• tmpfs，虚拟内存文件系统，该文件系统被挂载到/dev目录下，主要存放设备节点文件，用户进程通过访问/dev目录下的设备节点文件可以与硬件驱动程序交互。
• devpts，一种虚拟终端文件系统
  
• proc，虚拟文件系统，被挂载到/proc目录下，通过该文件系统可与内核数据结构交互，查看以及设定内核参数。
• sysfs，虚拟文件系统，被挂载到/sys目录下，它与proc类似，是2.6内核在吸收了proc文件系统的设计经验和教训的基础上所实现的一种较新的文件系统，为内核提供了统一的设备驱动模型。（引用：http://www.ibm.com/developerworks/cn/linux/l-cn-sysfs/index.html）

    open_devnull_stdio();
    klog_init();
    property_init();

    get_hardware_name(hardware, &revision);

    process_kernel_cmdline();

    union selinux_callback cb;
    cb.func_log = log_callback;
    selinux_set_callback(SELINUX_CB_LOG, cb);

    cb.func_audit = audit_callback;
    selinux_set_callback(SELINUX_CB_AUDIT, cb);

    selinux_initialize();
    /* These directories were necessarily created before initial policy load
     * and therefore need their security context restored to the proper value.
     * This must happen before /dev is populatedproperty_init(); by ueventd.
     */
    restorecon("/dev");
    restorecon("/dev/socket");
    restorecon("/dev/__properties__");
    restorecon_recursive("/sys");

    is_charger = !strcmp(bootmode, "charger");

    INFO("property init\n");
    property_load_boot_defaults();

open_devnull_stdio()

void open_devnull_stdio(void)
{
    int fd;
    static const char *name = "/dev/__null__";
    if (mknod(name, S_IFCHR | 0600, (1 << 8) | 3) == 0) {
        fd = open(name, O_RDWR);
        unlink(name);
        if (fd >= 0) {
            dup2(fd, 0);
            dup2(fd, 1);
            dup2(fd, 2);
            if (fd > 2) {
                close(fd);
            }
            return;
        }
    }

    exit(1);
}

    1 char    Memory devices
            1 = /dev/mem      Physical memory access
            2 = /dev/kmem     Kernel virtual memory access
            3 = /dev/null     Null device
            4 = /dev/port     I/O port access
            5 = /dev/zero     Null byte source
            6 = /dev/core     OBSOLETE - replaced by /proc/kcore
            7 = /dev/full     Returns ENOSPC on write
            8 = /dev/random   Nondeterministic random number gen.
            9 = /dev/urandom  Faster, less secure random number gen.
           10 = /dev/aio      Asynchronous I/O notification interface
           11 = /dev/kmsg     Writes to this come out as printk's
           12 = /dev/oldmem   Used by crashdump kernels to access
                      the memory of the kernel that crashed.

klog_init()

void klog_init(void)
{
    static const char *name = "/dev/__kmsg__";

    if (klog_fd >= 0) return; /* Already initialized */

    if (mknod(name, S_IFCHR | 0600, (1 << 8) | 11) == 0) {
        klog_fd = open(name, O_WRONLY);
        if (klog_fd < 0)
                return;
        fcntl(klog_fd, F_SETFD, FD_CLOEXEC);
        unlink(name);
    }
}

P.S.根据unlink的mannul，（man 2 unlink)，其中写道：
If the name was the last link to a file but any processes still have the file open the  file  will  remain  in existence until the last file descriptor referring to it is closed.

static int klog_level = KLOG_DEFAULT_LEVEL;
int klog_get_level(void) {
    return klog_level;
}
void klog_set_level(int level) {
    klog_level = level;
}
#define LOG_BUF_MAX 512
void klog_vwrite(int level, const char *fmt, va_list ap)
{
    char buf[LOG_BUF_MAX];

    if (level > klog_level) return;
    if (klog_fd < 0) klog_init();
    if (klog_fd < 0) return;

    vsnprintf(buf, LOG_BUF_MAX, fmt, ap);
    buf[LOG_BUF_MAX - 1] = 0;

    write(klog_fd, buf, strlen(buf));
}

void klog_write(int level, const char *fmt, ...)
{
    va_list ap;
    va_start(ap, fmt);
    klog_vwrite(level, fmt, ap);
    va_end(ap);
}

klog.h

#define KLOG_ERROR_LEVEL   3
#define KLOG_WARNING_LEVEL 4
#define KLOG_NOTICE_LEVEL  5
#define KLOG_INFO_LEVEL    6
#define KLOG_DEBUG_LEVEL   7

#define KLOG_ERROR(tag,x...)   klog_write(KLOG_ERROR_LEVEL, "<3>" tag ": " x)
#define KLOG_WARNING(tag,x...) klog_write(KLOG_WARNING_LEVEL, "<4>" tag ": " x)
#define KLOG_NOTICE(tag,x...)  klog_write(KLOG_NOTICE_LEVEL, "<5>" tag ": " x)
#define KLOG_INFO(tag,x...)    klog_write(KLOG_INFO_LEVEL, "<6>" tag ": " x)
#define KLOG_DEBUG(tag,x...)   klog_write(KLOG_DEBUG_LEVEL, "<7>" tag ": " x)

