Sense fetching [Was: cdrtools /devel ...]
Joerg.Schilling at fokus.fraunhofer.de
Thu Nov 11 10:05:40 UTC 2010
Alexander Motin <mav at FreeBSD.org> wrote:
> >>> Given the fact that many drives will probably only return 18 bytes of sense
> >>> data, this will happen every time libscg is told to fetch more sense than the
> >>> drive is willing to return.
> >>> Is there a way to distinct an old kernel from a new one?
> >> I don't see the problem. Previous kernel in most cases reported
> >> sesnse_resid == 0, lying that there is more sense data then really is.
> >> New one should report real (often positive) value. In both cases
> >> sesnse_resid value measured from the value submitted to the kernel.
> > Did the old kernel return a zero sense_resid for any implemented SCSI
> > transport? Libscg is a generic SCSI transport library and cdrecord is just one
> > user of this lib.
> Not sure I understand your question. Zero sesnse_resid is absolutely
> normal situation if device gave same amount of sense as application
> requested. As I can see, many of SCSI controllers report sesnse_resid
> properly. I may assume that some, like atapicd don't -- in that case
> you'll also see 0 there.
FreeBSD-CAM did try to fetcth more than 18 bytes of sense data and it may be
that some drives did return only 18 bytes. In this case, I would asume that
there is a resid > 0.
> > Do you know the CAM behavior for other SCSI transports?
> I don't have real SCSI CD to test, but a as I can see, most of SCSI
> controllers return sense data automatically. Sense fetching changes
> should not affect/break anything there.
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
EMail:joerg at schily.isdn.cs.tu-berlin.de (home) Jörg Schilling D-13353 Berlin
js at cs.tu-berlin.de (uni)
joerg.schilling at fokus.fraunhofer.de (work) Blog: http://schily.blogspot.com/
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