ARCHIVE_READ_DISK(3) BSD Library Functions Manual 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 charac-
ter 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 at-
tributes) 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 infor-
mation 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 de-
fault, 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 at-
tributes.
ARCHIVE_READDISK_RESTORE_ATIME
Restore access time of traversed files. By default, ac-
cess 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 de-
fault, 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 de-
stroyed 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 sim-
ple 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 in-
formation will be obtained using that file descriptor, on plat-
forms 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 ap-
propriate. 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, direc-
tory 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. Re-
turns 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. Re-
turns 0 if the current filesystem is not a remote filesystem. Re-
turns -1 if it is unknown.
archive_read_disk_set_matching()
Allows the caller to set struct archive *_ma to compare each en-
try 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 param-
eter 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* cus-
tom 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 impossi-
ble.
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 rea-
son. 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 ap-
peared 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 de-
faults because getgrgid(3) and getpwuid(3) are sometimes too large for
particular applications. The current design allows the application au-
thor 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 informa-
tion 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.
BSD April 3, 2017 BSD
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