FreeBSD Man Pagesarchive_write_set_format_ustar(3)
NAME
archive_write_new, archive_write_set_format_cpio,
archive_write_set_format_pax, archive_write_set_format_pax_restricted,
archive_write_set_format_shar, archive_write_set_format_shar_binary,
archive_write_set_format_ustar, archive_write_set_bytes_per_block,
archive_write_set_bytes_in_last_block, archive_write_set_compressor_gzip,
archive_write_set_compressor_bzip2, archive_write_open,
archive_write_open_fd, archive_write_open_file, archive_write_prepare,
archive_write_header, archive_write_data, archive_write_close,
archive_write_finish -- functions for creating archives
SYNOPSIS
#include <archive.h>
struct archive *
archive_write_new(void);
int
archive_write_set_bytes_per_block(archive *, int bytes_per_block);
int
archive_write_set_bytes_in_last_block(archive *, int);
int
archive_write_set_compressor_gzip(struct archive *);
int
archive_write_set_compressor_bzip2(struct archive *);
int
archive_write_set_format_cpio(struct archive *);
int
archive_write_set_format_pax(struct archive *);
int
archive_write_set_format_pax_restricted(struct archive *);
int
archive_write_set_format_shar(struct archive *);
int
archive_write_set_format_shar_binary(struct archive *);
int
archive_write_set_format_ustar(struct archive *);
int
archive_write_open(struct archive *, void *client_data,
archive_open_archive_callback *, archive_write_archive_callback *,
archive_close_archive_callback *);
int
archive_write_open_fd(struct archive *, int fd);
int
archive_write_open_file(struct archive *, const char *filename);
archive_write_close(struct archive *);
void
archive_write_finish(struct archive *);
DESCRIPTION
These functions provide a complete API for creating streaming archive
files. The general process is to first create the struct archive object,
set any desired options, initialize the archive, append entries, then
close the archive and release all resources. The following summary
describes the functions in approximately the order they are ordinarily
used:
archive_write_new()
Allocates and initializes a struct archive object suitable for
writing a tar archive.
archive_write_set_bytes_per_block()
Sets the block size used for writing the archive data. Every
call to the write callback function, except possibly the last
one, will use this value for the length. The third parameter is
a boolean that specifies whether or not the final block written
will be padded to the full block size. If it is zero, the last
block will not be padded. If it is non-zero, padding will be
added both before and after compression. The default is to use a
block size of 10240 bytes and to pad the last block.
archive_write_set_bytes_in_last_block()
Sets the block size used for writing the last block. If this
value is zero, the last block will be padded to the same size as
the other blocks. Otherwise, the final block will be padded to a
multiple of this size. In particular, setting it to 1 will cause
the final block to not be padded. For compressed output, any
padding generated by this option is applied only after the com-
pression. The uncompressed data is always unpadded. The default
is to pad the last block to the full block size (note that
archive_write_open_file() will set this based on the file type).
Unlike the other ``set'' functions, this function can be called
after the archive is opened.
archive_write_set_format_cpio(), archive_write_set_format_pax(),
archive_write_set_format_pax_restricted(),
archive_write_set_format_shar(),
archive_write_set_format_shar_binary(),
archive_write_set_format_ustar()
Sets the format that will be used for the archive. The library
can write POSIX octet-oriented cpio format archives, POSIX-stan-
dard ``pax interchange'' format archives, traditional ``shar''
archives, enhanced ``binary'' shar archives that store a variety
of file attributes and handle binary files, and POSIX-standard
``ustar'' archives. The pax interchange format is a backwards-
compatible tar format that adds key/value attributes to each
entry and supports arbitrary filenames, linknames, uids, sizes,
etc. ``Restricted pax interchange format'' is the library
default; this is the same as pax format, but suppresses the pax
extended header for most normal files. In most cases, this will
result in ordinary ustar archives.
accepts pointers to three callback functions which will be
invoked by the compression layer to write the constructed ar-
chive. In order to support external compression programs, the
compression is permitted to fork and invoke the callbacks from a
separate process. In particular, clients should not assume that
they can communicate between the callbacks and the mainline code
using shared variables. (The standard gzip, bzip2, and "none"
compression methods do not fork.)
archive_write_open_fd()
A convenience form of archive_write_open() that accepts a file
descriptor.
archive_write_open_file()
A convenience form of archive_write_open() that accepts a file-
name. A NULL argument indicates that the output should be writ-
ten to standard output; an argument of ``-'' will open a file
with that name. If you have not invoked
archive_write_set_bytes_in_last_block(), then
archive_write_open_file() will adjust the last-block padding
depending on the file: it will enable padding when writing to
standard output or to a character or block device node, it will
disable padding otherwise. You can override this by manually
invoking archive_write_set_bytes_in_last_block() either before or
after calling archive_write_open().
archive_write_header()
Build and write a header using the data in the provided struct
archive_entry structure.
archive_write_data()
Write data corresponding to the header just written. Returns
number of bytes written or -1 on error.
archive_write_close()
Complete the archive and invoke the close callback.
archive_write_finish()
Invokes archive_write_close() if it was not invoked manually,
then release all resources.
