On Sun, 30.01.2005 at 23:24:37 +0100, Poul-Henning Kamp wrote: > The amount of metadata in GBDE is pretty straight forward: > > 1. If do not use off-line keyfiles: deduct one sector. > > 2. Deduct the key sectors (1 to 4) > > 3. Find zone size: > > nsect = sectorsize / 16 > nzone = nsect + 1 > > 4. Find number of zones: > > z = remaining_sectors / nzone > > 5. Find usable size: > > size = z * nsect > > 6. Find overhead/metadata as: > > total_sectors - size
This translates to: overhead = sectors - (sectors-4-1)/((sectorsize/16) + 1) * sectorsize/16 So, if I understand that correctly, I need one additional sector every 16 sectors and 5 sectors for the keys (using all the gbde init defaults). What's wrong with the attached program then? It gives wrong results :( % cc -Wall gbde.c -o gbde && ./gbde $((31744*512)) Wanted size: 16252928 bytes in 31744 sectors (blocksize 512) Needed size: 16763392 bytes in 32741 sectors (blocksize 512) This should be 32768 sectors, as can be seen from my earlier mail. Ulrich Spoerlein -- PGP Key ID: F0DB9F44 Encrypted mail welcome! Fingerprint: F1CE D062 0CA9 ADE3 349B 2FE8 980A C6B5 F0DB 9F44 Ok, which part of "Ph'nglui mglw'nafh Cthulhu R'lyeh wgah'nagl fhtagn." didn't you understand?
#include <stdio.h>
#include <stdlib.h>
int
main(int argc, char **argv) {
int okeysec = 1;
int nkeysec = 4;
int sectorsize = 512;
long long size, wanted_sec, needed_sec;
if (argc < 2)
exit(1);
size = atoll(argv[1]);
if (argc == 3)
sectorsize = atoi(argv[2]);
/* Round up to nearest multiple of sectorsize */
if (size % sectorsize)
size += sectorsize - size % sectorsize;
wanted_sec = size / sectorsize;
printf("Wanted size: %lld bytes in %lld sectors (blocksize %d)\n",
wanted_sec*sectorsize, wanted_sec, sectorsize);
needed_sec = wanted_sec + (wanted_sec*16)/sectorsize + okeysec + nkeysec;
printf("Needed size: %lld bytes in %lld sectors (blocksize %d)\n",
needed_sec*sectorsize, needed_sec, sectorsize);
return (0);
}
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