Messages in this thread | | | Subject | Zero-clearing all zero-clearable bytes. | From | Tetsuo Handa <> | Date | Sat, 22 Nov 2008 12:36:56 +0900 |
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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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