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<p>ARCHIVE_WRITE_DISK(3) BSD Library Functions Manual
ARCHIVE_WRITE_DISK(3)</p>
<p style="margin-top: 1em"><b>NAME</b></p>
<p style="margin-left:6%;"><b>archive_write_disk_new</b>,
<b>archive_write_disk_set_options</b>,
<b>archive_write_disk_set_skip_file</b>,
<b>archive_write_disk_set_group_lookup</b>,
<b>archive_write_disk_set_standard_lookup</b>,
<b>archive_write_disk_set_user_lookup</b> — functions
for creating objects on disk</p>
<p style="margin-top: 1em"><b>LIBRARY</b></p>
<p style="margin-left:6%;">Streaming Archive Library
(libarchive, -larchive)</p>
<p style="margin-top: 1em"><b>SYNOPSIS</b></p>
<p style="margin-left:6%;"><b>#include
<archive.h></b></p>
<p style="margin-left:6%; margin-top: 1em"><i>struct
archive *</i></p>
<p style="margin-left:12%;"><b>archive_write_disk_new</b>(<i>void</i>);</p>
<p style="margin-left:6%; margin-top: 1em"><i>int</i></p>
<p style="margin-left:12%;"><b>archive_write_disk_set_options</b>(<i>struct archive *</i>,
<i>int flags</i>);</p>
<p style="margin-left:6%; margin-top: 1em"><i>int</i></p>
<p style="margin-left:12%;"><b>archive_write_disk_set_skip_file</b>(<i>struct archive *</i>,
<i>dev_t</i>, <i>ino_t</i>);</p>
<p style="margin-left:6%; margin-top: 1em"><i>int</i></p>
<p><b>archive_write_disk_set_group_lookup</b>(<i>struct archive *</i>,
<i>void *</i>,
<i>gid_t (*)(void *, const char *gname, gid_t gid)</i>,
<i>void (*cleanup)(void *)</i>);</p>
<p style="margin-left:6%; margin-top: 1em"><i>int</i></p>
<p style="margin-left:12%;"><b>archive_write_disk_set_standard_lookup</b>(<i>struct archive *</i>);</p>
<p style="margin-left:6%; margin-top: 1em"><i>int</i></p>
<p><b>archive_write_disk_set_user_lookup</b>(<i>struct archive *</i>,
<i>void *</i>,
<i>uid_t (*)(void *, const char *uname, uid_t uid)</i>,
<i>void (*cleanup)(void *)</i>);</p>
<p style="margin-top: 1em"><b>DESCRIPTION</b></p>
<p style="margin-left:6%;">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
<b>archive_read</b>() 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 <b>archive_write_disk</b>() family functions. This
interface is deliberately very similar to the
<b>archive_write</b>() interface used to write objects to a
streaming archive.</p>
<p style="margin-top: 1em"><b>archive_write_disk_new</b>()</p>
<p style="margin-left:17%;">Allocates and initializes a
struct archive object suitable for writing objects to
disk.</p>
<p style="margin-top: 1em"><b>archive_write_disk_set_skip_file</b>()</p>
<p style="margin-left:17%;">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.</p>
<p style="margin-top: 1em"><b>archive_write_disk_set_options</b>()</p>
<p style="margin-left:17%;">The options field consists of a
bitwise OR of one or more of the following values:</p>
<p><b>ARCHIVE_EXTRACT_ACL</b></p>
<p style="margin-left:27%;">Attempt to restore Access
Control Lists. By default, extended ACLs are ignored.</p>
<p><b>ARCHIVE_EXTRACT_CLEAR_NOCHANGE_FFLAGS</b></p>
<p style="margin-left:27%;">Before removing a file system
object prior to replacing it, clear platform-specific file
flags which might prevent its removal.</p>
<p><b>ARCHIVE_EXTRACT_FFLAGS</b></p>
<p style="margin-left:27%;">Attempt to restore file
attributes (file flags). By default, file attributes are
ignored. See chattr(1) (Linux) or chflags(1) (FreeBSD, Mac
OS X) for more information on file attributes.</p>
<p><b>ARCHIVE_EXTRACT_MAC_METADATA</b></p>
<p style="margin-left:27%;">Mac OS X specific. Restore
metadata using copyfile(3). By default, copyfile(3) metadata
is ignored.</p>
<p><b>ARCHIVE_EXTRACT_NO_OVERWRITE</b></p>
<p style="margin-left:27%;">Existing files on disk will not
be overwritten. By default, existing regular files are
truncated and overwritten; existing directories will have
their permissions updated; other pre-existing objects are
unlinked and recreated from scratch.</p>
<p><b>ARCHIVE_EXTRACT_OWNER</b></p>
<p style="margin-left:27%;">The user and group IDs should
be set on the restored file. By default, the user and group
IDs are not restored.</p>
<p><b>ARCHIVE_EXTRACT_PERM</b></p>
<p style="margin-left:27%;">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
<b>ARCHIVE_EXTRACT_OWNER</b> 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 obeyed.</p>
<p><b>ARCHIVE_EXTRACT_SECURE_NOABSOLUTEPATHS</b></p>
<p style="margin-left:27%;">Refuse to extract an absolute
path. The default is to not refuse such paths.</p>
<p><b>ARCHIVE_EXTRACT_SECURE_NODOTDOT</b></p>
<p style="margin-left:27%;">Refuse to extract a path that
contains a <i>..</i> element anywhere within it. The default
is to not refuse such paths. Note that paths ending in
<i>..</i> always cause an error, regardless of this
flag.</p>
<p><b>ARCHIVE_EXTRACT_SECURE_SYMLINKS</b></p>
<p style="margin-left:27%;">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 archives that (deliberately or otherwise) extract
files outside of the current directory. The default is not
to perform this check. If</p>
<p><b>ARCHIVE_EXTRACT_SPARSE</b></p>
<p style="margin-left:27%;">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. <b>ARCHIVE_EXTRACT_UNLINK</b> 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.</p>
<p><b>ARCHIVE_EXTRACT_TIME</b></p>
<p style="margin-left:27%;">The timestamps (mtime, ctime,
and atime) should be restored. By default, they are ignored.
