diff --git a/scstadmin/scstadmin.sysfs/scst-1.0.0/lib/SCST/SCST.pm b/scstadmin/scstadmin.sysfs/scst-1.0.0/lib/SCST/SCST.pm
index 2ac879f0a..703aa61e4 100644
--- a/scstadmin/scstadmin.sysfs/scst-1.0.0/lib/SCST/SCST.pm
+++ b/scstadmin/scstadmin.sysfs/scst-1.0.0/lib/SCST/SCST.pm
@@ -477,7 +477,7 @@ sub setScstAttribute {
 	my $attribute = shift;
 	my $value = shift;
 
-	return TRUE if (!defined($attribute) || !defined($value));
+	return TRUE if (!length($attribute) || !length($value));
 
 	my $bytes = - ENOENT;
 	my $path = make_path(SCST_ROOT_DIR(), $attribute);
@@ -523,7 +523,7 @@ sub targets {
 	my $self = shift;
 	my $driver = shift;
 
-	return (undef, "Too few arguments") if (!defined($driver));
+	return (undef, "Too few arguments") if (!length($driver));
 
 	my $tHandle = new IO::Handle;
 	my $_path = make_path(SCST_TARGETS_DIR(), $driver);
@@ -558,7 +558,7 @@ sub groups {
 	my $driver = shift;
 	my $target = shift;
 
-	return (undef, "Too few arguments") if (!defined($driver) || !defined($target));
+	return (undef, "Too few arguments") if (!length($driver) || !length($target));
 
 	my $gHandle = new IO::Handle;
 	my $_path = make_path(SCST_TARGETS_DIR(), $driver, $target,
@@ -599,8 +599,8 @@ sub initiators {
 	my @initiators;
 	my $errorString;
 
-	return (undef, "Too few arguments") if (!defined($driver) || !defined($target) ||
-			 !defined($group));
+	return (undef, "Too few arguments")
+	    if (!length($driver) || !length($target) || !length($group));
 
 	my $iHandle = new IO::Handle;
 	my $_path = make_path(SCST_TARGETS_DIR(), $driver, $target, SCST_GROUPS,
@@ -637,11 +637,11 @@ sub luns {
 	my $group = shift;
 	my $errorString;
 
-	return (undef, "Too few arguments") if (!defined($driver) || !defined($target));
+	return (undef, "Too few arguments") if (!length($driver) || !length($target));
 
 	my $_path;
 
-	if (defined($group)) {
+	if (length($group)) {
 		$_path = make_path(SCST_TARGETS_DIR(), $driver, $target,
 				   SCST_GROUPS, $group, SCST_LUNS);
 	} else {
@@ -652,7 +652,7 @@ sub luns {
 	my $lHandle = new IO::Handle;
 
 	if (!(opendir $lHandle, $_path)) {
-		if (defined($group) && $self->groupExists($driver, $target, $group) != TRUE) {
+		if (length($group) && $self->groupExists($driver, $target, $group) != TRUE) {
 			$errorString = "initiators(): Group '$group' does not exist";
 		} elsif ($self->driverExists($driver) != TRUE) {
 			$errorString = "luns(): Driver '$driver' is not available";
@@ -780,7 +780,7 @@ sub deviceGroupDevices {
 	my @devices;
 	my $errorString;
 
-	return (undef, "Too few arguments") if (!defined($group));
+	return (undef, "Too few arguments") if (!length($group));
 
 	my $dHandle = new IO::Handle;
 	my $_path = make_path(SCST_DEV_GROUP_DIR(), $group, SCST_DG_DEVICES);
@@ -812,7 +812,7 @@ sub targetGroups {
 	my @tgroups;
 	my $errorString;
 
-	return (undef, "Too few arguments") if (!defined($group));
+	return (undef, "Too few arguments") if (!length($group));
 
 	my $dHandle = new IO::Handle;
 	my $_path = make_path(SCST_DEV_GROUP_DIR(), $group, SCST_DG_TGROUPS);
@@ -845,7 +845,7 @@ sub targetGroupTargets {
 	my @targets;
 	my $errorString;
 
-	return (undef, "Too few arguments") if (!defined($group) || !defined($tgroup));
+	return (undef, "Too few arguments") if (!length($group) || !length($tgroup));
 
 	my $dHandle = new IO::Handle;
 	my $_path = make_path(SCST_DEV_GROUP_DIR(), $group, SCST_DG_TGROUPS, $tgroup);
@@ -881,7 +881,7 @@ sub driverExists {
 	my $dHandle = new IO::Handle;
 	my $result;
 
