No /dev/sg0 with sata dvd player

Fred Krogh · Posted: Tue Jan 27, 2015 5:12 pm Post subject: No /dev/sg0 with sata dvd player

I can't write on dvd+rw disks, although reading commercial disks works fine. I suspect that in addition to /dev/sr0, I should have a /dev/sg0, If that is the case, how do I get that into /dev. If not, what should I be looking for. I have the following scsi references in /usr/src/linux/.config.

NeddySeagoon · Posted: Tue Jan 27, 2015 5:25 pm Post subject:

Fred Krogh,

I suspect its CONFIG_CHR_DEV_SG=y
_________________
Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.

Fred Krogh · Posted: Tue Jan 27, 2015 5:34 pm Post subject:

I have CONFIG_CHR_DEV_SG=m, I can try changing that to a y, but will need to reboot to try it and that I can only do after clearing up some other things. Will let you know if that makes a difference. Thanks.

Fred Krogh · Posted: Tue Jan 27, 2015 6:40 pm Post subject:

I have just rebooted with a DVD+RW disk in the drive that I can't do anything with. So now I have CONFIG_CHR_DEV_SG=y, but still no /dev/sg0. I also needed to add a softlink to get /dev/dvd pointing to /dev/sr0. So I'm hoping for another suggestion. Thanks.

NeddySeagoon · Posted: Tue Jan 27, 2015 7:29 pm Post subject:

Fred Krogh,

As a test use mknod to add a few /dev/sg nodes.

sg0 is

Fred Krogh · Posted: Wed Jan 28, 2015 3:11 pm Post subject:

Using mknod, I now have in /dev

NeddySeagoon · Posted: Wed Jan 28, 2015 6:08 pm Post subject:

Fred Krogh,

The kernel you are running was built on

Fred Krogh · Posted: Wed Jan 28, 2015 8:41 pm Post subject:

You are correct. Evidently I updated the config files, but did not recompile the kernel. Damn. I'll post more when I have the kernel redone. Sorry.

Fred Krogh · Posted: Wed Jan 28, 2015 8:56 pm Post subject:

Now on a reboot, I have /dev/sr0, /dev/sg0, /dev/sg1, and /dev/sg2. I still can't format a dvd in such a way that I can look at it. I still get: cdrom: sr0: dirty DVD+RW media, "finalizing". Sometime in the distant (say 3 years?) past, I think I had this working. I've also tried to get this to work using fdisk, and mkfs.ext2 /dev/sr0. This one complains that

NeddySeagoon · Posted: Wed Jan 28, 2015 9:09 pm Post subject:

Fred Krogh,

I always used UDF on dvd+rw. You must use a filesystem with a 32k block size as thats the block size on the underlying media. UDF is designed for this sort of thing.
I recall that with UDF, it would gather writes into 32k chunks to avoid 8 read/erase/write cycles ber physical block written.
I suspect that with other filesystems the kernel caching will help a lot.

I've not used packet writining like this since before April 2009, when this system was put together.
I'll put a little time into it this week but it will be the weekend before I can fix my old PC, which has a failed PSU.
_________________
Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.

Fred Krogh · Posted: Wed Jan 28, 2015 9:15 pm Post subject:

I'm not familiar with UDF. If it is just a matter of formatting the dvd to use it, I'm all for it. If this is what you are suggesting I'll do some looking into this. (At the moment as you know -- many thanks -- I'm more concerned about the monitor problem.)

NeddySeagoon · Posted: Wed Jan 28, 2015 9:42 pm Post subject:

Fred,

Read http://fy.chalmers.se/~appro/linux/DVD+RW/
Its old and mostly still correct, even though its written around the ide-scsi layer which nobody uses.

udftools is still in the tree. You will need UDF support in the kernel.
You can practice with UDF in an empty file - no need to destroy any media.
When it works, try