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ARCHIVE_WRITE_DISK(3)  FreeBSD Library Functions Manual	 ARCHIVE_WRITE_DISK(3)

     archive_write_disk_new, archive_write_disk_set_options,
     archive_write_disk_set_skip_file, archive_write_disk_set_group_lookup,
     archive_write_disk_set_user_lookup, archive_write_header,
     archive_write_data, archive_write_finish_entry, archive_write_close,
     archive_write_free	-- functions for creating objects on disk

     #include <archive.h>

     struct archive *

     archive_write_disk_set_options(struct archive *, int flags);

     archive_write_disk_set_skip_file(struct archive *,	dev_t, ino_t);

     archive_write_disk_set_group_lookup(struct	archive	*, void	*,
	 gid_t (*)(void	*, const char *gname, gid_t gid),
	 void (*cleanup)(void *));

     archive_write_disk_set_standard_lookup(struct archive *);

     archive_write_disk_set_user_lookup(struct archive *, void *,
	 uid_t (*)(void	*, const char *uname, uid_t uid),
	 void (*cleanup)(void *));

     archive_write_header(struct archive *, struct archive_entry *);

     archive_write_data(struct archive *, const	void *,	size_t);

     archive_write_finish_entry(struct archive *);

     archive_write_close(struct	archive	*);

     archive_write_free(struct archive *);

     These functions provide a complete	API for	creating objects on disk from
     struct archive_entry descriptions.	 They are most naturally used when
     extracting	objects	from an	archive	using the archive_read() interface.
     The general process is to read struct archive_entry objects from an ar-
     chive, then write those objects to	a struct archive object	created	using
     the archive_write_disk() family functions.	 This interface	is deliber-
     ately very	similar	to the archive_write() interface used to write objects
     to	a streaming archive.

	     Allocates and initializes a struct	archive	object suitable	for
	     writing objects to	disk.

	     Records the device	and inode numbers of a file that should	not be
	     overwritten.  This	is typically used to ensure that an extraction
	     process does not overwrite	the archive from which objects are
	     being read.  This capability is technically unnecessary but can
	     be	a significant performance optimization in practice.

	     The options field consists	of a bitwise OR	of one or more of the
	     following values:
		     The user and group	IDs should be set on the restored
		     file.  By default,	the user and group IDs are not
		     Full permissions (including SGID, SUID, and sticky	bits)
		     should be restored	exactly	as specified, without obeying
		     the current umask.	 Note that SUID	and SGID bits can only
		     be	restored if the	user and group ID of the object	on
		     disk are correct.	If ARCHIVE_EXTRACT_OWNER is not	speci-
		     fied, then	SUID and SGID bits will	only be	restored if
		     the default user and group	IDs of newly-created objects
		     on	disk happen to match those specified in	the archive
		     entry.  By	default, only basic permissions	are restored,
		     and umask is obeyed.
		     The timestamps (mtime, ctime, and atime) should be
		     restored.	By default, they are ignored.  Note that
		     restoring of atime	is not currently supported.
		     Existing files on disk will not be	overwritten.  By
		     default, existing regular files are truncated and over-
		     written; existing directories will	have their permissions
		     updated; other pre-existing objects are unlinked and
		     recreated from scratch.
		     Existing files on disk will be unlinked before any
		     attempt to	create them.  In some cases, this can prove to
		     be	a significant performance improvement.	By default,
		     existing files are	truncated and rewritten, but the file
		     is	not recreated.	In particular, the default behavior
		     does not break existing hard links.
		     Attempt to	restore	ACLs.  By default, extended ACLs are
		     Attempt to	restore	extended file flags.  By default, file
		     flags are ignored.
		     Attempt to	restore	POSIX.1e extended attributes.  By
		     default, they are ignored.
		     Refuse to extract any object whose	final location would
		     be	altered	by a symlink on	disk.  This is intended	to
		     help guard	against	a variety of mischief caused by	ar-
		     chives that (deliberately or otherwise) extract files
		     outside of	the current directory.	The default is not to
		     perform this check.  If ARCHIVE_EXTRACT_UNLINK is speci-
		     fied together with	this option, the library will remove
		     any intermediate symlinks it finds	and return an error
		     only if such symlink could	not be removed.
		     Refuse to extract a path that contains a .. element any-
		     where within it.  The default is to not refuse such
		     paths.  Note that paths ending in .. always cause an
		     error, regardless of this flag.
		     Scan data for blocks of NUL bytes and try to recreate
		     them with holes.  This results in sparse files, indepen-
		     dent of whether the archive format	supports or uses them.

