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_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_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_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_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
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 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.