Re: General USB questions and comments

From: Oliver Neukum (
Date: Sat Jan 06 2001 - 08:27:34 PST

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    > Some questions (mostly based on Linux and the USB driver "scanner"):
    > * Is there any way to get the vendor and device ids for a given device
    > file name? One problem for SANE-USB backends is that they can't easily

    No that I know of. Could you live with an IOCTL for that ?
    I wouldn't be hard to add to the kernel.

    > * What's the meaning of the other files under /proc/bus/usb/? I'm
    > talking of e.g. 001/001.

    These are the USB equivalent of sg devices. You are supposed to use
    them with the aid of libusb.

    > * For find-scanner the idea was to scan /proc/bus/usb/devices. Look for
    > new devices (starting with "T:" lines) and save all devices
    > containing an "I: ... Driver=usbscanner" line. Get vendor and
    > product ids from the "P:" line. Question: How to get the device file
    > from this information? Can I just assume that the first usbscanner entry

    You can't. Device numbers depend on the order plugging in and out.

    > in this list is /dev/usbscanner0? Can the number of one device
    > change if another one is conncted?

    You cannot assume that the first device is usbscanner0. While a device is
    plugged in, it's device node doesn't change. Note: You can't tell easily
    whether it was replugged.

                    Oliver Neukum

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