libudev manual

First, initialization

First call udev_new to create a udev library context.The udev library context adopts the reference counting mechanism. The default reference count of the created context is 1. Use udev_ref and udev_unref to increase or decrease the reference count. If the reference count is 0, the internal resources are released.

Second, enumerate devices

Use udev_enumerate_new to create an enumerator that scans the system for connected devices.Use udev_enumerate_ref and udev_enumerate_unref to increase or decrease the citation count.

Use the udev_enumerate_add_match / nomatch_xxx series of functions to add enumeration filters and filter keyWords are represented by characters, such as "block" devices.

Use the udev_enumerate_scan_xxx series of functions to scan the /sys directory for all devices that match the filter.The data structure after scanning is a linked list, use udev_enumerate_get_list_entry to get the first node of the linked list, use udev_list_entry_foreach Traverse the entire linked list.

3. Monitoring device plugging and unplugging udev's equipment plugging and unplugging is implemented based on netlink.

Use udev_monitor_new_from_netlink to create a new monitor, the second parameter of the function is the name of the event source, optional "kernel" or "udev".Event notifications based on "kernel" are earlier than "udev", but the related device nodes may not be created, so the design of general applications should be monitored based on "udev".

Use udev_monitor_filter_add_match_subsystem_devtype to add a udev event filter based on device type, eg: "block" devices.

Use udev_monitor_enable_receiving to start the monitoring process.For monitoring, you can use udev_monitor_get_fd to get a file descriptor, and based on the returned fd, you can perform the poll operation to simplify program design.

After the plug event arrives, you can use udev_monitor_receive_device to get the device mapping that generated the event.Calling udev_device_get_action can get a string: "add" or "remove", and "change", "online", "offline", etc., but the last threeIt is unknown under what circumstances it will occur.

Fourth, get device information

Use udev_list_entry_get_name to get the sys path of a device node, based on this path use udev_device_new_from_syspath can create a map of udev devices, which can be used to get device properties.To get device properties use udev_device_get_properties_list_entry to return a linked list that stores all property information of the device, use udev_list_entry_foreach Traverse the list and use udev_list_entry_get_name and udev_list_entry_get_value to get the name and value of the attribute.

Reprinted: libudev instruction manual_coroutinesBlog - CSDN Blog_libudev

(SAW: Game Over!)