Re: [REQUEST] Option for skipping unreadable blocks on Video DVD

Robert Hancock
2007-11-18T04:58:32Z

Tobias wrote:
> If you are accessing a scratched Video DVD and the device cannot read it, the
> process ends.
> What about a more tolerant way to handle unreadable blocks.
> Especially on Video DVDs single blocks are not that important than on data
> dvds.

If the DVD player process ends from this, I'd say that's the fault of
the player software not handling errors properly.

I think that if they are using the normal block layer accesses on the
DVD device, there may be some retries that occur which are likely
undesirable in this case since they will just stall playback. If they
are using SG_IO to feed raw requests into the drive (which I imagine
they need to do for CSS authentication, etc. anyway), then all error
handling is passed up to the user application.

>
> So is there a way that the kernel tells the device to skip these bad blocks?

We don't know they're bad until we try and read them. How long the drive
will stall trying to read that sector before giving up and returning an
error is up to the drive. I'm not sure if the MMC command set allows any
way to tell the drive to give up more quickly or not..

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