fixes for mtr_unique.pl

mysql-test/lib/mtr_unique.pl:
  - add info message to mtr_require_unique_id_and_wait as suggested
  - fix for security issue
  - locks for pids of processes that don't exist anymore are reused, if ps is present and working as expected

mysql-test/lib/mtr_unique.pl

@@ -35,6 +35,13 @@ sub mtr_require_unique_id($$$) {
 	my $min = shift;
 	my $max = shift;
 	my $ret = undef;
+	my $changed = 0;
+
+	my $can_use_ps = `ps -e | grep '^[ ]*$$ '`;
+
+	if(eval("readlink '$file'") || eval("readlink '$file.sem'")) {
+		die 'lock file is a symbolic link';
+	}
 
 	chmod 0777, "$file.sem";
 	open SEM, ">", "$file.sem" or die "can't write to $file.sem";
@@ -43,6 +50,11 @@ sub mtr_require_unique_id($$$) {
 		open FILE, ">", $file or die "can't create $file";
 		close FILE;
 	}
+
+	if(eval("readlink '$file'") || eval("readlink '$file.sem'")) {
+		die 'lock file is a symbolic link';
+	}
+
 	chmod 0777, $file;
 	open FILE, "+<", $file or die "can't open $file";
 	select undef,undef,undef,0.2;
@@ -52,15 +64,30 @@ sub mtr_require_unique_id($$$) {
 		chomp;
 		my ($id, $pid) = split / /;
 		$taken{$id} = $pid;
+		if($can_use_ps) {
+			my $res = `ps -e | grep '^[ ]*$pid '`;
+			if(!$res) {
+				print "Ignoring slot $id used by missing process $pid.\n";
+				delete $taken{$id};
+				++$changed;
+			}
+		}
 	}
-	seek FILE, 0, 2;
 	for(my $i=$min; $i<=$max; ++$i) {
 		if(! exists $taken{$i}) {
-			print FILE "$i $$\n";
 			$ret = $i;
+			$taken{$i} = $$;
+			++$changed;
 			last;
 		}
 	}
+	if($changed) {
+		seek FILE, 0, 0;
+		truncate FILE, 0 or die "can't truncate $file";
+		for my $k (keys %taken) {
+			print FILE $k . ' ' . $taken{$k} . "\n";
+		}
+	}
 	close FILE;
 	flock SEM, LOCK_UN or warn "can't unlock $file.sem";
 	close SEM;
@@ -75,8 +102,9 @@ sub mtr_require_unique_id($$$) {
 sub mtr_require_unique_id_and_wait($$$) {
 	my $ret = mtr_require_unique_id($_[0],$_[1],$_[2]);
 	while(! defined $ret) {
-		sleep 10;
+		sleep 30;
 		$ret = mtr_require_unique_id($_[0],$_[1],$_[2]);
+		print "Waiting for unique id to become available...\n" unless $ret;
 	}
 	return $ret;
 }
@@ -88,8 +116,17 @@ sub mtr_release_unique_id($$) {
 	my $file = shift;
 	my $myid = shift;
 
+	if(eval("readlink '$file'") || eval("readlink '$file.sem'")) {
+		die 'lock file is a symbolic link';
+	}
+
 	open SEM, ">", "$file.sem" or die "can't write to $file.sem";
 	flock SEM, LOCK_EX or die "can't lock $file.sem";
+
+	if(eval("readlink '$file'") || eval("readlink '$file.sem'")) {
+		die 'lock file is a symbolic link';
+	}
+
 	if(! -e $file) {
 		open FILE, ">", $file or die "can't create $file";
 		close FILE;