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To:     linux-bluetooth@vger.kernel.org
From:   "Peter A. Bigot" <pab@pabigot.com>
Subject: how to cleanly shutdown an application using HCI_CHANNEL_USER
Organization: Peter Bigot Consulting, LLC
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I'm using an AF_BLUETOOTH socket bound with HCI_CHANNEL_USER from a
user-mode application with cap_net_admin=ep.  As expected this
requires the device be down, and brings the device up automatically.

When I close that socket and exit the application, the device appears
to remain up forever.  Which prevents me from re-starting the
application.

I tried to issue HCIDEVDOWN before closing, but that produces EBADFD
because ioctls cannot be performed with HCI_CHANNEL_RAW.

I can bring the interface down from within the application if, after
closing the socket, I wait a second or so, then create a new bound
HCI_CHANNEL_RAW socket and issue HCIDEVDOWN on it.

Is there some other way to cleanly shut down an application that used
HCI_CHANNEL_USER so that the device is returned to down state on exit?
Or is this supposed to happen automatically (I see code that suggests
it should)?

Kernel version is 5.11.0-7620-generic (System76), and I'm using go
1.16, if that's relevant.

Thanks!

Peter