1// +build linux
2
3package overlay2 // import "github.com/docker/docker/daemon/graphdriver/overlay2"
4
5import (
6	"bytes"
7	"encoding/json"
8	"flag"
9	"fmt"
10	"os"
11	"runtime"
12
13	"github.com/docker/docker/pkg/reexec"
14	"golang.org/x/sys/unix"
15)
16
17func init() {
18	reexec.Register("docker-mountfrom", mountFromMain)
19}
20
21func fatal(err error) {
22	fmt.Fprint(os.Stderr, err)
23	os.Exit(1)
24}
25
26type mountOptions struct {
27	Device string
28	Target string
29	Type   string
30	Label  string
31	Flag   uint32
32}
33
34func mountFrom(dir, device, target, mType string, flags uintptr, label string) error {
35	options := &mountOptions{
36		Device: device,
37		Target: target,
38		Type:   mType,
39		Flag:   uint32(flags),
40		Label:  label,
41	}
42
43	cmd := reexec.Command("docker-mountfrom", dir)
44	w, err := cmd.StdinPipe()
45	if err != nil {
46		return fmt.Errorf("mountfrom error on pipe creation: %v", err)
47	}
48
49	output := bytes.NewBuffer(nil)
50	cmd.Stdout = output
51	cmd.Stderr = output
52	if err := cmd.Start(); err != nil {
53		w.Close()
54		return fmt.Errorf("mountfrom error on re-exec cmd: %v", err)
55	}
56	// write the options to the pipe for the untar exec to read
57	if err := json.NewEncoder(w).Encode(options); err != nil {
58		w.Close()
59		return fmt.Errorf("mountfrom json encode to pipe failed: %v", err)
60	}
61	w.Close()
62
63	if err := cmd.Wait(); err != nil {
64		return fmt.Errorf("mountfrom re-exec error: %v: output: %v", err, output)
65	}
66	return nil
67}
68
69// mountfromMain is the entry-point for docker-mountfrom on re-exec.
70func mountFromMain() {
71	runtime.LockOSThread()
72	flag.Parse()
73
74	var options *mountOptions
75
76	if err := json.NewDecoder(os.Stdin).Decode(&options); err != nil {
77		fatal(err)
78	}
79
80	if err := os.Chdir(flag.Arg(0)); err != nil {
81		fatal(err)
82	}
83
84	if err := unix.Mount(options.Device, options.Target, options.Type, uintptr(options.Flag), options.Label); err != nil {
85		fatal(err)
86	}
87
88	os.Exit(0)
89}
90