
ARCHIVE_WRITE_DISK(3)	 BSD Library Functions Manual	 ARCHIVE_WRITE_DISK(3)

NAME
     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_standard_lookup,
     archive_write_disk_set_user_lookup, archive_write_header,
     archive_write_data, archive_write_data_block, archive_write_finish_entry,
     archive_write_close, archive_write_finish archive_write_free — functions
     for creating objects on disk

LIBRARY
     Streaming Archive Library (libarchive, ‐larchive)

SYNOPSIS
     #include <archive.h>

     struct archive *
     archive_write_disk_new(void);

     int
     archive_write_disk_set_options(struct archive *, int flags);

     int
     archive_write_disk_set_skip_file(struct archive *, dev_t, ino_t);

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

     int
     archive_write_disk_set_standard_lookup(struct archive *);

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

     int
     archive_write_header(struct archive *, struct archive_entry *);

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

     ssize_t
     archive_write_data_block(struct archive *, const void *, size_t size,
	 int64_t offset);

     int
     archive_write_finish_entry(struct archive *);

     int
     archive_write_close(struct archive *);

     int
     archive_write_finish(struct archive *);

     int
     archive_write_free(struct archive *);

DESCRIPTION
     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.

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

     archive_write_disk_set_skip_file()
	     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.

     archive_write_disk_set_options()
	     The options field consists of a bitwise OR of one or more of the
	     following values:
	     ARCHIVE_EXTRACT_OWNER
		     The user and group IDs should be set on the restored
		     file.  By default, the user and group IDs are not
		     restored.
	     ARCHIVE_EXTRACT_PERM
		     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.
	     ARCHIVE_EXTRACT_TIME
		     The timestamps (mtime, ctime, and atime) should be
		     restored.	By default, they are ignored.  Note that
		     restoring of atime is not currently supported.
	     ARCHIVE_EXTRACT_NO_OVERWRITE
		     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.
	     ARCHIVE_EXTRACT_UNLINK
		     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.
	     ARCHIVE_EXTRACT_ACL
		     Attempt to restore ACLs.  By default, extended ACLs are
		     ignored.
	     ARCHIVE_EXTRACT_FFLAGS
		     Attempt to restore extended file flags.  By default, file
		     flags are ignored.
	     ARCHIVE_EXTRACT_XATTR
		     Attempt to restore POSIX.1e extended attributes.  By
		     default, they are ignored.
	     ARCHIVE_EXTRACT_SECURE_SYMLINKS
		     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.
	     ARCHIVE_EXTRACT_SECURE_NODOTDOT
		     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.
	     ARCHIVE_EXTRACT_SPARSE
		     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.

     archive_write_disk_set_group_lookup(),
	     archive_write_disk_set_user_lookup()
	     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.

     archive_write_disk_set_standard_lookup()
	     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
	     getgrnam(3).

     archive_write_header()
	     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.

     archive_write_data()
	     Write data corresponding to the header just written.  Returns
	     number of bytes written or ‐1 on error.

     archive_write_data_block()
	     Write data corresponding to the header just written.  This is
	     like archive_write_data() except that it performs a seek on the
	     file being written to the specified offset before writing the
	     data.  This is useful when restoring sparse files from archive
	     formats that support sparse files.  Returns number of bytes writ‐
	     ten or ‐1 on error.  (Note: This is currently not supported for
	     archive_write handles, only for archive_write_disk handles.)

     archive_write_finish_entry()
	     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.
	     However, some file attributes are written to disk only after the
	     file is closed, so this can be necessary if you need to work with
	     the file on disk right away.

     archive_write_close()
	     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.

     archive_write_finish()
	     This is a deprecated synonym for archive_write_free().

     archive_write_free()
	     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).

RETURN VALUES
     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.

     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, or ‐1 on error.

ERRORS
     Detailed error codes and textual descriptions are available from the
     archive_errno() and archive_error_string() functions.

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

HISTORY
     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.

AUTHORS
     The libarchive library was written by Tim Kientzle ⟨kientzle@acm.org⟩.

BUGS
     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
     ignored.

     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 particu‐
     lar 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.

BSD			       February 2, 2012 			   BSD
