Android没法自动创建以usb开头的节点

Android无法自动创建以usb开头的节点

自己写了一个USB Power Control的驱动，并杯具的给节点的名字取为 usb_power_control

在Android里面整了半天不出来，自己不能创建　/dev/usb_power_control 这个节点，但是手动创建可以成功

最后只好从文件系统入手，找原因，

Android 的驱动节点创建是由 init 这个进程完成的，

init 这个进程在创建设备节点的时候，会对以“usb”为开头的设置节点进行了过滤，具体代码在：

system/core/init/devices.c

if (!strncmp(uevent->subsystem, "usb", 3)) {
            if (!strcmp(uevent->subsystem, "usb")) {
                /* This imitates the file system that would be created
                 * if we were using devfs instead.
                 * Minors are broken up into groups of 128, starting at "001"
                 */
                int bus_id = uevent->minor / 128 + 1;
                int device_id = uevent->minor % 128 + 1;
                /* build directories */
                mkdir("/dev/bus", 0755);
                mkdir("/dev/bus/usb", 0755);
                snprintf(devpath, sizeof(devpath), "/dev/bus/usb/%03d", bus_id);
                mkdir(devpath, 0755);
                snprintf(devpath, sizeof(devpath), "/dev/bus/usb/%03d/%03d", bus_id, device_id);
                devpath_ready = 1;
            } else {
                /* ignore other USB events */
                return;
            }   
        } else if (!strncmp(uevent->subsystem, "graphics", 8)) {

修改这个地方就可以自动创建/dev/usb_power_control 等以usb 开头的设备节点了。

if (!strncmp(uevent->subsystem, "usb", 3)) {
            if(!strcmp(!strncmp(name, "usb_power_control", 17)){ //add by tianfeng for usb power control
            	  base = "/dev/";
            }else if(!strcmp(!strncmp(name, "hiddev", 6)){ //add by tianfeng for /dev/usb/hiddev0
            	  
            	  base = "/dev/usb";
            	  mkdir("/dev/usb", 0755);
            }else if (!strcmp(uevent->subsystem, "usb")) {
                /* This imitates the file system that would be created
                 * if we were using devfs instead.
                 * Minors are broken up into groups of 128, starting at "001"
                 */
                int bus_id = uevent->minor / 128 + 1;
                int device_id = uevent->minor % 128 + 1;
                /* build directories */
                mkdir("/dev/bus", 0755);
                mkdir("/dev/bus/usb", 0755);
                snprintf(devpath, sizeof(devpath), "/dev/bus/usb/%03d", bus_id);
                mkdir(devpath, 0755);
                snprintf(devpath, sizeof(devpath), "/dev/bus/usb/%03d/%03d", bus_id, device_id);
                devpath_ready = 1;
            } else {
                /* ignore other USB events */
                return;
            }   
} else if (!strncmp(uevent->subsystem, "graphics", 8)) {

hiddev 这个节点不能创建也跟这个有关~~

Android没法自动创建以usb开头的节点

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