more work at refactoring of the way attributes are handled:

* finished and integrated support for declaring known attributes from
  within plugins (they need to install a AttrInfo module)
* implemented support for checking which attributes are applicable to
  systems and clients respectively
* adjusted slxconfig to new attribute handling (systems only at the moment)

git-svn-id: http://svn.openslx.org/svn/openslx/trunk@1442 95ad53e4-c205-0410-b2fa-d234c58c8868

4 files changed, 587 insertions, 388 deletions

diff --git a/config-db/OpenSLX/AttrInfo/Core.pm b/config-db/OpenSLX/AttrInfo/Core.pm
index a1c06019..9716fb34 100644
--- a/config-db/OpenSLX/AttrInfo/Core.pm
+++ b/config-db/OpenSLX/AttrInfo/Core.pm
@@ -18,331 +18,336 @@ use warnings;
 
 use OpenSLX::Utils;
 
-use vars qw(@ISA @EXPORT $VERSION %AttrInfo);
+sub new
+{
+	my $class = shift;
 
-use Exporter;
-$VERSION = 1.01;
-@ISA     = qw(Exporter);
+	my $self = {
+	};
 
-@EXPORT = qw( %AttrInfo );
+	return bless $self, $class;
+}
 
-%AttrInfo = (
-	'automnt_dir' => {
-		applies_to_systems => 1,
-		applies_to_clients => 1,
-		description => unshiftHereDoc(<<'		End-of-Here'),
-			!!!descriptive text missing here!!!
-		End-of-Here
-		content_regex => undef,
-		content_descr => undef,
-	},
-	'automnt_src' => {
-		applies_to_systems => 1,
-		applies_to_clients => 1,
-		description => unshiftHereDoc(<<'		End-of-Here'),
-			!!!descriptive text missing here!!!
-		End-of-Here
-		content_regex => undef,
-		content_descr => undef,
-	},
-	'country' => {
-		applies_to_systems => 1,
-		applies_to_clients => 1,
-		description => unshiftHereDoc(<<'		End-of-Here'),
-			!!!descriptive text missing here!!!
-		End-of-Here
-		content_regex => undef,
-		content_descr => undef,
-	},
-	'dm_allow_shutdown' => {
-		applies_to_systems => 1,
-		applies_to_clients => 1,
-		description => unshiftHereDoc(<<'		End-of-Here'),
-			!!!descriptive text missing here!!!
-		End-of-Here
-		content_regex => undef,
-		content_descr => undef,
-	},
-	'hw_graphic' => {
-		applies_to_systems => 1,
-		applies_to_clients => 1,
-		description => unshiftHereDoc(<<'		End-of-Here'),
-			!!!descriptive text missing here!!!
-		End-of-Here
-		content_regex => undef,
-		content_descr => undef,
-	},
-	'hw_monitor' => {
-		applies_to_systems => 1,
-		applies_to_clients => 1,
-		description => unshiftHereDoc(<<'		End-of-Here'),
-			!!!descriptive text missing here!!!
-		End-of-Here
-		content_regex => undef,
-		content_descr => undef,
-	},
-	'hw_mouse' => {
-		applies_to_systems => 1,
-		applies_to_clients => 1,
-		description => unshiftHereDoc(<<'		End-of-Here'),
-			!!!descriptive text missing here!!!
-		End-of-Here
-		content_regex => undef,
-		content_descr => undef,
-	},
-	'late_dm' => {
-		applies_to_systems => 1,
-		applies_to_clients => 1,
-		description => unshiftHereDoc(<<'		End-of-Here'),
-			!!!descriptive text missing here!!!
-		End-of-Here
-		content_regex => undef,
-		content_descr => undef,
-	},
-	'netbios_workgroup' => {
-		applies_to_systems => 1,
-		applies_to_clients => 1,
-		description => unshiftHereDoc(<<'		End-of-Here'),
-			!!!descriptive text missing here!!!
-		End-of-Here
-		content_regex => undef,
-		content_descr => undef,
-	},
-	'nis_domain' => {
-		applies_to_systems => 1,
-		applies_to_clients => 1,
-		description => unshiftHereDoc(<<'		End-of-Here'),
-			!!!descriptive text missing here!!!
-		End-of-Here
-		content_regex => undef,
-		content_descr => undef,
-	},
-	'nis_servers' => {
-		applies_to_systems => 1,
-		applies_to_clients => 1,
-		description => unshiftHereDoc(<<'		End-of-Here'),
-			!!!descriptive text missing here!!!
-		End-of-Here
-		content_regex => undef,
-		content_descr => undef,
-	},
-	'sane_scanner' => {
-		applies_to_systems => 1,
-		applies_to_clients => 1,
-		description => unshiftHereDoc(<<'		End-of-Here'),
-			!!!descriptive text missing here!!!
-		End-of-Here
-		content_regex => undef,
-		content_descr => undef,
-	},
-	'scratch' => {
-		applies_to_systems => 1,
-		applies_to_clients => 1,
-		description => unshiftHereDoc(<<'		End-of-Here'),
-			!!!descriptive text missing here!!!
-		End-of-Here
-		content_regex => undef,
-		content_descr => undef,
-	},
-	'slxgrp' => {
-		applies_to_systems => 1,
-		applies_to_clients => 1,
-		description => unshiftHereDoc(<<'		End-of-Here'),
-			!!!descriptive text missing here!!!
-		End-of-Here
-		content_regex => undef,
-		content_descr => undef,
-	},
-	'start_alsasound' => {
-		applies_to_systems => 1,
-		applies_to_clients => 1,
-		description => unshiftHereDoc(<<'		End-of-Here'),
-			!!!descriptive text missing here!!!
-		End-of-Here
-		content_regex => undef,
