Sense fetching [Was: cdrtools /devel ...]

Joerg Schilling Joerg.Schilling at
Thu Nov 11 10:33:07 UTC 2010

Alexander Motin <mav at> wrote:

> > The question still remains whether the previous implementation did return resid 
> >> 0 in some cases. In this case, I would need to implement both variants in the 
> > libscg adaption layer and I would need to know whether I am running on an old 
> > version or on a new version kernel. Do you know of a simple method to implement 
> > this distinction?
> Yes, some drivers were permanently reporting zero resid, while others
> (mostly real SCSI) were reporting proper values. Now it is the same,
> just more cases should work properly.
> Why do you want/need to distinguish them? You should already handle
> non-zero resid properly. Zero resid may be wrong in some cases, but at
> first I don't see fatal problem from it and at second I don't see what
> can you do about it.
> If I am missing something - sorry, explain it to me please.

Compare the number of sense bytes I like to request (18) with the number 
previous FreeBSD versions did actually request. It is obvious that in case 
there is a resid reported onm an old kernel, libscg (with your chanhge) would 
believe that probably less that the absolute minumum of sense data is available.


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