Note that restoring of atime is not currently supported.</p>
<p><b>ARCHIVE_EXTRACT_UNLINK</b></p>
<p style="margin-left:27%;">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.</p>
<p><b>ARCHIVE_EXTRACT_XATTR</b></p>
<p style="margin-left:27%;">Attempt to restore extended
file attributes. By default, they are ignored. See xattr(7)
(Linux), xattr(2) (Mac OS X), or getextattr(8) (FreeBSD) for
more information on extended file attributes.</p>
<p style="margin-top: 1em"><b>archive_write_disk_set_group_lookup</b>(),
<b>archive_write_disk_set_user_lookup</b>()</p>
<p style="margin-left:17%;">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.</p>
<p style="margin-top: 1em"><b>archive_write_disk_set_standard_lookup</b>()</p>
<p style="margin-left:17%;">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 simple memory
cache to reduce the number of calls to getpwnam(3) and
getgrnam(3).</p>
<p style="margin-left:6%;">More information about the
<i>struct archive</i> 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).</p>
<p style="margin-top: 1em"><b>RETURN VALUES</b></p>
<p style="margin-left:6%;">Most functions return
<b>ARCHIVE_OK</b> (zero) on success, or one of several
non-zero error codes for errors. Specific error codes
include: <b>ARCHIVE_RETRY</b> for operations that might
succeed if retried, <b>ARCHIVE_WARN</b> for unusual
conditions that do not prevent further operations, and
<b>ARCHIVE_FATAL</b> for serious errors that make remaining
operations impossible.</p>
<p style="margin-left:6%; margin-top: 1em"><b>archive_write_disk_new</b>()
returns a pointer to a newly-allocated struct archive
object.</p>
<p style="margin-left:6%; margin-top: 1em"><b>archive_write_data</b>()
returns a count of the number of bytes actually written, or
-1 on error.</p>
<p style="margin-top: 1em"><b>ERRORS</b></p>
<p style="margin-left:6%;">Detailed error codes and textual
descriptions are available from the <b>archive_errno</b>()
and <b>archive_error_string</b>() functions.</p>
<p style="margin-top: 1em"><b>SEE ALSO</b></p>
<p style="margin-left:6%;">archive_read(3),
archive_write(3), tar(1), libarchive(3)</p>
<p style="margin-top: 1em"><b>HISTORY</b></p>
<p style="margin-left:6%;">The <b>libarchive</b> library
first appeared in FreeBSD 5.3. The
<b>archive_write_disk</b> interface was added to
<b>libarchive 2.0</b> and first appeared in
FreeBSD 6.3.</p>
<p style="margin-top: 1em"><b>AUTHORS</b></p>
<p style="margin-left:6%;">The <b>libarchive</b> library
was written by Tim Kientzle <kientzle@acm.org>.</p>
<p style="margin-top: 1em"><b>BUGS</b></p>
<p style="margin-left:6%;">Directories are actually
extracted in two distinct phases. Directories are created
during <b>archive_write_header</b>(), but final permissions
are not set until <b>archive_write_close</b>(). This
separation is necessary to correctly handle borderline cases
such as a non-writable directory containing 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 <b>archive_read_extract</b>() or before
calling <b>archive_read_close</b>(), you may confuse the
permission-setting logic with the result that directory
permissions are restored incorrectly.</p>
<p style="margin-left:6%; margin-top: 1em">The library
attempts to create objects with filenames longer than
<b>PATH_MAX</b> 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.</p>
<p style="margin-left:6%; margin-top: 1em">Restoring the
path <i>aa/../bb</i> does create each intermediate
directory. In particular, the directory <i>aa</i> is created
as well as the final object <i>bb</i>. In theory, this can
be exploited to create an entire directory hierarchy with a
single request. Of course, this does not work if the
<b>ARCHIVE_EXTRACT_NODOTDOT</b> option is specified.</p>
<p style="margin-left:6%; margin-top: 1em">Implicit
directories are always created obeying the current umask.
Explicit objects are created obeying the current umask
unless <b>ARCHIVE_EXTRACT_PERM</b> is specified, in which
case they current umask is ignored.</p>
<p style="margin-left:6%; margin-top: 1em">SGID and SUID
bits are restored only if the correct user and group could
be set. If <b>ARCHIVE_EXTRACT_OWNER</b> 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.</p>
<p style="margin-left:6%; margin-top: 1em">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.</p>
<p style="margin-left:6%; margin-top: 1em">There should be
a corresponding <b>archive_read_disk</b> interface that
walks a directory hierarchy and returns archive entry
objects.</p>
<p style="margin-left:6%; margin-top: 1em">BSD
April 3, 2017 BSD</p>
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