Jim Kronebusch wrote:
> On Wed, 15 Aug 2007 13:53:15 -0400 (EDT), Peter Billson wrote
>> Hello *,
>> I have a problem with accessing USB drives through an un-powered USB hub.
>>
>> The problem is a well known issue due to changes in the 2.6 kernel so
>> that USB works "right." The "fix" is simply to echo a value to the
>> proper place under /sys/bus/usb/devices when the USB drive is plugged
>> in.
>>
>> I have a simple little shell script to do the job and it works fine if
>> run manually.
>>
>> My problem is I can not seem to get the script to execute automatically
>> on the LTSP client when a USB device is plugged in. I am sure this is
>> just my total lack of knowledge about udev and am hoping that someone
>> can point me to how and where to add the correct udev rule so that this
>> magic happens.
>
> This is a very basic explanation from a person with very minimal knowledge on
> the topic.
> But from what I understand the usb device sends a signal when plugged in.
> So you plug
> in your USB hub and no devices are plugged in when the signal is sent thus no
> drives are
> mounted. Now when you plug a drive into the hub a signal is sent, but it
> stops at the
> hub and never makes it to the client, so no drive is mounted. If you plug
> the drive
> into the hub, then plug the hub into the client, there is a drive present
> when the
> signal is sent so the drive is mounted. I think Scott Balnaeves said that
> you could
> possibly probe the usb device every so often to see if a drive was present,
> but I can't
> exactly remember. If you contact him I'm sure he'll shed a great amount of
> light on
> what is happening.
>
> Jim
Jim,
Thanks for the reply. I didn't get too much into the actual problem
since the problem itself isn't LTSP related.
The actual "problem" is that the newer 2.6 kernels enforce the USB
power limits that are part of the USB specification. Older kernels did not.
Soooo technically the older kernels (where the USB thumb drives
worked on unpowered hubs) where broken and the new kernels (where the
thumb drives don't work) are fixed.
Much grumbling has ensued but the kernel guys are correct in their
implementation. After all if you just start ignoring standards and doing
what is convenient you would end up with M$ Vista!
Anyway, in my case the thumb drive is seen when it is plugged into
the hub but the kernel chooses not to configure it based on how much
power it draws.
Forcing the kernel to configure the device is trivial - my little
script does that - but my LTSP related problem is that I can not figure
out how to write a udev rule to run the script automatically on the client.
I was hoping Scotty (the self-taught LTSP udev guru) was not too busy
and had some helpful advice but I am sure he is busy.
Pete Billson
--
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ELB Internet Service, Inc.
Reliable Tech Support for New Jersey's Public Libraries
>
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