pkg/cgroups: implement functions to get information from a host device

Add functions to convert a host device to a cgroup device or linux device,
the first one is used to update the device cgroup and the second one to
update the resources in the OCI spec.

Signed-off-by: Julio Montes <[email protected]>

virtcontainers/pkg/cgroups/utils.go

@@ -7,8 +7,13 @@ package cgroups
 
 import (
 	"fmt"
+	"os"
 	"path/filepath"
 	"regexp"
+
+	"github.com/opencontainers/runc/libcontainer/configs"
+	"github.com/opencontainers/runtime-spec/specs-go"
+	"golang.org/x/sys/unix"
 )
 
 // prepend a kata specific string to oci cgroup path to
@@ -63,3 +68,53 @@ func IsSystemdCgroup(cgroupPath string) bool {
 	// it's a correct systemd cgroup path.
 	return found != nil && cgroupPath[found[0]:found[1]] == cgroupPath
 }
+
+func DeviceToCgroupDevice(device string) (*configs.Device, error) {
+	var st unix.Stat_t
+	linuxDevice := configs.Device{
+		Allow:       true,
+		Permissions: "rwm",
+		Path:        device,
+	}
+
+	if err := unix.Stat(device, &st); err != nil {
+		return nil, err
+	}
+
+	devType := st.Mode & unix.S_IFMT
+
+	switch devType {
+	case unix.S_IFCHR:
+		linuxDevice.Type = 'c'
+	case unix.S_IFBLK:
+		linuxDevice.Type = 'b'
+	default:
+		return nil, fmt.Errorf("unsupported device type: %v", devType)
+	}
+
+	major := int64(unix.Major(st.Rdev))
+	minor := int64(unix.Minor(st.Rdev))
+	linuxDevice.Major = major
+	linuxDevice.Minor = minor
+
+	linuxDevice.Gid = st.Gid
+	linuxDevice.Uid = st.Uid
+	linuxDevice.FileMode = os.FileMode(st.Mode)
+
+	return &linuxDevice, nil
+}
+
+func DeviceToLinuxDevice(device string) (specs.LinuxDeviceCgroup, error) {
+	dev, err := DeviceToCgroupDevice(device)
+	if err != nil {
+		return specs.LinuxDeviceCgroup{}, err
+	}
+
+	return specs.LinuxDeviceCgroup{
+		Allow:  dev.Allow,
+		Type:   string(dev.Type),
+		Major:  &dev.Major,
+		Minor:  &dev.Minor,
+		Access: dev.Permissions,
+	}, nil
+}

virtcontainers/pkg/cgroups/utils_test.go

@@ -6,6 +6,8 @@
 package cgroups
 
 import (
+	"io/ioutil"
+	"os"
 	"path/filepath"
 	"strings"
 	"testing"
@@ -102,3 +104,60 @@ func TestValidCgroupPath(t *testing.T) {
 	}
 
 }
+
+func TestDeviceToCgroupDevice(t *testing.T) {
+	assert := assert.New(t)
+
+	f, err := ioutil.TempFile("", "device")
+	assert.NoError(err)
+	f.Close()
+
+	// fail: regular file to device
+	dev, err := DeviceToCgroupDevice(f.Name())
+	assert.Error(err)
+	assert.Nil(dev)
+
+	// fail: no such file
+	os.Remove(f.Name())
+	dev, err = DeviceToCgroupDevice(f.Name())
+	assert.Error(err)
+	assert.Nil(dev)
+
+	devPath := "/dev/null"
+	if _, err := os.Stat(devPath); os.IsNotExist(err) {
+		t.Skipf("no such device: %v", devPath)
+		return
+	}
+	dev, err = DeviceToCgroupDevice(devPath)
+	assert.NoError(err)
+	assert.NotNil(dev)
+	assert.Equal(dev.Type, 'c')
+	assert.Equal(dev.Path, devPath)
+	assert.NotZero(dev.Major)
+	assert.NotZero(dev.Minor)
+	assert.NotEmpty(dev.Permissions)
+	assert.NotZero(dev.FileMode)
+	assert.Zero(dev.Uid)
+	assert.Zero(dev.Gid)
+	assert.True(dev.Allow)
+}
+
+func TestDeviceToLinuxDevice(t *testing.T) {
+	assert := assert.New(t)
+
+	devPath := "/dev/null"
+	if _, err := os.Stat(devPath); os.IsNotExist(err) {
+		t.Skipf("no such device: %v", devPath)
+		return
+	}
+	dev, err := DeviceToLinuxDevice(devPath)
+	assert.NoError(err)
+	assert.NotNil(dev)
+	assert.Equal(dev.Type, "c")
+	assert.NotNil(dev.Major)
+	assert.NotZero(*dev.Major)
+	assert.NotNil(dev.Minor)
+	assert.NotZero(*dev.Minor)
+	assert.NotEmpty(dev.Access)
+	assert.True(dev.Allow)
+}