[ale] instruction needed

[Dow Hurst]

I can answer that now!  The sg device is a character based, 
not block based, SCSI interface for SCSI commands.

It is not:
The ide-scsi CDROM or DVD device which is /dev/scd[n]
or /dev/sr[n]


In Mike Panetta's words:
The sg devices are not block devices, they are character 
devices meant to be used when you want to send raw scsi 
commands to a device (EG like cdrecord does to write to a
CD) not to access them in the traditional manner.  I believe 
both /dev/sr[n] and /dev/scd[n] are the same devices.  Check 
the major and minor numbers on them to make sure.  I think 
its all just a naming convention.
End quote.


He is correct and I've been very happy using /dev/scd0 
correctly now for accessing my DVD burner.  The 
/dev/sd[a-d][n] devices are for accessing block based SCSI 
devices off of a SCSI controller, like a real SCSI hard 
drive.  They can also be a USB based block device like a CF 
or SD card.  The sbp2 module is a firewire interface treated 
like a SCSI device that will mount the firewire device as a 
block device.  So, the firewire DVD burner is accessed thru 
/dev/scd1 and the ATAPI-IDE DVD-ROM, that is emulated SCSI, 
is accessed via /dev/scd0.  The power of searching the list 
arises once more!!


So in the list of modules dependencies loaded on my machine 
via /sbin/lsmod shows:

Firewire DVD= ieee1394, ohci1394, sbp2
IDE-SCSI CD = scsi_mod, ide-scsi, sr_mod
General SCSI= scsi_mod, sr_mod, sg, sd_mod, st
USB-SCSI    = scsi_mod, usb-storage

 From the SCSI How-To:
The high level drivers are in modules named "sd_mod", 
"sr_mod", "st", and "sg", for disk, cdrom, tape, and scsi 
generics support respectively.
End quote.

So scsi_mod has to load, then the other stuff works with it 
for real SCSI and emulated SCSI devices based on a SCSI, 
USB, or ATAPI-IDE.  The USB subsystem has it own set of 
modules that make the USB hardware run and the emulated SCSI 
is laid on top of that.  The firewire 1394 bus is similar in 
that it has its own core and the sbp2 driver works with that 
and the SCSI core.

General USB = usbcore, usb-storage, hid, usb-uhci, ehci-hcd
General 1394= ieee1394, ohci1394

Just run /sbin/lsmod and examine which modules depend on others.

That is the power of Google!  Hope this helps,
Dow





Sean Kilpatrick wrote:
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> 
> I'm curious again.
> 
> First, the facts.
> 
> Needing workable scanning software, I took advice
> heard at the Ale meeting last week and downloaded
> a (free) copy of Vuescan <http://www.hamrick.com>.
> 
> Unpacked the tarball and tried to run the program.
> Got an error message about needing the "sg driver."
> Having no idea what that might be, I asked my son
> for some advice and he offered a number of suggestions.
> The easiest to impliment was change ownership and
> group for the "sg0" device.
> Which I did.
> The scanner software now works. Well.
> 
> Great program. It costs $50/$80 for the Windows
> and Mac versions (personal/professional) but is free
> for Linux. It is good enough to pay for. Works with
> a huge range of scanners (including high-end film
> scanners) on usb, firewire, and SCSI.
> 
> My question is simple: what's an "sg" device?
> 
> Sean
> 
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> =rQQS
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> 
> _______________________________________________
> Ale mailing list
> Ale at ale.org
> http://www.ale.org/mailman/listinfo/ale
> 

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Dow Hurst                  Office: 770-499-3428            *
Systems Support Specialist    Fax: 770-423-6744            *
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Chemistry Department SC428  Email:   dhurst at kennesaw.edu   *
Kennesaw State University         Dow.Hurst at mindspring.com *
Kennesaw, GA 30144                                         *
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