golang+shell快速实现容器运行时

docker save -o busybox.tar busybox

tar xf busybox.tar

ls020584afccce44678ec82676db80f68d50ea5c766b6e9d9601f7b5fc86dfb96d.json  busybox.tar2ec9d8fd000cf6929df9aa7a58b6d872f5588e097d18d91cadc2a08dd563d590       manifest.json79cf3ae80ddd8a3f5e5f09849fa9b8b35ade13b5c9571b534d3651c6d50668e2       repositoriesb534869c81f05ce6fbbdd3a3293e64fd032e059ab4b28a0e0d5b485cf904be4b.json

mkdir layer1 layer2tar xf 2ec9d8fd000cf6929df9aa7a58b6d872f5588e097d18d91cadc2a08dd563d590/layer.tar -C layer1tar xf 79cf3ae80ddd8a3f5e5f09849fa9b8b35ade13b5c9571b534d3651c6d50668e2/layer.tar -C layer2

mkdir ./rootfs/{merged,diff,work} -p
mount -t overlay overlay -o lowerdir=./layer1:./layer2,upperdir=./rootfs/diff,workdir=./rootfs/work ./rootfs/merged
overlayfs有以下概念：merged: 挂载点diff 是upperwork 是work

package main
import (    "flag"    "fmt"    "os"    "os/exec"    "syscall"    "path/filepath"
    "github.com/docker/docker/pkg/reexec")
func init() {    // 使用reexec注册函数，reexec提供了执行自身的方法，从而对默认的初始命名空间信息进行修改    reexec.Register("docker-shim", nsInitialisation)    if reexec.Init() {        os.Exit(0)    }}
func nsInitialisation() {    newrootPath := os.Args[1]
    // 挂载proc    if err := mountProc(newrootPath); err != nil {        fmt.Printf("Error mounting /proc - %s\n", err)        os.Exit(1)    }
    // 执行pivot_root    if err := pivotRoot(newrootPath); err != nil {        fmt.Printf("Error running pivot_root - %s\n", err)        os.Exit(1)    }
    // 配置hostname    if err := syscall.Sethostname([]byte("my-docker")); err != nil {        fmt.Printf("Error setting hostname - %s\n", err)        os.Exit(1)    }    nsRun()}
func nsRun() {    cmd := exec.Command("/bin/sh")
    cmd.Stdin = os.Stdin    cmd.Stdout = os.Stdout    cmd.Stderr = os.Stderr
    if err := cmd.Run(); err != nil {        fmt.Printf("Error running the /bin/sh command - %s\n", err)        os.Exit(1)    }}
func main() {    var rootfsPath string    flag.StringVar(&rootfsPath, "rootfs", "./rootfs/merged", "Path to the root filesystem to use")    flag.Parse()
    cmd := reexec.Command("docker-shim", rootfsPath)
    cmd.Stdin = os.Stdin    cmd.Stdout = os.Stdout    cmd.Stderr = os.Stderr
    // 创建命名空间    cmd.SysProcAttr = &syscall.SysProcAttr{        Cloneflags: syscall.CLONE_NEWNS |            syscall.CLONE_NEWUTS |            syscall.CLONE_NEWIPC |            syscall.CLONE_NEWPID |            syscall.CLONE_NEWNET |            syscall.CLONE_NEWUSER,        // UID映射        UidMappings: []syscall.SysProcIDMap{            {                ContainerID: s.Getuid(),0,                HostID:      o                Size:        1,            },        },        // GID映射        GidMappings: []syscall.SysProcIDMap{            {                ContainerID: 0,                HostID:      os.Getgid(),                Size:        1,            },        },    }
    if err := cmd.Run(); err != nil {        fmt.Printf("Error running the reexec.Command - %s\n", err)        os.Exit(1)    }}
// 相当于 pivot_root . .pivot_rootfunc pivotRoot(newroot string) error {    putold := filepath.Join(newroot, "/.pivot_root")
    // 挂载newroot到自身，目的是为了确保newroot和putold处于不同目录，    // MS_BIND：执行bind挂载，使文件或者子目录树在文件系统内的另一个点上可视。    // MS_REC：创建递归绑定挂载，递归更改传播类型    if err := syscall.Mount(newroot, newroot, "", syscall.MS_BIND|syscall.MS_REC, ""); err != nil {        return err    }
    // 创建put_old目录    if err := os.MkdirAll(putold, 0700); err != nil {        return err    }
    // 调用 pivot_root    if err := syscall.PivotRoot(newroot, putold); err != nil {        return err    }
    // 切换到根目录，不然的话为pivot_root后的当前目录    if err := os.Chdir("/"); err != nil {        return err    }
    // 卸载pivot_root    putold = "/.pivot_root"    if err := syscall.Unmount(putold, syscall.MNT_DETACH); err != nil {        return err    }
    // 删除put_old目录    if err := os.RemoveAll(putold); err != nil {        return err    }
    return nil}
// 挂载func mountProc(newroot string) error {    source := "proc"    target := filepath.Join(newroot, "/proc")    fstype := "proc"    flags := 0    data := ""
    // 创建Proc目录    os.MkdirAll(target, 0755)    // 挂载proc    // mount -t proc proc ./proc    if err := syscall.Mount(source, target, fstype, uintptr(flags), data); err != nil {        return err    }
    return nil}

go build main.go -o docker./docker

# 查找IDps -ef | grep docker-shimroot     32133 32128  0 13:07 pts/1    00:00:00 docker-shim ./rootfs/mergedroot     32149 14085  0 13:08 pts/0    00:00:00 grep --color=auto docker-shim
# 查看PID命名空间nsenter -t 32133 -n ip link showip link add veth0 type veth peer name veth1ip link set veth0 netns 32133
查看命名空间内网卡信息nsenter -t 32133 -n ip link show

ip addr add 100.100.1.1/24 dev veth1ip link set veth1 up

ip link set veth0 name  eth0ip addr add 100.100.1.2/24 dev eth0ip link set eth0 upip link set lo upip route add default via 100.100.1.1ping 100.100.1.2

iptables -t nat -A POSTROUTING -s 100.100.1.0/255.255.255.0 -o eth0 -j MASQUERADEiptables -A FORWARD -i eth0 -o veth1 -j ACCEPTiptables -A FORWARD -o eth0 -i veth1 -j ACCEPT

echo "nameserver 8.8.8.8" > /etc/resolv.confping baidu.com