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67618a2eac
- Update bunlded libarchive version used on Windows/Mac - Enable requested zstd support while we are at it. Closes #211
212 lines
7.2 KiB
HTML
212 lines
7.2 KiB
HTML
<!-- Creator : groff version 1.22.4 -->
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
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<p>ARCHIVE_ENTRY_LINKIFY(3) BSD Library Functions Manual
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ARCHIVE_ENTRY_LINKIFY(3)</p>
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<p style="margin-top: 1em"><b>NAME</b></p>
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<p style="margin-left:6%;"><b>archive_entry_linkresolver</b>,
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<b>archive_entry_linkresolver_new</b>,
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<b>archive_entry_linkresolver_set_strategy</b>,
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<b>archive_entry_linkresolver_free</b>,
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<b>archive_entry_linkify</b> — hardlink resolver
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functions</p>
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<p style="margin-top: 1em"><b>LIBRARY</b></p>
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<p style="margin-left:6%;">Streaming Archive Library
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(libarchive, -larchive)</p>
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<p style="margin-top: 1em"><b>SYNOPSIS</b></p>
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<p style="margin-left:6%;"><b>#include
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<archive_entry.h></b></p>
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<p style="margin-left:6%; margin-top: 1em"><i>struct
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archive_entry_linkresolver *</i></p>
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<p style="margin-left:12%;"><b>archive_entry_linkresolver_new</b>(<i>void</i>);</p>
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<p style="margin-left:6%; margin-top: 1em"><i>void</i></p>
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<p><b>archive_entry_linkresolver_set_strategy</b>(<i>struct archive_entry_linkresolver *resolver</i>,
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<i>int format</i>);</p>
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<p style="margin-left:6%; margin-top: 1em"><i>void</i></p>
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<p><b>archive_entry_linkresolver_free</b>(<i>struct archive_entry_linkresolver *resolver</i>);</p>
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<p style="margin-left:6%; margin-top: 1em"><i>void</i></p>
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<p><b>archive_entry_linkify</b>(<i>struct archive_entry_linkresolver *resolver</i>,
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<i>struct archive_entry **entry</i>,
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<i>struct archive_entry **sparse</i>);</p>
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<p style="margin-top: 1em"><b>DESCRIPTION</b></p>
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<p style="margin-left:6%;">Programs that want to create
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archives have to deal with hardlinks. Hardlinks are handled
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in different ways by the archive formats. The basic
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strategies are:</p>
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<p style="margin-top: 1em">1.</p>
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<p style="margin-left:13%;">Ignore hardlinks and store the
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body for each reference (old cpio, zip).</p>
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<p style="margin-top: 1em">2.</p>
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<p style="margin-left:13%;">Store the body the first time
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an inode is seen (ustar, pax).</p>
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<p style="margin-top: 1em">3.</p>
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<p style="margin-left:13%;">Store the body the last time an
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inode is seen (new cpio).</p>
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<p style="margin-left:6%; margin-top: 1em">The
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<b>archive_entry_linkresolver</b> functions help by
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providing a unified interface and handling the complexity
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behind the scene.</p>
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<p style="margin-left:6%; margin-top: 1em">The
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<b>archive_entry_linkresolver</b> functions assume that
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<i>archive_entry</i> instances have valid nlinks, inode and
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device values. The inode and device value is used to match
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entries. The nlinks value is used to determined if all
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references have been found and if the internal references
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can be recycled.</p>
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<p style="margin-left:6%; margin-top: 1em">The
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<b>archive_entry_linkresolver_new</b>() function allocates a
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new link resolver. The instance can be freed using
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<b>archive_entry_linkresolver_free</b>(). All deferred
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entries are flushed and the internal storage is freed.</p>
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<p style="margin-left:6%; margin-top: 1em">The
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<b>archive_entry_linkresolver_set_strategy</b>() function
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selects the optimal hardlink strategy for the given format.