 #define KLOG_DEFAULT_LEVEL  3  /* messages <= this level are logged */

property_init();

这一句用来初始化Android的属性系统，将在init之属性系统中专门介绍。

get_hardware_name

get_hardware_name(hardware, &revision)通过读取/proc/cpuinfo文件获取硬件信息，以笔者的山寨机为例，该文件内容如下。

shell@android:/ $ cat /proc/cpuinfo                                        
Processor       : ARMv7 Processor rev 1 (v7l)
processor       : 0
BogoMIPS        : 348.76

processor       : 1
BogoMIPS        : 348.76

processor       : 2
BogoMIPS        : 348.76

processor       : 3
BogoMIPS        : 348.76

Features        : swp half thumb fastmult vfp edsp thumbee neon vfpv3 tls vfpv4
CPU implementer : 0x41
CPU architecture: 7
CPU variant     : 0x0
CPU part        : 0xc05
CPU revision    : 1

Hardware        : QRD MSM8625Q SKUD
Revision        : 0000
Serial          : 0000000000000000

process_kernel_cmdline

接下来init程序调用函数process_kernel_cmdline解析内核启动参数。内核通常由bootloader（启动引导程序）加载启动，目前广泛使用的bootloader大都基于u-boot定制。内核允许bootloader启动自己时传递参数。在内核启动完毕之后，启动参数可通过/proc/cmdline查看。

static void process_kernel_cmdline(void)
{
    /* don't expose the raw commandline to nonpriv processes */
    chmod("/proc/cmdline", 0440);

    /* first pass does the common stuff, and finds if we are in qemu.
     * second pass is only necessary for qemu to export all kernel params
     * as props.
     */
    import_kernel_cmdline(0, import_kernel_nv);
    if (qemu[0])
        import_kernel_cmdline(1, import_kernel_nv);

    /* now propogate the info given on command line to internal variables
     * used by init as well as the current required properties
     */
    export_kernel_boot_props();
}

import_kernel_cmdline函数将/proc/cmdline内容读入到内部缓冲区中，并将cmdline内容的以空格拆分成小段字符串，依次传递给import_kernel_nv函数处理。以前面/proc/cmdline的输出为例子，该字符串共可以拆分成以下几段

qemu.gles=0
qemu=1
console=ttyS0
android.qemud=ttyS1
android.checkjni=1
ndns=1

import_kernel_nv

static void import_kernel_nv(char *name, int for_emulator)
{
    char *value = strchr(name, '=');
    int name_len = strlen(name);

    if (value == 0) return;
    *value++ = 0;
    if (name_len == 0) return;

    if (for_emulator) {
        /* in the emulator, export any kernel option with the
         * ro.kernel. prefix */
        char buff[PROP_NAME_MAX];
        int len = snprintf( buff, sizeof(buff), "ro.kernel.%s", name );

        if (len < (int)sizeof(buff))
            property_set( buff, value );
        return;
    }

    if (!strcmp(name,"qemu")) {
        strlcpy(qemu, value, sizeof(qemu));
    } else if (!strncmp(name, "androidboot.", 12) && name_len > 12) {
        const char *boot_prop_name = name + 12;
        char prop[PROP_NAME_MAX];
        int cnt;

        cnt = snprintf(prop, sizeof(prop), "ro.boot.%s", boot_prop_name);
        if (cnt < PROP_NAME_MAX)
            property_set(prop, value);
    }
}

此时回到process_kernel_cmdline函数，继续执行

if (qemu[0])
     import_kernel_cmdline(1, import_kernel_nv);

root@generic:/ # getprop | grep ro.kernel.                                     
[ro.kernel.android.checkjni]: [1]
[ro.kernel.android.qemud]: [ttyS1]
[ro.kernel.console]: [ttyS0]
[ro.kernel.ndns]: [1]
[ro.kernel.qemu.gles]: [0]
[ro.kernel.qemu]: [1]

export_kernel_boot_props()

SELinux

    union selinux_callback cb;
    cb.func_log = log_callback;
    selinux_set_callback(SELINUX_CB_LOG, cb);

    cb.func_audit = audit_callback;
    selinux_set_callback(SELINUX_CB_AUDIT, cb);

    selinux_initialize();
    /* These directories were necessarily created before initial policy load
     * and therefore need their security context restored to the proper value.
     * This must happen before /dev is populated by ueventd.
     */
    restorecon("/dev");
    restorecon("/dev/socket");
    restorecon("/dev/__properties__");
    restorecon_recursive("/sys");

回到init函数<part2>继续分析

    is_charger = !strcmp(bootmode, "charger");

    INFO("property init\n");
    property_load_boot_defaults();

接下来调用INFO宏打印一条log语句，此宏定义在init/log.h中，其实现如下

#define ERROR(x...)   KLOG_ERROR("init", x)
#define NOTICE(x...)  KLOG_NOTICE("init", x)
#define INFO(x...)    KLOG_INFO("init", x)

到这里init.c main函数之<part2>代码分析分析完毕。

接下来<part3>代码涉及init进程核心功能：init.rc解析。这部分代码逻辑我们将在独立文章《Android init源代码分析（2）init.rc解析》中介绍。