ARCHIVE_READ_DISK(3) Introduction to Library Functions ARCHIVE_READ_DISK(3)

NAME

archive_read_disk_new, archive_read_disk_open,
archive_read_disk_open_w, archive_read_disk_set_behavior,
archive_read_disk_set_symlink_logical,
archive_read_disk_set_symlink_physical,
archive_read_disk_set_symlink_hybrid,
archive_read_disk_entry_from_file, archive_read_disk_gname,
archive_read_disk_uname, archive_read_disk_set_uname_lookup,
archive_read_disk_set_gname_lookup,
archive_read_disk_set_standard_lookup, archive_read_disk_descend,
archive_read_disk_can_descend, archive_read_disk_current_filesystem,
archive_read_disk_current_filesystem_is_synthetic,
archive_read_disk_current_filesystem_is_remote,
archive_read_disk_set_matching,
archive_read_disk_set_metadata_filter_callback, - functions for reading
objects from disk

LIBRARY

Streaming Archive Library (libarchive, -larchive)

SYNOPSIS

#include <archive.h>

struct archive *
archive_read_disk_new(void);

int
archive_read_disk_open(struct archive *, const char *);

int
archive_read_disk_open_w(struct archive *, const wchar_t *);

int
archive_read_disk_set_behavior(struct archive *, int);

int
archive_read_disk_set_symlink_logical(struct archive *);

int
archive_read_disk_set_symlink_physical(struct archive *);

int
archive_read_disk_set_symlink_hybrid(struct archive *);

const char *
archive_read_disk_gname(struct archive *, gid_t);

const char *
archive_read_disk_uname(struct archive *, uid_t);

int
archive_read_disk_set_gname_lookup(struct archive *, void *,
const char *(*lookup)(void *, gid_t), void (*cleanup)(void *));

int
archive_read_disk_set_uname_lookup(struct archive *, void *,
const char *(*lookup)(void *, uid_t), void (*cleanup)(void *));

int
archive_read_disk_set_standard_lookup(struct archive *);

int
archive_read_disk_entry_from_file(struct archive *,
struct archive_entry *, int fd, const struct stat *);

int
archive_read_disk_descend(struct archive *);

int
archive_read_disk_can_descend(struct archive *);

int
archive_read_disk_current_filesystem(struct archive *);

int
archive_read_disk_current_filesystem_is_synthetic(struct archive *);

int
archive_read_disk_current_filesystem_is_remote(struct archive *);

int
archive_read_disk_set_matching(struct archive *, struct archive *,
void
(*excluded_func)(struct archive *, void *, struct archive entry *),
void *);

int
archive_read_disk_set_metadata_filter_callback(struct archive *,
int
(*metadata_filter_func)(struct archive *, void*, struct
archive_entry *), void *);

DESCRIPTION

These functions provide an API for reading information about objects on
disk. In particular, they provide an interface for populating struct
archive_entry objects.

archive_read_disk_new()
Allocates and initializes a struct archive object suitable for
reading object information from disk.

archive_read_disk_open()
Opens the file or directory from the given path and prepares
the struct archive to read it from disk.

archive_read_disk_open_w()
Opens the file or directory from the given path as a wide
character string and prepares the struct archive to read it
from disk.

archive_read_disk_set_behavior()
Configures various behavior options when reading entries from
disk. The flags field consists of a bitwise OR of one or more
of the following values:
ARCHIVE_READDISK_HONOR_NODUMP
Skip files and directories with the nodump file
attribute (file flag) set. By default, the nodump file
attribute is ignored.
ARCHIVE_READDISK_MAC_COPYFILE
Mac OS X specific. Read metadata (ACLs and extended
attributes) with copyfile(3). By default, metadata is
read using copyfile(3).
ARCHIVE_READDISK_NO_ACL
Do not read Access Control Lists. By default, ACLs are
read from disk.
ARCHIVE_READDISK_NO_FFLAGS
Do not read file attributes (file flags). By default,
file attributes are read from disk. See chattr(1)
(Linux) or chflags(1) (FreeBSD, Mac OS X) for more
information on file attributes.
ARCHIVE_READDISK_NO_TRAVERSE_MOUNTS
Do not traverse mount points. By default, mount points
are traversed.
ARCHIVE_READDISK_NO_XATTR
Do not read extended file attributes (xattrs). By
default, extended file attributes are read from disk.
See xattr(7) (Linux), xattr(2) (Mac OS X), or
getextattr(8) (FreeBSD) for more information on
extended file attributes.
ARCHIVE_READDISK_RESTORE_ATIME
Restore access time of traversed files. By default,
access time of traversed files is not restored.
ARCHIVE_READDISK_NO_SPARSE
Do not read sparse file information. By default,
sparse file information is read from disk.

archive_read_disk_set_symlink_logical(),
archive_read_disk_set_symlink_physical(),
archive_read_disk_set_symlink_hybrid()
This sets the mode used for handling symbolic links. The
"logical" mode follows all symbolic links. The "physical" mode
does not follow any symbolic links. The "hybrid" mode
currently behaves identically to the "logical" mode.

archive_read_disk_gname(), archive_read_disk_uname()
Returns a user or group name given a gid or uid value. By
default, these always return a NULL string.

archive_read_disk_set_gname_lookup(),
archive_read_disk_set_uname_lookup()
These allow you to override the functions used for user and
group name lookups. 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 or when new lookup functions are
registered.

archive_read_disk_set_standard_lookup()
This convenience function installs a standard set of user and
group name lookup functions. These functions use getpwuid(3)
and getgrgid(3) to convert ids to names, defaulting to NULL if
the names cannot be looked up. These functions also implement
a simple memory cache to reduce the number of calls to
getpwuid(3) and getgrgid(3).

archive_read_disk_entry_from_file()
Populates a struct archive_entry object with information about
a particular file. The archive_entry object must have already
been created with archive_entry_new(3) and at least one of the
source path or path fields must already be set. (If both are
set, the source path will be used.)

