Validate that root and state paths are different.

Using the same path for both results in confusing errors when runtime.newBundle()
attempts to create the directories for the Task

Signed-off-by: Daniel Nephin <dnephin@gmail.com>

server/server.go

@@ -39,12 +39,15 @@ import (
 
 // New creates and initializes a new containerd server
 func New(ctx context.Context, config *Config) (*Server, error) {
-	if config.Root == "" {
+	switch {
+	case config.Root == "":
 		return nil, errors.New("root must be specified")
-	}
+	case config.State == "":
-	if config.State == "" {
 		return nil, errors.New("state must be specified")
+	case config.Root == config.State:
+		return nil, errors.New("root and state must be different paths")
 	}
+
 	if err := os.MkdirAll(config.Root, 0711); err != nil {
 		return nil, err
 	}

server/server_test.go

@@ -0,0 +1,17 @@
+package server
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"golang.org/x/net/context"
+)
+
+func TestNewErrorsWithSamePathForRootAndState(t *testing.T) {
+	path := "/tmp/path/for/testing"
+	_, err := New(context.Background(), &Config{
+		Root:  path,
+		State: path,
+	})
+	assert.EqualError(t, err, "root and state must be different paths")
+}