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

From: Bill Davidsen
Date: Sat Feb 18 2006 - 11:38:53 EST


Christoph Hellwig wrote:

On Fri, Feb 17, 2006 at 03:55:34PM -0500, Bill Davidsen wrote:


Christoph Hellwig wrote:



You can access SCSI CDs using /dev/sr* for burning CDs. It's backed by the
same highlevel code as SG_IO on /dev/hd* while the lowerlevel handling is
done transparently by the scsi midlayer, the same code used by /dev/sg* for
the below-blocklayer handling.



This may be true if you create your own /dev entries, or are a udev guru and can get it to generate the right entries. And if you use ATAPI devices it works fine... But with Fedora and SuSE it appears that USB devices which appear as SCSI aren't functional. I tested the Fedora myself, and after killing udevd and making some entries by hand it worked once.

Now if you can access SCSI burners more power to you, with FC4 up to recent updates, my one convenient real SCSI device most definitely doesn't work, and I havd to fall the system back to Slackware and 2.4 which was on it before.

Because you know how to get around the problems doesn't really suggest that there aren't any.



How are the dev entires related to CD burning? If the device entries
don't appear for you that's a problem, but you deserve what you get
for using a POS like udev. If you have a sd or sr node you can use
SG_IO on it, period. Whether you can actually burn a CD of course
depends on the capability of the device. I don't have a CD burner
connected through usb, but I couldn't think of a reason the usb <-> atapi
bridge would make problems with the scsi commands used to burn a CD.



I'm sorry if I didn't make that clear. Some developers are saying that the application shouldn't be finding devices because udev does that so it doesn't matter that doing device location in the application is complex and poorly defined because udev does it for you. I was making the point that in the most common distributions (Fedora and SuSE) pluggable burners don't get proper entries in /dev to make cdrecord work. Based on a single report sent directly to me that seems to be the case in ubuntu as well, but I haven't personally tried it.

I was refuting the claim that applications no longer need to find their own devices; in many cases they do.

Burning using the USB devices works fine if the right devices are found and created.

--
bill davidsen <davidsen@xxxxxxx>
CTO TMR Associates, Inc
Doing interesting things with small computers since 1979

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