staging: android: logger: clarify non-update of w_off in do_write_log_from_user

Add comment to explain when w_off is not updated in case of failed second
fragment copy to buffer.

Signed-off-by: Tim Bird <tim.bird@am.sony.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/android/logger.c

@@ -330,6 +330,12 @@ static ssize_t do_write_log_from_user(struct logger_log *log,
 
 	if (count != len)
 		if (copy_from_user(log->buffer, buf + len, count - len))
+			/*
+			 * Note that by not updating w_off, this abandons the
+			 * portion of the new entry that *was* successfully
+			 * copied, just above.  This is intentional to avoid
+			 * message corruption from missing fragments.
+			 */
 			return -EFAULT;
 
 	log->w_off = logger_offset(log, log->w_off + count);