-	$result = defined($driver) &&
+	$result = length($driver) &&
 	    opendir($dHandle, make_path(SCST_TARGETS_DIR(), $driver));
 	close $dHandle if ($result);
 
@@ -895,7 +895,7 @@ sub driverDynamicAttributes {
 	my $available;
 	my $errorString;
 
-	return (undef, "Too few arguments") if (!defined($driver));
+	return (undef, "Too few arguments") if (!length($driver));
 
 	my $io = new IO::File make_path(SCST_TARGETS_DIR(), $driver,
 					SCST_MGMT_IO), O_RDONLY;
@@ -935,6 +935,8 @@ sub checkDriverDynamicAttributes {
 	my $driver = shift;
 	my $check = shift;
 
+	return TRUE if (!length($driver));
+
 	my ($available, $errorString) = $self->driverDynamicAttributes($driver);
 
 	if (!defined($available)) {
@@ -969,7 +971,7 @@ sub addDriverDynamicAttribute {
 	my $value = shift;
 
 	return SCST_C_DRV_ADDATTR_FAIL
-	    if (!defined($driver) || !defined($attribute) || !defined($value));
+	    if (!length($driver) || !defined($attribute) || !defined($value));
 
 	my ($path, $cmd);
 	$path = make_path(SCST_TARGETS_DIR(), $driver, SCST_MGMT_IO);
@@ -1007,7 +1009,7 @@ sub removeDriverDynamicAttribute {
 	my $value = shift;
 
 	return SCST_C_DRV_REMATTR_FAIL
-	    if (!defined($driver) || !defined($attribute) || !defined($value));
+	    if (!length($driver) || !defined($attribute) || !defined($value));
 
 	my ($path, $cmd);
 	$path = make_path(SCST_TARGETS_DIR(), $driver, SCST_MGMT_IO);
@@ -1043,7 +1045,7 @@ sub targetExists {
 	my $driver = shift;
 	my $target = shift;
 
-	return defined($driver) && defined($target) &&
+	return length($driver) && length($target) &&
 	    $target ne '.' && $target ne '..' && $target ne 'module' &&
 	    (-d make_path(SCST_TARGETS_DIR(), $driver, $target)) ? TRUE : FALSE;
 }
@@ -1061,7 +1063,7 @@ sub targetType {
 	my $target = shift;
 	my $errorString;
 
-	return (undef, "Too few arguments") if (!defined($driver) || !defined($target));
+	return (undef, "Too few arguments") if (!length($driver) || !length($target));
 
 	if ($self->driverIsVirtualCapable($driver)) {
 		my $attribs;
@@ -1138,7 +1140,7 @@ sub targetDynamicAttributes {
 	my $available;
 	my $errorString;
 
-	return (undef, "Too few arguments") if (!defined($driver));
+	return (undef, "Too few arguments") if (!length($driver));
 
 	my $io = new IO::File make_path(SCST_TARGETS_DIR(), $driver,
 					SCST_MGMT_IO), O_RDONLY;
@@ -1213,7 +1215,7 @@ sub addTargetDynamicAttribute {
 	my $value = shift;
 
 	return SCST_C_TGT_ADDATTR_FAIL
-	    if (!defined($driver) || !defined($target) ||
+	    if (!length($driver) || !defined($target) ||
 		!defined($attribute) || !defined($value));
 
 	my ($path, $cmd);
@@ -1455,8 +1457,8 @@ sub addGroup {
 	my $target = shift;
 	my $group = shift;
 
-	return SCST_C_GRP_ADD_FAIL if (!defined($driver) || !defined($target) ||
-				       !defined($group));
+	return SCST_C_GRP_ADD_FAIL if (!length($driver) || !length($target) ||
+				       !length($group));
 
 	my ($path, $cmd);
 	$path = make_path(SCST_TARGETS_DIR(), $driver, $target, SCST_GROUPS,
@@ -1496,8 +1498,8 @@ sub removeGroup {
 	my $target = shift;
 	my $group = shift;
 
-	return SCST_C_GRP_REM_FAIL if (!defined($driver) || !defined($target) ||
-				       !defined($group));
+	return SCST_C_GRP_REM_FAIL if (!length($driver) || !length($target) ||
+				       !length($group));
 
 	my ($path, $cmd);
 	$path = make_path(SCST_TARGETS_DIR(), $driver, $target, SCST_GROUPS,
@@ -1594,7 +1596,7 @@ sub addDeviceGroupDevice {
 	my $dgroups;
 	my $errorString;
 
