NAME

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

LIBRARY

       Streaming Archive Library (libarchive, -larchive)

SYNOPSIS

       #include <archive_entry.h>

       struct archive_entry_linkresolver *
       archive_entry_linkresolver_new(void);

       void
       archive_entry_linkresolver_set_strategy(struct archive_entry_linkresolver *resolver, int format);

       void
       archive_entry_linkresolver_free(struct archive_entry_linkresolver *resolver);

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

DESCRIPTION

       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 archive_entry_linkresolver  functions  help  by  providing  a  unified  interface  and  handling  the
       complexity behind the scene.

       The archive_entry_linkresolver functions assume that archive_entry 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 references can be recycled.

       The archive_entry_linkresolver_new() function allocates a new link resolver.  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  optimal  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 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 internal 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 arbitrary deferred entry and the entry  itself  is  removed  from  the
            internal  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 remains 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 returned entry as long as it is not NULL.

RETURN VALUES

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

SEE ALSO

       archive_entry(3)

Debian                                          February 2, 2012                        ARCHIVE_ENTRY_LINKIFY(3)