-		content_descr => undef,
-	},
-	'start_atd' => {
-		applies_to_systems => 1,
-		applies_to_clients => 1,
-		description => unshiftHereDoc(<<'		End-of-Here'),
-			!!!descriptive text missing here!!!
-		End-of-Here
-		content_regex => undef,
-		content_descr => undef,
-	},
-	'start_cron' => {
-		applies_to_systems => 1,
-		applies_to_clients => 1,
-		description => unshiftHereDoc(<<'		End-of-Here'),
-			!!!descriptive text missing here!!!
-		End-of-Here
-		content_regex => undef,
-		content_descr => undef,
-	},
-	'start_dreshal' => {
-		applies_to_systems => 1,
-		applies_to_clients => 1,
-		description => unshiftHereDoc(<<'		End-of-Here'),
-			!!!descriptive text missing here!!!
-		End-of-Here
-		content_regex => undef,
-		content_descr => undef,
-	},
-	'start_ntp' => {
-		applies_to_systems => 1,
-		applies_to_clients => 1,
-		description => unshiftHereDoc(<<'		End-of-Here'),
-			!!!descriptive text missing here!!!
-		End-of-Here
-		content_regex => undef,
-		content_descr => undef,
-	},
-	'start_nfsv4' => {
-		applies_to_systems => 1,
-		applies_to_clients => 1,
-		description => unshiftHereDoc(<<'		End-of-Here'),
-			!!!descriptive text missing here!!!
-		End-of-Here
-		content_regex => undef,
-		content_descr => undef,
-	},
-	'start_printer' => {
-		applies_to_systems => 1,
-		applies_to_clients => 1,
-		description => unshiftHereDoc(<<'		End-of-Here'),
-			!!!descriptive text missing here!!!
-		End-of-Here
-		content_regex => undef,
-		content_descr => undef,
-	},
-	'start_samba' => {
-		applies_to_systems => 1,
-		applies_to_clients => 1,
-		description => unshiftHereDoc(<<'		End-of-Here'),
-			!!!descriptive text missing here!!!
-		End-of-Here
-		content_regex => undef,
-		content_descr => undef,
-	},
-	'start_snmp' => {
-		applies_to_systems => 1,
-		applies_to_clients => 1,
-		description => unshiftHereDoc(<<'		End-of-Here'),
-			!!!descriptive text missing here!!!
-		End-of-Here
-		content_regex => undef,
-		content_descr => undef,
-	},
-	'start_sshd' => {
-		applies_to_systems => 1,
-		applies_to_clients => 1,
-		description => unshiftHereDoc(<<'		End-of-Here'),
-			!!!descriptive text missing here!!!
-		End-of-Here
-		content_regex => undef,
-		content_descr => undef,
-	},
-	'start_syslogd' => {
-		applies_to_systems => 1,
-		applies_to_clients => 1,
-		description => unshiftHereDoc(<<'		End-of-Here'),
-			!!!descriptive text missing here!!!
-		End-of-Here
-		content_regex => undef,
-		content_descr => undef,
-	},
-	'start_x' => {
-		applies_to_systems => 1,
-		applies_to_clients => 1,
-		description => unshiftHereDoc(<<'		End-of-Here'),
-			!!!descriptive text missing here!!!
-		End-of-Here
-		content_regex => undef,
-		content_descr => undef,
-	},
-	'start_xdmcp' => {
-		applies_to_systems => 1,
-		applies_to_clients => 1,
-		description => unshiftHereDoc(<<'		End-of-Here'),
-			!!!descriptive text missing here!!!
-		End-of-Here
-		content_regex => undef,
-		content_descr => undef,
-	},
-	'tex_enable' => {
-		applies_to_systems => 1,
-		applies_to_clients => 1,
-		description => unshiftHereDoc(<<'		End-of-Here'),
-			!!!descriptive text missing here!!!
-		End-of-Here
-		content_regex => undef,
-		content_descr => undef,
-	},
-	'timezone' => {
-		applies_to_systems => 1,
-		applies_to_clients => 1,
-		description => unshiftHereDoc(<<'		End-of-Here'),
-			textual timezone (e.g. 'Europe/Berlin')
-		End-of-Here
-		content_regex => undef,
-		content_descr => undef,
-	},
-	'tvout' => {
-		applies_to_systems => 1,
-		applies_to_clients => 1,
-		description => unshiftHereDoc(<<'		End-of-Here'),
-			!!!descriptive text missing here!!!
-		End-of-Here
-		content_regex => undef,
-		content_descr => undef,
-	},
-	'vmware' => {
-		applies_to_systems => 1,
-		applies_to_clients => 1,
-		description => unshiftHereDoc(<<'		End-of-Here'),
-			!!!descriptive text missing here!!!
-		End-of-Here
-		content_regex => undef,
-		content_descr => undef,
-	},
-
-	'ramfs_fsmods' => {
-		applies_to_systems => 1,
-		applies_to_clients => 0,
-		description => unshiftHereDoc(<<'		End-of-Here'),
-			list of filesystem kernel modules to load
-		End-of-Here
-		content_regex => undef,
-		content_descr => undef,
-	},
-	'ramfs_miscmods' => {
-		applies_to_systems => 1,
-		applies_to_clients => 0,
-		description => unshiftHereDoc(<<'		End-of-Here'),
-			list of miscellaneous kernel modules to load
-		End-of-Here
-		content_regex => undef,
-		content_descr => undef,
-	},
-	'ramfs_nicmods' => {
-		applies_to_systems => 1,
-		applies_to_clients => 0,
-		description => unshiftHereDoc(<<'		End-of-Here'),
-			list of network card modules to load
-		End-of-Here
