如何在init.rc中添加/dev/字符设备节点创建权限

android如何在init.rc中添加/dev/字符设备节点创建权限

system/core/init/init.c
system/core/init/keywords.h:77: KEYWORD(device, COMMAND, 4, do_device)
do_device
add_devperms_partners

/init.rc中我们可以为/dev/下具体设备节点的当被创建时,控制信息
on early-init
    device /dev/gpio 644 system wifi
    device /dev/snd* 664 system audio

其中*表示prefix为1,没有*表示prefix为0[luther.gliethttp]
上面的device关键字后面的system和wifi字符串描述对应的id为
static struct android_id_info android_ids[] = {
    { "root",      AID_ROOT, },
    { "system",    AID_SYSTEM, },
    { "radio",     AID_RADIO, },
    { "bluetooth", AID_BLUETOOTH, },
    { "graphics",  AID_GRAPHICS, },
    { "input",     AID_INPUT, },
    { "audio",     AID_AUDIO, },
    { "camera",    AID_CAMERA, },
    { "log",       AID_LOG, },
    { "compass",   AID_COMPASS, },
    { "mount",     AID_MOUNT, },
    { "wifi",      AID_WIFI, },
    { "dhcp",      AID_DHCP, },
    { "adb",       AID_ADB, },
    { "install",   AID_INSTALL, },
    { "media",     AID_MEDIA, },
    { "shell",     AID_SHELL, },
    { "cache",     AID_CACHE, },
    { "diag",      AID_DIAG, },
    { "net_bt_admin", AID_NET_BT_ADMIN, },
    { "net_bt",    AID_NET_BT, },
    { "sdcard_rw", AID_SDCARD_RW, },
    { "vpn",       AID_VPN, },
    { "keystore",  AID_KEYSTORE, },
    { "inet",      AID_INET, },
    { "net_raw",   AID_NET_RAW, },
    { "net_admin", AID_NET_ADMIN, },
    { "misc",      AID_MISC, },
    { "nobody",    AID_NOBODY, },
};
// =======================================
system/core/init/init.c
int main(int argc, char **argv)
{
......
    INFO("reading config file\n");
    parse_config_file("/init.rc");

    /* pull the kernel commandline and ramdisk properties file in */
    qemu_init();
    import_kernel_cmdline(0);

    get_hardware_name();
    snprintf(tmp, sizeof(tmp), "/init.%s.rc", hardware);
    parse_config_file(tmp);

// 需要在on early-init加入device
// 这样下面的device_init();创建节点动作
// 才会根据这里的对device设备的描述创建出相应权限的节点[luther.gliethttp]
    action_for_each_trigger("early-init", action_add_queue_tail);
    drain_action_queue();

// 因为device_init()将依赖sysfs文件系统提供的uevent机制
// 对builtin到kernel中的所有char,block,net等设备,
// 在/dev/目录下动态创建出对应的节点,此时会使用到
// init.rc中device添加的内容device信息,
// 因此device命令必须添加到early-init字段中
// 即[luther.gliethttp]
// on early-init
//          device /dev/gpio 644 system wifi
//          device /dev/snd* 644system audio
    INFO("device init\n");
    device_fd = device_init();
......
}