225 lines
5.9 KiB
Groff
225 lines
5.9 KiB
Groff
.\" Copyright (c) 2010 Joerg Sonnenberger
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.Dd February 2, 2012
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.Dt ARCHIVE_ENTRY_LINKIFY 3
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.Os
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.Sh NAME
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.Nm archive_entry_linkresolver ,
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.Nm archive_entry_linkresolver_new ,
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.Nm archive_entry_linkresolver_set_strategy ,
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.Nm archive_entry_linkresolver_free ,
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.Nm archive_entry_linkify
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.Nd hardlink resolver functions
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.Sh LIBRARY
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Streaming Archive Library (libarchive, -larchive)
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.Sh SYNOPSIS
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.In archive_entry.h
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.Ft struct archive_entry_linkresolver *
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.Fn archive_entry_linkresolver_new void
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.Ft void
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.Fo archive_entry_linkresolver_set_strategy
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.Fa "struct archive_entry_linkresolver *resolver"
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.Fa "int format"
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.Fc
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.Ft void
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.Fo archive_entry_linkresolver_free
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.Fa "struct archive_entry_linkresolver *resolver"
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.Fc
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.Ft void
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.Fo archive_entry_linkify
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.Fa "struct archive_entry_linkresolver *resolver"
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.Fa "struct archive_entry **entry"
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.Fa "struct archive_entry **sparse"
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.Fc
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.Sh DESCRIPTION
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Programs that want to create archives have to deal with hardlinks.
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Hardlinks are handled in different ways by the archive formats.
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The basic strategies are:
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.Bl -enum
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.It
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Ignore hardlinks and store the body for each reference (old cpio, zip).
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.It
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Store the body the first time an inode is seen (ustar, pax).
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.It
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Store the body the last time an inode is seen (new cpio).
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.El
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.Pp
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The
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.Nm
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functions help by providing a unified interface and handling the complexity
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behind the scene.
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.Pp
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The
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.Nm
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functions assume that
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.Vt archive_entry
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instances have valid nlinks, inode and device values.
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The inode and device value is used to match entries.
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The nlinks value is used to determined if all references have been found and
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if the internal references can be recycled.
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.Pp
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The
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.Fn archive_entry_linkresolver_new
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function allocates a new link resolver.
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The instance can be freed using
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.Fn archive_entry_linkresolver_free .
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All deferred entries are flushed and the internal storage is freed.
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.Pp
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The
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.Fn archive_entry_linkresolver_set_strategy
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function selects the optimal hardlink strategy for the given format.
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The format code can be obtained from
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.Xr archive_format 3 .
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The function can be called more than once, but it is recommended to
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flush all deferred entries first.
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.Pp
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The
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.Fn archive_entry_linkify
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function is the core of
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.Nm .
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The
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.Fn entry
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argument points to the
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.Vt archive_entry
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that should be written.
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Depending on the strategy one of the following actions is taken:
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.Bl -enum
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.It
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For the simple archive formats
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.Va *entry
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is left unmodified and
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.Va *sparse
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is set to
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.Dv NULL .
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.It
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For tar like archive formats,
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.Va *sparse
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is set to
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.Dv NULL .
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If
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.Va *entry
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is
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.Dv NULL ,
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no action is taken.
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If the hardlink count of
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.Va *entry
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is larger than 1 and the file type is a regular file or symbolic link,
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the internal list is searched for a matching inode.
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If such an inode is found, the link count is decremented and the file size
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of
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.Va *entry
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is set to 0 to notify that no body should be written.
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If no such inode is found, a copy of the entry is added to the internal cache
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with a link count reduced by one.
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.It
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For new cpio like archive formats a value for
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.Va *entry
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of
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.Dv NULL
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is used to flush deferred entries.
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In that case
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.Va *entry
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is set to an arbitrary deferred entry and the entry itself is removed from the
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internal list.
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If the internal list is empty,
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.Va *entry
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is set to
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.Dv NULL .
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In either case,
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.Va *sparse
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is set to
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.Dv NULL
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and the function returns.
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If the hardlink count of
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.Va *entry
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is one or the file type is a directory or device,
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.Va *sparse
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is set to
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.Dv NULL
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and no further action is taken.
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Otherwise, the internal list is searched for a matching inode.
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If such an inode is not found, the entry is added to the internal list,
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both
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.Va *entry
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and
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.Va *sparse
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are set to
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.Dv NULL
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and the function returns.
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If such an inode is found, the link count is decremented.
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If it remains larger than one, the existing entry on the internal list
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is swapped with
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.Va *entry
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after retaining the link count.
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The existing entry is returned in
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.Va *entry .
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If the link count reached one, the new entry is also removed from the
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internal list and returned in
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.Va *sparse .
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Otherwise
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.Va *sparse
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is set to
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.Dv NULL .
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.El
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.Pp
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The general usage is therefore:
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.Bl -enum
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.It
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For each new archive entry, call
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.Fn archive_entry_linkify .
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.It
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Keep in mind that the entries returned may have a size of 0 now.
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.It
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If
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.Va *entry
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is not
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.Dv NULL ,
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archive it.
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.It
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If
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.Va *sparse
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is not
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.Dv NULL ,
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archive it.
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.It
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After all entries have been written to disk, call
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.Fn archive_entry_linkify
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with
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.Va *entry
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set to
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.Dv NULL
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and archive the returned entry as long as it is not
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.Dv NULL .
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.El
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.Sh RETURN VALUES
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.Fn archive_entry_linkresolver_new
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returns
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.Dv NULL
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on
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.Xr malloc 3
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failures.
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.Sh SEE ALSO
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.Xr archive_entry 3
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