Re: Bug in linux kernel when playing DVDs.

[Denis Vlasenko]

On 29 April 2003 14:11, James Courtier-Dutton wrote:
> >See? Sector # is increasing... Linux retries the read several times,
> >then reports EIO to userspace and goes to next sectors.
> > Unfortunately, they are bad too, so the loop repeats. Eventually it
> > will pass by all bad sectors (if not, it's a bug) but it can take
> > longish time.
> >
> >Apart of making max retry # settable by the user, I don't see how
> >this can be made better. Pity. This is common problem on CDs...
>
> What is this EIO report. The CPU is never returned to user space
> apps, so the app never sees any error.

Are you sure that CPU never returned to the app?
(strace is your friend...)

> As for retries, for DVD playing we do not want the Linux kernel to do
> any retries, because during DVD playback, we just want a very quick
> response saying there was an error.

Kernel is not yet telepathic.

> The DVD playing application can
> then skip forward 0.5 seconds and continue. If one sector fails on a
> DVD, there is little or not point in reading the next sector. One has
> to start reading from the next VOBU. (i.e. about 0.5 seconds skip.)

You need a way to tell kernel that you want such behavior.
"skip 0.5 sec on error" requirement is rather hard
to describe to the kernel.
--
vda