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\appendix
\newpage
\section{The common Ecc header format}
\label{eh}
The ecc header is defined in the include file {\em dvdisaster.h}.
Its C definition is as follows:
\begin{tabbing}
xxx \= xxxxxxxxxxxxxxxxxxxxxxx \= xxx \kill
typedef struct \_EccHeader \\
\{\>gint8 cookie[12]; \>{\em /* "*dvdisaster*" */}\\
\>gint8 method[4]; \>{\em /* e.g. "RS01" */}\\
\>gint8 methodFlags[4]; \>{\em /* 0-2 for free use by the respective methods; 3 see above */}\\
\>guint8 mediumFP[16]; \>{\em /* fingerprint of FINGERPRINT SECTOR */}\\
\>guint8 mediumSum[16]; \>{\em /* complete md5sum of whole medium */}\\
\>guint8 eccSum[16]; \>{\em /* md5sum of ecc code section of .ecc file */}\\
\>guint8 sectors[8]; \>{\em /* number of sectors medium is supposed to have w/o ecc*/}\\
\>gint32 dataBytes; \>{\em /* data bytes per ecc block */}\\
\>gint32 eccBytes; \>{\em /* ecc bytes per ecc block */}\\
\>gint32 creatorVersion; \>{\em /* which dvdisaster version created this */}\\
\>gint32 neededVersion; \>{\em /* oldest version which can decode this file */}\\
\>gint32 fpSector; \>{\em /* sector used to calculate mediumFP */}\\
\>guint32 selfCRC; \>{\em /* CRC32 of EccHeader (currently RS02 only) -- since V0.66 --*/}\\
\>guint8 crcSum[16]; \>{\em /* md5sum of crc code section of RS02 .iso file */}\\
\>gint32 inLast; \>{\em /* bytes contained in last sector */}\\
\>guint64 sectorsPerLayer; \>{\em /* layer size for RS03 */}\\
\>guint64 sectorsAddedByEcc; \>{\em /* sectors added by RS02 */}\\
\>gint8 padding[3960]; \>{\em /* pad to 4096 bytes: room for future expansion */}\\
\} EccHeader;
\end{tabbing}
\bigskip
The ecc header is used in all ecc formats (RS01, RS02, RS03) of dvdisaster,
but not all fields apply to all formats. See the following table for the meaning
and usage of the fields:
\bigskip
\begin{tabular}{|l|p{10cm}|c|}
\hline
Field & Usage & Format(s) \\
\hline
$cookie$ & Magic byte sequence for recognizing the header.\newline
Contains the string {\tt *dvdisaster*}. & all \\
\hline
$method$ & 4 characters describing the format; currently allowed:\newline
{\tt RS01}, {\tt RS02}, {\tt RS03}. & all \\
\hline
$methodFlags$ & 4 bytes for further specification of the format. &\\
\cline{2-3}
& Byte 0 contains the following flag: &\\
& Bit 0 - The {\em mediumSum} field is valid. & RS03 \\
& Bit 1 - Set to 1 in ecc files. & RS03 \\
\cline{2-3}
& Bytes 1-2 are unused in the current methods. & \\
\cline{2-3}
& Byte 3 contains the following flags:\newline
Bit 0 - ecc data was created by a development release.\newline
Bit 1 - ecc data was created by a release candidate.\newline
If these bits are present, the user will be hinted that he is using
ecc data from a non-stable dvdisaster version. & all \\
\hline
\end{tabular}
{\footnotesize (continued on next page)}
\vfill
\newpage
\begin{tabular}{|l|p{10cm}|c|}
\hline
$mediumFP$ & The md5sum of the sector specified by the {\em fpSector}.
The sector should be chosen to have a huge probability being unique to the medium;
currently sector 16 (the ISO filesystem root sector) is used. & all \\
\hline
$mediumSum$ & The md5sum of the ISO image. For RS01 this is the md5sum of the
whole image; for RS02 it is calculated for the original ISO image (without
the added RS02 sectors). RS03 uses this value only when bit 1 in
{\em methodFlags} is set. & all \\
\hline
$eccSum$ & On RS01 this is the md5sum of the ecc file excluding the first 4096
bytes. For RS02 this is the md5sum calculated over the md5sums of the $nroots$
ecc layers. RS03 does not use this value. & RS01, RS02 \\
\hline
$sectors$ & For error correction files this is the number of sectors in the
protected medium. If augmented images are used, this denotes the number of
sectors in the original ISO image (without the added RS02/RS03 sectors). & all \\
\hline
$dataBytes$ & The number of data layers, including the CRC layer. & all \\
\hline
$eccBytes$ & The number of ecc layers (= number of roots) for the parity.
$dataBytes + eccBytes = 255$. & all\\
\hline
$creatorVersion$ & The dvdisaster version used for creating this ecc data.
A decimal value 102345 would mean dvdisaster version 10.23.45. & all \\
\hline
$neededVersion$ & The minimum dvdisaster version required for
processing this ecc data. Version encoding as above. & all \\
\hline
$fpSector$ & The sector used for calculating $mediumFP$. & all \\
\hline
$selfCRC$ & A CRC32 checksum of the ecc header itself. Not used
header fields are set to zero and the selfCRC field is initialized to the
value 0x4c5047 (little endian). & \\
\hline
$crcSum$ & md5sum of the CRC layer in RS02 encoded images. & RS02 \\
\hline
$inLast$ & The number of Bytes contained in the last image sector. This allows for
encoding of files with arbitrary length, not just ISO images.
dvdisaster versions prior to V0.66 do not use this field and always assume it
to be 2048 which is the default for iso images. & all \\
\hline
$sectorsPerLayer$ & The number of sectors per layer. & RS03 \\
\hline
$sectorsAddedByEcc$ & The total number of sectors (Headers, CRC, ECC) added. & RS02 \\
\hline
$padding$ & The ecc header is zero padded to a length of 4096 bytes. Future codes
may allocate additional space for the zero padding. See the note below for
usage of the upper 2048 bytes on RS02/RS03. & all \\
\hline
Byte 2048-4096 & A copy of the first CRC layer sector. & RS02 \\
\hline
\end{tabular}
|
