Uevent 是内核通知 android 有状态变化的一种方法，比如USB线插入、拔出，电池电量变化等等。其本质是内核发送（可以通过 socket）一个字符串，应用层（android）接收并解释该字符串，获取相应信息。
Kernel
- uevent 的发起在 linux 内核中，通过函数
int kobject_uevent_env(struct kobject *kobj, enum kobject_action action, char *envp_ext[])发送事件
Android
- android 中通过 UEventObserver 来接收 uevent 事件
相关源码
- frameworks/base/core/java/android/os/UEventObserver.java
- frameworks/base/core/jni/android_os_UEventObserver.cpp
- hardware/libhardware_legacy/uevent.c
- hardware/libhardware_legacy/include/hardware_legacy/uevent.h
代码实例
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// UEventObserver 使用
final UEventObserver observer = new UEventObserver() {
@Override
public void onUEvent(UEvent event) {
final String value = event.get("WIRELESS_MICROPHONE_CHANNEL");
Log.d(TAG, "onUEvent() event: " + event + ", value: " + value);
if (value != null && !"ff".equals(value)) {
final String[] arr = value.split(" ");
for (int i = 0; i < arr.length; i += 2) {
if (i + 1 < arr.length) {
final GmdChannels.Table table = GmdChannels.resolveTable(null, arr[i] + arr[i + 1]);
Log.d(TAG, "onUEvent() table: " + table);
}
}
}
}
};
observer.startObserving("WIRELESS_MICROPHONE_CHANNEL");
扩展
- linux 获取热插拔事件：
udevadm monitor --env```bash monitor will print the received events for: UDEV - the event which udev sends out after rule processing KERNEL - the kernel uevent
KERNEL[439851.722529] remove /devices/pci0000:00/0000:00:14.0/usb1/1-4/1-4:1.0/ttyUSB0/tty/ttyUSB0 (tty) ACTION=remove DEVNAME=/dev/ttyUSB0 DEVPATH=/devices/pci0000:00/0000:00:14.0/usb1/1-4/1-4:1.0/ttyUSB0/tty/ttyUSB0 MAJOR=188 MINOR=0 SEQNUM=4609 SUBSYSTEM=tty
KERNEL[439851.722652] unbind /devices/pci0000:00/0000:00:14.0/usb1/1-4/1-4:1.0/ttyUSB0 (usb-serial) ACTION=unbind DEVPATH=/devices/pci0000:00/0000:00:14.0/usb1/1-4/1-4:1.0/ttyUSB0 SEQNUM=4610 SUBSYSTEM=usb-serial
KERNEL[439851.722738] remove /devices/pci0000:00/0000:00:14.0/usb1/1-4/1-4:1.0/ttyUSB0 (usb-serial) ACTION=remove DEVPATH=/devices/pci0000:00/0000:00:14.0/usb1/1-4/1-4:1.0/ttyUSB0 SEQNUM=4611 SUBSYSTEM=usb-serial
KERNEL[439851.722821] unbind /devices/pci0000:00/0000:00:14.0/usb1/1-4/1-4:1.0 (usb) ACTION=unbind DEVPATH=/devices/pci0000:00/0000:00:14.0/usb1/1-4/1-4:1.0 DEVTYPE=usb_interface INTERFACE=255/0/0 PRODUCT=67b/2303/300 SEQNUM=4612 SUBSYSTEM=usb TYPE=0/0/0
KERNEL[439851.722950] remove /devices/pci0000:00/0000:00:14.0/usb1/1-4/1-4:1.0 (usb) ACTION=remove DEVPATH=/devices/pci0000:00/0000:00:14.0/usb1/1-4/1-4:1.0 DEVTYPE=usb_interface INTERFACE=255/0/0 MODALIAS=usb:v067Bp2303d0300dc00dsc00dp00icFFisc00ip00in00 PRODUCT=67b/2303/300 SEQNUM=4613 SUBSYSTEM=usb TYPE=0/0/0
KERNEL[439851.723224] unbind /devices/pci0000:00/0000:00:14.0/usb1/1-4 (usb) ACTION=unbind BUSNUM=001 DEVNAME=/dev/bus/usb/001/007 DEVNUM=007 DEVPATH=/devices/pci0000:00/0000:00:14.0/usb1/1-4 DEVTYPE=usb_device MAJOR=189 MINOR=6 PRODUCT=67b/2303/300 SEQNUM=4614 SUBSYSTEM=usb TYPE=0/0/0
