Re: CD writing in future Linux (stirring up a hornets' nest)

[Matthias Andree]

Jan Engelhardt wrote:
>> Please explain me:
>>
>> -	how to use /dev/hd* in order to scan an image from a scanner
>> -	how to use /dev/hd* in order to talk to a CPU device
>> -	how to use /dev/hd* in order to talk to a tape device
>> -	how to use /dev/hd* in order to talk to a printer
>> -	how to use /dev/hd* in order to talk to a jukebox
>> -	how to use /dev/hd* in order to talk to a graphical device

> With /dev/sg, this was possible?

Theoretically, yes, provided there was an application talking raw SCSI to
the device in question. /dev/sg is a generic SCSI device that allows the
sending of commands. It does not implement higher-level device models such
as direct access (/dev/sd*), CD-ROM (/dev/sr*), sequential access
(/dev/[n]st*) or similar. It's kind of "raw SCSI".

OTOH, there is, according to kernel developers, no difference between
/dev/sg and /dev/hd for SCSI command access via the SG_IO ioctl, so unless
someone documents /dev/hd* bugs that /dev/sg* doesn't share, it appears as
though the user space would have to live with a /dev/hd* that unifies the
mid-level "raw SCSI command" and the high-level (block device) access.
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