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<div id="projectbrief">Aaru Data Preservation Suite - Format Library</div>
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<div class="headertitle"><div class="title">TapeFileHeader Struct Reference</div></div>
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<p>Header for a tape file metadata block containing file layout information.
<a href="#details">More...</a></p>
<p><code>#include &lt;<a class="el" href="tape_8h_source.html">aaruformat/structs/tape.h</a>&gt;</code></p>
<table class="memberdecls">
<tr class="heading"><td colspan="2"><h2 id="header-pub-attribs" class="groupheader"><a id="pub-attribs" name="pub-attribs"></a>
Data Fields</h2></td></tr>
<tr class="memitem:a36fe923f8d67004e0b0ae8eaf6535e1d" id="r_a36fe923f8d67004e0b0ae8eaf6535e1d"><td class="memItemLeft" align="right" valign="top">uint32_t&#160;</td><td class="memItemRight" valign="bottom"><a class="el" href="#a36fe923f8d67004e0b0ae8eaf6535e1d">identifier</a></td></tr>
<tr class="memdesc:a36fe923f8d67004e0b0ae8eaf6535e1d"><td class="mdescLeft">&#160;</td><td class="mdescRight">Block type identifier. <br /></td></tr>
<tr class="memitem:a319aea86a448c0b969de944f22e551c0" id="r_a319aea86a448c0b969de944f22e551c0"><td class="memItemLeft" align="right" valign="top">uint32_t&#160;</td><td class="memItemRight" valign="bottom"><a class="el" href="#a319aea86a448c0b969de944f22e551c0">entries</a></td></tr>
<tr class="memdesc:a319aea86a448c0b969de944f22e551c0"><td class="mdescLeft">&#160;</td><td class="mdescRight">Number of file entries following this header. <br /></td></tr>
<tr class="memitem:a74b5289640a6c45eece7bd58550e59c0" id="r_a74b5289640a6c45eece7bd58550e59c0"><td class="memItemLeft" align="right" valign="top">uint64_t&#160;</td><td class="memItemRight" valign="bottom"><a class="el" href="#a74b5289640a6c45eece7bd58550e59c0">length</a></td></tr>
<tr class="memdesc:a74b5289640a6c45eece7bd58550e59c0"><td class="mdescLeft">&#160;</td><td class="mdescRight">Size of entry data in bytes (excluding this header). <br /></td></tr>
<tr class="memitem:a5172ee4bf0b5820a66d04aff1e3809db" id="r_a5172ee4bf0b5820a66d04aff1e3809db"><td class="memItemLeft" align="right" valign="top">uint64_t&#160;</td><td class="memItemRight" valign="bottom"><a class="el" href="#a5172ee4bf0b5820a66d04aff1e3809db">crc64</a></td></tr>
<tr class="memdesc:a5172ee4bf0b5820a66d04aff1e3809db"><td class="mdescLeft">&#160;</td><td class="mdescRight">CRC64-ECMA checksum of the entry data. <br /></td></tr>
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<a name="details" id="details"></a><h2 id="header-details" class="groupheader">Detailed Description</h2>
<div class="textblock"><p>Header for a tape file metadata block containing file layout information. </p>
<p>This structure serves as the header for a TapeFileBlock, which documents all logical files present on the tape medium. The block consists of this fixed-size header followed by a variable-length array of <a class="el" href="structTapeFileEntry.html" title="Describes a single logical file on a tape medium.">TapeFileEntry</a> structures (one per file).</p>
<p><b>Block Structure:</b> </p><div class="fragment"><div class="line">+-------------------------+</div>
<div class="line">| <a class="code hl_struct" href="structTapeFileHeader.html">TapeFileHeader</a> | &lt;- Fixed 24-<span class="keywordtype">byte</span> header</div>
<div class="line">+-------------------------+</div>
<div class="line">| <a class="code hl_struct" href="structTapeFileEntry.html">TapeFileEntry</a> 0 | &lt;- First file entry</div>
<div class="line">+-------------------------+</div>
<div class="line">| <a class="code hl_struct" href="structTapeFileEntry.html">TapeFileEntry</a> 1 | &lt;- Second file entry</div>
<div class="line">+-------------------------+</div>
<div class="line">| ... |</div>
<div class="line">+-------------------------+</div>
<div class="line">| <a class="code hl_typedef" href="tape_8h.html#ade8125364d763d57d167c0b521beaf64">TapeFileEntry</a> (n-1) | &lt;- Last file entry</div>
<div class="line">+-------------------------+</div>
<div class="ttc" id="astructTapeFileEntry_html"><div class="ttname"><a href="structTapeFileEntry.html">TapeFileEntry</a></div><div class="ttdoc">Describes a single logical file on a tape medium.</div><div class="ttdef"><b>Definition</b> <a href="tape_8h_source.html#l00133">tape.h:134</a></div></div>
