ktest.pl: Fix the logic for truncating the size of the log file for email

The logic for truncating the log file for emailing based on the
MAIL_MAX_SIZE option is confusing and incorrect. Simplify it and have the
tail of the log file truncated to the max size specified in the config.

Cc: stable@vger.kernel.org
Fixes: 855d8abd ("ktest.pl: Change the logic to control the size of the log file emailed")
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

tools/testing/ktest/ktest.pl

@@ -1499,17 +1499,16 @@ sub dodie {
 	my $log_file;
 
 	if (defined($opt{"LOG_FILE"})) {
-	    my $whence = 0; # beginning of file
-	    my $pos = $test_log_start;
+	    my $whence = 2; # End of file
+	    my $log_size = tell LOG;
+	    my $size = $log_size - $test_log_start;
 
 	    if (defined($mail_max_size)) {
-		my $log_size = tell LOG;
-		$log_size -= $test_log_start;
-		if ($log_size > $mail_max_size) {
-		    $whence = 2; # end of file
-		    $pos = - $mail_max_size;
+		if ($size > $mail_max_size) {
+		    $size = $mail_max_size;
 		}
 	    }
+	    my $pos = - $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";