-		content_regex => undef,
-		content_descr => undef,
-	},
-	'ramfs_screen' => {
-		applies_to_systems => 1,
-		applies_to_clients => 0,
-		description => unshiftHereDoc(<<'		End-of-Here'),
-			resolution of splash screen to use in stage3
-		End-of-Here
-		content_regex => undef,
-		content_descr => undef,
-	},
-);
+sub AttrInfo
+{
+	return {
+		'automnt_dir' => {
+			applies_to_systems => 1,
+			applies_to_clients => 1,
+			description => unshiftHereDoc(<<'			End-of-Here'),
+				!!!descriptive text missing here!!!
+			End-of-Here
+			content_regex => undef,
+			content_descr => undef,
+		},
+		'automnt_src' => {
+			applies_to_systems => 1,
+			applies_to_clients => 1,
+			description => unshiftHereDoc(<<'			End-of-Here'),
+				!!!descriptive text missing here!!!
+			End-of-Here
+			content_regex => undef,
+			content_descr => undef,
+		},
+		'country' => {
+			applies_to_systems => 1,
+			applies_to_clients => 1,
+			description => unshiftHereDoc(<<'			End-of-Here'),
+				!!!descriptive text missing here!!!
+			End-of-Here
+			content_regex => undef,
+			content_descr => undef,
+		},
+		'dm_allow_shutdown' => {
+			applies_to_systems => 1,
+			applies_to_clients => 1,
+			description => unshiftHereDoc(<<'			End-of-Here'),
+				!!!descriptive text missing here!!!
+			End-of-Here
+			content_regex => undef,
+			content_descr => undef,
+		},
+		'hw_graphic' => {
+			applies_to_systems => 1,
+			applies_to_clients => 1,
+			description => unshiftHereDoc(<<'			End-of-Here'),
+				!!!descriptive text missing here!!!
+			End-of-Here
+			content_regex => undef,
+			content_descr => undef,
+		},
+		'hw_monitor' => {
+			applies_to_systems => 1,
+			applies_to_clients => 1,
+			description => unshiftHereDoc(<<'			End-of-Here'),
+				!!!descriptive text missing here!!!
+			End-of-Here
+			content_regex => undef,
+			content_descr => undef,
+		},
+		'hw_mouse' => {
+			applies_to_systems => 1,
+			applies_to_clients => 1,
+			description => unshiftHereDoc(<<'			End-of-Here'),
+				!!!descriptive text missing here!!!
+			End-of-Here
+			content_regex => undef,
+			content_descr => undef,
+		},
+		'late_dm' => {
+			applies_to_systems => 1,
+			applies_to_clients => 1,
+			description => unshiftHereDoc(<<'			End-of-Here'),
+				!!!descriptive text missing here!!!
+			End-of-Here
+			content_regex => undef,
+			content_descr => undef,
+		},
+		'netbios_workgroup' => {
+			applies_to_systems => 1,
+			applies_to_clients => 1,
+			description => unshiftHereDoc(<<'			End-of-Here'),
+				!!!descriptive text missing here!!!
+			End-of-Here
+			content_regex => undef,
+			content_descr => undef,
+		},
+		'nis_domain' => {
+			applies_to_systems => 1,
+			applies_to_clients => 1,
+			description => unshiftHereDoc(<<'			End-of-Here'),
+				!!!descriptive text missing here!!!
+			End-of-Here
+			content_regex => undef,
+			content_descr => undef,
+		},
+		'nis_servers' => {
+			applies_to_systems => 1,
+			applies_to_clients => 1,
+			description => unshiftHereDoc(<<'			End-of-Here'),
+				!!!descriptive text missing here!!!
+			End-of-Here
+			content_regex => undef,
+			content_descr => undef,
+		},
+		'sane_scanner' => {
+			applies_to_systems => 1,
+			applies_to_clients => 1,
+			description => unshiftHereDoc(<<'			End-of-Here'),
+				!!!descriptive text missing here!!!
+			End-of-Here
+			content_regex => undef,
+			content_descr => undef,
+		},
+		'scratch' => {
+			applies_to_systems => 1,
+			applies_to_clients => 1,
+			description => unshiftHereDoc(<<'			End-of-Here'),
+				!!!descriptive text missing here!!!
+			End-of-Here
+			content_regex => undef,
+			content_descr => undef,
+		},
+		'slxgrp' => {
+			applies_to_systems => 1,
+			applies_to_clients => 1,
+			description => unshiftHereDoc(<<'			End-of-Here'),
+				!!!descriptive text missing here!!!
+			End-of-Here
+			content_regex => undef,
+			content_descr => undef,
+		},
+		'start_alsasound' => {
+			applies_to_systems => 1,
+			applies_to_clients => 1,
+			description => unshiftHereDoc(<<'			End-of-Here'),
+				!!!descriptive text missing here!!!
+			End-of-Here
+			content_regex => undef,
+			content_descr => undef,
+		},
+		'start_atd' => {
+			applies_to_systems => 1,
+			applies_to_clients => 1,
+			description => unshiftHereDoc(<<'			End-of-Here'),
+				!!!descriptive text missing here!!!
+			End-of-Here
+			content_regex => undef,
+			content_descr => undef,
+		},
+		'start_cron' => {
+			applies_to_systems => 1,
+			applies_to_clients => 1,
+			description => unshiftHereDoc(<<'			End-of-Here'),
+				!!!descriptive text missing here!!!
+			End-of-Here
+			content_regex => undef,
