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Could you recommend a way to figure out which driver is being used for a USB device. Sort of a usb equivalent of lspci -k command.

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2 Answers 2

up vote 15 down vote accepted

Finding the Kernel Driver(s)

The victim device

$ lsusb 
Bus 010 Device 002: ID 046d:c01e Logitech, Inc. MX518 Optical Mouse
Bus 010 Device 003: ID 051d:0002 American Power Conversion Uninterruptible Power Supply

We're going to try to find out what driver is used for the APC UPS. Note that there are two answers to this question: The driver that the kernel would use, and the driver that is currently in use. Userspace can instruct the kernel to use a different driver (and in the case of my APC UPS, nut has).

Method 1: Using usbutils (easy)

The usbutils package (on Debian, at least) includes a script called usb-devices. If you run it, it outputs information about the devices on the system, including which driver is used:

$ usb-devices
T:  Bus=10 Lev=01 Prnt=01 Port=01 Cnt=02 Dev#=  3 Spd=1.5 MxCh= 0
D:  Ver= 1.10 Cls=00(>ifc ) Sub=00 Prot=00 MxPS= 8 #Cfgs=  1
P:  Vendor=051d ProdID=0002 Rev=01.06
S:  Manufacturer=American Power Conversion
S:  Product=Back-UPS RS 1500 FW:8.g9 .D USB FW:g9 
S:  SerialNumber=XXXXXXXXXXXX  
C:  #Ifs= 1 Cfg#= 1 Atr=a0 MxPwr=24mA
I:  If#= 0 Alt= 0 #EPs= 1 Cls=03(HID  ) Sub=00 Prot=00 Driver=usbfs

Note that this lists the current driver, not the default one. There isn't a way to find the default one.

Method 2: Using debugfs (requires root)

If you have debugfs mounted, the kernel maintains a file in the same format as usb-devices prints out at /sys/kernel/debug/usb/devices; you can view with less, etc. Note that debugfs interfaces are not stable, so different kernel versions may print in a different format, or be missing the file entirely.

Once again, this only shows the current driver, not the default.

Method 3: Using only basic utilities to read /sys directly (best for scripting or recovery)

You can get the information out of /sys, thought its more painful than lspci. These /sys interfaces should be reasonably stable, so if you're writing a shell script, this is probably how you want to do it.

Initially, lsusb seems to count devices from 1, /sys from 0. So 10-2 is a good guess for where to find the APC UPS lsusb gives as bus 10, device 3. Unfortunately, over time that mapping breaks down—sysfs re-uses numbers even when device numbers aren't. The devnum file's contents will match the device number given by lsusb, so you can do something like this:

$ grep -l '^3$' /sys/bus/usb/devices/10-*/devnum     # the ^ and $ to prevent also matching 13, 31, etc.

So, in this case, it's definitely 10-2.

$ cd /sys/bus/usb/devices/10-2
$ ls
10-2:1.0             bDeviceClass     bMaxPower           descriptors  ep_00         maxchild   remove     urbnum
authorized           bDeviceProtocol  bNumConfigurations  dev          idProduct     power      serial     version
avoid_reset_quirk    bDeviceSubClass  bNumInterfaces      devnum       idVendor      product    speed
bcdDevice            bmAttributes     busnum              devpath      ltm_capable   quirks     subsystem
bConfigurationValue  bMaxPacketSize0  configuration       driver       manufacturer  removable  uevent

We can be sure this is the right device by cating a few of the files:

$ cat idVendor idProduct manufacturer product 
American Power Conversion
Back-UPS RS 1500 FW:8.g9 .D USB FW:g9 

If you look in 10-2:1.0 (:1 is the "configuration", .0 the interface—a single USB device can do multiple things, and have multiple drivers; lsusb -v will show these), there is a modalias file and a driver symlink:

$ cat 10-2\:1.0/modalias 
$ readlink driver

So, the current driver is usbfs. You can find the default driver by asking modinfo about the modalias:

$ /sbin/modinfo `cat 10-2\:1.0/modalias`
filename:       /lib/modules/3.6-trunk-amd64/kernel/drivers/hid/usbhid/usbhid.ko
license:        GPL
description:    USB HID core driver
author:         Jiri Kosina
author:         Vojtech Pavlik
author:         Andreas Gal
alias:          usb:v*p*d*dc*dsc*dp*ic03isc*ip*in*
depends:        hid,usbcore
intree:         Y
vermagic:       3.6-trunk-amd64 SMP mod_unload modversions 
parm:           mousepoll:Polling interval of mice (uint)
parm:           ignoreled:Autosuspend with active leds (uint)
parm:           quirks:Add/modify USB HID quirks by specifying  quirks=vendorID:productID:quirks where vendorID, productID, and quirks are all in 0x-prefixed hex (array of charp)

So, the APC UPS defaults to the hid driver, which is indeed correct. And its currently using usbfs, which is correct since nut's usbhid-ups is monitoring it.

What about userspace (usbfs) drivers?

When the driver is usbfs, it basically means a userspace (non-kernel) program is functioning as the driver. Finding which program it is requires root (unless the program is running as your user) and is fairly easy: whichever program has the device file open.

We know that our "victim" device is bus 10, device 3. So the device file is /dev/bus/usb/010/003 (at least on a modern Debian), and lsof provides the answer:

# lsof /dev/bus/usb/010/003 
usbhid-up 4951  nut    4u   CHR 189,1154      0t0 8332 /dev/bus/usb/010/003

And indeed, its usbhid-ups as expected (lsof truncated the command name to make the layout fit, if you need the full name, you can use ps 4951 to get it, or probably some lsof output formatting options).

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I'm definitely gonna loose in my ever going debate with my friend of Windows vs Linux with this one :) . Will give it a few days to see if a simpler solution pops out. Thanks for the effort. –  Alan Jan 2 '13 at 13:37
@Alan OK, I've found two more ways, one of them is quite simple. Also, I've clarified which of two possible answers to "which driver?" each method provides. –  derobert Jan 2 '13 at 15:48
I don't think your claim about locating the device in /sys/bus/usb/devices is correct. I have a device on bus 1 that usb-devices says is device 12, but there's no /sys/bus/usb/devices/1-11 on my system. –  Cerin Apr 15 at 19:44
@Cerin indeed it isn't. I'll put in a better one. Thank you. –  derobert Apr 16 at 16:04

lsusb itself can get you good results. For compact output I use lsusb -t, where -t shows the devices as a tree; this format reports the driver as well.

Example output:

 $ lsusb -t
/:  Bus 04.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/2p, 5000M
/:  Bus 03.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/2p, 480M
/:  Bus 02.Port 1: Dev 1, Class=root_hub, Driver=ehci-pci/3p, 480M
    |__ Port 1: Dev 2, If 0, Class=Hub, Driver=hub/8p, 480M

If no driver is used, the line will look like this (the device in my example is a camera for which I did remove the driver from the kernel):

    |__ Port 6: Dev 4, If 1, Class=Video, Driver=, 480M
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