3 files changed, 50 insertions, 9 deletions

diff --git a/util/errors.go b/util/errors.go
index f10569e..3c87a2c 100644
--- a/util/errors.go
+++ b/util/errors.go
@@ -72,7 +72,7 @@ type ErrWriter struct {
 	err error
 }
 
-// NewErrWriter creates an ErrWriter which wraps the provided reader.
+// NewErrWriter creates an ErrWriter which wraps the provided writer.
 func NewErrWriter(writer io.Writer) *ErrWriter {
 	return &ErrWriter{w: writer, err: nil}
 }
@@ -116,7 +116,7 @@ func NeverError(err error) {
 }
 
 var (
-	// testEnvVarName is the name on an environment variable that should be
+	// testEnvVarName is the name of an environment variable that should be
 	// set to an empty mountpoint. This is only used for integration tests.
 	// If not set, integration tests are skipped.
 	testEnvVarName = "TEST_FILESYSTEM_ROOT"
diff --git a/util/util.go b/util/util.go
index 3de4a1a..1dab335 100644
--- a/util/util.go
+++ b/util/util.go
@@ -25,14 +25,17 @@ package util
 
 import (
 	"bufio"
-	"math"
+	"fmt"
+	"log"
 	"os"
 	"os/user"
 	"strconv"
 	"unsafe"
+
+	"golang.org/x/sys/unix"
 )
 
-// Ptr converts an Go byte array to a pointer to the start of the array.
+// Ptr converts a Go byte array to a pointer to the start of the array.
 func Ptr(slice []byte) unsafe.Pointer {
 	if len(slice) == 0 {
 		return nil
@@ -43,15 +46,15 @@ func Ptr(slice []byte) unsafe.Pointer {
 // ByteSlice takes a pointer to some data and views it as a slice of bytes.
 // Note, indexing into this slice is unsafe.
 func ByteSlice(ptr unsafe.Pointer) []byte {
-	// Silce must fix in 32-bit address space to build on 32-bit platforms.
-	return (*[math.MaxInt32]byte)(ptr)[:]
+	// Slice must fit in the smallest address space go supports.
+	return (*[1 << 30]byte)(ptr)[:]
 }
 
 // PointerSlice takes a pointer to an array of pointers and views it as a slice
 // of pointers. Note, indexing into this slice is unsafe.
 func PointerSlice(ptr unsafe.Pointer) []unsafe.Pointer {
-	// Silce must fix in 32-bit address space to build on 32-bit platforms.
-	return (*[math.MaxInt32 / 4]unsafe.Pointer)(ptr)[:]
+	// Slice must fit in the smallest address space go supports.
+	return (*[1 << 28]unsafe.Pointer)(ptr)[:]
 }
 
 // Index returns the first index i such that inVal == inArray[i].
@@ -118,12 +121,43 @@ func AtoiOrPanic(input string) int {
 	return i
 }
 
+// UserFromUID returns the User corresponding to the given user id.
+func UserFromUID(uid int64) (*user.User, error) {
+	return user.LookupId(strconv.FormatInt(uid, 10))
+}
+
 // EffectiveUser returns the user entry corresponding to the effective user.
 func EffectiveUser() (*user.User, error) {
-	return user.LookupId(strconv.Itoa(os.Geteuid()))
+	return UserFromUID(int64(os.Geteuid()))
 }
 
 // IsUserRoot checks if the effective user is root.
 func IsUserRoot() bool {
 	return os.Geteuid() == 0
 }
+
+// Chown changes the owner of a File to a User.
+func Chown(file *os.File, user *user.User) error {
+	uid := AtoiOrPanic(user.Uid)
+	gid := AtoiOrPanic(user.Gid)
+	return file.Chown(uid, gid)
+}
+
+// IsKernelVersionAtLeast returns true if the Linux kernel version is at least
+// major.minor. If something goes wrong it assumes false.
+func IsKernelVersionAtLeast(major, minor int) bool {
+	var uname unix.Utsname
+	if err := unix.Uname(&uname); err != nil {
+		log.Printf("Uname failed [%v], assuming old kernel", err)
+		return false
+	}
+	release := string(uname.Release[:])
+	log.Printf("Kernel version is %s", release)
+	var actualMajor, actualMinor int
+	if n, _ := fmt.Sscanf(release, "%d.%d", &actualMajor, &actualMinor); n != 2 {
+		log.Printf("Unrecognized uname format %q, assuming old kernel", release)
+		return false
+	}
+	return actualMajor > major ||
+		(actualMajor == major && actualMinor >= minor)
+}
diff --git a/util/util_test.go b/util/util_test.go
index 7739edd..70e7070 100644
--- a/util/util_test.go
+++ b/util/util_test.go
@@ -91,3 +91,10 @@ func TestNeverErrorNoPanic(t *testing.T) {
 
 	NeverError(nil)
 }
+
+func TestIsKernelVersionAtLeast(t *testing.T) {
+	// Even just running Go requires at least v2.6.23, so...
+	if !IsKernelVersionAtLeast(2, 6) {
+		t.Error("IsKernelVersionAtLeast() is broken")
+	}
+}