/****************************************************************************
 * sched/task/task_fork.c
 *
 * SPDX-License-Identifier: Apache-2.0
 *
 * 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/config.h>

#include <sys/wait.h>
#include <stdint.h>
#include <sched.h>
#include <string.h>
#include <assert.h>
#include <errno.h>
#include <debug.h>

#include <nuttx/addrenv.h>
#include <nuttx/queue.h>
#include <nuttx/semaphore.h>
#include <nuttx/environ.h>

#include "sched/sched.h"
#include "group/group.h"
#include "task/task.h"
#include "tls/tls.h"

/* fork() requires architecture-specific support as well as waipid(). */

#ifdef CONFIG_ARCH_HAVE_FORK

/****************************************************************************
 * Private Functions
 ****************************************************************************/

/****************************************************************************
 * Name: task_setup
 *
 * Description: allocates and configures the child task's TCB.
 *
 * Input Parameters:
 *   ptcb    - tcb of current calling task
 *   parent  - tcb of parent task who to fork
 *   child   - tcb of forked child task
 *   ttype   - child tcb flag type, KERNEL or TASK
 *   retaddr - Return address
 *
 * Returned Value:
 *   This is a NuttX internal function so it follows the convention that
 *   0 (OK) is returned on success and a negated is returned on failure.
 *
 ****************************************************************************/

static int task_setup(FAR struct tcb_s *ptcb,
                      FAR struct tcb_s *parent,
                      FAR struct tcb_s *child,
                      int ttype,
                      start_t retaddr)
{
  FAR char **argv;
  size_t stack_size;
  int priority;
  int ret;

  /* Duplicate the parent tasks environment */

  ret = env_dup(child->group->tg_info, environ);
  if (ret >= 0)
    {
      /* Associate file descriptors with the new task */

      ret = group_setuptaskfiles(child, NULL, false);
      if (ret >= OK)
        {
          /* Set the task name */

          argv = nxsched_get_stackargs(parent);
          nxtask_setup_name(child, argv[0]);

          /* Allocate the stack for the TCB */

          stack_size = (uintptr_t)(FAR char *)ptcb->stack_base_ptr -
                       (uintptr_t)(FAR char *)ptcb->stack_alloc_ptr +
                       ptcb->adj_stack_size;

          ret = up_create_stack(child, stack_size, ttype);
          if (ret >= OK)
            {
#if defined(CONFIG_ARCH_ADDRENV) && defined(CONFIG_ARCH_KERNEL_STACK)
              /* Allocate the kernel stack */

              if (ttype != TCB_FLAG_TTYPE_KERNEL)
                {
                  ret = up_addrenv_kstackalloc(child);
                }
#endif

              if (ret >= OK)
                {
                  /* Get the priority of the parent task */

#ifdef CONFIG_PRIORITY_INHERITANCE
                  priority = ptcb->base_priority;   /* "Normal," unboosted priority */
#else
                  priority = ptcb->sched_priority;  /* Current priority */
#endif

                  /* Setup thread local storage */

                  ret = tls_dup_info(child, parent);
                  if (ret >= OK)
                    {
                      /* Setup to pass parameters to the new task */

                      ret = nxtask_setup_stackargs(child,
                                                   argv[0], &argv[1]);

                      if (ret >= OK)
                        {
                          /* Initialize the task control block.
                           * This calls up_initial_state()
                           */

                          sinfo("Child priority=%d start=%p\n", priority,
                                                                retaddr);
                          ret = nxtask_setup_scheduler(child, priority,
                                                       retaddr,
                                                       ptcb->entry.main,
                                                       ttype);
                        }
                    }
                }
            }
        }
    }

  return ret;
}

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

/****************************************************************************
 * Name: nxtask_setup_fork
 *
 * Description:
 *   The fork() function has the same effect as posix fork(), except that the
 *   behavior is undefined if the process created by fork() either modifies
 *   any data other than a variable of type pid_t used to store the return
 *   value from fork(), or returns from the function in which fork() was
 *   called, or calls any other function before successfully calling _exit()
 *   or one of the exec family of functions.
 *
 *   This function provides one step in the overall fork() sequence:  It
 *   Allocates and initializes the child task's TCB.  The overall sequence
 *   is:
 *
 *   1) User code calls fork().  fork() is provided in
 *      architecture-specific code.
 *   2) fork()and calls nxtask_setup_fork().
 *   3) nxtask_setup_fork() allocates and configures the child task's TCB.
 *      This consists of:
 *      - Allocation of the child task's TCB.
 *      - Initialization of file descriptors and streams
 *      - Configuration of environment variables
 *      - Allocate and initialize the stack
 *      - Setup the input parameters for the task.
 *      - Initialization of the TCB (including call to up_initial_state())
 *   4) up_fork() provides any additional operating context. up_fork must:
 *      - Initialize special values in any CPU registers that were not
 *        already configured by up_initial_state()
 *   5) up_fork() then calls nxtask_start_fork()
 *   6) nxtask_start_fork() then executes the child thread.
 *
 * Input Parameters:
 *   retaddr - Return address
 *   argsize - Location to return the argument size
 *
 * Returned Value:
 *   Upon successful completion, nxtask_setup_fork() returns a pointer to
 *   newly allocated and initialized child task's TCB.  NULL is returned
 *   on any failure and the errno is set appropriately.
 *
 ****************************************************************************/

FAR struct tcb_s *nxtask_setup_fork(start_t retaddr)
{
  FAR struct tcb_s *ptcb = this_task();
  FAR struct tcb_s *parent = NULL;
  FAR struct tcb_s *child = NULL;
  size_t heap_size;
  int ttype = TCB_FLAG_TTYPE_TASK;
  int ret = OK;

