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The Question is:
Hi,
Indexf.sys - how do I recalculate the CRC in the file headers.
I'm writing a CD image producer that will merge both the pc fat16/32 disk
structure and ods2 volume info on the same disk (my build disk) prior to
dumping the resultant image onto a CD.
So far so Good and it works well but it dawned on me that the last step in
the process (the one where I create an output image file from the first 650
Mb (or less) of my build disk) could be eliminated entirly if I could just
bang in a dummy file header w
ith a block allocation starting at 0 and of length cd$size.
well that's easy but I cannot get the right parameters for generating the
crc using lib$crc_table and lib$crc, I'm passing the first 510 bytes as a
string to lib$crc.
Can you help?
Bob Fiander
The Answer is :
The OpenVMS Wizard would not expect the Microsoft FAT disk format and
the OpenVMS ODS-2 disk format to be able to coexist on the same volume,
due to an expectation of file structure block-level collisions between
the two formats. (ISO9660 and ODS-2, on the other hand, can coexist.)
The typical checksum used in ODS-2 headers is a simple additive word
scheme, not a CRC -- each word in the data range covered by the checksum
is simply successively added together.
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