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scratch.go
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scratch.go
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package dockerlaunch
import (
"bufio"
"io"
"os"
"path"
"strings"
"syscall"
log "github.com/Sirupsen/logrus"
"github.com/rancher/docker-from-scratch/util"
)
const caCrtDir = "/etc/ssl/certs"
const caCrtName = "ca-certificates.crt"
const caCrtDefault = "/usr/etc/ssl/certs/ca-certificates.crt"
var (
mounts [][]string = [][]string{
{"devtmpfs", "/dev", "devtmpfs", ""},
{"none", "/dev/pts", "devpts", ""},
{"none", "/proc", "proc", ""},
{"none", "/run", "tmpfs", ""},
{"none", "/sys", "sysfs", ""},
{"none", "/sys/fs/cgroup", "tmpfs", ""},
{"none", "/var/run", "tmpfs", ""},
}
)
func createMounts(mounts ...[]string) error {
for _, mount := range mounts {
log.Debugf("Mounting %s %s %s %s", mount[0], mount[1], mount[2], mount[3])
err := util.Mount(mount[0], mount[1], mount[2], mount[3])
if err != nil {
return err
}
}
return nil
}
func createDirs(dirs ...string) error {
for _, dir := range dirs {
if _, err := os.Stat(dir); os.IsNotExist(err) {
log.Debugf("Creating %s", dir)
err = os.MkdirAll(dir, 0755)
if err != nil {
return err
}
}
}
return nil
}
func mountCgroups() error {
f, err := os.Open("/proc/cgroups")
if err != nil {
return err
}
defer f.Close()
scanner := bufio.NewScanner(f)
hierarchies := make(map[string][]string)
for scanner.Scan() {
fields := strings.SplitN(scanner.Text(), "\t", 2)
cgroup := fields[0]
if cgroup == "" || cgroup[0] == '#' || len(fields) < 2 {
continue
}
hierarchy := fields[1]
hierarchies[hierarchy] = append(hierarchies[hierarchy], cgroup)
}
for _, hierarchy := range hierarchies {
if err := mountCgroup(strings.Join(hierarchy, ",")); err != nil {
return err
}
}
if err = scanner.Err(); err != nil {
return err
}
log.Debug("Done mouting cgroupfs")
return nil
}
func createSymlink(src, dest string) error {
if _, err := os.Stat(dest); os.IsNotExist(err) {
log.Debugf("Symlinking %s => %s", src, dest)
if err = os.Symlink(src, dest); err != nil {
return err
}
}
return nil
}
func mountCgroup(cgroup string) error {
if err := createDirs("/sys/fs/cgroup/" + cgroup); err != nil {
return err
}
if err := createMounts([][]string{{"none", "/sys/fs/cgroup/" + cgroup, "cgroup", cgroup}}...); err != nil {
return err
}
parts := strings.Split(cgroup, ",")
if len(parts) > 1 {
for _, part := range parts {
if err := createSymlink("/sys/fs/cgroup/"+cgroup, "/sys/fs/cgroup/"+part); err != nil {
return err
}
}
}
return nil
}
func execDocker(docker string, args []string) error {
log.Debugf("Launching Docker %s %s", docker, args)
return syscall.Exec(docker, append([]string{docker}, args...), os.Environ())
}
func copyFile(src, folder, name string) error {
dst := path.Join(folder, name)
if _, err := os.Stat(dst); err == nil {
return nil
}
if err := createDirs(folder); err != nil {
return err
}
srcFile, err := os.Open(src)
if err != nil {
return err
}
defer srcFile.Close()
dstFile, err := os.Create(dst)
if err != nil {
return err
}
defer dstFile.Close()
_, err = io.Copy(dstFile, srcFile)
return err
}
func createPasswd() error {
if _, err := os.Stat("/etc/passwd"); err == nil {
return nil
}
f, err := os.Create("/etc/passwd")
if err != nil {
return err
}
defer f.Close()
_, err = f.Write([]byte("root:x:0:0:root:/root:/bin/bash\n"))
return err
}
func LaunchDocker(docker string, args ...string) error {
os.Setenv("PATH", "/sbin:/usr/sbin:/usr/bin")
if err := createPasswd(); err != nil {
return err
}
if err := createDirs("/tmp", "/root/.ssh"); err != nil {
return err
}
if err := createMounts(mounts...); err != nil {
return err
}
if err := mountCgroups(); err != nil {
return err
}
if err := copyFile(caCrtDefault, caCrtDir, caCrtName); err != nil {
return err
}
return execDocker(docker, args)
}