-	return SCST_C_DGRP_ADD_DEV_FAIL if (!defined($group) || !defined($device));
+	return SCST_C_DGRP_ADD_DEV_FAIL if (!length($group) || !length($device));
 
 	my ($path, $cmd);
 	$path = make_path(SCST_DEV_GROUP_DIR(), $group, SCST_DG_DEVICES,
@@ -1644,8 +1646,7 @@ sub addTargetGroup {
 	my $group = shift;
 	my $tgroup = shift;
 
-	return SCST_C_DGRP_ADD_GRP_FAIL if (!defined($group) ||
-					    !defined($tgroup));
+	return SCST_C_DGRP_ADD_GRP_FAIL if (!length($group) || !length($tgroup));
 
 	my ($path, $cmd);
 	$path = make_path(SCST_DEV_GROUP_DIR(), $group, SCST_DG_TGROUPS,
@@ -1679,9 +1680,8 @@ sub addTargetGroupTarget {
 	my $tgroup = shift;
 	my $tgt = shift;
 
-	return SCST_C_TGRP_ADD_TGT_FAIL if (!defined($group) ||
-					    !defined($tgroup) ||
-					    !defined($tgt));
+	return SCST_C_TGRP_ADD_TGT_FAIL
+	    if (!length($group) || !length($tgroup) || !length($tgt));
 
 	my ($path, $cmd);
 	$path = make_path(SCST_DEV_GROUP_DIR(), $group, SCST_DG_TGROUPS,
@@ -1717,7 +1717,7 @@ sub removeDeviceGroupDevice {
 	my $group = shift;
 	my $device = shift;
 
-	return SCST_C_DGRP_REM_DEV_FAIL if (!defined($group) || !defined($device));
+	return SCST_C_DGRP_REM_DEV_FAIL if (!length($group) || !length($device));
 
 	my ($path, $cmd);
 	$path = make_path(SCST_DEV_GROUP_DIR(), $group, SCST_DG_DEVICES,
@@ -1756,7 +1756,7 @@ sub removeTargetGroup {
 	my $group = shift;
 	my $tgroup = shift;
 
-	return SCST_C_DGRP_REM_GRP_FAIL if (!defined($group) || !defined($tgroup));
+	return SCST_C_DGRP_REM_GRP_FAIL if (!length($group) || !length($tgroup));
 
 	my ($path, $cmd);
 	$path = make_path(SCST_DEV_GROUP_DIR(), $group, SCST_DG_TGROUPS,
@@ -1792,7 +1792,7 @@ sub removeTargetGroupTarget {
 	my $tgroup = shift;
 	my $tgt = shift;
 
-	return SCST_C_TGRP_REM_TGT_FAIL if (!defined($group) || !defined($tgroup) || !defined($tgt));
+	return SCST_C_TGRP_REM_TGT_FAIL if (!length($group) || !length($tgroup) || !length($tgt));
 
 	my ($path, $cmd);
 	$path = make_path(SCST_DEV_GROUP_DIR(), $group, SCST_DG_TGROUPS,
@@ -1834,8 +1834,8 @@ sub addInitiator {
 	my $initiator = shift;
 
 	return SCST_C_GRP_ADD_INI_FAIL
-	    if (!defined($driver) || !defined($target) ||
-		!defined($group) || !defined($initiator));
+	    if (!length($driver) || !length($target) ||
+		!length($group) || !length($initiator));
 
 	my ($path, $cmd);
 	$path = make_path(SCST_TARGETS_DIR(), $driver, $target, SCST_GROUPS,
@@ -1854,9 +1854,9 @@ sub addInitiator {
 		return FALSE if ($self->{'debug'} || $bytes > 0);
 	}
 
-	return SCST_C_GRP_REM_INI_FAIL if (!defined($driver) ||
-					   !defined($target) ||
-					   !defined($initiator));
+	return SCST_C_GRP_REM_INI_FAIL if (!length($driver) ||
+					   !length($target) ||
+					   !length($initiator));
 
 	my $rc = $self->driverExists($driver);
 	return SCST_C_DRV_NO_DRIVER if (!$rc);
@@ -1884,7 +1884,7 @@ sub removeInitiator {
 	my $group = shift;
 	my $initiator = shift;
 
