xattr/xattr.go: Add new higher level helpers for xattr

Signed-off-by: Harshavardhana <fharshav@redhat.com>

xattr/xattr.go

@@ -0,0 +1,53 @@
+// +build linux
+
+package xattr
+
+import (
+	"syscall"
+
+	"github.com/docker/libcontainer/system"
+)
+
+func XattrEnabled(path string) bool {
+	if Setxattr(path, "user.test", "") == syscall.ENOTSUP {
+		return false
+	}
+	return true
+}
+
+func stringsfromByte(buf []byte) (result []string) {
+	offset := 0
+	for index, b := range buf {
+		if b == 0 {
+			result = append(result, string(buf[offset:index]))
+			offset = index + 1
+		}
+	}
+	return
+}
+
+func Listxattr(path string) ([]string, error) {
+	size, err := system.Llistxattr(path, nil)
+	if err != nil {
+		return nil, err
+	}
+	buf := make([]byte, size)
+	read, err := system.Llistxattr(path, buf)
+	if err != nil {
+		return nil, err
+	}
+	names := stringsfromByte(buf[:read])
+	return names, nil
+}
+
+func Getxattr(path, attr string) (string, error) {
+	value, err := system.Lgetxattr(path, attr)
+	if err != nil {
+		return "", err
+	}
+	return string(value), nil
+}
+
+func Setxattr(path, xattr, value string) error {
+	return system.Lsetxattr(path, xattr, []byte(value), 0)
+}

xattr/xattr_test.go

@@ -0,0 +1,77 @@
+// +build linux
+
+package xattr_test
+
+import (
+	"os"
+	"testing"
+
+	"github.com/docker/libcontainer/xattr"
+)
+
+func testXattr(t *testing.T) {
+	tmp := "xattr_test"
+	out, err := os.OpenFile(tmp, os.O_WRONLY, 0)
+	if err != nil {
+		t.Fatal("failed")
+	}
+	attr := "user.test"
+	out.Close()
+
+	if !xattr.XattrEnabled(tmp) {
+		t.Log("Disabled")
+		t.Fatal("failed")
+	}
+	t.Log("Success")
+
+	err = xattr.Setxattr(tmp, attr, "test")
+	if err != nil {
+		t.Fatal("failed")
+	}
+
+	var value string
+	value, err = xattr.Getxattr(tmp, attr)
+	if err != nil {
+		t.Fatal("failed")
+	}
+	if value != "test" {
+		t.Fatal("failed")
+	}
+	t.Log("Success")
+
+	var names []string
+	names, err = xattr.Listxattr(tmp)
+	if err != nil {
+		t.Fatal("failed")
+	}
+
+	var found int
+	for _, name := range names {
+		if name == attr {
+			found = 1
+		}
+	}
+	// Listxattr doesn't return trusted.* and system.* namespace
+	// attrs when run in unprevileged mode.
+	if found != 1 {
+		t.Fatal("failed")
+	}
+	t.Log("Success")
+
+	big := "0000000000000000000000000000000000000000000000000000000000000000000008c6419ad822dfe29283fb3ac98dcc5908810cb31f4cfe690040c42c144b7492eicompslf20dxmlpgz"
+	// Test for long xattrs larger than 128 bytes
+	err = xattr.Setxattr(tmp, attr, big)
+	if err != nil {
+		t.Fatal("failed to add long value")
+	}
+	value, err = xattr.Getxattr(tmp, attr)
+	if err != nil {
+		t.Fatal("failed to get long value")
+	}
+	t.Log("Success")
+
+	if value != big {
+		t.Fatal("failed, value doesn't match")
+	}
+	t.Log("Success")
+}