Python implementation of initrd's INIT script

#!/usr/bin/python

import os
import sys
import subprocess

# 参数表，内核参数和全局变量
opts = {
    "root"  :   "",
    "init"  :   "/sbin/init",
    "rootdelay" :   10
}

# 输出普通信息
def msg (s):
    if opts.get("quiet") == False:
        print(s)

# 输出错误信息
def err (s):
    print("ERROR: %s" % s)

# 检查设备是否存在
def poll_device (c1, c2):
    device=c1
    seconds=c2 if c2>=0 else 10

    if opts["udevd_running"]:
        import time
        import stat
        msg("Waiting %d seconds for device %s ..." % (seconds, device))
        while seconds>0:
            try:
                if stat.S_ISBLK(os.stat(device)[stat.ST_MODE]):
                    break
            except OSError:
                seconds-=1

    return os.path.lexists(device)

# 交互式命令行界面
def launch_interactive_shell ():
    import code

    class FileCacher:
        def __init__(self): self.reset()
        def reset(self): self.out = []
        def write(self,line): self.out.append(line)
        def flush(self):
            output = '\n'.join(self.out)
            self.reset()
            return output

    class Shell(code.InteractiveConsole):
        def __init__(self):
            self.stdout = sys.stdout
            self.cache = FileCacher()
            code.InteractiveConsole.__init__(self)
            return

        def get_output(self): sys.stdout = self.cache
        def return_output(self): sys.stdout = self.stdout

        def push(self,line):
            self.get_output()
            code.InteractiveConsole.push(self,line)
            self.return_output()
            output = self.cache.flush()
            print(output, end='')
            #print(output)

    sh = Shell()
    sh.interact()

# 处理内核参数
def parse_cmdline ():
    cmds = open("/proc/cmdline", "r").read().split()
    for item in cmds:
        try:
            (name, value) = item.split('=')
        except ValueError:
            name = item
            value = False
        try:
            opts[name] = int(value)
        except ValueError:
            opts[name] = value.strip()

# 从文件获取变量
def get_env_from (path):
    for line in open(path, "r"):
        exp = line.split("#")[0]
        if len(exp)>0:
            name = exp.split('=')[0].strip()
            try:
                opts[name] = exp.split('=')[1].strip()
            except IndexError:
                opts[name] = ""

# 挂载根目录
def default_mount_handler (dest):
    if not poll_device(opts["root"], opts["rootdelay"]):
            err("Root device '%s' doesn't exist." % opts["root"])
            print("You are now being dropped into an emergency shell.")
            launch_interactive_shell()

    try:
        fstype=opts["rootfstype"]
    except:
        fstype=subprocess.check_output( \
            ["/sbin/blkid","-u","filesystem","-o","value","-s","TYPE","-p",opts["root"]]) \
            .decode("ascii").strip()
        if len(fstype) == 0:
            err("Unable to determine the file system type of %s:" % opts["root"])
            print("Either it contains no filesystem, an unknown filesystem,")
            print("or more than one valid file system signature was found.")
            print()
            print("Try adding")
            print("     rootfstype=your_filesystem_type")
            print("to the kernel command line.")
            print()
            print("You are now being dropped into an emergency shell.")
            launch_interactive_shell()
            msg("Trying to continue (this will most likely fail) ...")

    flags=''
    if opts.get("rootflags"):
        if opts.get("rw")!=None:
            flags=opts.get("rootflags")+",rw"
        elif opts.get("ro")!=None:
            flags=opts.get("rootflags")+",ro"
    else:
        if opts.get("rw")!=None:
            flags="rw"
        elif opts.get("ro")!=None:
            flags="ro"

    if flags=='':
        flags="ro"

    subprocess.call(["/bin/mount", "-t", fstype, "-o", flags, opts["root"], dest])

# 主程序
if __name__ == "__main__":
    subprocess.call(["/bin/busybox", "--install", "-s"])
    subprocess.call(["/bin/mount", "-t", "proc", "proc", "/proc", "-o", "nosuid,noexec,nodev"])
    subprocess.call(["/bin/mount", "-t", "sysfs", "sys", "/sys", "-o", "nosuid,noexec,nodev"])
    subprocess.call(["/bin/mount", "-t", "tmpfs", "run", "/run", "-o", "nosuid,noexec,nodev,mode=755,size=10M"])

    if open("/proc/filesystems").read().find("devtmpfs") >= 0:
        subprocess.call(["/bin/mount", "-n", "-t", "devtmpfs", "udev", "/dev", "-o", "mode=0755,size=10M,nosuid"])
    else:
        subprocess.call(["/bin/mount", "-n", "-t", "tmpfs", "udev", "/dev", "-o", "mode=0755,size=10M,nosuid"])
        subprocess.call(["/bin/mknod", "/dev/null", "c", "1", "3"])
        subprocess.call(["/bin/mknod", "/dev/zero", "c", "1", "5"])
        subprocess.call(["/bin/mknod", "/dev/console", "c", "5", "1"])
        subprocess.call(["/bin/mknod", "/dev/mem", "c", "1", "1"])

    parse_cmdline()
    print("/sbin/modprobe", file=open("/proc/sys/kernel/modprobe", "w"))

    if os.path.lexists("/sbin/udevd"):
        msg(":: Starting udevd...")
        subprocess.call(["/sbin/udevd", "--daemon", "--resolve-names=never"])
        opts["udevd_running"]=True
        msg("done.")
    else:
        opts["udevd_running"]=False

    if opts.get("disablehooks"):
        for d in opts.get("disablehooks").split(","):
            opts["dishook_"+d]=True

    if opts.get("disablemodules"):
        for d in opts.get("disablemodules").split(","):
            opts["dismod_"+d]=True

    if opts.get("earlymodules"):
        for m in opts.get("disablehooks").split(","):
            subprocess.call(["/sbin/modprobe", "-q", m])

    get_env_from("/config")

    if opts.get("MODULES"):
        for m in opts.get("MODULES")[1:-1].split():
            if not opts.get("dismod_"+m):
                subprocess.call(["/sbin/modprobe", "-q", m])

    if os.path.isdir("/hooks") and opts.get("HOOKS"):
        # 还没完全实现，只能处理udev
        if opts.get("HOOKS").find("udev")>0:
            subprocess.call(["/sbin/udevadm", "trigger", "--action=add", "--type=subsystems"])
            subprocess.call(["/sbin/udevadm", "trigger", "--action=add", "--type=devices"])
            subprocess.call(["/sbin/udevadm", "settle"])

    if opts.get("break"):
        print(":: Break requested, type 'exit' to resume operation")
        launch_interactive_shell()

    if os.path.isfile("/message"):
        msg(file(message, "r").read())

    os.mkdir("/new_root")
    default_mount_handler("/new_root")

    if not os.path.isfile("/new_root"+opts["init"]):
        err(opts["init"]+" does not exist.")
        print("Bailing out, you are on your own. Good luck.")
        print()
        launch_interactive_shell()

    if opts["udevd_running"]:
        subprocess.call(["/sbin/udevadm", "control", "--exit"])
        subprocess.call(["/sbin/udevadm", "info", "--cleanup-db"])

    for d in ("/proc", "/sys", "/dev", "/run"):
        if os.path.isdir("/new_root"+d):
            subprocess.call(["/bin/mount", "--move", d, "/new_root"+d])
        else:
            subprocess.call(["/bin/umount", d])

    os.execv("/sbin/switch_root", \
        ["/sbin/switch_root", "-c", "/dev/console", "/new_root", opts["init"]])