<div class="ttc" id="astructTapeFileHeader_html"><div class="ttname"><a href="structTapeFileHeader.html">TapeFileHeader</a></div><div class="ttdoc">Header for a tape file metadata block containing file layout information.</div><div class="ttdef"><b>Definition</b> <a href="tape_8h_source.html#l00237">tape.h:238</a></div></div>
<div class="ttc" id="atape_8h_html_ade8125364d763d57d167c0b521beaf64"><div class="ttname"><a href="tape_8h.html#ade8125364d763d57d167c0b521beaf64">TapeFileEntry</a></div><div class="ttdeci">struct TapeFileEntry TapeFileEntry</div></div>
</div><!-- fragment --><p><b>Purpose:</b> The tape file block enables:</p><ul>
<li>Quick lookup of file locations without scanning the entire tape</li>
<li>Validation of file boundaries and partition assignments</li>
<li>Random access to specific files in the image</li>
<li>Preservation of the original tape's logical organization</li>
<li>Documentation of tape structure for archival purposes</li>
</ul>
<p><b>Identifier Field:</b> The identifier field must be set to BlockType::TapeFileBlock to indicate this block type. This allows the Aaru format parser to recognize and correctly interpret the block during image loading.</p>
<p><b>Entry Count:</b> The entries field specifies the number of <a class="el" href="structTapeFileEntry.html" title="Describes a single logical file on a tape medium.">TapeFileEntry</a> structures that follow the header. A tape with no files would have entries=0, though this is unusual. Maximum value is 2^32-1 (4,294,967,295 files), though practical limits are much lower.</p>
<p><b>Block Length:</b> The length field contains the size in bytes of the data following this header (i.e., the array of <a class="el" href="structTapeFileEntry.html" title="Describes a single logical file on a tape medium.">TapeFileEntry</a> structures). This is calculated as: length = entries × sizeof(TapeFileEntry)</p>
<p>The header itself is NOT included in the length value. Total block size is: total_size = sizeof(TapeFileHeader) + length</p>
<p><b>CRC64 Checksum:</b> The crc64 field contains a CRC64-ECMA checksum computed over the entry data (the array of <a class="el" href="structTapeFileEntry.html" title="Describes a single logical file on a tape medium.">TapeFileEntry</a> structures, excluding this header). This provides integrity verification to detect corruption in the file table. The CRC is calculated using the ECMA polynomial.</p>
<p><b>File Order:</b> Entries should be ordered by partition number (ascending), then by file number (ascending) within each partition. This ordering facilitates efficient lookup and matches the physical organization of most tape formats.</p>
<p><b>Alignment:</b> When written to the Aaru image, this block is aligned to the image's block alignment boundary (typically 2^blockAlignmentShift bytes). Padding may be inserted before the block to achieve proper alignment.</p>
<p><b>Index Integration:</b> After writing this block to the image file, an <a class="el" href="structIndexEntry.html" title="Single index entry describing a block&#39;s type, (optional) data classification, and file offset.">IndexEntry</a> is created with:</p><ul>
<li>blockType = TapeFileBlock</li>
<li>dataType = 0 (tape file blocks have no subtype)</li>
<li>offset = file position where this header was written</li>
</ul>
<dl class="section note"><dt>Note</dt><dd>This block is optional. Tape images without file structure metadata can omit it, representing the tape as a simple linear sequence of blocks.</dd>
<dd>
If a tape has multiple partitions, files from all partitions are included in a single TapeFileBlock (distinguished by their Partition field).</dd>
<dd>
Empty tapes (no files) may still have a <a class="el" href="structTapeFileHeader.html" title="Header for a tape file metadata block containing file layout information.">TapeFileHeader</a> with entries=0, length=0, though such blocks are typically omitted.</dd></dl>
<dl class="section warning"><dt>Warning</dt><dd>The entries count must accurately reflect the number of <a class="el" href="structTapeFileEntry.html" title="Describes a single logical file on a tape medium.">TapeFileEntry</a> structures in the block. Mismatches will cause parsing errors.</dd>
<dd>
The CRC64 must be recalculated any time the entry data changes. Stale CRC values will cause integrity check failures.</dd></dl>
<dl class="section see"><dt>See also</dt><dd><a class="el" href="structTapeFileEntry.html" title="Describes a single logical file on a tape medium.">TapeFileEntry</a> for the structure of individual file <a class="el" href="#a319aea86a448c0b969de944f22e551c0" title="Number of file entries following this header.">entries</a> </dd>
