// froyo\init\devices.c

static struct perms_ devperms[] = {
    { "/dev/null",          0666,   AID_ROOT,       AID_ROOT,       0 },
    { "/dev/zero",          0666,   AID_ROOT,       AID_ROOT,       0 },
    { "/dev/full",          0666,   AID_ROOT,       AID_ROOT,       0 },
    { "/dev/ptmx",          0666,   AID_ROOT,       AID_ROOT,       0 },
    { "/dev/tty",           0666,   AID_ROOT,       AID_ROOT,       0 },
    { "/dev/random",        0666,   AID_ROOT,       AID_ROOT,       0 },
    { "/dev/urandom",       0666,   AID_ROOT,       AID_ROOT,       0 },
    { "/dev/ashmem",        0666,   AID_ROOT,       AID_ROOT,       0 },
    { "/dev/binder",        0666,   AID_ROOT,       AID_ROOT,       0 },
	    /* logger should be world writable (for logging) but not readable */
    { "/dev/log/",          0662,   AID_ROOT,       AID_LOG,        1 },
    /* the msm hw3d client device node is world writable/readable. */
    { "/dev/msm_hw3dc",     0666,   AID_ROOT,       AID_ROOT,       0 },
    /* gpu driver for adreno200 is globally accessible */
    { "/dev/kgsl",          0666,   AID_ROOT,       AID_ROOT,       0 },
        /* these should not be world writable */
    { "/dev/diag",          0660,   AID_RADIO,      AID_RADIO,        0 },
    

// froyo\init\init.c

device_fd = device_init();

// froyo\init\devices.c

int device_init(void)
{
    suseconds_t t0, t1;
    int fd;
    fd = open_uevent_socket(); // 1. uevent 수신하기 위한 소켓을 생성
    if(fd < 0)
        return -1;
    fcntl(fd, F_SETFD, FD_CLOEXEC);
    fcntl(fd, F_SETFL, O_NONBLOCK);
    t0 = get_usecs();
    coldboot(fd, "/sys/class");
    coldboot(fd, "/sys/block");
    coldboot(fd, "/sys/devices");
    t1 = get_usecs();
    log_event_print("coldboot %ld uS\n", ((long) (t1 - t0)));
    return fd;
}

// froyo\init\devices.c

static void coldboot(int event_fd, const char *path)
{
    DIR *d = opendir(path);
    if(d) {
        do_coldboot(event_fd, d);
        closedir(d);
    }
}

// froyo\init\devices.c

static void do_coldboot(int event_fd, DIR *d)
{
    struct dirent *de;
    int dfd, fd;
    dfd = dirfd(d);
    fd = openat(dfd, "uevent", O_WRONLY);
    if(fd >= 0) {
        write(fd, "add\n", 4);
        close(fd);
        handle_device_fd(event_fd);
    }
    while((de = readdir(d))) {
        DIR *d2;
        if(de->d_type != DT_DIR || de->d_name[0] == '.')
            continue;
        fd = openat(dfd, de->d_name, O_RDONLY | O_DIRECTORY);
        if(fd < 0)
            continue;
        d2 = fdopendir(fd);
        if(d2 == 0)
            close(fd);
        else {
            do_coldboot(event_fd, d2);
            closedir(d2);
        }
    }
}

// froyo\init\devices.c

#define UEVENT_MSG_LEN  1024
void handle_device_fd(int fd)
{
    for(;;) {
        char msg[UEVENT_MSG_LEN+2];
        char cred_msg[CMSG_SPACE(sizeof(struct ucred))];
        struct iovec iov = {msg, sizeof(msg)};
        struct sockaddr_nl snl;
        struct msghdr hdr = {&snl, sizeof(snl), &iov, 1, cred_msg, sizeof(cred_msg), 0};
        ssize_t n = recvmsg(fd, &hdr, 0);
        if (n <= 0) {
            break;
        }
        if ((snl.nl_groups != 1) || (snl.nl_pid != 0)) {
            /* ignoring non-kernel netlink multicast message */
            continue;
        }
        struct cmsghdr * cmsg = CMSG_FIRSTHDR(&hdr);
        if (cmsg == NULL || cmsg->cmsg_type != SCM_CREDENTIALS) {
            /* no sender credentials received, ignore message */
            continue;
        }
        struct ucred * cred = (struct ucred *)CMSG_DATA(cmsg);
        if (cred->uid != 0) {
            /* message from non-root user, ignore */
            continue;
        }
        if(n >= UEVENT_MSG_LEN)   /* overflow -- discard */
            continue;
        msg[n] = '\0';
        msg[n+1] = '\0';
        struct uevent uevent;
        parse_event(msg, &uevent);
        handle_device_event(&uevent);
        handle_firmware_event(&uevent);
    }
}

// froyo\init\devices.c

static void handle_device_event(struct uevent *uevent)
{

    ...

    /* are we block or char? where should we live? */
    if(!strncmp(uevent->subsystem, "block", 5)) {
        block = 1;
        base = "/dev/block/";
        mkdir(base, 0755);
    }
    
    ...
    
    if(!strcmp(uevent->action, "add")) {
        make_device(devpath, block, uevent->major, uevent->minor);
        return;
    }
    
    ...
    
}

// froyo\init\devices.c

static void make_device(const char *path, int block, int major, int minor)
{
    unsigned uid;
    unsigned gid;
    mode_t mode;
    dev_t dev;
    if(major > 255 || minor > 255)
        return;
    mode = get_device_perm(path, &uid, &gid) | (block ? S_IFBLK : S_IFCHR);
    dev = (major << 8) | minor;
    /* Temporarily change egid to avoid race condition setting the gid of the
     * device node. Unforunately changing the euid would prevent creation of
     * some device nodes, so the uid has to be set with chown() and is still
     * racy. Fixing the gid race at least fixed the issue with system_server
     * opening dynamic input devices under the AID_INPUT gid. */
    setegid(gid);
    mknod(path, mode, dev);
    chown(path, uid, -1);
    setegid(AID_ROOT);
}

// froyo\init\init.c

int main(int argc, char **argv) {
    
    ...
    
    for(;;) {
        
        ...
        
        nr = poll(ufds, fd_count, timeout);
        
        ...
        
        if (ufds[0].revents == POLLIN)
            handle_device_fd(device_fd);
        
        ...
    }
    
    ...
    
}