Sven Anders wrote:
>
> The Problem was:
>
> I could not read a whole CD image on my Toshiba SCSI DVD-ROM (SD-M1201)
> with dd accessing /dev/scd0.
> It worked perfectly on my Phillips SCSI CD-Writer.
>
> 1. It does not work.
> There is a bug in the Linux SCSI CD device driver (sr.c). The driver
> tries to read some blocks ahead, but when it fails at the end of the
> disk, it receives an error and stops.
> The CD-Writer returns a correct VOLUME_OVERFLOW sense key and the
> driver will correctly read the last blocks. At my DVD CD-ROM, the
> driver receives a 0x70 sense-key (instead of the correct 0xf0) and
> fails.
>
> There is definitly data missing! The problem is not a try to read
> beyond the end of the data blocks. It is a problem of the read-ahead
> mechanism.
>
> 2. It works, if you are using the (new) sg-device driver and the sg-tools
> (here: sg_dd2048 accessing /dev/sg1).
> I think it works, because the driver does not try to read ahead.
The sg_dd2048 utility will also work on the original sg
driver found in 2.0 and up to 2.2.6 as well. It reads
multiple blocks at once but not beyond the bounds of
the segment it has been asked to transfer to or from.
It would seem using dd on a DVD cdrom via the sr device
(ie /dev/scd0) needs some further examination.
Doug Gilbert
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