-	return SCST_C_GRP_REM_INI_FAIL if (!defined($driver) || !defined($target) || !defined($group) || !defined($initiator));
+	return SCST_C_GRP_REM_INI_FAIL if (!length($driver) || !length($target) || !length($group) || !length($initiator));
 
 	my ($path, $cmd);
 	$path = make_path(SCST_TARGETS_DIR(), $driver, $target, SCST_GROUPS,
@@ -2021,12 +2021,12 @@ sub addLun {
 	my $attributes = shift;
 	my $group = shift;
 
-	my $err = defined($group) ? SCST_C_GRP_ADD_LUN_FAIL :
+	my $err = length($group) ? SCST_C_GRP_ADD_LUN_FAIL :
 	    SCST_C_TGT_ADD_LUN_FAIL;
 
-	return $err if (!defined($driver) || !defined($target) ||
-			!defined($device) || !defined($lun) ||
-			!defined($attributes));
+	return $err if (!length($driver) || !length($target) ||
+			!length($device) || !length($lun) ||
+			!length($attributes));
 
 	my $o_string = "";
 	foreach my $attribute (keys %{$attributes}) {
@@ -2037,7 +2037,7 @@ sub addLun {
 	$o_string =~ s/\s$//;
 
 	my ($path, $cmd);
-	if (defined($group)) {
+	if (length($group)) {
 		$path = make_path(SCST_TARGETS_DIR(), $driver, $target,
 				  SCST_GROUPS, $group, SCST_LUNS, SCST_MGMT_IO);
 	} else {
@@ -2059,14 +2059,14 @@ sub addLun {
 		return FALSE if ($self->{'debug'} || $bytes > 0);
 	}
 
-	if (defined($group)) {
+	if (length($group)) {
 		my $rc = $self->groupExists($driver, $target, $group);
 		return SCST_C_GRP_NO_GROUP if (!$rc);
 		return $rc if ($rc > 1);
 	}
 
 	my $rc = $self->lunExists($driver, $target, $lun, $group);
-	return (defined($group) ? SCST_C_GRP_LUN_EXISTS :
+	return (length($group) ? SCST_C_GRP_LUN_EXISTS :
 		SCST_C_TGT_LUN_EXISTS) if ($rc == TRUE);
 	return $rc if ($rc > 1);
 
@@ -2096,14 +2096,14 @@ sub removeLun {
 	my $lun = shift;
 	my $group = shift;
 
-	my $err = defined($group) ? SCST_C_GRP_REM_LUN_FAIL :
+	my $err = length($group) ? SCST_C_GRP_REM_LUN_FAIL :
 	    SCST_C_TGT_ADD_LUN_FAIL;
 
-	return $err if (!defined($driver) || !defined($target) ||
-			!defined($lun));
+	return $err if (!length($driver) || !length($target) ||
+			!length($lun));
 
 	my ($path, $cmd);
-	if (defined($group)) {
+	if (length($group)) {
 		$path = make_path(SCST_TARGETS_DIR(), $driver, $target,
 				  SCST_GROUPS, $group, SCST_LUNS,
 				  SCST_MGMT_IO);
@@ -2133,14 +2133,14 @@ sub removeLun {
 	return SCST_C_TGT_NO_TARGET if (!$rc);
 	return $rc if ($rc > 1);
 
-	if (defined($group)) {
+	if (length($group)) {
 		$rc = $self->groupExists($driver, $target, $group);
 		return SCST_C_GRP_NO_GROUP if (!$rc);
 		return $rc if ($rc > 1);
 	}
 
 	$rc = $self->lunExists($driver, $target, $lun, $group);
-	return (defined($group) ? SCST_C_GRP_NO_LUN : SCST_C_TGT_NO_LUN)
+	return (length($group) ? SCST_C_GRP_NO_LUN : SCST_C_TGT_NO_LUN)
 	    if (!$rc);
 	return $rc if ($rc > 1);
 
@@ -2158,7 +2158,7 @@ sub replaceLun {
 
 	my $err;
 
-	return TRUE if (!defined($lun));
+	return TRUE if (!length($lun));
 
 	my $rc = $self->driverExists($driver);
 	return SCST_C_DRV_NO_DRIVER if (!$rc);
@@ -2168,7 +2168,7 @@ sub replaceLun {
 	return SCST_C_TGT_NO_TARGET if (!$rc);
 	return $rc if ($rc > 1);
 
-	if (defined($group)) {
+	if (length($group)) {
 		$rc = $self->groupExists($driver, $target, $group);
 		return SCST_C_GRP_NO_GROUP if (!$rc);
 		return $rc if ($rc > 1);
@@ -2228,13 +2228,13 @@ sub clearLuns {
 	my $target = shift;
 	my $group = shift;
 
