Hello.
I often create a Live CD.
When creating a Live CD, loopback mounted ext3 image files are used.
These image files are then compressed so that the ISO image will fit within
a CD-R's capacity (i.e. 700MB).
Compressing whole image files includes compressing deleted/unused bytes within
a block. This means that non-zero bytes in deleted/unused blocks affect
compression ratio.
I'm using the below program to improve compression ratio.
----------
#define _FILE_OFFSET_BITS 64
#define _LARGEFILE_SOURCE
#define _LARGEFILE64_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
int main(int argc, char *argv[]) {
int fd;
static char buffer[4096];
memset(buffer, 0, sizeof(buffer));
snprintf(buffer, sizeof(buffer) - 1, "%s/XXXXXX", argc > 1 ? argv[1] : "");
if ((fd = mkstemp(buffer)) != EOF) {
unlink(buffer);
memset(buffer, 255, sizeof(buffer));
while (write(fd, buffer, sizeof(buffer)) > 0);
sync();
close(fd);
}
return 0;
}
----------
But this program cannot clear some bytes within a block for file data (e.g.
offset from 1 to 511 of a data block used by a file with only 1 byte data)
and blocks for directory entries.
Any suggestions?
Regards.
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