text: /*
   * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
   *
   * SPDX-License-Identifier: BSD-2-Clause
   */
  
  #include <Kernel/Arch/InterruptDisabler.h>
  #include <Kernel/Process.h>
  #include <Kernel/TTY/TTY.h>
  
  namespace Kernel {
  
  ErrorOr<FlatPtr> Process::sys$getsid(pid_t pid)
  {
      VERIFY_PROCESS_BIG_LOCK_ACQUIRED(this)
      TRY(require_promise(Pledge::proc));
      if (pid == 0)
          return sid().value();
      auto process = Process::from_pid(pid);
      if (!process)
          return ESRCH;
      if (sid() != process->sid())
          return EPERM;
      return process->sid().value();
  }
  
  ErrorOr<FlatPtr> Process::sys$setsid()
  {
      VERIFY_PROCESS_BIG_LOCK_ACQUIRED(this)
      TRY(require_promise(Pledge::proc));
      InterruptDisabler disabler;
      bool found_process_with_same_pgid_as_my_pid = false;
      Process::for_each_in_pgrp(pid().value(), [&](auto&) {
          found_process_with_same_pgid_as_my_pid = true;
          return IterationDecision::Break;
      });
      if (found_process_with_same_pgid_as_my_pid)
          return EPERM;
      // Create a new Session and a new ProcessGroup.
  
      m_pg = TRY(ProcessGroup::try_create(ProcessGroupID(pid().value())));
      m_tty = nullptr;
      ProtectedDataMutationScope scope { *this };
      m_protected_values.sid = pid().value();
      return sid().value();
  }
  
  ErrorOr<FlatPtr> Process::sys$getpgid(pid_t pid)
  {
      VERIFY_PROCESS_BIG_LOCK_ACQUIRED(this)
      TRY(require_promise(Pledge::proc));
      if (pid == 0)
          return pgid().value();
      auto process = Process::from_pid(pid);
      if (!process)
          return ESRCH;
      return process->pgid().value();
  }
  
  ErrorOr<FlatPtr> Process::sys$getpgrp()
  {
      VERIFY_PROCESS_BIG_LOCK_ACQUIRED(this)
      TRY(require_promise(Pledge::stdio));
      return pgid().value();
  }
  
  SessionID Process::get_sid_from_pgid(ProcessGroupID pgid)
  {
      // FIXME: This xor sys$setsid() uses the wrong locking mechanism.
  
      SessionID sid { -1 };
      Process::for_each_in_pgrp(pgid, [&](auto& process) {
          sid = process.sid();
          return IterationDecision::Break;
      });
  
      return sid;
  }
  
  ErrorOr<FlatPtr> Process::sys$setpgid(pid_t specified_pid, pid_t specified_pgid)
  {
      VERIFY_PROCESS_BIG_LOCK_ACQUIRED(this)
      TRY(require_promise(Pledge::proc));
      ProcessID pid = specified_pid ? ProcessID(specified_pid) : this->pid();
      if (specified_pgid < 0) {
          // The value of the pgid argument is less than 0, or is not a value supported by the implementation.
          return EINVAL;
      }
      auto process = Process::from_pid(pid);
      if (!process)
          return ESRCH;
      if (process != this && process->ppid() != this->pid()) {
          // The value of the pid argument does not match the process ID
          // of the calling process or of a child process of the calling process.
          return ESRCH;
      }
      if (process->is_session_leader()) {
          // The process indicated by the pid argument is a session leader.
          return EPERM;
      }
      if (process->ppid() == this->pid() && process->sid() != sid()) {
          // The value of the pid argument matches the process ID of a child
          // process of the calling process and the child process is not in
          // the same session as the calling process.
          return EPERM;
      }
  
      ProcessGroupID new_pgid = specified_pgid ? ProcessGroupID(specified_pgid) : process->pid().value();
      SessionID current_sid = sid();
      SessionID new_sid = get_sid_from_pgid(new_pgid);
      if (new_sid != -1 && current_sid != new_sid) {
          // Can't move a process between sessions.
          return EPERM;
      }
      if (new_sid == -1 && new_pgid != process->pid().value()) {
          // The value of the pgid argument is valid, but is not
          // the calling pid, and is not an existing process group.
          return EPERM;
      }
      // FIXME: There are more EPERM conditions to check for here..
      process->m_pg = TRY(ProcessGroup::try_find_or_create(new_pgid));
      return 0;
  }
  
  }
  