如何写ubuntu的rules（基础）

• 1.系统按照字母表顺序读取rules文件，如果想要被优先读取，可以以0开头命名
• 2.rules文件中有两种关键词：匹配关键词使用==，分配关键词使用=。
• 3.匹配关键词指用户不可更改的东西，如KERNEL(设备在内核中的名字)和ATTR(设备的属性)等；分配关键词指用户可以更改的东西，如NAME(设备在/dev下的名字)和MODE(设备权限)等
• 4.SYMLINK使用+=，是设备的链接或叫别名，我们一般使用SYMLINK，不修改NAME。也可以设置多个链接SYMLINK+="cdrom cdrom0"
• 5.可以使用命令udevadm info -a -p $(udevadm info -q path -n /dev/video0)查询设备信息，这里是摄像头。本机输出如下

  looking at device '/devices/pci0000:00/0000:00:14.0/usb1/1-10/1-10:1.0/video4linux/video0':
    KERNEL=="video0"
    SUBSYSTEM=="video4linux"
    DRIVER==""
    ATTR{dev_debug}=="0"
    ATTR{index}=="0"
    ATTR{name}=="KS2A418-60: KS2A418-60"

  looking at parent device '/devices/pci0000:00/0000:00:14.0/usb1/1-10/1-10:1.0':
    KERNELS=="1-10:1.0"
    SUBSYSTEMS=="usb"
    DRIVERS=="uvcvideo"
    ATTRS{authorized}=="1"
    ATTRS{bAlternateSetting}==" 0"
    ATTRS{bInterfaceClass}=="0e"
    ATTRS{bInterfaceNumber}=="00"
    ATTRS{bInterfaceProtocol}=="00"
    ATTRS{bInterfaceSubClass}=="01"
    ATTRS{bNumEndpoints}=="01"
    ATTRS{iad_bFirstInterface}=="00"
    ATTRS{iad_bFunctionClass}=="0e"
    ATTRS{iad_bFunctionProtocol}=="00"
    ATTRS{iad_bFunctionSubClass}=="03"
    ATTRS{iad_bInterfaceCount}=="02"
    ATTRS{interface}=="KS2A418-60"
    ATTRS{supports_autosuspend}=="1"

  looking at parent device '/devices/pci0000:00/0000:00:14.0/usb1/1-10':
    KERNELS=="1-10"
    SUBSYSTEMS=="usb"
    DRIVERS=="usb"
    ATTRS{authorized}=="1"
    ATTRS{avoid_reset_quirk}=="0"
    ATTRS{bConfigurationValue}=="1"
    ATTRS{bDeviceClass}=="ef"
    ATTRS{bDeviceProtocol}=="01"
    ATTRS{bDeviceSubClass}=="02"
    ATTRS{bMaxPacketSize0}=="64"
    ATTRS{bMaxPower}=="500mA"
    ATTRS{bNumConfigurations}=="1"
    ATTRS{bNumInterfaces}==" 4"
    ATTRS{bcdDevice}=="4607"
    ATTRS{bmAttributes}=="80"
    ATTRS{busnum}=="1"
    ATTRS{configuration}==""
    ATTRS{devnum}=="4"
    ATTRS{devpath}=="10"
    ATTRS{idProduct}=="4920"
    ATTRS{idVendor}=="2304"
    ATTRS{ltm_capable}=="no"
    ATTRS{manufacturer}=="KINGSEN"
    ATTRS{maxchild}=="0"
    ATTRS{product}=="KS2A418-60"
    ATTRS{quirks}=="0x0"
    ATTRS{removable}=="unknown"
    ATTRS{speed}=="480"
    ATTRS{urbnum}=="5070"
    ATTRS{version}==" 2.00"

  looking at parent device '/devices/pci0000:00/0000:00:14.0/usb1':
    KERNELS=="usb1"
    SUBSYSTEMS=="usb"
    DRIVERS=="usb"
    ATTRS{authorized}=="1"
    ATTRS{authorized_default}=="1"
    ATTRS{avoid_reset_quirk}=="0"
    ATTRS{bConfigurationValue}=="1"
    ATTRS{bDeviceClass}=="09"
    ATTRS{bDeviceProtocol}=="01"
    ATTRS{bDeviceSubClass}=="00"
    ATTRS{bMaxPacketSize0}=="64"
    ATTRS{bMaxPower}=="0mA"
    ATTRS{bNumConfigurations}=="1"
    ATTRS{bNumInterfaces}==" 1"
    ATTRS{bcdDevice}=="0415"
    ATTRS{bmAttributes}=="e0"
    ATTRS{busnum}=="1"
    ATTRS{configuration}==""
    ATTRS{devnum}=="1"
    ATTRS{devpath}=="0"
    ATTRS{idProduct}=="0002"
    ATTRS{idVendor}=="1d6b"
    ATTRS{interface_authorized_default}=="1"
    ATTRS{ltm_capable}=="no"
    ATTRS{manufacturer}=="Linux 4.15.0-65-generic xhci-hcd"
    ATTRS{maxchild}=="16"
    ATTRS{product}=="xHCI Host Controller"
    ATTRS{quirks}=="0x0"
    ATTRS{removable}=="unknown"
    ATTRS{serial}=="0000:00:14.0"
    ATTRS{speed}=="480"
    ATTRS{urbnum}=="75"
    ATTRS{version}==" 2.00"

  looking at parent device '/devices/pci0000:00/0000:00:14.0':
    KERNELS=="0000:00:14.0"
    SUBSYSTEMS=="pci"
    DRIVERS=="xhci_hcd"
    ATTRS{broken_parity_status}=="0"
    ATTRS{class}=="0x0c0330"
    ATTRS{consistent_dma_mask_bits}=="64"
    ATTRS{d3cold_allowed}=="1"
    ATTRS{dbc}=="disabled"
    ATTRS{device}=="0xa2af"
    ATTRS{dma_mask_bits}=="64"
    ATTRS{driver_override}=="(null)"
    ATTRS{enable}=="1"
    ATTRS{index}=="2"
    ATTRS{irq}=="121"
    ATTRS{label}=="Onboard - Other"
    ATTRS{local_cpulist}=="0-7"
    ATTRS{local_cpus}=="ff"
    ATTRS{msi_bus}=="1"
    ATTRS{numa_node}=="-1"
    ATTRS{revision}=="0x00"
    ATTRS{subsystem_device}=="0xa2af"
    ATTRS{subsystem_vendor}=="0x1849"
    ATTRS{vendor}=="0x8086"

  looking at parent device '/devices/pci0000:00':
    KERNELS=="pci0000:00"
    SUBSYSTEMS==""
    DRIVERS==""

• 6.上面显示了设备树中摄像头的所有父节点，一般选择离设备近的父节点的信息，而且只能选择一个父节点 。
• 7.例子

# :=表示之后不可更改
SUBSYSTEMS=="usb", ATTRS{idProduct}=="4920", ATTRS{idVendor}=="2304", MODE:="0666", SYMLINK+="my_camera"
# 或者
KERNEL=="video0", KERNELS=="1-10:1.0", MODE:="0666", SYMLINK+="my_camera"

• 8.参考这里和这里