archive_write_disk(3) BSD 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_user_lookup, archive_write_header, archive_write_data,
archive_write_finish_entry, archive_write_close, archive_write_finish -- functions for cre-
ating objects on disk
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_finish(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 archive, then write those objects to a struct archive object
created using the archive_write_disk() family functions. This interface is deliberately
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
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 ar-
chive 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 restored.
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 specified, 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
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 regu-
lar files are truncated and overwritten; 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
Attempt to restore ACLs. By default, extended ACLs are ignored.
Attempt to restore extended file flags. By default, file flags are ignored.
Attempt to restore POSIX.1e extended attributes. By default, they are
Refuse to extract any object whose final location would be altered by a sym-
link on disk. This is intended to help guard against a variety of mischief
caused by archives that (deliberately or otherwise) extract files outside of
the current directory. The default is not to perform this check. If
ARCHIVE_EXTRACT_UNLINK is specified 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 anywhere 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, independent 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 function 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 func-
tions. 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 imple-
ment a simple 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 struc-
ture. See archive_entry(3) for information on creating and populating struct
Write data corresponding to the header just written. Returns number of bytes writ-
ten 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()
Set any attributes that could not be set during the initial restore. For example,
directory timestamps are not restored initially because restoring a subsequent file
would alter that timestamp. Similarly, non-writable directories are initially cre-
ated 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
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
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 impossible. 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 appro-
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 <firstname.lastname@example.org>.
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 correctly handle borderline cases such as a non-writable direc-
tory containing files, but can cause unexpected results. In particular, directory permis-
sions 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 permissions are restored incorrectly.
The library attempts to create objects with filenames longer than PATH_MAX by creating pre-
fixes 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 heirarchy 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 particular applications. The cur-
rent design allows the application author to use a more compact implementation when appro-
There should be a corresponding archive_read_disk interface that walks a directory heirarchy
and returns archive entry objects.
BSD August 5, 2008 BSD