ktest.pl: Change the logic to control the size of the log file emailed

If the log file for a given test is larger than the max size given then use
set the seek from the end of the log file instead of from the start of the
test.
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

tools/testing/ktest/ktest.pl

@@ -1499,18 +1499,21 @@ sub dodie {
 	my $log_file;
 
 	if (defined($opt{"LOG_FILE"})) {
-	    my $size = 0;
+	    my $whence = 0; # beginning of file
+	    my $pos = $test_log_start;
+
 	    if (defined($mail_max_size)) {
 		my $log_size = tell LOG;
 		$log_size -= $test_log_start;
 		if ($log_size > $mail_max_size) {
-		    $size = $log_size - $mail_max_size;
+		    $whence = 2; # end of file
+		    $pos = - $mail_max_size;
 		}
 	    }
 	    $log_file = "$tmpdir/log";
 	    open (L, "$opt{LOG_FILE}") or die "Can't open $opt{LOG_FILE} to read)";
 	    open (O, "> $tmpdir/log") or die "Can't open $tmpdir/log\n";
-	    seek(L, $test_log_start + $size, 0);
+	    seek(L, $pos, $whence);
 	    while (<L>) {
 		print O;
 	    }