More information about the struct archive object and the overall design
of the library can be found in the libarchive(3) overview.
IMPLEMENTATION
Compression support is built-in to libarchive, which uses zlib and bzlib
to handle gzip and bzip2 compression, respectively.
CLIENT CALLBACKS
To use this library, you will need to define and register callback func-
tions that will be invoked to write data to the resulting archive. These
functions are registered by calling archive_write_open():
typedef int archive_open_archive_callback(struct archive *, void
*client_data)
The open callback is invoked by archive_write_open(). It should return
ARCHIVE_OK if the underlying file or data source is successfully opened.
If the open fails, it should call archive_set_error() to register an
is especially critical when writing archives to tape drives. On success,
the write callback should return the number of bytes actually written.
On error, the callback should invoke archive_set_error() to register an
error code and message and return -1.
typedef int archive_close_archive_callback(struct archive *, void
*client_data)
The close callback is invoked by archive_close when the archive process-
ing is complete. The callback should return ARCHIVE_OK on success. On
failure, the callback should invoke archive_set_error() to register an
error code and message and regurn ARCHIVE_FATAL.
EXAMPLE
The following sketch illustrates basic usage of the library. In this
example, the callback functions are simply wrappers around the standard
open(2), write(2), and close(2) system calls.
void
write_archive(const char **filename)
{
struct mydata *mydata = malloc(sizeof(struct mydata));
struct archive *a;
struct archive_entry *entry;
struct stat st;
char buff[8192];
int len;
a = archive_write_new();
mydata->name = name;
archive_write_set_compression_gzip(a);
archive_write_set_format_ustar(a);
archive_write_open(a, mydata, myopen, mywrite, myclose);
while (*filename) {
stat(*filename, &st);
entry = archive_entry_new();
archive_entry_copy_stat(entry, &st);
archive_entry_set_pathname(entry, *filename);
archive_write_header(a, entry);
fd = open(*filename, O_RDONLY);
len = read(fd, buff, sizeof(buff));
while ( len >= 0 ) {
archive_write_data(a, buff, len);
len = read(fd, buff, sizeof(buff));
}
archive_entry_free(entry);
filename++;
}
archive_write_finish(a);
}
int
myopen(struct archive *a, void *client_data)
{
struct mydata *mydata = client_data;
mydata->fd = open(mydata->name, O_WRONLY | O_CREAT, 0644);
return (mydata->fd >= 0);
}
int
myclose(struct archive *a, void *client_data)
{
struct mydata *mydata = client_data;
if (mydata->fd > 0)
close(mydata->fd);
return (0);
}
RETURN VALUES
Most functions return zero on success, non-zero on error. The
archive_errno() and archive_error_string() functions can be used to
retrieve an appropriate error code and a textual error message.
archive_write_new() returns a pointer to a newly-allocated struct archive
object.
archive_write_data() returns a count of the number of bytes actually
written. On error, -1 is returned and the archive_errno() and
archive_error_string() functions will return appropriate values. Note
that if the client-provided write callback function returns a non-zero
value, that error will be propagated back to the caller through whatever
API function resulted in that call, which may include
archive_write_header(), archive_write_data(), or archive_write_close().
The client callback can call archive_set_error() to provide values that
can then be retrieved by archive_errno() and archive_error_string().
SEE ALSO
tar(1), libarchive(3), tar(5)
HISTORY
The libarchive library first appeared in FreeBSD 5.3.
AUTHORS
The libarchive library was written by Tim Kientzle <kientzle@acm.org>.
BUGS
There are many peculiar bugs in historic tar implementations that may
cause certain programs to reject archives written by this library. For
example, several historic implementations calculated header checksums
incorrectly and will thus reject valid archives; GNU tar does not fully
support pax interchange format; some old tar implementations required
specific field terminations.
The default pax interchange format eliminates most of the historic tar
limitations and provides a generic key/value attribute facility for ven-
dor-defined extensions. One oversight in POSIX is the failure to provide
a standard attribute for large device numbers. This library uses
``SCHILY.devminor'' and ``SCHILY.devmajor'' for device numbers that
exceed the range supported by the backwards-compatible ustar header.
These keys are compatible with Joerg Schilling's star archiver. Other
implementations may not recognize these keys and will thus be unable to
correctly restore large device numbers archived by this library.
FreeBSD 5.4 January 8, 2005 FreeBSD 5.4
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