-	my $err = defined($group) ? SCST_C_GRP_CLR_LUN_FAIL :
+	my $err = length($group) ? SCST_C_GRP_CLR_LUN_FAIL :
 	    SCST_C_TGT_CLR_LUN_FAIL;
 
-	return $err if (!defined($driver) || !defined($target));
+	return $err if (!length($driver) || !length($target));
 
 	my ($path, $cmd);
-	if (defined($group)) {
+	if (length($group)) {
 		$path = make_path(SCST_TARGETS_DIR(), $driver, $target,
 				  SCST_GROUPS, $group, SCST_LUNS,
 				  SCST_MGMT_IO);
@@ -2264,7 +2264,7 @@ sub clearLuns {
 	return SCST_C_TGT_NO_TARGET if (!$rc);
 	return $rc if ($rc > 1);
 
-	if (defined($group)) {
+	if (length($group)) {
 		$rc = $self->groupExists($driver, $target, $group);
 		return SCST_C_GRP_NO_GROUP if (!$rc);
 		return $rc if ($rc > 1);
@@ -2277,6 +2277,8 @@ sub deviceHandler {
 	my $self = shift;
 	my $device = shift;
 
+	return undef if (!length($device));
+
 	my $handler = readlink(make_path(SCST_DEVICES_DIR(), $device,
 					 'handler'));
 	$handler =~ s/.*\///;
@@ -2289,7 +2291,7 @@ sub devices {
 	my @devices;
 
 	my $dHandle = new IO::Handle;
-	my $_path = !defined($handler) ? SCST_DEVICES_DIR() :
+	my $_path = !length($handler) ? SCST_DEVICES_DIR() :
 	    make_path(SCST_HANDLERS_DIR(), $handler);
 	if (!(opendir $dHandle, $_path)) {
 		return (undef, "devices(): Unable to read directory '$_path': $!");
@@ -2299,7 +2301,7 @@ sub devices {
 		next if ($device eq '.' || $device eq '..');
 
 		my $isdev = (-d make_path(SCST_DEVICES_DIR(), $device));
-		if ($isdev && (!defined($handler) ||
+		if ($isdev && (!length($handler) ||
 			       $handler eq $self->deviceHandler($device))) {
 			push @devices, $device;
 		}
@@ -2314,11 +2316,11 @@ sub deviceOpen {
 	my $self = shift;
 	my $device = shift;
 
-	return FALSE if (!defined($device));
+	return FALSE if (!length($device));
 
 	my ($devices, $errorString) = $self->devices();
 
-	return SCST_C_FATAL_ERROR if (!defined($devices));
+	return SCST_C_FATAL_ERROR if (!length($devices));
 
 	foreach my $_device (@{$devices}) {
 		return TRUE if ($device eq $_device);
@@ -2570,7 +2572,7 @@ sub setDriverAttribute {
 	my $attribute = shift;
 	my $value = shift;
 
-	return TRUE if (!defined($attribute) || !defined($value));
+	return TRUE if (!length($attribute) || !length($value));
 
 	my $path = make_path(SCST_TARGETS_DIR(), $driver, $attribute);
 
@@ -2601,7 +2603,7 @@ sub targetAttributes {
 	my %attributes = ( );
 	my $errorString;
 
-	return (undef, "Too few arguments") if (!defined($driver) || !defined($target));
+	return (undef, "Too few arguments") if (!length($driver) || !length($target));
 
 	my $pHandle = new IO::Handle;
 	my $_path = make_path(SCST_TARGETS_DIR(), $driver, $target);
@@ -2705,7 +2707,8 @@ sub setTargetAttribute {
 	my $attribute = shift;
 	my $value = shift;
 
-	return TRUE if (!defined($attribute) || !defined($value));
+	return TRUE if (!length($driver) || !length($target) ||
+			!length($attribute) || !length($value));
 
 	my ($path, $cmd);
 	$path = make_path(SCST_TARGETS_DIR(), $driver, $target, $attribute);
@@ -2830,7 +2833,7 @@ sub setGroupAttribute {
 	my $attribute = shift;
 	my $value = shift;
 
-	return TRUE if (!defined($attribute) || !defined($value));
+	return TRUE if (!length($attribute) || !length($value));
 
 	my ($path, $cmd);
 	$path = make_path(SCST_TARGETS_DIR(), $driver, $target, SCST_GROUPS,
@@ -2876,7 +2879,7 @@ sub lunAttributes {
 
 	my ($_path, $luncrattr);
 
