在本文將使用libudev庫來訪問hidraw的設備。通過libudev庫，我們可以查詢設備的廠家ID(Vendor ID, VID)，產品ID(Product ID, PID)，序列號和設備字符串等而不需要打開設備。進一步，libudev可以告訴我們在/dev目錄下設備節點的具體位置路徑，為應用程序提供一種具有足夠魯棒性而又和系統廠家獨立的訪問設備的方式。使用libudev庫，需要包含libudev.h頭文件，并且在編譯時加上-ludev告訴編譯器去鏈接udev庫。
將列出當前連接在系統中的所有hidraw設備，并且輸出它們的設備節點路徑、生產商、序列號等信息。
為了獲取這些信息，需要創建一個udev_enumerate對象，其中“hidraw”字符串作為過濾條件，
libudev將返回所有匹配這個過濾字符串的udev_device對象。
這個列子的步驟如下：
1、 初始化庫，獲取一個struct udev句柄
2、枚舉設備
3、對找到的匹配設備輸出它的節點名稱，找到實際USB設備的起始節點，打印出USB設備的IDs和序列號等，最后解引用設備對象
4、解引用枚舉對象
5、解引用udev對象
具體代碼如下:
#include <libudev.h>
#include <stdio.h>
#include <stdlib.h>
#include <locale.h>
#include <unistd.h>
int main (void)
{
struct udev *udev;
struct udev_enumerate *enumerate;
struct udev_list_entry *devices, *dev_list_entry;
struct udev_device *dev;
/* Create the udev object */
udev = udev_new();
if (!udev) {
printf("Can't create udev\n");
exit(1);
}
/* Create a list of the devices in the 'hidraw' subsystem. */
enumerate = udev_enumerate_new(udev);
udev_enumerate_add_match_subsystem(enumerate, "hidraw");
udev_enumerate_scan_devices(enumerate);
devices = udev_enumerate_get_list_entry(enumerate);
/* For each item enumerated, print out its information.
udev_list_entry_foreach is a macro which expands to
a loop. The loop will be executed for each member in
devices, setting dev_list_entry to a list entry
which contains the device's path in /sys. */
udev_list_entry_foreach(dev_list_entry, devices) {
const char *path;
/* Get the filename of the /sys entry for the device
and create a udev_device object (dev) representing it */
path = udev_list_entry_get_name(dev_list_entry);
dev = udev_device_new_from_syspath(udev, path);
/* usb_device_get_devnode() returns the path to the device node
itself in /dev. */
printf("Device Node Path: %s\n", udev_device_get_devnode(dev));
/* The device pointed to by dev contains information about
the hidraw device. In order to get information about the
USB device, get the parent device with the
subsystem/devtype pair of "usb"/"usb_device". This will
be several levels up the tree, but the function will find
it.*/
dev = udev_device_get_parent_with_subsystem_devtype(
dev,
"usb",
"usb_device");
if (!dev) {
printf("Unable to find parent usb device.");
exit(1);
}
/* From here, we can call get_sysattr_value() for each file
in the device's /sys entry. The strings passed into these
functions (idProduct, idVendor, serial, etc.) correspond
directly to the files in the directory which represents
the USB device. Note that USB strings are Unicode, UCS2
encoded, but the strings returned from
udev_device_get_sysattr_value() are UTF-8 encoded. */
printf(" VID/PID: %s %s\n",
udev_device_get_sysattr_value(dev,"idVendor"),
udev_device_get_sysattr_value(dev, "idProduct"));
printf(" %s\n %s\n",
udev_device_get_sysattr_value(dev,"manufacturer"),
udev_device_get_sysattr_value(dev,"product"));
printf(" serial: %s\n",
udev_device_get_sysattr_value(dev, "serial"));
udev_device_unref(dev);
}
/* Free the enumerator object */
udev_enumerate_unref(enumerate);
udev_unref(udev);
return 0;
}
編譯程序：
gcc -Wall -g -o udev_example udev_example.c -ludev
以上就是本文的全部內容，希望對大家的學習有所幫助，也希望大家多多支持腳本之家。