+			content_descr => undef,
+		},
+		'start_dreshal' => {
+			applies_to_systems => 1,
+			applies_to_clients => 1,
+			description => unshiftHereDoc(<<'			End-of-Here'),
+				!!!descriptive text missing here!!!
+			End-of-Here
+			content_regex => undef,
+			content_descr => undef,
+		},
+		'start_ntp' => {
+			applies_to_systems => 1,
+			applies_to_clients => 1,
+			description => unshiftHereDoc(<<'			End-of-Here'),
+				!!!descriptive text missing here!!!
+			End-of-Here
+			content_regex => undef,
+			content_descr => undef,
+		},
+		'start_nfsv4' => {
+			applies_to_systems => 1,
+			applies_to_clients => 1,
+			description => unshiftHereDoc(<<'			End-of-Here'),
+				!!!descriptive text missing here!!!
+			End-of-Here
+			content_regex => undef,
+			content_descr => undef,
+		},
+		'start_printer' => {
+			applies_to_systems => 1,
+			applies_to_clients => 1,
+			description => unshiftHereDoc(<<'			End-of-Here'),
+				!!!descriptive text missing here!!!
+			End-of-Here
+			content_regex => undef,
+			content_descr => undef,
+		},
+		'start_samba' => {
+			applies_to_systems => 1,
+			applies_to_clients => 1,
+			description => unshiftHereDoc(<<'			End-of-Here'),
+				!!!descriptive text missing here!!!
+			End-of-Here
+			content_regex => undef,
+			content_descr => undef,
+		},
+		'start_snmp' => {
+			applies_to_systems => 1,
+			applies_to_clients => 1,
+			description => unshiftHereDoc(<<'			End-of-Here'),
+				!!!descriptive text missing here!!!
+			End-of-Here
+			content_regex => undef,
+			content_descr => undef,
+		},
+		'start_sshd' => {
+			applies_to_systems => 1,
+			applies_to_clients => 1,
+			description => unshiftHereDoc(<<'			End-of-Here'),
+				!!!descriptive text missing here!!!
+			End-of-Here
+			content_regex => undef,
+			content_descr => undef,
+		},
+		'start_syslogd' => {
+			applies_to_systems => 1,
+			applies_to_clients => 1,
+			description => unshiftHereDoc(<<'			End-of-Here'),
+				!!!descriptive text missing here!!!
+			End-of-Here
+			content_regex => undef,
+			content_descr => undef,
+		},
+		'start_x' => {
+			applies_to_systems => 1,
+			applies_to_clients => 1,
+			description => unshiftHereDoc(<<'			End-of-Here'),
+				!!!descriptive text missing here!!!
+			End-of-Here
+			content_regex => undef,
+			content_descr => undef,
+		},
+		'start_xdmcp' => {
+			applies_to_systems => 1,
+			applies_to_clients => 1,
+			description => unshiftHereDoc(<<'			End-of-Here'),
+				!!!descriptive text missing here!!!
+			End-of-Here
+			content_regex => undef,
+			content_descr => undef,
+		},
+		'tex_enable' => {
+			applies_to_systems => 1,
+			applies_to_clients => 1,
+			description => unshiftHereDoc(<<'			End-of-Here'),
+				!!!descriptive text missing here!!!
+			End-of-Here
+			content_regex => undef,
+			content_descr => undef,
+		},
+		'timezone' => {
+			applies_to_systems => 1,
+			applies_to_clients => 1,
+			description => unshiftHereDoc(<<'			End-of-Here'),
+				textual timezone (e.g. 'Europe/Berlin')
+			End-of-Here
+			content_regex => undef,
+			content_descr => undef,
+		},
+		'tvout' => {
+			applies_to_systems => 1,
+			applies_to_clients => 1,
+			description => unshiftHereDoc(<<'			End-of-Here'),
+				!!!descriptive text missing here!!!
+			End-of-Here
+			content_regex => undef,
+			content_descr => undef,
+		},
+		'vmware' => {
+			applies_to_systems => 1,
+			applies_to_clients => 1,
+			description => unshiftHereDoc(<<'			End-of-Here'),
+				!!!descriptive text missing here!!!
+			End-of-Here
+			content_regex => undef,
+			content_descr => undef,
+		},
+	
+		'ramfs_fsmods' => {
+			applies_to_systems => 1,
+			applies_to_clients => 0,
+			description => unshiftHereDoc(<<'			End-of-Here'),
+				list of filesystem kernel modules to load
+			End-of-Here
+			content_regex => undef,
+			content_descr => undef,
+		},
+		'ramfs_miscmods' => {
+			applies_to_systems => 1,
+			applies_to_clients => 0,
+			description => unshiftHereDoc(<<'			End-of-Here'),
+				list of miscellaneous kernel modules to load
+			End-of-Here
+			content_regex => undef,
+			content_descr => undef,
+		},
+		'ramfs_nicmods' => {
+			applies_to_systems => 1,
+			applies_to_clients => 0,
+			description => unshiftHereDoc(<<'			End-of-Here'),
+				list of network card modules to load
+			End-of-Here
+			content_regex => undef,
+			content_descr => undef,
+		},
+		'ramfs_screen' => {
+			applies_to_systems => 1,
+			applies_to_clients => 0,
+			description => unshiftHereDoc(<<'			End-of-Here'),
+				resolution of splash screen to use in stage3
+			End-of-Here
+			content_regex => undef,
+			content_descr => undef,
+		},
+	};
+}
 
