Merge pull request #202 from harshavardhana/xattr_list_xattr

Update system/xattrs_linux.go

system/xattrs_linux.go

@@ -5,8 +5,35 @@ import (
 	"unsafe"
 )
 
-// Returns a nil slice and nil error if the xattr is not set
+var _zero uintptr
+
+// Returns the size of xattrs and nil error
+// Requires path, takes allocated []byte or nil as last argument
+func Llistxattr(path string, dest []byte) (size int, err error) {
+	pathBytes, err := syscall.BytePtrFromString(path)
+	if err != nil {
+		return -1, err
+	}
+	var newpathBytes unsafe.Pointer
+	if len(dest) > 0 {
+		newpathBytes = unsafe.Pointer(&dest[0])
+	} else {
+		newpathBytes = unsafe.Pointer(&_zero)
+	}
+
+	_size, _, errno := syscall.Syscall6(syscall.SYS_LLISTXATTR, uintptr(unsafe.Pointer(pathBytes)), uintptr(newpathBytes), uintptr(len(dest)), 0, 0, 0)
+	size = int(_size)
+	if errno != 0 {
+		return -1, errno
+	}
+
+	return size, nil
+}
+
+// Returns a []byte slice if the xattr is set and nil otherwise
+// Requires path and its attribute as arguments
 func Lgetxattr(path string, attr string) ([]byte, error) {
+	var sz int
 	pathBytes, err := syscall.BytePtrFromString(path)
 	if err != nil {
 		return nil, err
@@ -16,26 +43,39 @@ func Lgetxattr(path string, attr string) ([]byte, error) {
 		return nil, err
 	}
 
-	dest := make([]byte, 128)
+	// Start with a 128 length byte array
+	sz = 128
+	dest := make([]byte, sz)
 	destBytes := unsafe.Pointer(&dest[0])
-	sz, _, errno := syscall.Syscall6(syscall.SYS_LGETXATTR, uintptr(unsafe.Pointer(pathBytes)), uintptr(unsafe.Pointer(attrBytes)), uintptr(destBytes), uintptr(len(dest)), 0, 0)
-	if errno == syscall.ENODATA {
-		return nil, nil
-	}
-	if errno == syscall.ERANGE {
+	_sz, _, errno := syscall.Syscall6(syscall.SYS_LGETXATTR, uintptr(unsafe.Pointer(pathBytes)), uintptr(unsafe.Pointer(attrBytes)), uintptr(destBytes), uintptr(len(dest)), 0, 0)
+
+	switch {
+	case errno == syscall.ENODATA:
+		return nil, errno
+	case errno == syscall.ENOTSUP:
+		return nil, errno
+	case errno == syscall.ERANGE:
+		// 128 byte array might just not be good enough,
+		// A dummy buffer is used ``uintptr(0)`` to get real size
+		// of the xattrs on disk
+		_sz, _, errno = syscall.Syscall6(syscall.SYS_LGETXATTR, uintptr(unsafe.Pointer(pathBytes)), uintptr(unsafe.Pointer(attrBytes)), uintptr(unsafe.Pointer(nil)), uintptr(0), 0, 0)
+		sz = int(_sz)
+		if sz < 0 {
+			return nil, errno
+		}
 		dest = make([]byte, sz)
 		destBytes := unsafe.Pointer(&dest[0])
-		sz, _, errno = syscall.Syscall6(syscall.SYS_LGETXATTR, uintptr(unsafe.Pointer(pathBytes)), uintptr(unsafe.Pointer(attrBytes)), uintptr(destBytes), uintptr(len(dest)), 0, 0)
-	}
-	if errno != 0 {
+		_sz, _, errno = syscall.Syscall6(syscall.SYS_LGETXATTR, uintptr(unsafe.Pointer(pathBytes)), uintptr(unsafe.Pointer(attrBytes)), uintptr(destBytes), uintptr(len(dest)), 0, 0)
+		if errno != 0 {
+			return nil, errno
+		}
+	case errno != 0:
 		return nil, errno
 	}
-
+	sz = int(_sz)
 	return dest[:sz], nil
 }
 
-var _zero uintptr
-
 func Lsetxattr(path string, attr string, data []byte, flags int) error {
 	pathBytes, err := syscall.BytePtrFromString(path)
 	if err != nil {

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")
+}