	     The struct	archive_entry objects contain both names and ids that
	     can be used to identify users and groups.	These names and	ids
	     describe the ownership of the file	itself and also	appear in ACL
	     lists.  By	default, the library uses the ids and ignores the
	     names, but	this can be overridden by registering user and group
	     lookup functions.	To register, you must provide a	lookup func-
	     tion which	accepts	both a name and	id and returns a suitable id.
	     You may also provide a void * pointer to a	private	data structure
	     and a cleanup function for	that data.  The	cleanup	function will
	     be	invoked	when the struct	archive	object is destroyed.

	     This convenience function installs	a standard set of user and
	     group lookup functions.  These functions use getpwnam(3) and
	     getgrnam(3) to convert names to ids, defaulting to	the ids	if the
	     names cannot be looked up.	 These functions also implement	a sim-
	     ple memory	cache to reduce	the number of calls to getpwnam(3) and

	     Build and write a header using the	data in	the provided struct
	     archive_entry structure.  See archive_entry(3) for	information on
	     creating and populating struct archive_entry objects.

	     Write data	corresponding to the header just written.  Returns
	     number of bytes written or	-1 on error.

	     Close out the entry just written.	Ordinarily, clients never need
	     to	call this, as it is called automatically by
	     archive_write_next_header() and archive_write_close() as needed.

	     Set any attributes	that could not be set during the initial
	     restore.  For example, directory timestamps are not restored ini-
	     tially because restoring a	subsequent file	would alter that time-
	     stamp.  Similarly,	non-writable directories are initially created
	     with write	permissions (so	that their contents can	be restored).
	     The archive_write_disk_new	library	maintains a list of all	such
	     deferred attributes and sets them when this function is invoked.

	     Invokes archive_write_close() if it was not invoked manually,
	     then releases all resources.
     More information about the	struct archive object and the overall design
     of	the library can	be found in the	libarchive(3) overview.	 Many of these
     functions are also	documented under archive_write(3).

     Most functions return ARCHIVE_OK (zero) on	success, or one	of several
     non-zero error codes for errors.  Specific	error codes include:
     ARCHIVE_RETRY for operations that might succeed if	retried, ARCHIVE_WARN
     for unusual conditions that do not	prevent	further	operations, and
     ARCHIVE_FATAL for serious errors that make	remaining operations impossi-
     ble.  The archive_errno() and archive_error_string() functions can	be
     used to retrieve an appropriate error code	and a textual error message.

     archive_write_disk_new() returns a	pointer	to a newly-allocated struct
     archive object.

     archive_write_data() returns a count of the number	of bytes actually
     written.  On error, -1 is returned	and the	archive_errno()	and
     archive_error_string() functions will return appropriate values.

     archive_read(3), archive_write(3),	tar(1),	libarchive(3)

     The libarchive library first appeared in FreeBSD 5.3.  The
     archive_write_disk	interface was added to libarchive 2.0 and first
     appeared in FreeBSD 6.3.

     The libarchive library was	written	by Tim Kientzle	<>.

     Directories are actually extracted	in two distinct	phases.	 Directories
     are created during	archive_write_header(),	but final permissions are not
     set until archive_write_close().  This separation is necessary to cor-
     rectly handle borderline cases such as a non-writable directory contain-
     ing files,	but can	cause unexpected results.  In particular, directory
     permissions are not fully restored	until the archive is closed.  If you
     use chdir(2) to change the	current	directory between calls	to
     archive_read_extract() or before calling archive_read_close(), you	may
     confuse the permission-setting logic with the result that directory per-
     missions are restored incorrectly.

     The library attempts to create objects with filenames longer than
     PATH_MAX by creating prefixes of the full path and	changing the current
     directory.	 Currently, this logic is limited in scope; the	fixup pass
     does not work correctly for such objects and the symlink security check
     option disables the support for very long pathnames.

     Restoring the path	aa/../bb does create each intermediate directory.  In
     particular, the directory aa is created as	well as	the final object bb.
     In	theory,	this can be exploited to create	an entire directory hierarchy
     with a single request.  Of	course,	this does not work if the
     ARCHIVE_EXTRACT_NODOTDOT option is	specified.

     Implicit directories are always created obeying the current umask.
     Explicit objects are created obeying the current umask unless
     ARCHIVE_EXTRACT_PERM is specified,	in which case they current umask is

     SGID and SUID bits	are restored only if the correct user and group	could
     be	set.  If ARCHIVE_EXTRACT_OWNER is not specified, then no attempt is
     made to set the ownership.	 In this case, SGID and	SUID bits are restored
     only if the user and group	of the final object happen to match those
     specified in the entry.

     The ``standard'' user-id and group-id lookup functions are	not the
     defaults because getgrnam(3) and getpwnam(3) are sometimes	too large for
     particular	applications.  The current design allows the application
     author to use a more compact implementation when appropriate.

     There should be a corresponding archive_read_disk interface that walks a
     directory hierarchy and returns archive entry objects.

FreeBSD	8.4-stable		August 5, 2008		    FreeBSD 8.4-stable


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