  DEBUGASSERT(retaddr != NULL);

  /* Get the type of the fork'ed task (kernel or user) */

  if ((atomic_read(&ptcb->flags) & TCB_FLAG_TTYPE_MASK) ==
      TCB_FLAG_TTYPE_KERNEL)
    {
      /* Fork'ed from a kernel thread */

      ttype = TCB_FLAG_TTYPE_KERNEL;
      parent = ptcb;
    }
  else if ((atomic_read(&ptcb->flags) & TCB_FLAG_TTYPE_MASK) ==
           TCB_FLAG_TTYPE_TASK)
    {
      parent = ptcb;
    }
  else if ((parent = nxsched_get_tcb(ptcb->group->tg_pid)) == NULL)
    {
      ret = -ENOENT;
    }

  if (ret >= OK)
    {
      /* Allocate a TCB for the child task. */

      child = kmm_zalloc(sizeof(struct tcb_s) + sizeof(struct task_group_s));
      if (!child)
        {
          serr("ERROR: Failed to allocate TCB\n");
          ret = -ENOMEM;
        }
      else
        {
          atomic_or(&child->flags, TCB_FLAG_FREE_TCB);

          /* Initialize the task join */

          nxtask_joininit(child);

          nxsem_init(&child->exit_sem, 0, 0);

          child->lockcount = ptcb->lockcount;

          /* Allocate a new task group with the same privileges
           * as the parent
           */

#if defined(CONFIG_MM_TASK_HEAP) && !defined(CONFIG_BUILD_KERNEL)
          heap_size = kumm_malloc_size(parent->group->tg_heap);
#else
          heap_size = 0;
#endif

#if defined(CONFIG_ARCH_ADDRENV)
          /* Join the parent address environment */

          if (ttype != TCB_FLAG_TTYPE_KERNEL)
            {
              ret = addrenv_join(parent, child);
            }
#endif

          if (ret >= OK)
            {
              ret = group_initialize(child, ttype, heap_size);
              if (ret >= 0)
                {
                  ret = task_setup(ptcb, parent, child, ttype, retaddr);
                  if (ret >= OK)
                    {
                      /* Now we have enough in place that we can join
                       * the group
                       */

                      group_postinitialize(child);
                      sinfo("parent=%p, returning child=%p\n",
                            parent, child);
                    }
                }
            }
        }
    }

  if (parent != ptcb)
    {
      nxsched_put_tcb(parent);
    }

  if (ret < OK)
    {
      set_errno(-ret);
      nxsched_release_tcb(child, ttype);
      child = NULL;
    }

  return child;
}

/****************************************************************************
 * Name: nxtask_start_fork
 *
 * Description:
 *   The fork() function has the same effect as fork(), except that the
 *   behavior is undefined if the process created by fork() either modifies
 *   any data other than a variable of type pid_t used to store the return
 *   value from fork(), or returns from the function in which fork() was
 *   called, or calls any other function before successfully calling _exit()
 *   or one of the exec family of functions.
 *
 *   This function provides one step in the overall fork() sequence:  It
 *   starts execution of the previously initialized TCB.  The overall
 *   sequence is:
 *
 *   1) User code calls fork()
 *   2) Architecture-specific code provides fork()and calls
 *      nxtask_setup_fork().
 *   3) nxtask_setup_fork() allocates and configures the child task's TCB.
 *      This consists of:
 *      - Allocation of the child task's TCB.
 *      - Initialization of file descriptors and streams
 *      - Configuration of environment variables
 *      - Allocate and initialize the stack
 *      - Setup the input parameters for the task.
 *      - Initialization of the TCB (including call to up_initial_state())
 *   4) fork() provides any additional operating context. fork must:
 *      - Initialize special values in any CPU registers that were not
 *        already configured by up_initial_state()
 *   5) fork() then calls nxtask_start_fork()
 *   6) nxtask_start_fork() then executes the child thread.
 *
 * Input Parameters:
 *   child - The tcb_s struct instance that created by
 *           nxtask_setup_fork() method
 *   wait_child - whether need to wait until the child is running finished
 *
 * Returned Value:
 *   Upon successful completion, fork() returns 0 to the child process and
 *   returns the process ID of the child process to the parent process.
 *   Otherwise, -1 is returned to the parent, no child process is created,
 *   and errno is set to indicate the error.
 *
 ****************************************************************************/

pid_t nxtask_start_fork(FAR struct tcb_s *child)
{
  pid_t pid;

  sinfo("Starting Child TCB=%p\n", child);
  DEBUGASSERT(child);

  /* Get the assigned pid before we start the task */

  pid = child->pid;

  /* Activate the task */

  nxtask_activate(child);

  return pid;
}

/****************************************************************************
 * Name: nxtask_abort_fork
 *
 * Description:
 *   Recover from any errors after nxtask_setup_fork() was called.
 *
 * Returned Value:
 *   None
 *
 ****************************************************************************/

void nxtask_abort_fork(FAR struct tcb_s *child, int errcode)
{
  /* The TCB was added to the active task list by nxtask_setup_scheduler() */

  dq_rem((FAR dq_entry_t *)child, list_inactivetasks());

  /* Release the TCB */

  nxsched_release_tcb(child,
                      atomic_read(&child->flags) & TCB_FLAG_TTYPE_MASK);

  set_errno(errcode);
}

#endif /* CONFIG_ARCH_HAVE_FORK */