Determine USB device file Path

问题

How can i get USB device file path correctly in Linux. I used command: find / -iname "usb" and got the result as below:

/dev/bus/usb
/sys/bus/usb
/sys/bus/usb/drivers/usb
/sys/kernel/debug/usb

Under /dev/bus/usb i see:

001  002  003  004  005  006

But I think they aren't files as i need.

Under /sys/bus/usb/devices/:

sh-3.2# ls /sys/bus/usb/devices/
1-0:1.0  1-1:1.0  3-0:1.0  5-0:1.0  usb1     usb3     usb5
1-1      2-0:1.0  4-0:1.0  6-0:1.0  usb2     usb4     usb6

And Under /sys/bus/scsi/devices/ when i pluged an USB i see:

2:0:0:0      host0        host2        target2:0:0

And when i removed USB i see:

sh-3.2# ls
host0

So which device file is used for USB? How can i indentify it? I need to make a C program with USB device file...

Further more, could you explain to me the number 1-1:1.0? What does it mean?

Thank you.

回答1:

So which device file is used for USB? How can i indentify it?

What you see behind /sys/ is mainly configuration/information about devices. /dev/bus/usb is what you are looking for. I think that the following article can help you

http://www.linuxjournal.com/article/7466?page=0,0

Is quite old, but still it can help you. (In the article they speak about /proc/bus/usb, today we have /dev/bus/usb)

Further more, could you explain to me the number 1-1:1.0? What does it mean?

The generic form is

X-Y.Z:A.B

Each field identify the connection point of your device. The first two field are mandatory:

X is the USB bus of your motherboard where is connected the USB system.
Y is the port in use on the bus system

So the USB device identified with the string 3-3 is the device connected on the port 3 of the bus 3.

If you connect an USB hub, you are extending the connection capability of a single USB port. The Linux kernel identify this situation by appending the Z field.

Z is the port is use on an hub

So, the USB device identified with the string 1-2.5 is the device connected on the port 5 of the hub connected on the port 2 of the bus 1.

USB specification allow you to connect in cascade more then one USB hub, so the Linux kernel continue to append the port in use on the different hubs. So, the USB device identified with the string 1-2.1.1 is the device connected on the port 1 of the hub connected on the port 1 of the hub connected to the port 2 of the bus 1.

A fast way to retrieve these information is to read the kernel messages (if you can).

$ dmesg | grep usb
[... snip ...]
[ 2.047950] usb 4-1: new full-speed USB device number 2 using ohci_hcd
[ 2.202628] usb 4-1: New USB device found, idVendor=046d, idProduct=c318
[ 2.202638] usb 4-1: New USB device strings: Mfr=1, Product=2, SerialNumber=0
[ 2.202643] usb 4-1: Product: Logitech Illuminated Keyboard
[ 2.202648] usb 4-1: Manufacturer: Logitech
[... snip ...]

Then, the last two fields of the pattern (after colon) identify an internal section of an USB device :