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Re: [Libcdio-devel] Using major/minor device numbers to determine SCSI o

From: Steven M. Schultz
Subject: Re: [Libcdio-devel] Using major/minor device numbers to determine SCSI or ATAPI
Date: Thu, 28 Apr 2005 17:59:34 -0700 (PDT)

On Thu, 28 Apr 2005, R. Bernstein wrote:

> where the access (at leat in in media players) is bytes, cdparanoia
> wants to see data read as 16-bit integers, I guess so it can analyze
        Ok - that makes sense.

> the audio data (which right now I believe it does very little
> of). According to paranoia (but hey, it might be true as well), there
> some drives that return audio data big endian and some drives that

        Ahhhh.  I guess we've all seen stranger things in the world of 
        computer gear ;)

> return data little endian. In particular it thinks that ATAPI is
> defined to return data little endian while a true SCSI drive (i.e. not
> an ATAPI drive with SCSI emulation) is big endian.

        Ah, I don't think that's necessarily the case.  But without otherwise
        identical drives with the difference interface electronics (at one
        time there were numerous SCSI CDROM drives available - haven't seen
        one in a long time).
        In any case I am not sure it's the transport needs to be checked, but
        the capabilities of the drive.  Isn't there a bit/byte in the
        drive that can be fetched that says what order the audio data is
        presented in?  The MMC specs are online (had a copy - hundreds of
        pages - printed out at one time but tossed it a while back).

> On GNU/Linux it's not the device name that's important (/dev/sg0 or

        True - and I should have been a little more clear.  I used the device
        name as a shortcut to the major device number since for those systems
        I know about the name is in 1-1 mapping to the major device number.
        Thus 'sr' is always major 18 and sr0 could be either ATAPI or SCSI.

> # ls -l /dev/hdc
> brw-------  1 rocky disk 22, 0 Apr 25 14:41 /dev/hdc

> and from /usr/include/linux/major.h:
> #define IDE1_MAJOR     22

        Right - and on BSDI /dev/rsr0c is 18 (as you can check on 'awds1' ;)).
        That happens to be an ATAPI drive but a long time ago when it was
        a SCSI CD burner it was still 18 for a major number.

> so the claim is that /dev/hdc is some sort of IDE device which
> cdparanoia then uses to determine drive endian-ness.

        A more portable way would be to query the drive - I can't escape the
        feeling there's a MMC{2,3} 'mode sense' or 'inquiry' command that
        will get the info from the drive.


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