自己动手写 Docker 系列 -- 4.1 使用 busybox 创建容器

➜  dockerDemo git:(main) ✗ ./main run -ti /bin/sh{"level":"info","msg":"conmand all is /bin/sh","time":"2022-03-17T05:44:58+08:00"}{"level":"info","msg":"memory cgroup path: /sys/fs/cgroup/memory/mydocker-cgroup","time":"2022-03-17T05:44:58+08:00"}{"level":"info","msg":"memory cgroup path: /sys/fs/cgroup/memory/mydocker-cgroup","time":"2022-03-17T05:44:58+08:00"}{"level":"info","msg":"parent process run","time":"2022-03-17T05:44:58+08:00"}{"level":"info","msg":"init come on","time":"2022-03-17T05:44:58+08:00"}{"level":"info","msg":"command: /bin/sh, args: [/bin/sh]","time":"2022-03-17T05:44:58+08:00"}{"level":"info","msg":"RunContainerInitProcess command /bin/sh, args [/bin/sh]","time":"2022-03-17T05:44:58+08:00"}{"level":"info","msg":"find path: /bin/sh","time":"2022-03-17T05:44:58+08:00"}# pwd/home/lw/code/go/dockerDemo# ls -l总用量 4668drwxrwxr-x 2 lw lw    4096 3月  17 05:44 docsdrwxrwxr-x 3 lw lw    4096 3月   7 04:55 example-rw-rw-r-- 1 lw lw     382 3月  12 10:18 go.mod-rw-rw-r-- 1 lw lw    1965 3月  12 10:18 go.sum-rw-rw-r-- 1 lw lw   11558 3月  12 10:18 LICENSE-rwxrwxr-x 1 lw lw 4741951 3月  14 20:58 maindrwxrwxr-x 6 lw lw    4096 3月  12 10:20 mydocker-rw-rw-r-- 1 lw lw     473 3月  12 10:18 README.md# mount/dev/sda2 on / type ext4 (rw,relatime,errors=remount-ro)udev on /dev type devtmpfs (rw,nosuid,noexec,relatime,size=16103592k,nr_inodes=4025898,mode=755,inode64)devpts on /dev/pts type devpts (rw,nosuid,noexec,relatime,gid=5,mode=620,ptmxmode=000)tmpfs on /dev/shm type tmpfs (rw,nosuid,nodev,inode64)hugetlbfs on /dev/hugepages type hugetlbfs (rw,relatime,pagesize=2M)mqueue on /dev/mqueue type mqueue (rw,nosuid,nodev,noexec,relatime)tmpfs on /run type tmpfs (rw,nosuid,nodev,noexec,relatime,size=3227448k,mode=755,inode64)tmpfs on /run/lock type tmpfs (rw,nosuid,nodev,noexec,relatime,size=5120k,inode64)tmpfs on /run/user/125 type tmpfs (rw,nosuid,nodev,relatime,size=3227444k,mode=700,uid=125,gid=130,inode64)gvfsd-fuse on /run/user/125/gvfs type fuse.gvfsd-fuse (rw,nosuid,nodev,relatime,user_id=125,group_id=130)tmpfs on /run/user/0 type tmpfs (rw,nosuid,nodev,relatime,size=3227444k,mode=700,inode64)gvfsd-fuse on /run/user/0/gvfs type fuse.gvfsd-fuse (rw,nosuid,nodev,relatime,user_id=0,group_id=0)nsfs on /run/docker/netns/d503d5c5cda8 type nsfs (rw)sysfs on /sys type sysfs (rw,nosuid,nodev,noexec,relatime)securityfs on /sys/kernel/security type securityfs (rw,nosuid,nodev,noexec,relatime)tmpfs on /sys/fs/cgroup type tmpfs (ro,nosuid,nodev,noexec,mode=755,inode64)cgroup2 on /sys/fs/cgroup/unified type cgroup2 (rw,nosuid,nodev,noexec,relatime,nsdelegate)cgroup on /sys/fs/cgroup/systemd type cgroup (rw,nosuid,nodev,noexec,relatime,xattr,name=systemd)cgroup on /sys/fs/cgroup/net_cls,net_prio type cgroup (rw,nosuid,nodev,noexec,relatime,net_cls,net_prio)cgroup on /sys/fs/cgroup/pids type cgroup (rw,nosuid,nodev,noexec,relatime,pids)cgroup on /sys/fs/cgroup/cpuset type cgroup (rw,nosuid,nodev,noexec,relatime,cpuset)cgroup on /sys/fs/cgroup/cpu,cpuacct type cgroup (rw,nosuid,nodev,noexec,relatime,cpu,cpuacct)cgroup on /sys/fs/cgroup/rdma type cgroup (rw,nosuid,nodev,noexec,relatime,rdma)cgroup on /sys/fs/cgroup/misc type cgroup (rw,nosuid,nodev,noexec,relatime,misc)cgroup on /sys/fs/cgroup/perf_event type cgroup (rw,nosuid,nodev,noexec,relatime,perf_event)cgroup on /sys/fs/cgroup/blkio type cgroup (rw,nosuid,nodev,noexec,relatime,blkio)cgroup on /sys/fs/cgroup/hugetlb type cgroup (rw,nosuid,nodev,noexec,relatime,hugetlb)cgroup on /sys/fs/cgroup/memory type cgroup (rw,nosuid,nodev,noexec,relatime,memory)cgroup on /sys/fs/cgroup/devices type cgroup (rw,nosuid,nodev,noexec,relatime,devices)cgroup on /sys/fs/cgroup/freezer type cgroup (rw,nosuid,nodev,noexec,relatime,freezer)pstore on /sys/fs/pstore type pstore (rw,nosuid,nodev,noexec,relatime)efivarfs on /sys/firmware/efi/efivars type efivarfs (rw,nosuid,nodev,noexec,relatime)none on /sys/fs/bpf type bpf (rw,nosuid,nodev,noexec,relatime,mode=700)debugfs on /sys/kernel/debug type debugfs (rw,nosuid,nodev,noexec,relatime)tracefs on /sys/kernel/tracing type tracefs (rw,nosuid,nodev,noexec,relatime)fusectl on /sys/fs/fuse/connections type fusectl (rw,nosuid,nodev,noexec,relatime)configfs on /sys/kernel/config type configfs (rw,nosuid,nodev,noexec,relatime)proc on /proc type proc (rw,nosuid,nodev,noexec,relatime)systemd-1 on /proc/sys/fs/binfmt_misc type autofs (rw,relatime,fd=28,pgrp=0,timeout=0,minproto=5,maxproto=5,direct,pipe_ino=26120)/var/lib/snapd/snaps/core20_1361.snap on /snap/core20/1361 type squashfs (ro,nodev,relatime,x-gdu.hide)/var/lib/snapd/snaps/bare_5.snap on /snap/bare/5 type squashfs (ro,nodev,relatime,x-gdu.hide)/var/lib/snapd/snaps/gnome-3-38-2004_99.snap on /snap/gnome-3-38-2004/99 type squashfs (ro,nodev,relatime,x-gdu.hide)/var/lib/snapd/snaps/gtk-common-themes_1519.snap on /snap/gtk-common-themes/1519 type squashfs (ro,nodev,relatime,x-gdu.hide)/var/lib/snapd/snaps/snapd_14978.snap on /snap/snapd/14978 type squashfs (ro,nodev,relatime,x-gdu.hide)/var/lib/snapd/snaps/snap-store_558.snap on /snap/snap-store/558 type squashfs (ro,nodev,relatime,x-gdu.hide)/var/lib/snapd/snaps/core20_1376.snap on /snap/core20/1376 type squashfs (ro,nodev,relatime,x-gdu.hide)/dev/nvme0n1p1 on /boot/efi type vfat (rw,relatime,fmask=0077,dmask=0077,codepage=437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro)/var/lib/snapd/snaps/snapd_15177.snap on /snap/snapd/15177 type squashfs (ro,nodev,relatime,x-gdu.hide)overlay on /var/lib/docker/overlay2/d50aa7883be1a9bfc50a2519093575713c356885fd916d5973793492bb8d2d07/merged type overlay (rw,relatime,lowerdir=/var/lib/docker/overlay2/l/6DRQTGKE2LPQHTVVITKND2RW3J:/var/lib/docker/overlay2/l/YESCAXPAOBR6LE7TQHTNL3OF4Y,upperdir=/var/lib/docker/overlay2/d50aa7883be1a9bfc50a2519093575713c356885fd916d5973793492bb8d2d07/diff,workdir=/var/lib/docker/overlay2/d50aa7883be1a9bfc50a2519093575713c356885fd916d5973793492bb8d2d07/work)proc on /proc type proc (rw,nosuid,nodev,noexec,relatime)

➜  busybox git:(main) ✗ ./main run -ti /bin/sh{"level":"info","msg":"memory cgroup path: /sys/fs/cgroup/memory/mydocker-cgroup","time":"2022-03-17T06:17:48+08:00"}{"level":"info","msg":"memory cgroup path: /sys/fs/cgroup/memory/mydocker-cgroup","time":"2022-03-17T06:17:48+08:00"}{"level":"info","msg":"all command is : /bin/sh","time":"2022-03-17T06:17:48+08:00"}{"level":"info","msg":"parent process run","time":"2022-03-17T06:17:48+08:00"}{"level":"info","msg":"init come on","time":"2022-03-17T06:17:48+08:00"}{"level":"info","msg":"current location: /home/lw/code/go/dockerDemo/busybox","time":"2022-03-17T06:17:48+08:00"}{"level":"info","msg":"find path: /bin/sh","time":"2022-03-17T06:17:48+08:00"}/ # lsbin   dev   etc   home  main  proc  root  sys   tmp   usr   var/ # mount/dev/sda2 on / type ext4 (rw,relatime,errors=remount-ro)proc on /proc type proc (rw,nosuid,nodev,noexec,relatime)/ #

