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     archive_entry_linkresolver, archive_entry_linkresolver_new,
     archive_entry_linkresolver_set_strategy, archive_entry_linkresolver_free,
     archive_entry_linkify -- hardlink resolver	functions

     Streaming Archive Library (libarchive, -larchive)

     #include <archive_entry.h>

     struct archive_entry_linkresolver *

     archive_entry_linkresolver_set_strategy(struct archive_entry_linkresolver *resolver,
	 int format);

     archive_entry_linkresolver_free(struct archive_entry_linkresolver *resolver);

     archive_entry_linkify(struct archive_entry_linkresolver *resolver,
	 struct	archive_entry **entry, struct archive_entry **sparse);

     Programs that want	to create archives have	to deal	with hardlinks.
     Hardlinks are handled in different	ways by	the archive formats.  The ba-
     sic strategies are:

     1.	  Ignore hardlinks and store the body for each reference (old cpio,

     2.	  Store	the body the first time	an inode is seen (ustar, pax).

     3.	  Store	the body the last time an inode	is seen	(new cpio).

     The archive_entry_linkresolver functions help by providing	a unified in-
     terface and handling the complexity behind	the scene.

     The archive_entry_linkresolver functions assume that archive_entry	in-
     stances have valid	nlinks,	inode and device values.  The inode and	device
     value is used to match entries.  The nlinks value is used to determined
     if	all references have been found and if the internal references can be

     The archive_entry_linkresolver_new() function allocates a new link	re-
     solver.  The instance can be freed	using
     archive_entry_linkresolver_free().	 All deferred entries are flushed and
     the internal storage is freed.

     The archive_entry_linkresolver_set_strategy() function selects the	opti-
     mal hardlink strategy for the given format.  The format code can be ob-
     tained from archive_format(3).  The function can be called	more than
     once, but it is recommended to flush all deferred entries first.

     The archive_entry_linkify() function is the core of
     archive_entry_linkresolver.  The entry() argument points to the
     archive_entry that	should be written.  Depending on the strategy one of
     the following actions is taken:

     1.	  For the simple archive formats *entry	is left	unmodified and *sparse
	  is set to NULL.

     2.	  For tar like archive formats,	*sparse	is set to NULL.	 If *entry is
	  NULL,	no action is taken.  If	the hardlink count of *entry is	larger
	  than 1 and the file type is a	regular	file or	symbolic link, the in-
	  ternal list is searched for a	matching inode.	 If such an inode is
	  found, the link count	is decremented and the file size of *entry is
	  set to 0 to notify that no body should be written.  If no such inode
	  is found, a copy of the entry	is added to the	internal cache with a
	  link count reduced by	one.

     3.	  For new cpio like archive formats a value for	*entry of NULL is used
	  to flush deferred entries.  In that case *entry is set to an arbi-
	  trary	deferred entry and the entry itself is removed from the	inter-
	  nal list.  If	the internal list is empty, *entry is set to NULL.  In
	  either case, *sparse is set to NULL and the function returns.	 If
	  the hardlink count of	*entry is one or the file type is a directory
	  or device, *sparse is	set to NULL and	no further action is taken.
	  Otherwise, the internal list is searched for a matching inode.  If
	  such an inode	is not found, the entry	is added to the	internal list,
	  both *entry and *sparse are set to NULL and the function returns.
	  If such an inode is found, the link count is decremented.  If	it re-
	  mains	larger than one, the existing entry on the internal list is
	  swapped with *entry after retaining the link count.  The existing
	  entry	is returned in *entry.	If the link count reached one, the new
	  entry	is also	removed	from the internal list and returned in
	  *sparse.  Otherwise *sparse is set to	NULL.

     The general usage is therefore:

     1.	  For each new archive entry, call archive_entry_linkify().

     2.	  Keep in mind that the	entries	returned may have a size of 0 now.

     3.	  If *entry is not NULL, archive it.

     4.	  If *sparse is	not NULL, archive it.

     5.	  After	all entries have been written to disk, call
	  archive_entry_linkify() with *entry set to NULL and archive the re-
	  turned entry as long as it is	not NULL.

     archive_entry_linkresolver_new() returns NULL on malloc(3)	failures.


BSD			       February	2, 2012				   BSD


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