<dd>
<a class="el" href="structTapePartitionHeader.html" title="Header for a tape partition metadata block containing partition layout information.">TapePartitionHeader</a> for partition structure metadata </dd>
<dd>
<a class="el" href="enums_8h.html#a54420623f26ab6bb61042b41cccf37a3" title="List of known block types contained in an Aaru image.">BlockType</a> for block type <a class="el" href="#a36fe923f8d67004e0b0ae8eaf6535e1d" title="Block type identifier.">identifier</a> constants </dd></dl>
<p class="definition">Definition at line <a class="el" href="tape_8h_source.html#l00237">237</a> of file <a class="el" href="tape_8h_source.html">tape.h</a>.</p>
</div><a name="doc-variable-members" id="doc-variable-members"></a><h2 id="header-doc-variable-members" class="groupheader">Field Documentation</h2>
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<h2 class="memtitle"><span class="permalink"><a href="#a5172ee4bf0b5820a66d04aff1e3809db">&#9670;&#160;</a></span>crc64</h2>
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<p>CRC64-ECMA checksum of the entry data. </p>
<p>Computed over the array of <a class="el" href="structTapeFileEntry.html" title="Describes a single logical file on a tape medium.">TapeFileEntry</a> structures only. Does NOT include this header. Used for integrity verification. </p>
<p class="definition">Definition at line <a class="el" href="tape_8h_source.html#l00245">245</a> of file <a class="el" href="tape_8h_source.html">tape.h</a>.</p>
<p class="reference">Referenced by <a class="el" href="tape_8c_source.html#l00126">process_tape_files_block()</a>, and <a class="el" href="close_8c_source.html#l02669">write_tape_file_block()</a>.</p>
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<h2 class="memtitle"><span class="permalink"><a href="#a319aea86a448c0b969de944f22e551c0">&#9670;&#160;</a></span>entries</h2>
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<td class="memname">uint32_t TapeFileHeader::entries</td>
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<p>Number of file entries following this header. </p>
<p>Specifies how many <a class="el" href="structTapeFileEntry.html" title="Describes a single logical file on a tape medium.">TapeFileEntry</a> structures are in this block. Valid range: 0 to 2^32-1. </p>
<p class="definition">Definition at line <a class="el" href="tape_8h_source.html#l00241">241</a> of file <a class="el" href="tape_8h_source.html">tape.h</a>.</p>
<p class="reference">Referenced by <a class="el" href="tape_8c_source.html#l00126">process_tape_files_block()</a>.</p>
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<h2 class="memtitle"><span class="permalink"><a href="#a36fe923f8d67004e0b0ae8eaf6535e1d">&#9670;&#160;</a></span>identifier</h2>
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<p>Block type identifier. </p>
<p>Must be set to BlockType::TapeFileBlock. This magic value allows parsers to identify the block type. </p>
<p class="definition">Definition at line <a class="el" href="tape_8h_source.html#l00239">239</a> of file <a class="el" href="tape_8h_source.html">tape.h</a>.</p>
<p class="reference">Referenced by <a class="el" href="tape_8c_source.html#l00126">process_tape_files_block()</a>, and <a class="el" href="close_8c_source.html#l02669">write_tape_file_block()</a>.</p>
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<a id="a74b5289640a6c45eece7bd58550e59c0" name="a74b5289640a6c45eece7bd58550e59c0"></a>
<h2 class="memtitle"><span class="permalink"><a href="#a74b5289640a6c45eece7bd58550e59c0">&#9670;&#160;</a></span>length</h2>
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<p>Size of entry data in bytes (excluding this header). </p>
<p>Calculated as: entries × sizeof(TapeFileEntry). This is the number of bytes following the header. </p>
<p class="definition">Definition at line <a class="el" href="tape_8h_source.html#l00243">243</a> of file <a class="el" href="tape_8h_source.html">tape.h</a>.</p>
<p class="reference">Referenced by <a class="el" href="close_8c_source.html#l02669">write_tape_file_block()</a>.</p>
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<hr/>The documentation for this struct was generated from the following file:<ul>
<li>include/aaruformat/structs/<a class="el" href="tape_8h_source.html">tape.h</a></li>
</ul>
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