On Wed, 17 Mar 2004, Matthias Andree wrote:
> On Wed, 17 Mar 2004, Alan Stern wrote:
>
> > Another possibility (should have thought of this before) is that the
> > control transfers come from a different process, maybe a child of the one
> > you're tracing. Not that it really matters...
>
> Hotplug would be the only interesting one running at the same time.
Of course! Just put the clues together, Watson!
1. Problem is caused by control messages, but strace shows iscan
only uses bulk messages.
2. You observe an excessive amount of hotplug activity.
3. No such problems exist under 2.4.
Conclusion: the hotplug programs are submitting the control requests and
confusing the scanner.
What version of the hotplug package do you have installed?
I'll have to look more deeply to see why it's starting up so many times
and why it's using timeouts that are way too short. In the meantime, you
could simply try disabling hotplug entirely. See if that doesn't fix the
problem.
> > Attached are versions of the patch for both 2.6 and 2.4. It will be
> > interesting to compare the results.
>
> I wonder if it will really be interesting.
>
> Linux 2.4 produces no more proc_control: logs after starting iscan, but
> I have successfully done a preview and then a full scan in 400 dpi of an
> ISO-A4 sheet - this should amount to c. 46 MB data through USB 1.1.
>
> I'm gzipping the logs as they are 50 kByte each and gain >= 90%.
Clearly there's a difference between when the two kernels generate hotplug
events. I'll look into that too.
In any case, the control requests being submitted by the hotplug program
are completely unnecessary. They are asking the scanner to transmit data
which the kernel already knows and makes available through sysfs.
Alan Stern
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