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:
- Ignore hardlinks and store the body for each reference
(old cpio, zip).
- Store the body the first time an inode is seen (ustar,
pax).
- 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:
- For the simple archive formats
*entry is left unmodified and
*sparse is set to
NULL
.
- 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.
- 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:
- For each new archive entry, call
archive_entry_linkify().
- Keep in mind that the entries returned may have a size of
0 now.
- If *entry is not
NULL
, archive it.
- If *sparse is not
NULL
, archive it.
- 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)