reading a DVD TOC from a kernel module

[Slava Imameyev]

Hi,

Recently I stumbled across the following problem -

  - It is impossible to retrieve a DVD TOC from the kernel module

To clarify - a kernel module can get a pointer to any object in a DVD stack, but the module is external to the DVD stack so to be graceful it invokes only public functions, also the module can't allocate a SCSITask class object as doesn't inherit from any SCSI related class. So the only option is to invoke readTOC() which fails for DVD.

Is this failure a deliberate by design? What are the reasons for this? 

On Windows there was no problem in issuing a SCSI request from a kernel module which retrieved a DVD TOC ( at least it didn't failed though I can't bet that it returned a correct information ).

Regards,

Slava

[Chris Sarcone]

Slava --

Recently I stumbled across the following problem -

  - It is impossible to retrieve a DVD TOC from the kernel module

To clarify - a kernel module can get a pointer to any object in a DVD stack, but the module is external to the DVD stack so to be graceful it invokes only public functions, also the module can't allocate a SCSITask class object as doesn't inherit from any SCSI related class. So the only option is to invoke readTOC() which fails for DVD.

DVDs do not have a Table Of Contents like CDs do. They have Disc (neé DVD) structures.

Is this failure a deliberate by design? What are the reasons for this? 

The reason is that they are different as defined by the SCSI MMC and Mt Fuji specs. I suggest you read the specification and figure out exactly what your software requires, then issue the proper command(s).

On Windows there was no problem in issuing a SCSI request from a kernel module which retrieved a DVD TOC ( at least it didn't failed though I can't bet that it returned a correct information ).

I won't speculate as to why Windows returns something without an error. The drive returns an error, so OS X returns an error.

HTH,

-- Chris

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[Slava Imameyev]

Thanks

> I won't speculate as to why Windows returns something without an error. The drive returns an error, so OS X returns an error.

 I checked the TOC returned by Windows - it contains some reasonable values and consistent across different PCs, also this is a requirement from Microsoft for drivers to support READ TOC command.

> I suggest you read the specification and figure out exactly what your software requires, then issue the proper command(s).

 There are compatibility issues when a software for Windows need to be ported on Mac( it is impossible to say a customer - "Mac doesn't support this" especially for heterogeneous hardware ) .

  Windows supports a reach SCSI interface available from both user and kernel mode ( and this doesn't create any security issues ) and never fails READ TOC command for DVD, it is reasonable to expect the same for Mac OS X but it happens not to be the case - a Mac OS X interface is prohibitively restrictive, especially for DVD.

 The most bewildering is that readToc() function is present in every DVD related class of a driver stack and there is no any mention that it actually always fails. In fact I will have to build a TOC by hand or else a compatibility with Windows is impossible.

 Also, I do not se any reason for restricting access to the SCSITask class.