to the optical file system." />
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<meta name="description" content="Read about special attributes unique to the optical file system." />
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<meta name="copyright" content="(C) Copyright IBM Corporation 2000, 2006" />
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<meta name="DC.Identifier" content="specialattributes" />
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<!-- All rights reserved. Licensed Materials Property of IBM -->
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<link rel="stylesheet" type="text/css" href="./ibmdita.css" />
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<link rel="stylesheet" type="text/css" href="./ic.css" />
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<title>Using special attributes </title>
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</head>
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<body id="specialattributes"><a name="specialattributes"><!-- --></a>
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<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">Using special attributes </h1>
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<div><p>Read about special attributes unique to the optical file system.</p>
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<div class="section"><p>Attributes for files and directories that are not standard and
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therefore not recognized by HFS are referred to by HFS as <em>extended attributes</em>.
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They are usually defined by a business application, but some are recognized
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by the optical file system as having special meaning.</p>
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</div>
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<div class="section"><h4 class="sectiontitle">OPT.CHGATDTTM attribute</h4><p>This optical attribute reflects
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the last date and time that the file attributes were written. It is returned
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to the user application as an extended attribute through the Retrieve Directory
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Entry Attributes (QHFRTVAT) command.</p>
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</div>
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<div class="section"><h4 class="sectiontitle">QOPT.IOMETH attribute</h4><p>This is a special extended
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attribute to the optical file system. Provided supported is only by directly-attached
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optical support devices; it is ignored by LAN support. The system also ignores
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this attribute when the media format is Universal Disk Format.</p>
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<p>When
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an extended attribute of this name is passed by the application as the attribute
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name field in the Attribute Information Table (AIT) during an open stream
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file request, the optical file system knows that a special method of I/O is
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being requested. The optical file system retrieves the special method of I/O
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from the attribute value field in the AIT.</p>
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<p> Currently, there is only
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one special method of I/O supported by the optical file system: You can request
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this method of I/O when the attribute value field for the QOPT.IOMETH attribute
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contains the value (EXPNBUFF). The optical software recognizes this special
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extended attribute as a requested I/O method, and not as a normal extended
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attribute. It is not hereafter associated with the file in any way, and does
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not appear when attributes for the file are retrieved. All read operations
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for the process use expanding buffer I/O until the file is closed. Methodology
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and restrictions for using expanding buffer I/O are listed here. In order
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to determine if expanding buffer I/O should be used, see Expanding buffer
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I/O through HFS.</p>
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<p>An HFS attribute in an attribute information table
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consists of several fields. These fields and the values you specify when opening
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a file for expanding buffer I/O are summarized in the following table.</p>
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<div class="tablenoborder"><table cellpadding="4" cellspacing="0" summary="" frame="border" border="1" rules="all"><caption>Table 1. Expanding buffer attribute definition</caption><thead align="left"><tr><th valign="top" id="d0e43">Field</th>
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<th valign="top" id="d0e45">Data type (see note)</th>
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<th valign="top" id="d0e47">Value for EBIO</th>
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</tr>
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</thead>
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<tbody><tr><td valign="top" headers="d0e43 ">Attribute name</td>
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<td valign="top" headers="d0e45 ">CHAR(*)</td>
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<td valign="top" headers="d0e47 ">QOPT.IOMETH</td>
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</tr>
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<tr><td valign="top" headers="d0e43 ">Attribute value</td>
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<td valign="top" headers="d0e45 ">CHAR(*)</td>
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<td valign="top" headers="d0e47 ">EXPNBUFF</td>
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</tr>
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<tr><td valign="top" headers="d0e43 ">Length attribute name</td>
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<td valign="top" headers="d0e45 ">BIN(4)</td>
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<td valign="top" headers="d0e47 ">0000000B</td>
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</tr>
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<tr><td valign="top" headers="d0e43 ">Length attribute value</td>
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<td valign="top" headers="d0e45 ">BIN(4)</td>
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<td valign="top" headers="d0e47 ">00000008</td>
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</tr>
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<tr><td colspan="3" valign="top" headers="d0e43 d0e45 d0e47 "><div class="note"><span class="notetitle">Note:</span> </div>
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<ul><li>CHAR(*) indicates a variable number of bytes of character information. </li>
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<li>BIN(4) indicates 4 bytes of binary information.</li>
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<li>All character fields should be set in uppercase.</li>
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</ul>
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</td>
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</tr>
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</tbody>
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</table>
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</div>
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<div class="p">In addition to the values for attribute fields, two additional
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fields are required to build an attribute information table: <ul><li>The number of attributes defined in the table</li>
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<li>The table offset to each attribute, in bytes</li>
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</ul>
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</div>
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<div class="p">The Open Stream File (QHFOPNSF) API requires 10 bytes of open
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information as input. When you attempt to open a file for expanding buffer
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I/O, the open information is subject to the following restrictions: <ul><li>The action to take if a file exists must be to open the file.</li>
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<li>The action to take if a file does not exist must be to return an error. </li>
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<li>The lock mode for the file must be Deny Write or Deny Read/Write (exclusive). </li>
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<li>The access mode for the file must be Read Only.</li>
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</ul>
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</div>
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<p>If there is an expanded buffer I/O attribute in the attribute
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information table and any of these restrictions are not observed, an OPT1133
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message is issued, indicating which of the fields in the open information
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was passed in error.</p>
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<p>For information about the format of attributes,
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the Attribute Information Table, or the Open Stream File API, see the <a href="../apiref/api.htm">APIs topic</a>.</p>
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</div>
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<div class="section"><h4 class="sectiontitle">Restrictions for expanding buffer I/O</h4><div class="p">In addition
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to the restrictions that were detailed when opening a file for expanded buffer
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I/O, you cannot use the following APIs for expanding buffer I/O, after a file
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is opened: <ul><li>Write Stream File</li>
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<li>Set Stream File Size</li>
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<li>Lock or Unlock Range in Stream File</li>
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</ul>
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</div>
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</div>
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</div>
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<div>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="hfs.htm" title="Read this topic collection to learn how to program with the hierarchical file system (HFS).">Hierarchical file system (HFS) programming</a></div>
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</div>
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</div>
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</body>
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</html>
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