On 7/22/09, Christopher Piggott <cpiggott@xxxxxxxxx> wrote:
> I must be missing something really fundamental, because whatever rules
> I write, they don't seem to see attributes.
>
> Here is one example. I am inserting a device that is a CDMA modem.
> Its path is:
>
> /devices/pci0000:00/0000:00:1d.1/usb3/3-2/3-2:1.0/ttyUSB0/tty/ttyUSB0
>
> If I start in
> /sys/devices/pci0000:00/0000:00:1d.1/usb3/3-2/3-2:1.0/ttyUSB0/tty/ttyUSB0
> and start searching upward, I find a file named:
>
> /sys/devices/pci0000:00/0000:00:1d.1/usb3/3-2/idVendor
>
> That file contains the string "1410" ... so far so good, that's
> exactly what I want.
>
> Next, I try to write a rule like this:
>
> ACTION=="add", , SYMLINK+="usb-cell"
>
> Nothing happens. It doesn't match, because idVendor is (apparently)
> not assigned. So, to troubleshoot this I try something else:
>
> ACTION=="add", RUN+="/usr/bin/logger add devpath=%p driver=$driver
> id=%b links=$links vendor=$attr{idVendor}, product=$attr{product}"
>
> What that should do is that any time ANYTHING is added it uses logger
> to write a line to the log file. I remove and reinsert the device
> and, indeed, logger gets called. What gets logged is a string like
> this:
>
> logger: add
> devpath=/devices/pci0000:00/0000:00:1d.1/usb3/3-2/3-2:1.0/ttyUSB0/tty/ttyUSB0
> driver=option id=3-2:1.0 links=char/188:0
> serial/by-path/pci-0000:00:1d.1-usb-0:2:1.0-port0
> serial/by-id/usb-Novatel_Wireless_Inc._Novatel_Wireless_CDMA_091073597351000-if00-port0
> vendor=, product=
>
>
> So ... lots of useful stuff there. It logged, it sees a device path
> that makes sense, but vendor and product are not assigned.
Two general things may be worth knowing -
1) "udevadm info" is a good way to see a list of env keys or
attributes you can match on.
2) libptp and libmtp match on idVendor / idProduct, so it is possible.
More specific gotchas
- The documentation for $attr{} is a little misleading. It will only
look at the actual device and a maximum of one "ancestor". It will
only look at an ancestor device if it was used to fulfil a match
(presumably an ATTRS match, but it could be anything). That explains
why it doesn't expand to anything in your debug rule.
- Similarly, in you first rule,
ATTRS{idVendor}=="1410",
DRIVERS=="option",
ATTRS{port_number}=="0"
all these matches must apply to the same device. I suspect idVendor
and DRIVER are on the same usb ancestor device, but port_number is
not. If port_number is an attribute of the actual device, you can use
ATTR{} to match it instead, and that should work.
I guess would be easier to do this if you could match on SYMLINKs,
(you can't). Then people who want human-readable aliases could add
rules like
SYMLINK=="serial/by-id/usb-Novatel_Wireless_Inc._Novatel_Wireless_CDMA_091073597351000-if00-port0",
SYMLINK="usb-cell".
I'm not sure if it's worthwhile, or how to document it so people would
find it :-). The code would be easy though.
Alan
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