KERNEL[439851.723412] remove /devices/pci0000:00/0000:00:14.0/usb1/1-4 (usb) ACTION=remove BUSNUM=001 DEVNAME=/dev/bus/usb/001/007 DEVNUM=007 DEVPATH=/devices/pci0000:00/0000:00:14.0/usb1/1-4 DEVTYPE=usb_device MAJOR=189 MINOR=6 PRODUCT=67b/2303/300 SEQNUM=4615 SUBSYSTEM=usb TYPE=0/0/0
UDEV [439851.742306] remove /devices/pci0000:00/0000:00:14.0/usb1/1-4/1-4:1.0/ttyUSB0/tty/ttyUSB0 (tty) ACTION=remove DEVLINKS=/dev/serial/by-path/pci-0000:00:14.0-usb-0:4:1.0-port0 /dev/serial/by-id/usb-Prolific_Technology_Inc._USB-Serial_Controller-if00-port0 DEVNAME=/dev/ttyUSB0 DEVPATH=/devices/pci0000:00/0000:00:14.0/usb1/1-4/1-4:1.0/ttyUSB0/tty/ttyUSB0 ID_BUS=usb ID_MM_CANDIDATE=1 ID_MODEL=USB-Serial_Controller ID_MODEL_ENC=USB-Serial\x20Controller ID_MODEL_FROM_DATABASE=PL2303 Serial Port ID_MODEL_ID=2303 ID_PATH=pci-0000:00:14.0-usb-0:4:1.0 ID_PATH_TAG=pci-0000_00_14_0-usb-0_4_1_0 ID_PCI_CLASS_FROM_DATABASE=Serial bus controller ID_PCI_INTERFACE_FROM_DATABASE=XHCI ID_PCI_SUBCLASS_FROM_DATABASE=USB controller ID_REVISION=0300 ID_SERIAL=Prolific_Technology_Inc._USB-Serial_Controller ID_TYPE=generic ID_USB_DRIVER=pl2303 ID_USB_INTERFACES=:ff0000: ID_USB_INTERFACE_NUM=00 ID_VENDOR=Prolific_Technology_Inc. ID_VENDOR_ENC=Prolific\x20Technology\x20Inc. ID_VENDOR_FROM_DATABASE=Prolific Technology, Inc. ID_VENDOR_ID=067b MAJOR=188 MINOR=0 SEQNUM=4609 SUBSYSTEM=tty TAGS=:systemd: USEC_INITIALIZED=383000322005
UDEV [439851.745929] unbind /devices/pci0000:00/0000:00:14.0/usb1/1-4/1-4:1.0/ttyUSB0 (usb-serial) ACTION=unbind DEVPATH=/devices/pci0000:00/0000:00:14.0/usb1/1-4/1-4:1.0/ttyUSB0 SEQNUM=4610 SUBSYSTEM=usb-serial USEC_INITIALIZED=439851745784
UDEV [439851.748056] remove /devices/pci0000:00/0000:00:14.0/usb1/1-4/1-4:1.0/ttyUSB0 (usb-serial) ACTION=remove DEVPATH=/devices/pci0000:00/0000:00:14.0/usb1/1-4/1-4:1.0/ttyUSB0 SEQNUM=4611 SUBSYSTEM=usb-serial USEC_INITIALIZED=439851738136
UDEV [439851.750135] unbind /devices/pci0000:00/0000:00:14.0/usb1/1-4/1-4:1.0 (usb) ACTION=unbind DEVPATH=/devices/pci0000:00/0000:00:14.0/usb1/1-4/1-4:1.0 DEVTYPE=usb_interface INTERFACE=255/0/0 PRODUCT=67b/2303/300 SEQNUM=4612 SUBSYSTEM=usb TYPE=0/0/0 USEC_INITIALIZED=383000318053
UDEV [439851.752553] remove /devices/pci0000:00/0000:00:14.0/usb1/1-4/1-4:1.0 (usb) ACTION=remove DEVPATH=/devices/pci0000:00/0000:00:14.0/usb1/1-4/1-4:1.0 DEVTYPE=usb_interface INTERFACE=255/0/0 MODALIAS=usb:v067Bp2303d0300dc00dsc00dp00icFFisc00ip00in00 PRODUCT=67b/2303/300 SEQNUM=4613 SUBSYSTEM=usb TYPE=0/0/0 USEC_INITIALIZED=439851738527
UDEV [439851.755089] unbind /devices/pci0000:00/0000:00:14.0/usb1/1-4 (usb) ACTION=unbind BUSNUM=001 DEVNAME=/dev/bus/usb/001/007 DEVNUM=007 DEVPATH=/devices/pci0000:00/0000:00:14.0/usb1/1-4 DEVTYPE=usb_device MAJOR=189 MINOR=6 PRODUCT=67b/2303/300 SEQNUM=4614 SUBSYSTEM=usb TYPE=0/0/0 USEC_INITIALIZED=383000316424
UDEV [439851.756934] remove /devices/pci0000:00/0000:00:14.0/usb1/1-4 (usb) ACTION=remove BUSNUM=001 DEVNAME=/dev/bus/usb/001/007 DEVNUM=007 DEVPATH=/devices/pci0000:00/0000:00:14.0/usb1/1-4 DEVTYPE=usb_device MAJOR=189 MINOR=6 PRODUCT=67b/2303/300 SEQNUM=4615 SUBSYSTEM=usb TYPE=0/0/0 USEC_INITIALIZED=439851738953 ```