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Re: Virtual Device

At 1:35 AM +0200 on 10/18/06, Rene Trost wrote:
In my opinion a fully compatible virtual cd/dvd-drive would take the disk-image idea to the >next level.

Conceptually their is nothing wrong with what your describing (though you may make a lot of vendors who use CD's as copy protection very upset). However, actually making it work is MUCH, MUCH harder than I think you realize. The problem is that burning a CD is very, very different than just writing bytes to a volume. Their are nearly at a bunch of different burn modes that all use different CDB's. To do what your describing I a completely reliable way you'd basically need to "record" the CDB's sent to the drive and then "replay" them on a different machine. You'd also need to emulate the expected reply for each CDB for the particular drive your emulating. Drive behavior varies wildly between vendors and even between models made by a particular vendor. It's better now than it used to be (the standards are a lot more accepted than they were 5 years ago), but it''s still a pretty massive undertaking.

Of course, if you want to MOUNT the "recording" you made, that's a separate step too. You'd need to strip the data out of the command stream your receiving and then store the data appropriately depending on the details of the the recording mode being used.

The reason why your DiskImage idea won't work is that CD's are accessed differently than standard block media (the reasons are complicated and messy, mostly having to do with the fact that the CD standard is relatively old and wasn't originally designed as a data storage medium). If you manage to make and existing image look like a CD in IOKit, IOKit does exactly what you want and starts treating that image as a CD. Which promptly breaks because it's NOT a CD and isn't expecting to be treated like one. I doubt your getting that far- it would be pretty tricky to get to that point and is a lot more involved than tweaking registry keys. It's more likely that you've corrupted the image in some way and the DiskImage kext is choking.

Hopefully that's given you a better picture of what's involved. If your serious about pursing it, I'd suggest you take a closer look at the CD/DVD burning specifications and tackle it from that direction, rather than trying to jury rig something with the existing DiskImage architecture. Best of luck! If nothing else it sounds like a really interesting challenge!
--
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References: 
 >Virtual Device (From: Rene Trost <email@hidden>)
 >Re: Virtual Device (From: Michael Smith <email@hidden>)
 >Re: Virtual Device (From: Rene Trost <email@hidden>)



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