Support adding devices by dir

This enables cases where devices exist in a subdirectory of /dev,
particularly where those device names are not portable across machines,
which makes it problematic to specify from a runtime such as cri.

Added this to `ctr` as well so I could test that the code at least
works.

Signed-off-by: Brian Goff <cpuguy83@gmail.com>

oci/spec_opts_linux_test.go

@@ -18,9 +18,14 @@ package oci
 
 import (
 	"context"
+	"io/ioutil"
+	"os"
+	"path/filepath"
 	"testing"
 
+	"github.com/containerd/containerd/pkg/testutil"
 	specs "github.com/opencontainers/runtime-spec/specs-go"
+	"golang.org/x/sys/unix"
 )
 
 func TestAddCaps(t *testing.T) {
@@ -106,3 +111,113 @@ func TestDropCaps(t *testing.T) {
 		}
 	}
 }
+
+func TestGetDevices(t *testing.T) {
+	testutil.RequiresRoot(t)
+
+	dir, err := ioutil.TempDir("/dev", t.Name())
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(dir)
+
+	zero := filepath.Join(dir, "zero")
+	if err := ioutil.WriteFile(zero, nil, 0600); err != nil {
+		t.Fatal(err)
+	}
+
+	if err := unix.Mount("/dev/zero", zero, "", unix.MS_BIND, ""); err != nil {
+		t.Fatal(err)
+	}
+	defer unix.Unmount(filepath.Join(dir, "zero"), unix.MNT_DETACH)
+
+	t.Run("single device", func(t *testing.T) {
+		t.Run("no container path", func(t *testing.T) {
+			devices, err := getDevices(dir, "")
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			if len(devices) != 1 {
+				t.Fatalf("expected one device %v", devices)
+			}
+			if devices[0].Path != zero {
+				t.Fatalf("got unexpected device path %s", devices[0].Path)
+			}
+		})
+		t.Run("with container path", func(t *testing.T) {
+			newPath := "/dev/testNew"
+			devices, err := getDevices(dir, newPath)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			if len(devices) != 1 {
+				t.Fatalf("expected one device %v", devices)
+			}
+			if devices[0].Path != filepath.Join(newPath, "zero") {
+				t.Fatalf("got unexpected device path %s", devices[0].Path)
+			}
+		})
+	})
+	t.Run("With symlink in dir", func(t *testing.T) {
+		if err := os.Symlink("/dev/zero", filepath.Join(dir, "zerosym")); err != nil {
+			t.Fatal(err)
+		}
+		devices, err := getDevices(dir, "")
+		if err != nil {
+			t.Fatal(err)
+		}
+		if len(devices) != 1 {
+			t.Fatalf("expected one device %v", devices)
+		}
+		if devices[0].Path != filepath.Join(dir, "zero") {
+			t.Fatalf("got unexpected device path, expected %q, got %q", filepath.Join(dir, "zero"), devices[0].Path)
+		}
+	})
+	t.Run("No devices", func(t *testing.T) {
+		dir := dir + "2"
+		if err := os.MkdirAll(dir, 0755); err != nil {
+			t.Fatal(err)
+		}
+		defer os.RemoveAll(dir)
+
+		t.Run("empty dir", func(T *testing.T) {
+			devices, err := getDevices(dir, "")
+			if err != nil {
+				t.Fatal(err)
+			}
+			if len(devices) != 0 {
+				t.Fatalf("expected no devices, got %+v", devices)
+			}
+		})
+		t.Run("symlink to device in dir", func(t *testing.T) {
+			if err := os.Symlink("/dev/zero", filepath.Join(dir, "zerosym")); err != nil {
+				t.Fatal(err)
+			}
+			defer os.Remove(filepath.Join(dir, "zerosym"))
+
+			devices, err := getDevices(dir, "")
+			if err != nil {
+				t.Fatal(err)
+			}
+			if len(devices) != 0 {
+				t.Fatalf("expected no devices, got %+v", devices)
+			}
+		})
+		t.Run("regular file in dir", func(t *testing.T) {
+			if err := ioutil.WriteFile(filepath.Join(dir, "somefile"), []byte("hello"), 0600); err != nil {
+				t.Fatal(err)
+			}
+			defer os.Remove(filepath.Join(dir, "somefile"))
+
+			devices, err := getDevices(dir, "")
+			if err != nil {
+				t.Fatal(err)
+			}
+			if len(devices) != 0 {
+				t.Fatalf("expected no devices, got %+v", devices)
+			}
+		})
+	})
+}