/****************************************************************************
 * libs/libc/misc/lib_fdcheck.c
 *
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.  The
 * ASF licenses this file to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance with the
 * License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
 * License for the specific language governing permissions and limitations
 * under the License.
 *
 ****************************************************************************/

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <nuttx/fdcheck.h>
#include <nuttx/lib/math32.h>

#include <debug.h>
#include <stdio.h>

#ifdef CONFIG_FDCHECK

/****************************************************************************
 * Pre-processor Definitions
 ****************************************************************************/

#define FD_SHIFT  0
#define FD_BITS   LOG2_CEIL(OPEN_MAX)
#define FD_MASK   ((1 << FD_BITS) - 1)

#define PID_SHIFT (FD_BITS + FD_SHIFT)
#define PID_BITS  (8 * sizeof(int) - 1 - PID_SHIFT)
#define PID_MASK  ((1 << PID_BITS) - 1)

/****************************************************************************
 * Public Functions
 ****************************************************************************/

/****************************************************************************
 * Name: fdcheck_restore
 *
 * Description: Obtain original fd information
 *
 * Val carries the pid and fd information.
 * The original fd information is stored in low bit of val.
 * The pid information is stored in the high bit of val.
 * For ease of understanding, let's give an example where
 * the following information is represented in 32-bit binary format
 *
 *  val       00000000 00000000 01010101 10001010
 *  fd        00000000 00000000 00000000 10001010
 *  pid       00000000 00000000 00000000 01010101
 *
 * In this function, we also check if the pid information is correct.
 * If there is an error, it will panic.
 *
 * Input Parameters:
 *   val - this val carrying pid and original fd information
 *
 * Returned Value: none
 *
 ****************************************************************************/

int fdcheck_restore(int val)
{
  int pid_expect;
  int pid_now;
  int ppid_now;

  if (val <= 2)
    {
      return val;
    }

  pid_expect = (val >> PID_SHIFT);
  pid_now = (getpid() & PID_MASK);
  ppid_now = (getppid() & PID_MASK);
  if (pid_expect != pid_now && pid_expect != ppid_now && pid_expect != 0)
    {
      ferr("pid_expect %d pid_now %d ppid_now %d\n",
        pid_expect, pid_now, ppid_now);
      PANIC();
    }

  return val & FD_MASK;
}

/****************************************************************************
 * Name: fdcheck_protect
 *
 * Description: Obtain the combined value of fd and pid
 *
 * the return value carries the pid and fd information.
 * The original fd information is stored in low bit of val.
 * The pid information is stored in high bit of val.
 * For ease of understanding, let's give an example where
 * the following information is represented in 32-bit binary format
 *
 *  fd        00000000 00000000 00000000 10001010
 *  pid       00000000 00000000 00000000 01010101
 *  val       00000000 00000000 01010101 10001010
 *
 * Input Parameters:
 *   fd - original fd
 *
 * Returned Value: the combined value of fd and pid
 *
 ****************************************************************************/

int fdcheck_protect(int fd)
{
  if (fd <= 2)
    {
      return fd;
    }

  return (fd & FD_MASK) | ((getpid() & PID_MASK) << PID_SHIFT);
}

#endif