Provided by: linux-doc-2.6.15_2.6.15-23.39_all
usb_make_path - returns stable device path in the usb tree
int usb_make_path (struct usb_device * dev, char * buf, size_t size);
dev the device whose path is being constructed
buf where to put the string
size how big is ‘‘buf’’?
Returns length of the string (> 0) or negative if size was too small.
This identifier is intended to be ‘‘stable’’, reflecting physical paths
in hardware such as physical bus addresses for host controllers or
ports on USB hubs. That makes it stay the same until systems are
physically reconfigured, by re-cabling a tree of USB devices or by
moving USB host controllers. Adding and removing devices, including
virtual root hubs in host controller driver modules, does not change
these path identifers; neither does rebooting or re-enumerating. These
are more useful identifiers than changeable (‘‘unstable’’) ones like
bus numbers or device addresses.
With a partial exception for devices connected to USB 2.0 root hubs,
these identifiers are also predictable. So long as the device tree
isn’t changed, plugging any USB device into a given hub port always
gives it the same path. Because of the use of ‘‘companion’’
controllers, devices connected to ports on USB 2.0 root hubs (EHCI host
controllers) will get one path ID if they are high speed, and a
different one if they are full or low speed.