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ARCHIVE_ENTRY_LINKIFY(3) BSD Library Functions Manual
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ARCHIVE_ENTRY_LINKIFY(3)
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NAME
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archive_entry_linkresolver,
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archive_entry_linkresolver_new,
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archive_entry_linkresolver_set_strategy,
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archive_entry_linkresolver_free,
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archive_entry_linkify — hardlink resolver
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functions
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LIBRARY
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Streaming Archive Library
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(libarchive, -larchive)
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SYNOPSIS
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#include
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<archive_entry.h>
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struct
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archive_entry_linkresolver *
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archive_entry_linkresolver_new(void);
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void
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archive_entry_linkresolver_set_strategy(struct archive_entry_linkresolver *resolver,
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int format);
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void
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archive_entry_linkresolver_free(struct archive_entry_linkresolver *resolver);
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void
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archive_entry_linkify(struct archive_entry_linkresolver *resolver,
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struct archive_entry **entry,
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struct archive_entry **sparse);
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DESCRIPTION
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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:
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1.
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Ignore hardlinks and store the
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body for each reference (old cpio, zip).
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2.
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Store the body the first time
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an inode is seen (ustar, pax).
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3.
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Store the body the last time an
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inode is seen (new cpio).
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The
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archive_entry_linkresolver functions help by
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providing a unified interface and handling the complexity
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behind the scene.
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The
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archive_entry_linkresolver functions assume that
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archive_entry 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.
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The
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archive_entry_linkresolver_new() function allocates a
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new link resolver. The instance can be freed using
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archive_entry_linkresolver_free(). All deferred
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entries are flushed and the internal storage is freed.
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The
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archive_entry_linkresolver_set_strategy() 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.
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The
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archive_entry_linkify() function is the core of
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archive_entry_linkresolver. The entry()
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argument points to the archive_entry that should be
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written. Depending on the strategy one of the following
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actions is taken:
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1.
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For the simple archive formats
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*entry is left unmodified and *sparse is set
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to NULL.
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2.
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For tar like archive formats,
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*sparse is set to NULL. If *entry is NULL, no
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action is taken. If the hardlink count of *entry 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 *entry 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.
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3.
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For new cpio like archive
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formats a value for *entry of NULL is used to flush
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deferred entries. In that case *entry 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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*entry is set to NULL. In either case, *sparse
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is set to NULL and the function returns. If the hardlink
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count of *entry is one or the file type is a
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directory or device, *sparse 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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*entry and *sparse 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 *entry
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after retaining the link count. The existing entry is
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returned in *entry. 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 *sparse. Otherwise *sparse is set
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to NULL.
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The general
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usage is therefore:
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1.
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For each new archive entry,
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call archive_entry_linkify().
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2.
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Keep in mind that the entries
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returned may have a size of 0 now.
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3.
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If *entry is not NULL,
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archive it.
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4.
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If *sparse is not NULL,
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archive it.
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5.
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After all entries have been
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written to disk, call archive_entry_linkify() with
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*entry set to NULL and archive the returned entry as
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long as it is not NULL.
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RETURN VALUES
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archive_entry_linkresolver_new()
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returns NULL on malloc(3) failures.
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SEE ALSO
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archive_entry(3)
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BSD
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February 2, 2012 BSD
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