ARCHIVE_ENTRY_LINKIFY(3) BSD Library Functions Manual ARCHIVE_ENTRY_LINKIFY(3)

1mNAME0m
     1marchive_entry_linkresolver22m, 1marchive_entry_linkresolver_new22m,
     1marchive_entry_linkresolver_set_strategy22m, 1marchive_entry_linkresolver_free22m,
     1marchive_entry_linkify 22m— hardlink resolver functions

1mLIBRARY0m
     Streaming Archive Library (libarchive, -larchive)

1mSYNOPSIS0m
     1m#include <archive_entry.h>0m

     4mstruct24m 4marchive_entry_linkresolver24m 4m*0m
     1marchive_entry_linkresolver_new22m(4mvoid24m);

     4mvoid0m
     1marchive_entry_linkresolver_set_strategy22m(4mstruct24m 4marchive_entry_linkresolver24m 4m*resolver24m,
	 4mint24m 4mformat24m);

     4mvoid0m
     1marchive_entry_linkresolver_free22m(4mstruct24m 4marchive_entry_linkresolver24m 4m*resolver24m);

     4mvoid0m
     1marchive_entry_linkify22m(4mstruct24m 4marchive_entry_linkresolver24m 4m*resolver24m,
	 4mstruct24m 4marchive_entry24m 4m**entry24m, 4mstruct24m 4marchive_entry24m 4m**sparse24m);

1mDESCRIPTION0m
     Programs that want to create archives have to deal with hardlinks.
     Hardlinks are handled in different ways by the archive formats.  The
     basic strategies are:

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

     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 1marchive_entry_linkresolver 22mfunctions help by providing a unified
     interface and handling the complexity behind the scene.

     The 1marchive_entry_linkresolver 22mfunctions assume that 4marchive_entry0m
     instances 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 refer‐
     ences can be recycled.

     The 1marchive_entry_linkresolver_new22m() function allocates a new link
     resolver.	The instance can be freed using
     1marchive_entry_linkresolver_free22m().  All deferred entries are flushed and
     the internal storage is freed.

     The 1marchive_entry_linkresolver_set_strategy22m() function selects the opti‐
     mal hardlink strategy for the given format.  The format code can be
     obtained from archive_format(3).  The function can be called more than
     once, but it is recommended to flush all deferred entries first.

     The 1marchive_entry_linkify22m() function is the core of
     1marchive_entry_linkresolver22m.  The 1mentry22m() argument points to the
     4marchive_entry24m that should be written.  Depending on the strategy one of
     the following actions is taken:

     1.   For the simple archive formats 4m*entry24m is left unmodified and 4m*sparse0m
	  is set to NULL.

     2.   For tar like archive formats, 4m*sparse24m is set to NULL.  If 4m*entry24m is
	  NULL, no action is taken.  If the hardlink count of 4m*entry24m is larger
	  than 1 and the file type is a regular file or symbolic link, the
	  internal list is searched for a matching inode.  If such an inode is
	  found, the link count is decremented and the file size of 4m*entry24m 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 4m*entry24m of NULL is used
	  to flush deferred entries.  In that case 4m*entry24m 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, 4m*entry24m is set to NULL.  In
	  either case, 4m*sparse24m is set to NULL and the function returns.  If
	  the hardlink count of 4m*entry24m is one or the file type is a directory
	  or device, 4m*sparse24m 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 4m*entry24m and 4m*sparse24m are set to NULL and the function returns.
	  If such an inode is found, the link count is decremented.  If it
	  remains larger than one, the existing entry on the internal list is
	  swapped with 4m*entry24m after retaining the link count.  The existing
	  entry is returned in 4m*entry24m.  If the link count reached one, the new
	  entry is also removed from the internal list and returned in
	  4m*sparse24m.  Otherwise 4m*sparse24m is set to NULL.

     The general usage is therefore:

     1.   For each new archive entry, call 1marchive_entry_linkify22m().

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

     3.   If 4m*entry24m is not NULL, archive it.

     4.   If 4m*sparse24m is not NULL, archive it.

     5.   After all entries have been written to disk, call
	  1marchive_entry_linkify22m() with 4m*entry24m set to NULL and archive the
	  returned entry as long as it is not NULL.

1mRETURN VALUES0m
     1marchive_entry_linkresolver_new22m() returns NULL on malloc(3) failures.

1mSEE ALSO0m
     archive_entry(3)

BSD			       February 2, 2012 			   BSD
