Provided by: libarchive-dev_3.6.0-1ubuntu1_amd64 
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 — 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 *));
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 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.
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_ACL
Attempt to restore Access Control Lists. By default, extended ACLs are
ignored.
ARCHIVE_EXTRACT_CLEAR_NOCHANGE_FFLAGS
Before removing a file system object prior to replacing it, clear platform-
specific file flags which might prevent its removal.
ARCHIVE_EXTRACT_FFLAGS
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.
ARCHIVE_EXTRACT_MAC_METADATA
Mac OS X specific. Restore metadata using copyfile(3). By default,
copyfile(3) metadata is ignored.
ARCHIVE_EXTRACT_NO_OVERWRITE
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.
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 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.
ARCHIVE_EXTRACT_SAFE_WRITES
Extract files atomically, by first creating a unique temporary file and then
renaming it to its required destination name. This avoids a race where an
application might see a partial file (or no file) during extraction.
ARCHIVE_EXTRACT_SECURE_NOABSOLUTEPATHS
Refuse to extract an absolute path. The default is to not refuse such
paths.
ARCHIVE_EXTRACT_SECURE_NODOTDOT
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.
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 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.
ARCHIVE_EXTRACT_SPARSE
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.
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_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_XATTR
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.
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 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.
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 simple memory cache to reduce the number of calls to getpwnam(3) and
getgrnam(3).
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 impossible.
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
tar(1), archive_read(3), archive_write(3), 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 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 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
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 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.