plucky (3) archive_entry_linkify.3.gz

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)