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<p>ARCHIVE_WRITE(3) BSD Library Functions Manual
ARCHIVE_WRITE(3)</p>
<p style="margin-top: 1em"><b>NAME</b></p>
<p style="margin-left:6%;"><b>archive_write</b> —
functions for creating archives</p>
<p style="margin-top: 1em"><b>LIBRARY</b></p>
<p style="margin-left:6%;">Streaming Archive Library
(libarchive, -larchive)</p>
<p style="margin-top: 1em"><b>SYNOPSIS</b></p>
<p style="margin-left:6%;"><b>#include
<archive.h></b></p>
<p style="margin-top: 1em"><b>DESCRIPTION</b></p>
<p style="margin-left:6%;">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.</p>
<p style="margin-left:6%; margin-top: 1em"><b>Create
archive object</b> <br>
See archive_write_new(3).</p>
<p style="margin-left:6%; margin-top: 1em">To write an
archive, you must first obtain an initialized struct archive
object from <b>archive_write_new</b>().</p>
<p style="margin-left:6%; margin-top: 1em"><b>Enable
filters and formats, configure block size and padding</b>
<br>
See archive_write_filter(3), archive_write_format(3) and
archive_write_blocksize(3).</p>
<p style="margin-left:6%; margin-top: 1em">You can then
modify this object for the desired operations with the
various <b>archive_write_set_XXX</b>() functions. In
particular, you will need to invoke appropriate
<b>archive_write_add_XXX</b>() and
<b>archive_write_set_XXX</b>() functions to enable the
corresponding compression and format support.</p>
<p style="margin-left:6%; margin-top: 1em"><b>Set
options</b> <br>
See archive_write_set_options(3).</p>
<p style="margin-left:6%; margin-top: 1em"><b>Open
archive</b> <br>
See archive_write_open(3).</p>
<p style="margin-left:6%; margin-top: 1em">Once you have
prepared the struct archive object, you call
<b>archive_write_open</b>() 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, <i>FILE *</i> object,
or a block of memory from which to write the archive
data.</p>
<p style="margin-left:6%; margin-top: 1em"><b>Produce
archive</b> <br>
See archive_write_header(3) and archive_write_data(3).</p>
<p style="margin-left:6%; margin-top: 1em">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 <i>struct
stat</i> with a valid <i>st_mode</i> field, which specifies
the type of object and <i>st_size</i> field, which specifies
the size of the data portion of the object.</p>
<p style="margin-left:6%; margin-top: 1em"><b>Release
resources</b> <br>
See archive_write_free(3).</p>
<p style="margin-left:6%; margin-top: 1em">After all
entries have been written, use the
<b>archive_write_free</b>() function to release all
resources.</p>
<p style="margin-top: 1em"><b>EXAMPLES</b></p>
<p style="margin-left:6%;">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.</p>
<p style="margin-left:14%; margin-top: 1em">#ifdef
__linux__</p>
<table width="100%" border="0" rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="14%"></td>
<td width="10%">
<p>#define</p></td>
<td width="11%">
<p>_FILE_OFFSET_BITS 64</p></td>
<td width="65%">
</td></tr>
</table>
<p style="margin-left:14%;">#endif <br>
#include <sys/stat.h> <br>
#include <archive.h> <br>
#include <archive_entry.h> <br>
#include <fcntl.h> <br>
#include <stdlib.h> <br>
#include <unistd.h></p>
<p style="margin-left:14%; margin-top: 1em">struct mydata {
<br>
const char *name; <br>
int fd; <br>
};</p>
<p style="margin-left:14%; margin-top: 1em">int <br>
myopen(struct archive *a, void *client_data) <br>
{ <br>
struct mydata *mydata = client_data;</p>
<p style="margin-left:14%; margin-top: 1em">mydata->fd =
open(mydata->name, O_WRONLY | O_CREAT, 0644); <br>
if (mydata->fd >= 0) <br>
return (ARCHIVE_OK); <br>
else <br>
return (ARCHIVE_FATAL); <br>
}</p>
<p style="margin-left:14%; margin-top: 1em">la_ssize_t <br>
mywrite(struct archive *a, void *client_data, const void
*buff, size_t n) <br>
{ <br>
struct mydata *mydata = client_data;</p>
<p style="margin-left:14%; margin-top: 1em">return
(write(mydata->fd, buff, n)); <br>
}</p>
<p style="margin-left:14%; margin-top: 1em">int <br>
myclose(struct archive *a, void *client_data) <br>
{ <br>
struct mydata *mydata = client_data;</p>
<p style="margin-left:14%; margin-top: 1em">if
(mydata->fd > 0) <br>
close(mydata->fd); <br>
return (0); <br>
}</p>
<p style="margin-left:14%; margin-top: 1em">void <br>
write_archive(const char *outname, const char **filename)
<br>
{ <br>
struct mydata *mydata = malloc(sizeof(struct mydata)); <br>
struct archive *a; <br>
struct archive_entry *entry; <br>
struct stat st; <br>
char buff[8192]; <br>
int len; <br>
int fd;</p>
<p style="margin-left:14%; margin-top: 1em">a =
archive_write_new(); <br>
mydata->name = outname; <br>
/* Set archive format and filter according to output file
extension. <br>
* If it fails, set default format. Platform depended
function. <br>
* See supported formats in
archive_write_set_format_filter_by_ext.c */ <br>
if (archive_write_set_format_filter_by_ext(a, outname) !=
ARCHIVE_OK) { <br>
archive_write_add_filter_gzip(a); <br>
archive_write_set_format_ustar(a); <br>
} <br>
archive_write_open(a, mydata, myopen, mywrite, myclose);
<br>
while (*filename) { <br>
stat(*filename, &st); <br>
entry = archive_entry_new(); <br>
archive_entry_copy_stat(entry, &st); <br>
archive_entry_set_pathname(entry, *filename); <br>
archive_write_header(a, entry); <br>
if ((fd = open(*filename, O_RDONLY)) != -1) { <br>
len = read(fd, buff, sizeof(buff)); <br>
while (len > 0) { <br>
archive_write_data(a, buff, len); <br>
len = read(fd, buff, sizeof(buff)); <br>
} <br>
close(fd); <br>
} <br>
archive_entry_free(entry); <br>
filename++; <br>
} <br>
archive_write_free(a); <br>
}</p>
<p style="margin-left:14%; margin-top: 1em">int main(int
argc, const char **argv) <br>
{ <br>
const char *outname; <br>
argv++; <br>
outname = *argv++; <br>
write_archive(outname, argv); <br>
return 0; <br>
}</p>
<p style="margin-top: 1em"><b>SEE ALSO</b></p>
<p style="margin-left:6%;">tar(1),
archive_write_set_options(3), libarchive(3), cpio(5),
mtree(5), tar(5)</p>
<p style="margin-top: 1em"><b>HISTORY</b></p>
<p style="margin-left:6%;">The <b>libarchive</b> library
first appeared in FreeBSD 5.3.</p>
<p style="margin-top: 1em"><b>AUTHORS</b></p>
<p style="margin-left:6%;">The <b>libarchive</b> library
was written by Tim Kientzle <kientzle@acm.org>.</p>
<p style="margin-top: 1em"><b>BUGS</b></p>
<p style="margin-left:6%;">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.</p>
<p style="margin-left:6%; margin-top: 1em">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 <b>star</b> 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.</p>
<p style="margin-left:6%; margin-top: 1em">BSD
February 2, 2012 BSD</p>
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