-	if (defined($group)) {
+	if (length($group)) {
 		$_path = make_path(SCST_TARGETS_DIR(), $driver, $target,
 				   SCST_GROUPS, $group, SCST_LUNS, $lun);
 		($luncrattr, $errorString) =
@@ -2893,7 +2896,7 @@ sub lunAttributes {
 			$errorString = "lunAttributes(): Driver '$driver' is not available";
 		} elsif ($self->targetExists($driver, $target) != TRUE) {
 			$errorString = "lunAttributes(): Target '$target' is not available";
-		} elsif (defined($group) && $self->groupExists($driver, $target, $group) != TRUE) {
+		} elsif (length($group) && $self->groupExists($driver, $target, $group) != TRUE) {
 			$errorString = "lunAttributes(): Group '$group' does not exist";
 		} elsif ($self->lunExists($driver, $target, $lun, $group) != TRUE) {
 			$errorString = "lunAttributes(): LUN '$lun' does not exist";
@@ -2980,12 +2983,12 @@ sub setLunAttribute {
 	my $group = shift;
 
 	return SCST_C_LUN_SETATTR_FAIL
-	    if (!defined($driver) || !defined($target) || !defined($lun) ||
-		!defined($attribute) || !defined($value));
+	    if (!length($driver) || !length($target) || !length($lun) ||
+		!length($attribute) || !length($value));
 
 	my $path;
 
-	if (defined($group)) {
+	if (length($group)) {
 		$path = make_path(SCST_TARGETS_DIR(), $driver, $target,
 				  SCST_GROUPS, $group, SCST_LUNS, $lun,
 				  $attribute);
@@ -3014,14 +3017,14 @@ sub setLunAttribute {
 	return SCST_C_TGT_NO_TARGET if (!$rc);
 	return $rc if ($rc > 1);
 
-	if (defined($group)) {
+	if (length($group)) {
 		$rc = $self->groupExists($driver, $target, $group);
 		return SCST_C_GRP_NO_GROUP if (!$rc);
 		return $rc if ($rc > 1);
 	}
 
 	$rc = $self->lunExists($driver, $target, $lun, $group);
-	return (defined($group) ? SCST_C_GRP_NO_LUN : SCST_C_TGT_NO_LUN)
+	return (length($group) ? SCST_C_GRP_NO_LUN : SCST_C_TGT_NO_LUN)
 	    if (!$rc);
 	return $rc if ($rc > 1);
 
@@ -3131,7 +3134,7 @@ sub setInitiatorAttribute {
 	my $attribute = shift;
 	my $value = shift;
 
-	return TRUE if (!defined($attribute) || !defined($value));
+	return TRUE if (!length($attribute) || !length($value));
 
 	my $path = make_path(SCST_TARGETS_DIR(), $driver, $target, SCST_GROUPS,
 			     $group, SCST_LUNS, $initiator, $attribute);
@@ -3418,7 +3421,7 @@ sub setAluaAttribute {
 	my $attribute = shift;
 	my $value = shift;
 
-	return TRUE if (!defined($attribute) || !defined($value));
+	return TRUE if (!length($attribute) || !length($value));
 
 	my $bytes = - ENOENT;
 	my $path = make_path(SCST_DEV_GROUP_DIR(), $attribute);
@@ -3443,7 +3446,7 @@ sub setDeviceGroupAttribute {
 	my $attribute = shift;
 	my $value = shift;
 
-	return TRUE if (!defined($attribute) || !defined($value));
+	return TRUE if (!length($attribute) || !length($value));
 
 	my $bytes = - ENOENT;
 	my $path = make_path(SCST_DEV_GROUP_DIR(), $group, $attribute);
@@ -3473,8 +3476,8 @@ sub setTargetGroupAttribute {
 	my $attribute = shift;
 	my $value = shift;
 
-	return TRUE if (!defined($group) || !defined($tgroup) ||
-			!defined($attribute) || !defined($value));
+	return TRUE if (!length($group) || !length($tgroup) ||
+			!length($attribute) || !length($value));
 
 	my $bytes = - ENOENT;
 	my $path = make_path(SCST_DEV_GROUP_DIR(), $group, SCST_DG_TGROUPS, $tgroup, $attribute);
@@ -3509,9 +3512,9 @@ sub setTargetGroupTargetAttribute {
 	my $attribute = shift;
 	my $value = shift;
 