 1;
diff --git a/config-db/OpenSLX/ConfigDB.pm b/config-db/OpenSLX/ConfigDB.pm
index debbef9c..95183c95 100644
--- a/config-db/OpenSLX/ConfigDB.pm
+++ b/config-db/OpenSLX/ConfigDB.pm
@@ -104,8 +104,6 @@ use OpenSLX::Utils;
 =item C<new()>
 
 Returns an object representing a database handle to the config database.
-N.B. this class is implemented as a singleton, so several successive calls to
-new will return the *same* object
 
 =cut
 
@@ -283,11 +281,57 @@ sub getColumnsOfTable
 	my $self      = shift;
 	my $tableName = shift;
 
-	return 
+	return	
 		map { (/^(\w+)\W/) ? $1 : $_; } 
 		@{$DbSchema->{tables}->{$tableName}->{cols}};
 }
 
+=item C<getKnownSystemAttrs()>
+
+Returns the attribute names that apply to systems.
+
+=over
+
+=item Return Value
+
+An array of attribute names.
+
+=back
+
+=cut
+
+sub getKnownSystemAttrs
+{
+	my $self = shift;
+
+	return 
+		grep { $AttributeInfo{$_}->{"applies_to_systems"} }
+		keys %AttributeInfo
+}
+
+=item C<getKnownClientAttrs()>
+
+Returns the attribute names that apply to clients.
+
+=over
+
+=item Return Value
+
+An array of attribute names.
+
+=back
+
+=cut
+
+sub getKnownClientAttrs
+{
+	my $self = shift;
+
+	return 
+		grep { $AttributeInfo{$_}->{"applies_to_clients"} }
+		keys %AttributeInfo
+}
+
 =item C<fetchVendorOSByFilter([%$filter], [$resultCols])>
 
 Fetches and returns information about all vendor-OSes that match the given
@@ -318,8 +362,8 @@ sub fetchVendorOSByFilter
 	my $filter     = shift;
 	my $resultCols = shift;
 
-	my @vendorOS =
-	  $self->{'meta-db'}->fetchVendorOSByFilter($filter, $resultCols);
+	my @vendorOS 
+		= $self->{'meta-db'}->fetchVendorOSByFilter($filter, $resultCols);
 
 	return wantarray() ? @vendorOS : shift @vendorOS;
 }
@@ -493,6 +537,11 @@ is no filtering. See L</"Filters"> for more info.
 A comma-separated list of colunm names that shall be returned. If not defined,
 all available data must be returned.
 
