1USB_MAKE_PATH(9)        Host-Side Data Types and Macro        USB_MAKE_PATH(9)
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NAME

6       usb_make_path - returns stable device path in the usb tree
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SYNOPSIS

9       int usb_make_path(struct usb_device * dev, char * buf, size_t size);
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ARGUMENTS

12       dev
13           the device whose path is being constructed
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15       buf
16           where to put the string
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18       size
19           how big is “buf”?
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RETURN

22       Length of the string (> 0) or negative if size was too small.
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NOTE

25       This identifier is intended to be “stable”, reflecting physical paths
26       in hardware such as physical bus addresses for host controllers or
27       ports on USB hubs. That makes it stay the same until systems are
28       physically reconfigured, by re-cabling a tree of USB devices or by
29       moving USB host controllers. Adding and removing devices, including
30       virtual root hubs in host controller driver modules, does not change
31       these path identifiers; neither does rebooting or re-enumerating. These
32       are more useful identifiers than changeable (“unstable”) ones like bus
33       numbers or device addresses.
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35       With a partial exception for devices connected to USB 2.0 root hubs,
36       these identifiers are also predictable. So long as the device tree
37       isn't changed, plugging any USB device into a given hub port always
38       gives it the same path. Because of the use of “companion” controllers,
39       devices connected to ports on USB 2.0 root hubs (EHCI host controllers)
40       will get one path ID if they are high speed, and a different one if
41       they are full or low speed.
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44Kernel Hackers Manual 3.10         June 2019                  USB_MAKE_PATH(9)
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