Re: Matching different levels in sysfs

[Kay Sievers <kay.sievers@vrfy.org>]

On Wed, Jan 25, 2006 at 06:29:22PM -0600, Chris Adams wrote:
> I've got a USB device that I'd like to create a symlink for.  It is a
> USB-to-serial adapter board that I've used to hook up a GPS interface,
> so I'd like the GPS to show up as /dev/gps (I've got multiple
> USB-to-serial adapters, so tracking the correct /dev/ttyUSB and getting
> the permissions set correctly is otherwise a PITA).
> 
> The problem is that this particular USB-to-serial adapter has two serial
> ports and the GPS interface is only hooked up to one.  I can match the
> USB device by serial number, but that is at a different level from the
> individual port (the serial number is for the whole device).  udevinfo
> shows (interesting sections):
> 
> ########################################################################
> # udevinfo -a -p /sys/class/tty/ttyUSB2
> 
> udevinfo starts with the device the node belongs to and then walks up the
> device chain, to print for every device found, all possibly useful attributes
> in the udev key format.
> Only attributes within one device section may be used together in one rule,
> to match the device for which the node will be created.
> 
>   looking at class device '/sys/class/tty/ttyUSB2':
>     SYSFS{dev}="188:2"
> 
> follow the class device's "device"
>   looking at the device chain at '/sys/devices/pci0000:00/0000:00:10.4/usb1/1-6/1-6.1/1-6.1:1.1/ttyUSB2':
>     BUS="usb-serial"
>     ID="ttyUSB2"
>   looking at the device chain at '/sys/devices/pci0000:00/0000:00:10.4/usb1/1-6/1-6.1/1-6.1:1.1':
>     BUS="usb"
>     ID="1-6.1:1.1"
>     SYSFS{bAlternateSetting}=" 0"
>     SYSFS{bInterfaceClass}="ff"
>     SYSFS{bInterfaceNumber}="01"
>     SYSFS{bInterfaceProtocol}="ff"
>     SYSFS{bInterfaceSubClass}="ff"
>     SYSFS{bNumEndpoints}="02"
>     SYSFS{interface}="DLP2232M"
>     SYSFS{modalias}="usb:v0403p6010d0500dc00dsc00dp00icFFiscFFipFF"
> 
>   looking at the device chain at '/sys/devices/pci0000:00/0000:00:10.4/usb1/1-6/1-6.1':
>     BUS="usb"
>     ID="1-6.1"
>     SYSFS{bConfigurationValue}="1"
>     SYSFS{bDeviceClass}="00"
>     SYSFS{bDeviceProtocol}="00"
>     SYSFS{bDeviceSubClass}="00"
>     SYSFS{bMaxPower}="274mA"
>     SYSFS{bNumConfigurations}="1"
>     SYSFS{bNumInterfaces}=" 2"
>     SYSFS{bcdDevice}="0500"
>     SYSFS{bmAttributes}="80"
>     SYSFS{devnum}="6"
>     SYSFS{idProduct}="6010"
>     SYSFS{idVendor}="0403"
>     SYSFS{latency_timer}="16"
>     SYSFS{latency_timer}="16"
>     SYSFS{manufacturer}="FTDI"
>     SYSFS{maxchild}="0"
>     SYSFS{product}="DLP2232M"
>     SYSFS{serial}="FTOIQ4MN"
>     SYSFS{speed}="12"
>     SYSFS{version}=" 2.00"
> ########################################################################
> 
> I'd like to match SYSFS{bInterfaceNumber}="01" and
> SYSFS{serial}="FTOIQ4MN", but I don't see how.

Udev does not match on different levels with built-in logic, but you should be
able to use something like: SYSFS{bInterfaceNumber}="01", SYSFS{../serial}="FTOIQ4MN".

That makes you dependent on the hierarchy in /sys/devices, which is not guaranteed
to be stable if the kernel code may be changed, but it's very unlikely in this example,
that the usb sysfs layout will be changed, so you should be pretty safe with the "../".

Kay


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