+=item Param C<$attrFilter> [Optional]
+
+A hash-ref containing the filter criteria that shall be applied against
+attributes.
+
 =item Return Value
 
 An array of hash-refs containing the resulting data rows.
@@ -506,19 +555,11 @@ sub fetchSystemByFilter
 	my $self       = shift;
 	my $filter     = shift;
 	my $resultCols = shift;
+	my $attrFilter = shift;
 
-	my @systems = $self->{'meta-db'}->fetchSystemByFilter($filter, $resultCols);
-
-	# unless specific result cols have been given, we mix in the attributes
-	# of each system, too:
-	if (!defined $resultCols) {
-		foreach my $system (@systems) {
-			my @attrs = $self->{'meta-db'}->fetchSystemAttrs($system->{id});
-			foreach my $attr (@attrs) {
-				$system->{"attr_$attr->{name}"} = $attr->{value};
-			}
-		}
-	}
+	my @systems = $self->{'meta-db'}->fetchSystemByFilter(
+		$filter, $resultCols, $attrFilter
+	);
 
 	return wantarray() ? @systems : shift @systems;
 }
@@ -555,18 +596,91 @@ sub fetchSystemByID
 	
 	# unless specific result cols have been given, we mix in the attributes
 	# of each system, too:
-	if (!defined $resultCols) {
-		foreach my $system (@systems) {
-			my @attrs = $self->{'meta-db'}->fetchSystemAttrs($system->{id});
-			foreach my $attr (@attrs) {
-				$system->{"attr_$attr->{name}"} = $attr->{value};
-			}
-		}
-	}
+#	if (!defined $resultCols) {
+#		foreach my $system (@systems) {
+#			$system->{attrs} 
+#				= $self->{'meta-db'}->fetchSystemAttrs($system->{id});
+#		}
+#	}
 
 	return wantarray() ? @systems : shift @systems;
 }
 
+=item C<fetchSystemAttrs($systemID, [$attrNames])>
+
+Fetches and returns the information about the attributes of the system
+with the given ID.
+
+=over
+
+=item Param C<$systemID>
+
+The ID of the system whose attributes you are interested in.
+
+=item Param C<$attrNames> [Optional]
+
+A comma-separated list of attribute names that shall be returned. If not 
+defined,all available attributes will be returned.
+
+=item Return Value
+
+An array of hash-refs containing the resulting data rows (or a single hash-ref
+mapping all attribute names to the respective value).
+
+=back
+
+=cut
+
+sub fetchSystemAttrs
+{
+	my $self      = shift;
+	my $systemID  = shift;
+	my $attrNames = shift;
+
+	my @attrs = $self->{'meta-db'}->fetchSystemAttrs($systemID, $attrNames);
+
+	return wantarray() ? @attrs : shift @attrs;
+}
+
+=item C<fetchSystemAttrsAsHash($systemID, [$attrNames])>
+
+Fetches and returns the information about the attributes of the system
+with the given ID.
+
+=over
+
+=item Param C<$systemID>
+
+The ID of the system whose attributes you are interested in.
+
+=item Param C<$attrNames> [Optional]
+
+A comma-separated list of attribute names that shall be returned. If not 
+defined,all available attributes will be returned.
+
+=item Return Value
+
+A single hash-ref mapping all attribute names to their respective value.
+
+=back
+
+=cut
+
+sub fetchSystemAttrsAsHash
+{
+	my $self      = shift;
+	my $systemID  = shift;
+	my $attrNames = shift;
+
+	my @attrs = $self->{'meta-db'}->fetchSystemAttrs($systemID, $attrNames);
+
+	my $Result = {};
+	foreach my $attr (@attrs) {
+		$Result->{$attr->{name}} = $attr->{value};
+	}
+	return $Result;
+}
+
 =item C<fetchSystemIDsOfExport($id)>
 
 Fetches the IDs of all systems that make use of the export with the given ID.
@@ -2702,6 +2816,7 @@ sub _checkAndUpgradeDBSchemaIfNecessary
 				$DbSchema->{tables}->{$tableName}->{vals}
 			);
 		}
+		$metaDB->schemaSetDBVersion($DbSchema->{version});
 		vlog(1, _tr('DB has been created successfully'));
 	} elsif ($currVersion < $DbSchema->{version}) {
 		vlog(
@@ -2759,6 +2874,7 @@ sub _checkAndUpgradeDBSchemaIfNecessary
 				}
 			}
 		}
+		$metaDB->schemaSetDBVersion($DbSchema->{version});
 		vlog(1, _tr('upgrade done'));
 	} else {
 		vlog(1, _tr('DB matches current schema version (%s)', $currVersion));
@@ -2770,6 +2886,7 @@ sub _checkAndUpgradeDBSchemaIfNecessary
 sub _aref
 {    # transparently converts the given reference to an array-ref
 	my $ref = shift;
+
 	return [] unless defined $ref;
 	$ref = [$ref] unless ref($ref) eq 'ARRAY';
 
