Alexander Motin <mav_at_FreeBSD.org> wrote: > > Your patch to libscg looks definitely OK if we only look at the new corrected > > kernel driver behavior. > > > > There is a problem: > > > > In case that there is a sense data residual > 0, libscg will asume that there > > is less sense data that really present in case that a "new" libscg is runnung > > on an old kernel. > > > > 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. > > I see no advantage in removing the call to fillbytes(). > > scgcheck tests how much sense data received by counting 0x00 and 0xff > bytes. Zero-filling response buffer breaks that check. Though I have no > idea if other crdtools' applications depend on these zeros. There could > be some internal inconsistency. O, I need to check other low level transport adaptation layers and think about this statement. > > Did you test a modified libscg on an unmodified kernel? > > Unmodified kernel by default doesn't return any sense data at all for > new CAM-based ATA -- this changes should be invariant. New scgcheck runs > same bad as old. It just can't become worse. :) > > Legacy atapicam wrapper ignores sense_len on input and doesn't fill > sense_resig on output -- I haven't tested, but it also should be invariant. I am not only talking about ATAPI but abut SCSI in general. Do you know the CAM behavior for other SCSI transports? Jörg -- 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/ URL: http://cdrecord.berlios.de/private/ ftp://ftp.berlios.de/pub/schilyReceived on Mon Nov 08 2010 - 16:23:31 UTC
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