APC UPS control system manual 208, Usb

An alternative and more			permanent method			would be		to add
none /proc/bus/usb		usbfs	defaults	0	0
to /etc/fstab.		This will mount usbfs			at	each	reboot.
You	can then issue ‘cat		/proc/bus/usb/devices‘				to	extract
USB	device information,		and user	mode	drivers		can	use usbfs

to interact with USB devices.

There are a number of mount options supported by usbfs. Consult the source code (linux/drivers/usb/inode.c) for information about those options.

**NOTE**: The filesystem has been renamed from "usbdevfs" to "usbfs", to reduce confusion with "devfs". You may still see references to the older "usbdevfs" name.

For more information on mounting the usbfs file system, see the "USB Device Filesystem" section of the USB Guide. The latest copy of the USB Guide can be found at http://www.linux-usb.org/

THE /proc/bus/usb/BBB/DDD FILES:

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Each connected USB device has one file. The BBB indicates the bus number. The DDD indicates the device address on that bus. Both of these numbers are assigned sequentially, and can be reused, so you can’t rely on them for stable access to devices. For example, it’s relatively common for devices to re-enumerate while they are still connected (perhaps someone jostled their power supply, hub, or USB cable), so a device might be 002/027 when you first connect it and 002/048 sometime later.

These files can be read as binary data. The binary data consists of first the device descriptor, then the descriptors for each configuration of the device. That information is also shown in text form by the /proc/bus/usb/devices file, described later.

These files may also be used to write user-level drivers for the USB devices. You would open the /proc/bus/usb/BBB/DDD file read/write, read its descriptors to make sure it’s the device you expect, and then bind to an interface (or perhaps several) using an ioctl call. You would issue more ioctls to the device to communicate to it using control, bulk, or other kinds of USB transfers. The IOCTLs are listed in the linux/usbdevice_fs.h file, and at this writing the source code (linux/drivers/usb/devio.c) is the primary reference

for how to access devices through those files.

Note that since by default these BBB/DDD files are writable only by root, only root can write such user mode drivers. You can selectively grant read/write permissions to other users by using "chmod". Also, usbfs mount options such as "devmode=0666" may be helpful.

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