gconcat/gbde DVD encryption problem

[Pawel Jakub Dawidek]

On Mon, Dec 18, 2006 at 01:22:13PM +0000, RW wrote:
> A couple of years ago, I created some DVDs encrypted with gdbe. I used 2 
> concatenated,  file-backed md devices (to avoid the 2GB dvd file limit) and 
> burned them to dvd. The resulting DVD was accessed like this:
> 
> ----------------------------------------------------------
> mount  /dvdrw
> 
> mdconfig -a -t vnode -f /dvdrw/d1 -u 31
> mdconfig -a -t vnode -f /dvdrw/d2 -u 32
> 
> gconcat create datadvd /dev/md31 /dev/md32
> 
> gbde attach /dev/concat/datadvd
> 
> mount -o ro /dev/concat/datadvd.bde  /mnt/dvd
> ----------------------------------------------------------
> 
> The technique worked fine in  February 2005, with whatever was the latest 
> release, I haven't used the technique since then until a few days ago,  but 
> now I'm having a problem with FreeBSD 6.1. After the mdconfig I get "WARNING: 
> opening backing store: /dvdrw/d1 readonly", which I doubt is the problem. The 
> failure occurs here:
> 
> # gbde attach /dev/concat/datadvd
> Enter passphrase:
> gbde: Attach to concat/datadvd failed: could not access consumer
> 
> 
> The same problem exists on a newly created disk, so it probably not 
> corruption. And if I copy the two file to hard disk it works.  It just seems 
> to be a problem when they are on the DVD.
> 
> Any ideas on how to fix this. I'm not particularly bothered about the existing 
> disks, but I'd like to create some new ones.

The problem is because gbde(4) tries to open provider read-write, which
is not possible with CD-ROMs. You can work-around it by doing:

	(insert 1st CD)
	# dd if=/dev/acd0 of=/dvdrw/d1 bs=1m
	(insert 2nd CD)
	# dd if=/dev/acd0 of=/dvdrw/d2 bs=1m
	# mdconfig -a -f /dvdrw/d1 -u 31
	# mdconfig -a -f /dvdrw/d2 -u 32
	# gconcat create datadvd /dev/md31 /dev/md32
	# gbde attach /dev/concat/datadvd

-- 
Pawel Jakub Dawidek                       http://www.wheel.pl
pjd at FreeBSD.org                           http://www.FreeBSD.org
FreeBSD committer                         Am I Evil? Yes, I Am!
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 187 bytes
Desc: not available
Url : http://lists.freebsd.org/pipermail/freebsd-geom/attachments/20061218/a5359372/attachment.pgp