Talking to Jens Axboe

Jens Axboe is the developer and maintainer of the CD-ROM/DVD-ROM subsystem for Linux. His home page is at

Craig: In order to read DVD-ROMs, will only certain brands of DVD drives work under Linux?

Jens: No. Although we have had problems with a few drives in the past, they should all work fine now. Assuming that new drives follow the specifications outlined in Mt. Fuji, they are supported out-of-the-box as well.

Craig: Are there SCSI DVD drives, and are they supported?

Jens: SCSI DVD drives do exist, and they are supported as well as the ATAPI ones.

Craig: What version of the Linux kernel do you need to read DVD-ROMs?

Jens: Depends on what you plan to read. If you just want to read a regular data DVD, you can use whatever version of the kernel you have available. The ISO 9660 file system does seem to have a 4GB wraparound problem, so you may experience problems if the DVD is bigger than that. The solution to that problem is to use the UDF file system, which is included in the 2.3 kernels. For 2.2, you can grab UDF from Ben Fennema's page,

However, if you wish to view DVD movies, life isn't that easy because the kernel needs to support the DVD CSS ioctls for authentication. 2.3 kernels include the necessary code to do this, but 2.2 does not. I will try to put up patches on my home page for 2.2 kernels as soon as new ones come out.

Craig: Can I use DVD-ROMs on non-x86 hardware?

Jens: Sure you can. I know several people who are using it on PowerPC hardware, and I have a DVD attached to an Ultra Sparc at home.

Craig: Do you consider the current DVD support in Linux to be developer-ready or stable enough for all users?

Jens: The kernel side is stable enough for all users. The movie players still need a lot of work, though.

Craig: Any idea at what point Linux will support writing DVD-RAMs?

Jens: It already does. As seen from the kernel, we talk to a DVD-RAM just as we do any other SCSI hard drive. I recently received a DVD-RAM drive, and only a minor change was necessary to get it working (the use of 10-byte READ/WRITE commands, as the drive didn't properly support the older 6-byte variants). DVD-RAM drives under Linux appear as both a regular CD-ROM drive and a SCSI hard drive.

Craig: Can a Linux DVD-ROM read a DVD-RAM?

Jens: The DVD-RAM discs I have seen (Type-1, I believe) are encased in a cartridge and thus won't physically fit in a DVD-ROM drive. I've heard of a single-sided version that will fit in a DVD-ROM drive, but I have no experience with those. The DVD-ROM drives I have seen don't support reading of DVD-RAM discs, unfortunately. You can find DVD-ROM drives that will read single-sided discs; make sure you check with the vendor before you go out and buy one.

Craig: If I purchase a DVD-ROM and don't build UDF support (or any other DVD-related code support) in my kernel, will I still be able to use the drive as a CD-ROM?

Jens: Yes. If you discard the DVD-specific features of a DVD-ROM drive, it works just like an ordinary CD-ROM drive.

Craig: Are most DVDs UDF format or ISO 9660?

Jens: Most are “bridged”, with both UDF and ISO 9660 on them. So, you need either UDF or ISO 9660 support to use them. Later on, I think we can expect to see pure UDF DVD-ROM available.

Craig: Aside from increased capacity, what else does UDF do that ISO 9660 doesn't?

Jens: The most interesting aspect is that UDF is not a read-only file system like ISO 9660. UDF is also used when writing a CD-R or CD-RW disc, in what is known as packet writing (you might have seen it in Windows—drag and drop files to a writeable CD).

Craig: What do you think the impact of breaking the CSS copy protection was on Linux/DVD?

Jens: It suddenly made a lot of users want to view DVD movies, that's for sure! The sheer number of downloads for the DVD patch from my page went up by a factor of 10. After Slashdot printed several articles about DVD/Linux, the LiViD project attracted more developers, and things started moving forward again. Discussions on the mailing list had almost dried out completely at that point. So, apart from the fact that Derek Fawcus got into some legal trouble, the renewed attention was definitely a good thing, in my opinion.