-	return TRUE if (!defined($group) || !defined($tgroup) ||
-			!defined($tgt) || !defined($attribute) ||
-			!defined($value));
+	return TRUE if (!length($group) || !length($tgroup) ||
+			!length($tgt) || !length($attribute) ||
+			!length($value));
 
 	my $bytes = - ENOENT;
 	my $path = make_path(SCST_DEV_GROUP_DIR(), $group, SCST_DG_TGROUPS,
@@ -3572,7 +3575,7 @@ sub handlerExists {
 	my $self = shift;
 	my $handler = shift;
 
-	return FALSE if (!defined($handler));
+	return FALSE if (!length($handler));
 
 	my ($handlers, $errorString) = $self->handlers();
 
@@ -3591,7 +3594,7 @@ sub setHandlerAttribute {
 	my $attribute = shift;
 	my $value = shift;
 
-	return TRUE if (!defined($attribute) || !defined($value));
+	return TRUE if (!length($attribute) || !length($value));
 
 	my $bytes = - ENOENT;
 	my $path = make_path(SCST_HANDLERS_DIR(), $handler, $attribute);
@@ -3821,6 +3824,8 @@ sub deviceCreateAttributes {
 	my %attributes = ( );
 	my $errorString;
 
+	return (undef, "missing handler argument") if (!length($handler));
+
 	my $io = new IO::File make_path(SCST_HANDLERS_DIR(), $handler,
 					SCST_MGMT_IO), O_RDONLY;
 
@@ -3860,9 +3865,8 @@ sub openDevice {
 	my $device = shift;
 	my $attributes = shift;
 
-	return SCST_C_DEV_OPEN_FAIL if (!defined($handler) ||
-					!defined($device) ||
-					!defined($attributes));
+	return SCST_C_DEV_OPEN_FAIL
+	    if (!length($handler) || !length($device) || !length($attributes));
 
 	my $o_string = "";
 	foreach my $attribute (keys %{$attributes}) {
@@ -3912,8 +3916,7 @@ sub closeDevice {
 	my $handler = shift;
 	my $device = shift;
 
-	return SCST_C_DEV_CLOSE_FAIL if (!defined($handler) ||
-					 !defined($device));
+	return SCST_C_DEV_CLOSE_FAIL if (!length($handler) || !length($device));
 
 	my ($path, $cmd);
 	$path = make_path(SCST_HANDLERS_DIR(), $handler, SCST_MGMT_IO);
@@ -4196,7 +4199,7 @@ sub lunCreateAttributes {
 
 	my $_path;
 
-	if (defined($group)) {
+	if (length($group)) {
 		$_path = make_path(SCST_TARGETS_DIR(), $driver, $target,
 				   SCST_GROUPS, $group, SCST_LUNS,
 				   SCST_MGMT_IO);
@@ -4214,7 +4217,7 @@ sub lunCreateAttributes {
 		} elsif ($self->targetExists($driver, $target) != TRUE) {
 			$errorString = "lunCreateAttributes(): Target '$target' ".
 			    "is not available";
-		} elsif (defined($group) && $self->groupExists($driver, $target, $group) != TRUE) {
+		} elsif (length($group) && $self->groupExists($driver, $target, $group) != TRUE) {
 			$errorString = "lunCreateAttributes(): Group '$group' ".
 			    "does not exist";
 		} else {
@@ -4341,7 +4344,7 @@ sub sessions {
 	my %_sessions;
 	my $errorString;
 
-	return (undef, "Too few arguments") if (!defined($driver) || !defined($target));
+	return (undef, "Too few arguments") if (!length($driver) || !length($target));
 
 	my $sHandle = new IO::Handle;
 	my $_path = make_path(SCST_TARGETS_DIR(), $driver, $target,
diff --git a/scstadmin/scstadmin.sysfs/scstadmin b/scstadmin/scstadmin.sysfs/scstadmin
index 9dd72273c..0c4ee447e 100755
--- a/scstadmin/scstadmin.sysfs/scstadmin
+++ b/scstadmin/scstadmin.sysfs/scstadmin
@@ -1497,7 +1497,8 @@ sub serializeKeyAttr {
 	    foreach my $key (keys %{$$attributes{$attribute}->{'keys'}}) {
 		my $value =
 		    $$attributes{$attribute}->{'keys'}->{$key}->{'value'};
-		push (@values, $value) if ($value);
+		# $value = undef means that the attribute is write-only.
+		push (@values, $value) if (defined($value));
 	    }
 	    foreach my $value (sort @values) {
 		$result .= "$prefix$attribute " . escapeMeta($value) . "\n";
@@ -1532,7 +1533,8 @@ sub serializeNkAttr {
 	    && $attribute ne 'enabled'
 	    && $attribute ne 'hw_target') {
 	    my $value = $$attributes{$attribute}->{'value'};
-	    if ($value) {
+	    # $value = undef means that the attribute is write-only.
+	    if (defined($value)) {
 		$result .= "$prefix$attribute " . escapeMeta($value) . "\n";
 	    }
 	}
@@ -3140,7 +3142,7 @@ sub listDevices {
 	my $device = shift;
 	my $nonkey = shift;
 
