From mboxrd@z Thu Jan  1 00:00:00 1970
From: Aras Vaichas <arasv@magtech.com.au>
Date: Thu, 21 Aug 2008 01:37:33 +0000
Subject: ENV variable scope question
Message-Id: <48ACC6DD.4070705@magtech.com.au>
List-Id: <linux-hotplug.vger.kernel.org>
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To: linux-hotplug@vger.kernel.org

Hi, I'm looking to unload a userspace driver when a particular device is
removed.

My load rule is this:

ACTION="add",SUBSYSTEM="usb_endpoint",ATTR{device/manufacturer}="Crystalfontz",
RUN+="/usr/bin/sv up lcdd"

Now the problem was that when I disconnect the device there is no longer
a "device/manufacturer" file, so I added an environment variable
LCDD_DEVICE to the rule:

ACTION="add",SUBSYSTEM="usb_endpoint",ATTR{device/manufacturer}="Crystalfontz",
ENV{LCDD_DEVICE}="%k", RUN+="/usr/bin/sv up lcdd"

I had hoped to be able to match this LCDD_DEVICE variable when the
kernel name appeared in the remove event. So I tried:

ACTION="remove", ENV{LCDD_DEVICE}="%k", RUN+="... remove the driver ..."

But this rule never triggered.

I put in a debug line, and disconnected the device:

ACTION="remove", RUN+="/bin/sh -c 'logger B %k = $env{LCDD_DEVICE}'"

Jan  1 00:41:21 user.notice root: B usbdev1.23_ep81 Jan  1 00:41:21 user.notice root: B usbdev1.23_ep02 Jan  1 00:41:21 user.notice root: B usbdev1.23_ep00 = usbdev1.23_ep00
<--- !!!
Jan  1 00:41:21 user.notice root: B ttyUSB1 Jan  1 00:41:21 user.notice root: B ttyUSB1 Jan  1 00:41:21 user.notice root: B 1-1:1.0 Jan  1 00:41:21 user.notice root: B 1-1 
So there is a situation where %k  was equal to LCDD_DEVICE, but
regardless the rule didn't trigger. Did I get the syntax wrong?

Also, it appears that the scope of the environment variable LCDD_DEVICE
only occurs when the actual device has caused the uevent. OK.

So should I make my remove rule like this?

ACTION="remove", ENV{LCDD_DEVICE}!="", RUN+="... remove the driver ..."

Aras

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