StoneDB/sql/mysqld_daemon.cc

/* Copyright (c) 2015, 2021, Oracle and/or its affiliates.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License, version 2.0,
   as published by the Free Software Foundation.

   This program is also distributed with certain software (including
   but not limited to OpenSSL) that is licensed under separate terms,
   as designated in a particular file or component or in included license
   documentation.  The authors of MySQL hereby grant you an additional
   permission to link the program and your derivative works with the
   separately licensed software that they have included with MySQL.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License, version 2.0, for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA */

#include "mysqld_daemon.h"
#include "mysqld.h"
#include "log.h"

#include <unistd.h>
#ifdef HAVE_SYS_WAIT_H
#include <sys/wait.h>
#endif

/**
  Daemonize mysqld.

  This function does sysv style of daemonization of mysqld.

  @return - returns write end of the pipe file descriptor
            which is used to notify the parent to exit.
*/
int mysqld::runtime::mysqld_daemonize()
{
  int pipe_fd[2];
  if (pipe(pipe_fd) < 0)
    return -1;

  pid_t pid= fork();
  if (pid == -1)
  {
    // Error
    close(pipe_fd[0]);
    close(pipe_fd[1]);
    return -1;
  }

  if (pid != 0)
  {
    // Parent, close write end of pipe.
    close(pipe_fd[1]);

    // Wait for first child to fork successfully.
    int rc,status;
    char waitstatus;
    while ((rc= waitpid(pid, &status, 0)) == -1 &&
           errno == EINTR)
    {
      // Retry if errno is EINTR.
    }
    if (rc == -1)
    {
      fprintf(stderr, "Unable to wait for process %lld\n",
                      static_cast<long long>(pid));
      close(pipe_fd[0]);
      close(pipe_fd[1]);
      return -1;
    }

    // Exit parent on signal from grand child
    rc= read(pipe_fd[0], &waitstatus, 1);
    close(pipe_fd[0]);

    if (rc != 1)
    {
      fprintf(stderr, "Unable to determine if daemon is running: %s\n",
                      strerror(errno));
      exit(MYSQLD_ABORT_EXIT);
    }
    else if (waitstatus != 1)
    {
      fprintf(stderr, "Initialization of mysqld failed: %d\n", waitstatus);
      exit(MYSQLD_ABORT_EXIT);
    }
    _exit(MYSQLD_SUCCESS_EXIT);
  }
  else
  {
    // Child, close read end of pipe file descriptor.
    close(pipe_fd[0]);

    int stdinfd;
    if ((stdinfd= open("/dev/null", O_RDONLY)) <= STDERR_FILENO)
    {
      close(pipe_fd[1]);
      exit(MYSQLD_ABORT_EXIT);
    }

    if (! (dup2(stdinfd, STDIN_FILENO) != STDIN_FILENO)
        && (setsid() > -1))
    {
      close(stdinfd);
      pid_t grand_child_pid= fork();
      switch (grand_child_pid)
      {
        case 0: // Grand child
          return pipe_fd[1];
        case -1:
          close(pipe_fd[1]);
          _exit(MYSQLD_FAILURE_EXIT);
        default:
          _exit(MYSQLD_SUCCESS_EXIT);
      }
    }
    else
    {
      close(stdinfd);
      close(pipe_fd[1]);
      _exit(MYSQLD_SUCCESS_EXIT);
    }
  }
}

/**
  Signal parent to exit.

  @param pipe_write_fd File Descriptor of write end of pipe.

  @param status status of the initialization done by grand child.
                1 means initialization complete and the server
                  is ready to accept client connections.
                0 means intialization aborted due to some failure.

  @note This function writes the status to write end of pipe.
  This notifies the parent which is block on read end of pipe.
*/
void mysqld::runtime::signal_parent(int pipe_write_fd, char status)
{
  if (pipe_write_fd != -1)
  {
    while (write(pipe_write_fd, &status, 1) == -1 && errno == EINTR)
    {
    // Retry write syscall if errno is EINTR.
    }

    close(pipe_write_fd);
  }
}