Re: ENV variable scope question

[Aras Vaichas <arasv@magtech.com.au>]

Kay Sievers wrote:
> On Thu, Aug 21, 2008 at 03:37, Aras Vaichas <arasv@magtech.com.au> wrote:
>   
>> 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"
>>     
>
> Why do you match against the endpoint? These devices do not do anything.
>
> You should also never use the "device" link, it's deprecated and udev
> should print a warning to the logs.
>   
Well the problem was that the device uses a common USB-to-serial chip
(FTDI) and they didn't change the VID/PID numbers for their product.
This means that I could plug in a USB-to-serial cable which uses the
same chip and I wouldn't know the difference if I just looked at the
VID/PID numbers.

So to avoid any ambiguity I wanted to load the application only when the
exact device was plugged in. The manufacturer field seemed to be the
best discriminator.

Is there a better way to distinguish between the same USB-serial chip
that is used in different devices?

For example, I want to add a symlink for ttyUSB[0-9] only when the
Manufucturer is Crystalfontz, so I do:

ACTION="add", KERNEL="ttyUSB[0-9]",
ATTR{../../../../manufacturer}="Crystalfontz", SYMLINK+="lcd"

Is this safer? Should I use this same method for loading the driver?

>> ACTION="remove", ENV{LCDD_DEVICE}!="", RUN+="... remove the driver ..."
>>     
> By matching on the endpoint, you get several events which will all
> trigger your script. Try using the USB-device only, by adding:
>   ENV{DEVTYPE}="usb_device"
>   
Ok.

> Try setting:
>   ENV{REMOVE_CMD}="/bin/something"
> with the "add" rule, it should be called by udev itself on "remove".
>   
Good idea, use a standard naming scheme.

So, does udev maintain a separate environment space for each /dev point
that it processes?

Aras

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