Date: Mon, 31 Jan 2005 14:58:23 +0100 From: Ulrich Spoerlein <q@uni.de> To: Poul-Henning Kamp <phk@phk.freebsd.dk> Cc: freebsd-stable@freebsd.org Subject: Re: Size of metadata required for GBDE Message-ID: <20050131135823.GD828@galgenberg.net> In-Reply-To: <76988.1107123877@critter.freebsd.dk> References: <20050130221803.GB2600@galgenberg.net> <76988.1107123877@critter.freebsd.dk>
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On Sun, 30.01.2005 at 23:24:37 +0100, Poul-Henning Kamp wrote:
> The amount of metadata in GBDE is pretty straight forward:
>=20
> 1. If do not use off-line keyfiles: deduct one sector.
>=20
> 2. Deduct the key sectors (1 to 4)
>=20
> 3. Find zone size:
>=20
> nsect =3D sectorsize / 16
> nzone =3D nsect + 1
>=20
> 4. Find number of zones:
>=20
> z =3D remaining_sectors / nzone
>=20
> 5. Find usable size:
>=20
> size =3D z * nsect
>=20
> 6. Find overhead/metadata as:
>=20
> total_sectors - size
This translates to:
overhead =3D 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
--=20
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?
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#include <stdio.h>
#include <stdlib.h>
int
main(int argc, char **argv) {
int okeysec =3D 1;
int nkeysec =3D 4;
int sectorsize =3D 512;
long long size, wanted_sec, needed_sec;
if (argc < 2)
exit(1);
=20
size =3D atoll(argv[1]);
if (argc =3D=3D 3)
sectorsize =3D atoi(argv[2]);
=20
/* Round up to nearest multiple of sectorsize */
if (size % sectorsize)
size +=3D sectorsize - size % sectorsize;
wanted_sec =3D size / sectorsize;
printf("Wanted size: %lld bytes in %lld sectors (blocksize %d)\n",
wanted_sec*sectorsize, wanted_sec, sectorsize);
needed_sec =3D wanted_sec + (wanted_sec*16)/sectorsize + okeysec + nkeyse=
c;
printf("Needed size: %lld bytes in %lld sectors (blocksize %d)\n",
needed_sec*sectorsize, needed_sec, sectorsize);
return (0);
}
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