[NUT-devel] Incomplete description of checksum algorithm

[Rich Felker]

On Fri, Feb 17, 2006 at 07:05:48PM +0200, Oded Shimon wrote:
> > If the header is enclosed in
> > the checksum, it's natural to consider it part of the syncpoint packet
> > anyway. Also there's no reason a checksum needs to come from just one
> > buffer. As long as you pass a state pointer to your checksum function
> > you can checksum arbitrarily many different buffers as if they were
> > all connected..
> 
> Yes, I know, this is why I said I'm not against forward_ptr being in 
> checksum, but I am against forward_ptr being in syncpoints!
> 
> The point of forward_ptr being in syncpoints is to be able to add fields to 
> syncpoints, not to frame headers, cause we already have that, right?
> The structure is:
> 
> <startcode> <forward_ptr> <syncpoint> <reserved> <frame header> <checksum>
> 
> (reserved being reserved bytes for syncpoint)
> Now, where the hell does the forward_ptr point to? If it points to after 
> the checksum like all other headers, you won't know where the hell to start 
> parsing the frame header. Pointing to right before the frame header is 
> weird, because the checksum comes later. Putting the reserved bytes of the 
> _syncpoint_ after the frame header is even weirder (data of syncpoint cut 
> in two pieces??)

OK, I agree. Michael, do you have comments?

Rich