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ARCHIVE_WRITE(3) DragonFly Library Functions Manual ARCHIVE_WRITE(3)
NAME
archive_write - functions for creating archives
LIBRARY
Streaming Archive Library (libarchive, -larchive)
SYNOPSIS
#include <archive.h>
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.
Create archive object
See archive_write_new(3).
To write an archive, you must first obtain an initialized struct archive
object from archive_write_new().
Enable filters and formats, configure block size and padding
See archive_write_filter(3), archive_write_format(3) and
archive_write_blocksize(3).
You can then modify this object for the desired operations with the
various archive_write_set_XXX() functions. In particular, you will need
to invoke appropriate archive_write_add_XXX() and archive_write_set_XXX()
functions to enable the corresponding compression and format support.
Set options
See archive_write_set_options(3).
Open archive
See archive_write_open(3).
Once you have prepared the struct archive object, you call
archive_write_open() to actually open the archive and prepare it for
writing. There are several variants of this function; the most basic
expects you to provide pointers to several functions that can provide
blocks of bytes from the archive. There are convenience forms that allow
you to specify a filename, file descriptor, FILE * object, or a block of
memory from which to write the archive data.
Produce archive
See archive_write_header(3) and archive_write_data(3).
Individual archive entries are written in a three-step process: You first
initialize a struct archive_entry structure with information about the
new entry. At a minimum, you should set the pathname of the entry and
provide a struct stat with a valid st_mode field, which specifies the
type of object and st_size field, which specifies the size of the data
portion of the object.
Release resources
See archive_write_free(3).
After all entries have been written, use the archive_write_free()
function to release all resources.
EXAMPLES
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.
#ifdef __linux__
#define _FILE_OFFSET_BITS 64
#endif
#include <sys/stat.h>
#include <archive.h>
#include <archive_entry.h>
#include <fcntl.h>
#include <stdlib.h>
#include <unistd.h>
struct mydata {
const char *name;
int fd;
};
int
myopen(struct archive *a, void *client_data)
{
struct mydata *mydata = client_data;
mydata->fd = open(mydata->name, O_WRONLY | O_CREAT, 0644);
if (mydata->fd >= 0)
return (ARCHIVE_OK);
else
return (ARCHIVE_FATAL);
}
la_ssize_t
mywrite(struct archive *a, void *client_data, const void *buff, size_t n)
{
struct mydata *mydata = client_data;
return (write(mydata->fd, buff, n));
}
int
myclose(struct archive *a, void *client_data)
{
struct mydata *mydata = client_data;
if (mydata->fd > 0)
close(mydata->fd);
return (0);
}
void
write_archive(const char *outname, 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;
int fd;
a = archive_write_new();
mydata->name = outname;
/* Set archive format and filter according to output file extension.
* If it fails, set default format. Platform depended function.
* See supported formats in archive_write_set_format_filter_by_ext.c */
if (archive_write_set_format_filter_by_ext(a, outname) != ARCHIVE_OK) {
archive_write_add_filter_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);
if ((fd = open(*filename, O_RDONLY)) != -1) {
len = read(fd, buff, sizeof(buff));
while (len > 0) {
archive_write_data(a, buff, len);
len = read(fd, buff, sizeof(buff));
}
close(fd);
}
archive_entry_free(entry);
filename++;
}
archive_write_free(a);
}
int main(int argc, const char **argv)
{
const char *outname;
argv++;
outname = *argv++;
write_archive(outname, argv);
return 0;
}
SEE ALSO
tar(1), archive_write_set_options(3), libarchive(3), cpio(5), mtree(5),
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
vendor-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 device nodes with large device numbers from archives
created by this library.
DragonFly 5.9-DEVELOPMENT February 2, 2012 DragonFly 5.9-DEVELOPMENT