@@ -2779,7 +2896,6 @@ sub _aref
 sub _unique
 {    # return given array filtered to unique elements
 	my %seenIDs;
-
 	return grep { !$seenIDs{$_}++; } @_;
 }
 
diff --git a/config-db/OpenSLX/DBSchema.pm b/config-db/OpenSLX/DBSchema.pm
index 9b692b59..54596c9f 100644
--- a/config-db/OpenSLX/DBSchema.pm
+++ b/config-db/OpenSLX/DBSchema.pm
@@ -23,10 +23,13 @@ $VERSION = 0.2;
 @ISA = qw(Exporter);
 
 @EXPORT = qw(
-	$DbSchema %DbSchemaHistory
+	$DbSchema %DbSchemaHistory %AttributeInfo
 );
 
-our ($DbSchema, %DbSchemaHistory);
+our ($DbSchema, %DbSchemaHistory, %AttributeInfo);
+
+
+use OpenSLX::Basics;
 
 use POSIX qw(locale_h);
 my $lang = setlocale(LC_MESSAGES);
@@ -256,12 +259,22 @@ $DbSchema = {
 				},
 				{
 					'system_id' => 0,
+					'name' => 'ramfs_miscmods',
+					'value' => '',
+				},
+				{
+					'system_id' => 0,
 					'name' => 'ramfs_nicmods',
 					'value' 
 						=> 'forcedeth e1000 e100 tg3 via-rhine r8169 pcnet32',
 				},
 				{
 					'system_id' => 0,
+					'name' => 'ramfs_screen',
+					'value' => '',
+				},
+				{
+					'system_id' => 0,
 					'name' => 'sane_scanner',
 					'value' => '',
 				},
@@ -448,7 +461,7 @@ $DbSchema = {
 					foreach my $key (keys %$system) {
 						next if substr($key, 0, 5) ne 'attr_';
 						my $attrValue = $system->{$key} || '';
-						next if !length($attrValue);
+						next if $system->{id}>0 && !length($attrValue);
 						my $newAttrName = substr($key, 5);
 						$configDB->setSystemAttr(
 							$system->{id}, $newAttrName, $attrValue
@@ -516,4 +529,26 @@ $DbSchema = {
 	],
 );
 
+
+################################################################################
+###
+### Load all available AttrInfo modules and build the complete hash containing
+### info about all known attributes from that.
+###
+################################################################################
+
+%AttributeInfo = ();
+
+my $libPath = "$openslxConfig{'base-path'}/lib";
+foreach my $module (glob("$libPath/OpenSLX/AttrInfo/*.pm")) {
+	next if $module !~ m{/([^/]+)\.pm$};
+	my $class = "OpenSLX::AttrInfo::$1";
+	vlog(2, "loading attr-info from module '$module'");
+	my $instance = instantiateClass($class);
+	my $attrInfo = $instance->AttrInfo();
+	foreach my $attr (keys %$attrInfo) {
+		$AttributeInfo{$attr} = $attrInfo->{$attr};
+	}
+}
+
 1;
diff --git a/config-db/OpenSLX/MetaDB/DBI.pm b/config-db/OpenSLX/MetaDB/DBI.pm
index dbc1faa8..774ab90e 100644
--- a/config-db/OpenSLX/MetaDB/DBI.pm
+++ b/config-db/OpenSLX/MetaDB/DBI.pm
@@ -67,7 +67,7 @@ sub rollbackTransaction
 }
 
 ################################################################################
-### data access functions
+### data access
 ################################################################################
 sub _trim
 {
@@ -76,6 +76,62 @@ sub _trim
 	return $s;
 }
 
+sub _buildFilterClause
+{
+	my $self      = shift;
+	my $filter    = shift || {};
+	my $connector = shift;
+
+	my $filterClause = '';
+	my ($quotedVal);
+	foreach my $col (keys %$filter) {
+		$connector = !defined $connector ? 'WHERE' : 'AND';
+		if (defined $filter->{$col}) {
+			$quotedVal = $self->{dbh}->quote($filter->{$col});
+			$filterClause .= " $connector $col = $quotedVal";
+		} else {
+			$filterClause .= " $connector $col IS NULL";
+		}
+	}
+	
+	return $filterClause;
+}
+
+sub _buildAttrFilterClause
+{
+	my $self       = shift;
+	my $attrFilter = shift || {};
+	my $connector = shift;
+
+	my $attrFilterClause = '';
+	my ($quotedName, $quotedValue);
+	foreach my $name (keys %$attrFilter) {
+		$connector = !defined $connector ? 'WHERE' : 'AND';
+		$quotedName = $self->{dbh}->quote($name);
+		if (defined $attrFilter->{$name}) {
+			$quotedValue = $self->{dbh}->quote($attrFilter->{$name});
+			$attrFilterClause .= <<"			End-of-Here";
+				$connector EXISTS (
+					SELECT name FROM system_attr
+					WHERE name = $quotedName 
+					AND value = $quotedValue
+					AND system_id = system.id
+				)
+			End-of-Here
+		} else {
+			$attrFilterClause .= <<"			End-of-Here";
+				$connector NOT EXISTS (
+					SELECT name FROM system_attr
+					WHERE name = $quotedName 
+					AND system_id = system.id
+				)
+			End-of-Here
+		}
+	}
+
+	return $attrFilterClause;
+}
+
 sub _doSelect
 {
 	my $self      = shift;
@@ -117,13 +173,8 @@ sub fetchVendorOSByFilter
 	my $resultCols = shift;
 
