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)