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|
//go:build linux
// +build linux
package overlay
import (
"bytes"
"flag"
"fmt"
"os"
"path/filepath"
"runtime"
"strings"
"github.com/containers/storage/pkg/reexec"
"golang.org/x/sys/unix"
)
func init() {
reexec.Register("storage-mountfrom", mountOverlayFromMain)
}
func fatal(err error) {
fmt.Fprint(os.Stderr, err)
os.Exit(1)
}
type mountOptions struct {
Device string
Target string
Type string
Label string
Flag uint32
}
func mountOverlayFrom(dir, device, target, mType string, flags uintptr, label string) error {
options := &mountOptions{
Device: device,
Target: target,
Type: mType,
Flag: uint32(flags),
Label: label,
}
cmd := reexec.Command("storage-mountfrom", dir)
w, err := cmd.StdinPipe()
if err != nil {
return fmt.Errorf("mountfrom error on pipe creation: %w", err)
}
output := bytes.NewBuffer(nil)
cmd.Stdout = output
cmd.Stderr = output
if err := cmd.Start(); err != nil {
w.Close()
return fmt.Errorf("mountfrom error on re-exec cmd: %w", err)
}
// write the options to the pipe for the untar exec to read
if err := json.NewEncoder(w).Encode(options); err != nil {
w.Close()
return fmt.Errorf("mountfrom json encode to pipe failed: %w", err)
}
w.Close()
if err := cmd.Wait(); err != nil {
return fmt.Errorf("mountfrom re-exec output: %s: error: %w", output, err)
}
return nil
}
// mountfromMain is the entry-point for storage-mountfrom on re-exec.
func mountOverlayFromMain() {
runtime.LockOSThread()
flag.Parse()
var options *mountOptions
if err := json.NewDecoder(os.Stdin).Decode(&options); err != nil {
fatal(err)
}
// Mount the arguments passed from the specified directory. Some of the
// paths mentioned in the values we pass to the kernel are relative to
// the specified directory.
homedir := flag.Arg(0)
if err := os.Chdir(homedir); err != nil {
fatal(err)
}
pageSize := unix.Getpagesize()
if len(options.Label) < pageSize {
if err := unix.Mount(options.Device, options.Target, options.Type, uintptr(options.Flag), options.Label); err != nil {
fatal(err)
}
os.Exit(0)
}
// Those arguments still took up too much space. Open the diff
// directories and use their descriptor numbers as lowers, using
// /proc/self/fd as the current directory.
// Split out the various options, since we need to manipulate the
// paths, but we don't want to mess with other options.
var upperk, upperv, workk, workv, lowerk, lowerv, labelk, labelv, others string
for _, arg := range strings.Split(options.Label, ",") {
kv := strings.SplitN(arg, "=", 2)
switch kv[0] {
case "upperdir":
upperk = "upperdir="
upperv = kv[1]
case "workdir":
workk = "workdir="
workv = kv[1]
case "lowerdir":
lowerk = "lowerdir="
lowerv = kv[1]
case "label":
labelk = "label="
labelv = kv[1]
default:
if others == "" {
others = arg
} else {
others = others + "," + arg
}
}
}
// Make sure upperdir, workdir, and the target are absolute paths.
if upperv != "" && !filepath.IsAbs(upperv) {
upperv = filepath.Join(homedir, upperv)
}
if workv != "" && !filepath.IsAbs(workv) {
workv = filepath.Join(homedir, workv)
}
if !filepath.IsAbs(options.Target) {
options.Target = filepath.Join(homedir, options.Target)
}
// Get a descriptor for each lower, and use that descriptor's name as
// the new value for the list of lowers, because it's shorter.
if lowerv != "" {
lowers := strings.Split(lowerv, ":")
for i := range lowers {
lowerFd, err := unix.Open(lowers[i], unix.O_RDONLY, 0)
if err != nil {
fatal(err)
}
lowers[i] = fmt.Sprintf("%d", lowerFd)
}
lowerv = strings.Join(lowers, ":")
}
// Reconstruct the Label field.
options.Label = upperk + upperv + "," + workk + workv + "," + lowerk + lowerv + "," + labelk + labelv + "," + others
options.Label = strings.ReplaceAll(options.Label, ",,", ",")
// Okay, try this, if we managed to make the arguments fit.
var err error
if len(options.Label) < pageSize {
if err := os.Chdir("/proc/self/fd"); err != nil {
fatal(err)
}
err = unix.Mount(options.Device, options.Target, options.Type, uintptr(options.Flag), options.Label)
} else {
err = fmt.Errorf("cannot mount layer, mount data %q too large %d >= page size %d", options.Label, len(options.Label), pageSize)
}
// Clean up.
if err != nil {
fmt.Fprintf(os.Stderr, "creating overlay mount to %s, mount_data=%q\n", options.Target, options.Label)
fatal(err)
}
os.Exit(0)
}
|