docker pull busybox
// 可以看到busybox才2M不到，真小➜  dockerDemo git:(main) ✗ docker imagesREPOSITORY    TAG       IMAGE ID       CREATED        SIZEbusybox       latest    2fb6fc2d97e1   5 days ago     1.24MBhello-world   latest    feb5d9fea6a5   5 months ago   13.3kB
// 后台运行起来➜  dockerDemo git:(main) ✗ docker run -d busybox top -b29148027fac463baa870831bcbc4dcaea48d5f2253ebd95118b8c65136017021➜  dockerDemo git:(main) ✗ docker psCONTAINER ID   IMAGE     COMMAND    CREATED          STATUS          PORTS     NAMES29148027fac4   busybox   "top -b"   15 seconds ago   Up 15 seconds             loving_edison
// 打包运行的镜像，创建目录，解压到指定目录中➜  dockerDemo git:(main) ✗ docker export -o /home/lw/Downloads/busybox.tar 29148027fac4➜  dockerDemo git:(main) ✗ mkdir /opt/busybox➜  dockerDemo git:(main) ✗ tar -xvf /home/lw/Downloads/busybox.tar -C /opt/busybox/
// 可以看到和系统根目录还挺像➜  dockerDemo git:(main) ✗ ls /opt/busyboxbin  dev  etc  home  proc  root  sys  tmp  usr  var

func RunContainerInitProcess() error {  // 用setupMount代替原来的相关挂载操作  if err := setUpMount(); err != nil {    return err  }
  cmdArray := readUserCommand()  path, err := exec.LookPath(cmdArray[0])  if err != nil {    log.Errorf("can't find exec path: %s %v", cmdArray[0], err)    return err  }  log.Infof("find path: %s", path)  if err := syscall.Exec(path, cmdArray, os.Environ()); err != nil {    log.Errorf("syscall exec err: %v", err.Error())  }  return nil}
// 初始化挂载点func setUpMount() error {  // 首先设置根目录为私有模式，防止影响pivot_root，这一步是书中没有的，但没有运行不起来  if err := syscall.Mount("/", "/", "", syscall.MS_REC|syscall.MS_PRIVATE, ""); err != nil {    return fmt.Errorf("setUpMount Mount proc err: %v", err)  }
  // 获取当前路径  pwd, err := os.Getwd()  if err != nil {    return fmt.Errorf("get current location err: %v", err)  }  log.Infof("current location: %s", pwd)
  err = privotRoot(pwd)  if err != nil {    return err  }
  // mount proc  defaultMountFlags := syscall.MS_NOEXEC | syscall.MS_NOSUID | syscall.MS_NODEV  err = syscall.Mount("proc", "/proc", "proc", uintptr(defaultMountFlags), "")  if err != nil {    log.Errorf("proc挂载 failed: %v", err)    return err  }  syscall.Mount("tmpfs", "/dev", "tempfs", syscall.MS_NOSUID|syscall.MS_STRICTATIME, "mode=755")  return nil}
func privotRoot(root string) error {  // 为了使当前root的老root和新root不在同一个文件系统下，我们把root重新mount一次  // bind mount 是把相同的内容换了一个挂载点的挂载方法  if err := syscall.Mount(root, root, "bind", syscall.MS_BIND|syscall.MS_REC, ""); err != nil {    return fmt.Errorf("mount rootfs to itself error: %v", err)  }
  // 创建 rootfs、.pivot_root 存储 old_root  pivotDir := filepath.Join(root, ".pivot_root")  // 判断当前目录是否已有该文件夹  if _, err := os.Stat(pivotDir); err == nil {    // 存在则删除    if err := os.Remove(pivotDir); err != nil {      return err    }  }  if err := os.Mkdir(pivotDir, 0777); err != nil {    return fmt.Errorf("mkdir of pivot_root err: %v", err)  }
  // pivot_root 到新的rootfs，老的old_root现在挂载在rootfs/.pivot_root上  // 挂载点目前依然可以在mount命令中看到  if err := syscall.PivotRoot(root, pivotDir); err != nil {    return fmt.Errorf("pivot_root err: %v", err)  }
  // 修改当前工作目录到跟目录  if err := syscall.Chdir("/"); err != nil {    return fmt.Errorf("chdir root err: %v", err)  }
  // 取消临时文件.pivot_root的挂载并删除它  // 注意当前已经在根目录下，所以临时文件的目录也改变了  pivotDir = filepath.Join("/", ".pivot_root")  if err := syscall.Unmount(pivotDir, syscall.MNT_DETACH); err != nil {    return fmt.Errorf("unmount pivot_root dir err: %v", err)  }  return os.Remove(pivotDir)}