libcontainer: one more switch from syscall to x/sys/unix

Refactor DeviceFromPath in order to get rid of package syscall and
directly use the functions from x/sys/unix. This also allows to get rid
of the conversion from the OS-independent file mode values (from the os
package) to Linux specific values and instead let's us use the raw
file mode value directly.

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>

libcontainer/devices/devices_linux.go

@@ -2,11 +2,9 @@ package devices
 
 import (
  "errors"
- "fmt"
  "io/ioutil"
  "os"
  "path/filepath"
- "syscall" //only for Stat_t
 
  "github.com/opencontainers/runc/libcontainer/configs"
 
@@ -19,45 +17,41 @@ var (
 
 // Testing dependencies
 var (
- osLstat  = os.Lstat
+ unixLstat = unix.Lstat
  ioutilReadDir = ioutil.ReadDir
 )
 
 // Given the path to a device and its cgroup_permissions(which cannot be easily queried) look up the information about a linux device and return that information as a Device struct.
 func DeviceFromPath(path, permissions string) (*configs.Device, error) {
- fileInfo, err := osLstat(path)
+ var stat unix.Stat_t
+ err := unixLstat(path, &stat)
  if err != nil {
  return nil, err
  }
  var (
- devType rune
- mode = fileInfo.Mode()
- fileModePermissionBits = os.FileMode.Perm(mode)
+ devType rune
+ mode = stat.Mode
  )
  switch {
- case mode&os.ModeDevice == 0:
- return nil, ErrNotADevice
- case mode&os.ModeCharDevice != 0:
- fileModePermissionBits |= unix.S_IFCHR
+ case mode&unix.S_IFBLK != 0:
+ devType = 'b'
+ case mode&unix.S_IFCHR != 0:
  devType = 'c'
  default:
- fileModePermissionBits |= unix.S_IFBLK
- devType = 'b'
- }
- stat_t, ok := fileInfo.Sys().(*syscall.Stat_t)
- if !ok {
- return nil, fmt.Errorf("cannot determine the device number for device %s", path)
+ return nil, ErrNotADevice
  }
- devNumber := int(stat_t.Rdev)
+ devNumber := int(stat.Rdev)
+ uid := stat.Uid
+ gid := stat.Gid
  return &configs.Device{
  Type: devType,
  Path: path,
  Major: Major(devNumber),
  Minor: Minor(devNumber),
  Permissions: permissions,
- FileMode: fileModePermissionBits,
- Uid: stat_t.Uid,
- Gid: stat_t.Gid,
+ FileMode: os.FileMode(mode),
+ Uid: uid,
+ Gid: gid,
  }, nil
 }
 

libcontainer/devices/devices_test.go

@@ -6,14 +6,16 @@ import (
  "errors"
  "os"
  "testing"
+
+ "golang.org/x/sys/unix"
 )
 
 func TestDeviceFromPathLstatFailure(t *testing.T) {
  testError := errors.New("test error")
 
- // Override os.Lstat to inject error.
- osLstat = func(path string) (os.FileInfo, error) {
- return nil, testError
+ // Override unix.Lstat to inject error.
+ unixLstat = func(path string, stat *unix.Stat_t) error {
+ return testError
  }
 
  _, err := DeviceFromPath("", "")