Re: [linux-minidisc] SCSI support in libhimd

[Michael Karcher <Michael.Karcher@fu-berlin.de>]

Am Dienstag, den 08.06.2010, 13:32 +0200 schrieb Adrian Glaubitz:
> - extend himd_get_discid to cross check disc with discid from SCSI
>   retrieval
Why would you want to do that? "Because you can" is not an option.

If the discid from the Hi-MD medium mismatches the one in MCLISTxx.HMA,
the Disc is unplayable in Hi-MD equipment and the only way to fix it is
a reformat. This is because the MCLISTxx.HMA is authenticated against
data that can only be changed by the formatting instruction or by the
MCLISTxx.HMA updating stuff. The updating stuff only works if
MCLISTxx.HMA matches the disc ID in the external area.

So, the only thing we gain from cross-checking is being able to tell the
user that his medium is broken, as the DRM info is inconsistent, but how
to handle that in our tools? Should we deny access to the data currently
on the disc? (As it is now, we can read the image from one MD cloned
onto a different medium, which will fail if we abort on cross-check) Or
should we just ignore it?

Finally: What do you want to do on images?

> - move all functions from basictools/himdscsitest.c to libhimd/scsi.c
Sounds fine.

> - extend himd struct to include SCSI device information as well
How do you find out the SCSI device ID for libscg from the path we have?
I'm afraid we probably need to do that in a platform dependent way,
which is OK. I suggest to not encourage authors of libhimd users to
access the SCSI info, but handle it all inside libhimd.

> - new exports for libhimd:
>   - himd_format_medium
>   - himd_erase_medium
>   - himd_set_time
>   - himd_get_time
>   - himd_read_capacity
>   - himd_eject_medium
>   - himd_lock_disc(lock/unlock)
OK, have them fail on images sounds like a good plan. Or should we drop
image support?

> The most important point in this discussion will be the decision how
> we integrate libscg into our tree. Should we opt for an external
> dependency or should we include a fork into our tree?
As there are no prebuilt libraries of libscg, our users have to compile
it anyway, so it can be as well in our tree. This also makes it possible
to integrate the Mac patch to recognize "hard drives". When distributing
a patched version of libscg, please read the License before. IIRC it is
required that we change all modified files to indicate they are
modified, i.e. don't return "schily" as author.

Regards,
  Michael Karcher