On 10/20/2015 07:35 PM, Alan Stern wrote:
On Tue, 20 Oct 2015, Bin Liu wrote:
Hi,
On Tue, Oct 20, 2015 at 11:57 AM, Peter Stuge <peter@xxxxxxxx> wrote:
Greg K-H wrote:
Userspace still has the port open, so the number is not reused until
userspace closes the device node. Fix your userspace programs to
properly listen to the hangup signal to know to release the device
node
and you should be fine.
There's still a bit of a race condition here, isn't there?
Is there any good way to deal with that?
Yes, there is a race condition. If the program closes the device node
before the device is plugged in again, the ttyUSB number won't change;
otherwise it will. No, there is no good way to deal with this.
Well, I see some option for a walk around for this. You may use device
authorization. First of all you should set unauthorized as default
policy for hcd to which you connect serial converter. Then on system
boot,authorize your converter and run your userspace. When you get
disconnected event you should close opened ttyUSB and then authorize
newly connected converter (or wait until reset finishes and then
authorize it). This should work as tty will be allocated after
authorizing the device so ttyUSB0 should be always available for driver.
--
Krzysztof Opasiak
Samsung R&D Institute Poland
Samsung Electronics
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