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

Joerg Schilling Joerg.Schilling at
Thu Nov 11 13:17:28 UTC 2010

Alexander Motin <mav at> wrote:

> > 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.
> Kernel code I have changed affects only controllers without automatic
> sense fetching. For such controllers CAM previously always reported zero
> sense_resid, independently of requested size (which actually was also
> ignored in this case). So previously whatever you asked for 18 or 32
> bytes - sense_resid was always zero, like if you got full 18 or 32
> bytes. That was wrong. Now, in the same situation, if device wants to
> return let's say 20 bytes -- you will get 0 and 12 bytes of sense_resid
> respectively, meaning 18 and 20 bytes of received sense.
> AFAIK sense_resid always measured from the requested sense_len. In my
> patch for libscg you may see that I have changed both request and
> response paths. Resulted sense_count should be absolutely the same.

What is the requested size with the various HBAs in earlier kernels?


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