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The format code can be obtained from archive_format(3). The
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function can be called more than once, but it is recommended
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to flush all deferred entries first.</p>
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<p style="margin-left:6%; margin-top: 1em">The
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<b>archive_entry_linkify</b>() function is the core of
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<b>archive_entry_linkresolver</b>. The <b>entry</b>()
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argument points to the <i>archive_entry</i> that should be
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written. Depending on the strategy one of the following
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actions is taken:</p>
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<p style="margin-top: 1em">1.</p>
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<p style="margin-left:13%;">For the simple archive formats
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<i>*entry</i> is left unmodified and <i>*sparse</i> is set
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to NULL.</p>
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<p style="margin-top: 1em">2.</p>
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<p style="margin-left:13%;">For tar like archive formats,
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<i>*sparse</i> is set to NULL. If <i>*entry</i> is NULL, no
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action is taken. If the hardlink count of <i>*entry</i> is
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larger than 1 and the file type is a regular file or
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symbolic link, the internal list is searched for a matching
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inode. If such an inode is found, the link count is
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decremented and the file size of <i>*entry</i> is set to 0
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to notify that no body should be written. If no such inode
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is found, a copy of the entry is added to the internal cache
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with a link count reduced by one.</p>
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<p style="margin-top: 1em">3.</p>
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<p style="margin-left:13%;">For new cpio like archive
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formats a value for <i>*entry</i> of NULL is used to flush
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deferred entries. In that case <i>*entry</i> is set to an
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arbitrary deferred entry and the entry itself is removed
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from the internal list. If the internal list is empty,
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<i>*entry</i> is set to NULL. In either case, <i>*sparse</i>
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is set to NULL and the function returns. If the hardlink
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count of <i>*entry</i> is one or the file type is a
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directory or device, <i>*sparse</i> is set to NULL and no
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further action is taken. Otherwise, the internal list is
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searched for a matching inode. If such an inode is not
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found, the entry is added to the internal list, both
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<i>*entry</i> and <i>*sparse</i> are set to NULL and the
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function returns. If such an inode is found, the link count
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is decremented. If it remains larger than one, the existing
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entry on the internal list is swapped with <i>*entry</i>
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after retaining the link count. The existing entry is
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returned in <i>*entry</i>. If the link count reached one,
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the new entry is also removed from the internal list and
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returned in <i>*sparse</i>. Otherwise <i>*sparse</i> is set
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to NULL.</p>
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<p style="margin-left:6%; margin-top: 1em">The general
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usage is therefore:</p>
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<p style="margin-top: 1em">1.</p>
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<p style="margin-left:13%;">For each new archive entry,
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call <b>archive_entry_linkify</b>().</p>
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<p style="margin-top: 1em">2.</p>
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<p style="margin-left:13%;">Keep in mind that the entries
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returned may have a size of 0 now.</p>
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<p style="margin-top: 1em">3.</p>
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<p style="margin-left:13%;">If <i>*entry</i> is not NULL,
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archive it.</p>
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<p style="margin-top: 1em">4.</p>
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<p style="margin-left:13%;">If <i>*sparse</i> is not NULL,
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archive it.</p>
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<p style="margin-top: 1em">5.</p>
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<p style="margin-left:13%;">After all entries have been
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written to disk, call <b>archive_entry_linkify</b>() with
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<i>*entry</i> set to NULL and archive the returned entry as
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long as it is not NULL.</p>
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<p style="margin-top: 1em"><b>RETURN VALUES</b></p>
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<p style="margin-left:6%;"><b>archive_entry_linkresolver_new</b>()
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returns NULL on malloc(3) failures.</p>
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<p style="margin-top: 1em"><b>SEE ALSO</b></p>
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<p style="margin-left:6%;">archive_entry(3)</p>
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<p style="margin-left:6%; margin-top: 1em">BSD
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February 2, 2012 BSD</p>
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<hr>
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</body>
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</html>
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