Information is read from disk using the path name from the
struct archive_entry object. If a file descriptor is provided,
some information will be obtained using that file descriptor,
on platforms that support the appropriate system calls.

If a pointer to a struct stat is provided, information from
that structure will be used instead of reading from the disk
where appropriate. This can provide performance benefits in
scenarios where struct stat information has already been read
from the disk as a side effect of some other operation. (For
example, directory traversal libraries often provide this
information.)

Where necessary, user and group ids are converted to user and
group names using the currently-registered lookup functions
above. This affects the file ownership fields and ACL values
in the struct archive_entry object.

archive_read_disk_descend()
If the current entry can be descended, this function will mark
the directory as the next entry for archive_read_header(3) to
visit.

archive_read_disk_can_descend()
Returns 1 if the current entry is an unvisited directory and 0
otherwise.

archive_read_disk_current_filesystem()
Returns the index of the most recent filesystem entry that has
been visited through archive_read_disk

archive_read_disk_current_filesystem_is_synthetic()
Returns 1 if the current filesystem is a virtual filesystem.
Returns 0 if the current filesystem is not a virtual
filesystem. Returns -1 if it is unknown.

archive_read_disk_current_filesystem_is_remote()
Returns 1 if the current filesystem is a remote filesystem.
Returns 0 if the current filesystem is not a remote filesystem.
Returns -1 if it is unknown.

archive_read_disk_set_matching()
Allows the caller to set struct archive *_ma to compare each
entry during archive_read_header(3) calls. If matched based on
calls to archive_match_path_excluded,
archive_match_time_excluded, or archive_match_owner_excluded,
then the callback function specified by the _excluded_func
parameter will execute. This function will receive data
provided to the fourth parameter, void *_client_data.

archive_read_disk_set_metadata_filter_callback()
Allows the caller to set a callback function during calls to
archive_read_header(3) to filter out metadata for each entry.
The callback function receives the struct archive object, void*
custom filter data, and the struct archive_entry. If the
callback function returns an error, ARCHIVE_RETRY will be
returned and the entry will not be further processed.
More information about the struct archive object and the overall design
of the library can be found in the libarchive(3) overview.

EXAMPLES

The following illustrates basic usage of the library by showing how to
use it to copy an item on disk into an archive.

void
file_to_archive(struct archive *a, const char *name)
{
char buff[8192];
size_t bytes_read;
struct archive *ard;
struct archive_entry *entry;
int fd;

ard = archive_read_disk_new();
archive_read_disk_set_standard_lookup(ard);
entry = archive_entry_new();
fd = open(name, O_RDONLY);
if (fd < 0)
return;
archive_entry_copy_pathname(entry, name);
archive_read_disk_entry_from_file(ard, entry, fd, NULL);
archive_write_header(a, entry);
while ((bytes_read = read(fd, buff, sizeof(buff))) > 0)
archive_write_data(a, buff, bytes_read);
archive_write_finish_entry(a);
archive_read_free(ard);
archive_entry_free(entry);
}

RETURN VALUES

Most functions return ARCHIVE_OK (zero) on success, or one of several
negative 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_read_disk_new() returns a pointer to a newly-allocated struct
archive object or NULL if the allocation failed for any reason.

archive_read_disk_gname() and archive_read_disk_uname() return const
char * pointers to the textual name or NULL if the lookup failed for
any reason. The returned pointer points to internal storage that may
be reused on the next call to either of these functions; callers should
copy the string if they need to continue accessing it.

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_util(3), archive_write(3),
archive_write_disk(3), libarchive(3)

HISTORY

The libarchive library first appeared in FreeBSD 5.3. The
archive_read_disk interface was added to libarchive 2.6 and first
appeared in FreeBSD 8.0.

AUTHORS

The libarchive library was written by Tim Kientzle
<kientzle@FreeBSD.org>.

BUGS

The "standard" user name and group name lookup functions are not the
defaults because getgrgid(3) and getpwuid(3) are sometimes too large
for particular applications. The current design allows the application
author to use a more compact implementation when appropriate.

The full list of metadata read from disk by
archive_read_disk_entry_from_file() is necessarily system-dependent.

The archive_read_disk_entry_from_file() function reads as much
information as it can from disk. Some method should be provided to
limit this so that clients who do not need ACLs, for instance, can
avoid the extra work needed to look up such information.

This API should provide a set of methods for walking a directory tree.
That would make it a direct parallel of the archive_read(3) API. When
such methods are implemented, the "hybrid" symbolic link mode will make
sense.

illumos April 3, 2017 illumos