Re: [V4L] races in v4l read + write in 2.4

[Oliver Neukum]

On Monday 30 October 2000 20:39, Alan Cox wrote:
> > Exactly for this reason I've made a patch, that takes a semaphore in
> > read() and write().
>
> But you cant just go around taking semaphores blindly. Suppose you block in
> the read method and a 2nd one blocks on the semaphore - its now unkillable
> until the first moves on

What is the alternative ? Most devices' reads are not reentrant.
If the drivers themselves take the semaphores the effect is the same

I see that these applications will stay some time in the D state.
But if the read function might block they could end up in that state anyway.

Could you please explain the problem in greater detail ?

        Regards
                Oliver



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