How creation of new USB device file in /dev/bus/usb/001/ directory work?

Question

I noticed that every time I connect a USB device, a new device gets created in the /dev/bus/usb/001/ directory. Further on each reconnection of the same device, the "Device Number" and "ID" change.

So, I'd like to know how the creation of new device file (in /dev/bus/usb/001/) work? Can I control the behaviour, say limit the device number to 002, by making changes in some configuration file (if any)?

Here's a the output for reference:

$ ls /dev/bus/usb/001
001  002
$ lsusb
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 002 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 003 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 004 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 005 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 001 Device 002: ID 0781:5406 SanDisk Corp. Cruzer Micro U3
$ lsusb
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 002 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 003 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 004 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 005 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 001 Device 003: ID 08ec:0015 M-Systems Flash Disk Pioneers Kingston DataTraveler ELITE
$ lsusb 
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 002 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 003 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 004 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 005 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 001 Device 008: ID 0781:5406 SanDisk Corp. Cruzer Micro U3
$ ls /dev/bus/usb/001/
001  008

_{( Also I don't know why Kingston Flash Disk was shown in the output. I don't have a Kingston device!... Maybe it's just a glitch, or is it? )}

Another contextual topic of interest:

• How can I get all USB storage device to mount as read-only or offer no mount options at all?

Answer 1

正如 Gilles 在评论中指出的那样，这些设备/dev/bus/usb/XXX/YYY遵循内核中的命名策略。XXX是相当稳定的总线号，但YYY每次枚举 USB 设备时（当设备刚刚插入或重置时）都会发生变化。这是无法更改的，您也不应该更改它。

如果您需要更改设备上的权限（例如，为了测试目的而使非特权用户空间 USB 驱动程序成为可能），那么您可以制定 udev 规则。udev我用来控制权限以便adb能够连接到设备的示例：

# /etc/udev/rules.d/42-usb-permissions.rules
SUBSYSTEM!="usb", GOTO="end_skip_usb"

# CWM 6.0.4.3 in recovery mode
ATTRS{idVendor}=="18d1", ATTRS{idProduct}=="d001", GROUP="peter"

# CM 10.2 with MTP disabled
ATTRS{idVendor}=="18d1", ATTRS{idProduct}=="d002", GROUP="peter"

ATTRS{idVendor}=="148f", ATTRS{idProduct}=="5372", GROUP="peter"

LABEL="end_skip_usb"