-	return listDevice($device, $nonkey) if ($device);
+	return listDevice($device, $nonkey) if (length($device));
 	return listHandler();
 }
 
@@ -3164,7 +3166,7 @@ sub listDeviceGroups {
 	my $group = shift;
 	my $showall = shift;
 
-	return listDeviceGroup($group) if ($group);
+	return listDeviceGroup($group) if (length($group));
 
 	my ($groups, $errorString) = $SCST->deviceGroups();
 
@@ -3243,8 +3245,8 @@ sub listTargetGroups {
 	my $tgroup = shift;
 	my $indent = shift;
 
-	return listDeviceGroups(undef, TRUE) if ($group eq '');
-	return listTargetGroup($group, $tgroup) if ($tgroup);
+	return listDeviceGroups(undef, TRUE) if (!length($group));
+	return listTargetGroup($group, $tgroup) if (length($tgroup));
 
 	my ($tgroups, $errorString) = $SCST->targetGroups($group);
 
@@ -3332,7 +3334,7 @@ sub listDeviceGroupDevices {
 sub listDrivers {
 	my $driver = shift;
 
-	return listTargets($driver, undef) if ($driver);
+	return listTargets($driver, undef) if (length($driver));
 
 	my ($drivers, $errorString) = $SCST->drivers();
 
@@ -3360,9 +3362,10 @@ sub listTargets {
 	my $target = shift;
 	my %toprint;
 
-	return listGroups($driver, $target, undef) if ($target and $driver);
+	return listGroups($driver, $target, undef)
+	    if (length($target) and length($driver));
 
-	my $got_driver = defined($driver);
+	my $got_driver = !!length($driver);
 
 	my ($drivers, $errorString) = $SCST->drivers();
 
@@ -3469,7 +3472,7 @@ sub listGroup {
 	my $errorString;
 
 	($luns, $errorString) = $SCST->luns($driver, $target, $group) if (!$luns);
-	if (!defined($initiators) && defined($group)) {
+	if (!length($initiators) && length($group)) {
 		($initiators, $errorString) = $SCST->initiators($driver, $target, $group);
 		return TRUE if issueWarning($errorString);
 	}
@@ -3504,7 +3507,7 @@ sub listGroup {
 			print "\t(none)\n";
 		}
 
-		if (defined($group)) {
+		if (length($group)) {
 			print "\nAssigned Initiators:\n\n";
 
 			if ($#{$initiators} > -1) {
@@ -3523,7 +3526,7 @@ sub listGroup {
 			}
 		}
 	} else {
-		if (defined($group)) {
+		if (length($group)) {
 			print "Group '$group' has no associated LUNs or initiators.\n";
 		} else {
 			print "Driver/target '$driver/$target' has no associated LUNs.\n";
@@ -3539,7 +3542,7 @@ sub listGroups {
 	my $group = shift;
 	my $found = FALSE;
 
-	if ($group and $driver and $target) {
+	if (length($group) and length($driver) and length($target)) {
 		return listGroup($driver, $target, $group);
 	}
 
@@ -3948,7 +3951,7 @@ sub listLunAttributes {
 	return TRUE if issueWarning($errorString);
 
 	if (!scalar(keys %{$attributes})) {
-		if ($group) {
+		if (length($group)) {
 			print "No such driver/target/group/lun '$driver/$target/$group/$lun' found.\n";
 		} else {
 			print "No such driver/target/lun '$driver/$target/$lun' found.\n";
@@ -5160,7 +5163,7 @@ sub addLun {
 		return FALSE;
 	}
 
-	if (defined($group)) {
+	if (length($group)) {
 		print "\t-> Adding device '$device' at LUN $lun to driver/target/group ".
 		  "'$driver/$target/$group': ";
 	} else {
@@ -5351,7 +5354,7 @@ sub issueLip {
 	my $warn = shift;
 	my $errorString;
 
-	if (defined($driver) && defined($target)) {
+	if (length($driver) && length($target)) {
 		return _issueLip($driver, $target, $warn);
 	} else {
 		my $drivers;