ARCHIVE_READ_DISK(3) BSD Library Functions Manual ARCHIVE_READ_DISK(3)NAME
archive_read_disk_new, 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_close,
archive_read_finish — functions for reading objects from disk
SYNOPSIS
#include <archive.h>
struct archive *
archive_read_disk_new(void);
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 *);
int
archive_read_disk_gname(struct archive *, gid_t);
int
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_close(struct archive *);
int
archive_read_finish(struct archive *);
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_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 getpwid(3) and
getgrid(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 getpwid(3) and
getgrid(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 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
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, 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_close()
This currently does nothing.
archive_write_finish()
Invokes archive_write_close() if it was not invoked manually,
then releases all resources.
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_sourcepath(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_finish(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. The archive_errno(3) and archive_error_string(3) functions can be
used to retrieve an appropriate error code and a textual error message.
(See archive_util(3) for details.)
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.
SEE ALSOarchive_read(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 getgrid(3) and getpwid(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 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 March 10, 2009 BSD