 	$resultCols = '*' unless (defined $resultCols);
-	my $sql = "SELECT $resultCols FROM vendor_os";
-	my ($connector, $quotedVal);
-	foreach my $col (keys %$filter) {
-		$connector = !defined $connector ? 'WHERE' : 'AND';
-		$quotedVal = $self->{dbh}->quote($filter->{$col});
-		$sql .= " $connector $col = $quotedVal";
-	}
+	my $filterClause = $self->_buildFilterClause($filter);
+	my $sql = "SELECT $resultCols FROM vendor_os $filterClause";
 	return $self->_doSelect($sql);
 }
 
@@ -147,13 +198,8 @@ sub fetchExportByFilter
 	my $resultCols = shift;
 
 	$resultCols = '*' unless (defined $resultCols);
-	my $sql = "SELECT $resultCols FROM export";
-	my ($connector, $quotedVal);
-	foreach my $col (keys %$filter) {
-		$connector = !defined $connector ? 'WHERE' : 'AND';
-		$quotedVal = $self->{dbh}->quote($filter->{$col});
-		$sql .= " $connector $col = $quotedVal";
-	}
+	my $filterClause = $self->_buildFilterClause($filter);
+	my $sql = "SELECT $resultCols FROM export $filterClause";
 	return $self->_doSelect($sql);
 }
 
@@ -196,15 +242,17 @@ sub fetchSystemByFilter
 	my $self       = shift;
 	my $filter     = shift;
 	my $resultCols = shift;
+	my $attrFilter = shift;
 
 	$resultCols = '*' unless (defined $resultCols);
-	my $sql = "SELECT $resultCols FROM system";
-	my ($connector, $quotedVal);
-	foreach my $col (keys %$filter) {
-		$connector = !defined $connector ? 'WHERE' : 'AND';
-		$quotedVal = $self->{dbh}->quote($filter->{$col});
-		$sql .= " $connector $col = $quotedVal";
-	}
+	my $filterClause = $self->_buildFilterClause($filter, 'AND');
+	my $attrFilterClause = $self->_buildAttrFilterClause($attrFilter, 'AND');
+	my $sql = <<"	End-of-Here";
+		SELECT $resultCols FROM system
+		WHERE 1=1
+		$filterClause
+		$attrFilterClause
+	End-of-Here
 	return $self->_doSelect($sql);
 }
 
@@ -225,11 +273,16 @@ sub fetchSystemAttrs
 {
 	my $self      = shift;
 	my $systemID  = $self->{dbh}->quote(shift);
+	my $attrNames = shift;
 
 	my $sql = <<"	End-of-Here";
 		SELECT id, name, value FROM system_attr
 		WHERE system_id = $systemID
 	End-of-Here
+	if (defined $attrNames) {
+		my $attrList = join ',', map { $self->{dbh}->quote($_) } @$attrNames;
+		$sql .= " AND name IN ($attrList)";
+	}
 	return $self->_doSelect($sql);
 }
 
@@ -273,13 +326,8 @@ sub fetchClientByFilter
 	my $resultCols = shift;
 
 	$resultCols = '*' unless (defined $resultCols);
-	my $sql = "SELECT $resultCols FROM client";
-	my ($connector, $quotedVal);
-	foreach my $col (keys %$filter) {
-		$connector = !defined $connector ? 'WHERE' : 'AND';
-		$quotedVal = $self->{dbh}->quote($filter->{$col});
-		$sql .= " $connector $col = $quotedVal";
-	}
+	my $filterClause = $self->_buildFilterClause($filter);
+	my $sql = "SELECT $resultCols FROM client $filterClause";
 	return $self->_doSelect($sql);
 }
 
@@ -325,13 +373,8 @@ sub fetchGroupByFilter
 	my $resultCols = shift;
 
 	$resultCols = '*' unless (defined $resultCols);
-	my $sql = "SELECT $resultCols FROM groups";
-	my ($connector, $quotedVal);
-	foreach my $col (keys %$filter) {
-		$connector = !defined $connector ? 'WHERE' : 'AND';
-		$quotedVal = $self->{dbh}->quote($filter->{$col});
-		$sql .= " $connector $col = $quotedVal";
-	}
+	my $filterClause = $self->_buildFilterClause($filter);
+	my $sql = "SELECT $resultCols FROM groups $filterClause";
 	return $self->_doSelect($sql);
 }