NAME
archive_read_disk_new,
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 —
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_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 *);
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_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 atrribute 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 defaut, moint 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_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.
More information about the
struct archive object and the
overall design of the library can be found in the
libarchive(3) overview.
EXAMPLE
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
archive_read(3),
archive_util(3),
archive_write(3),
archive_write_disk(3),
tar(1),
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.