posix_spawn.c

// From https://android.googlesource.com/platform/external/dhcpcd-6.8.2/+/refs/heads/pie-dr1-release/compat/posix_spawn.c
/*
 * dhcpcd - DHCP client daemon
 * Copyright (c) 2006-2012 Roy Marples <[email protected]>
 * All rights reserved
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/* This implementation of posix_spawn is only suitable for the needs of dhcpcd
 * but it could easily be extended to other applications. */

#include <sys/types.h>
#include <sys/wait.h>
#include <errno.h>
#include <signal.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include "posix_spawn.h"

#ifndef _NSIG
#ifdef _SIG_MAXSIG
#define _NSIG _SIG_MAXSIG + 1
#else
/* Guess */
#define _NSIG SIGPWR + 1
#endif
#endif

extern char **environ;

static int
posix_spawnattr_handle(const posix_spawnattr_t *attrp)
{
  struct sigaction sa;
  int i;
  if (attrp->posix_attr_flags & POSIX_SPAWN_SETSIGMASK)
    sigprocmask(SIG_SETMASK, &attrp->posix_attr_sigmask, NULL);
  if (attrp->posix_attr_flags & POSIX_SPAWN_SETSIGDEF) {
    memset(&sa, 0, sizeof(sa));
    sa.sa_handler = SIG_DFL;
    for (i = 1; i < _NSIG; i++) {
      if (sigismember(&attrp->posix_attr_sigdefault, i)) {
        if (sigaction(i, &sa, NULL) == -1)
          return -1;
      }
    }
  }
  return 0;
}

inline static int
is_vfork_safe(short int flags)
{
  return !(flags & (POSIX_SPAWN_SETSIGDEF | POSIX_SPAWN_SETSIGMASK));
}

int
posix_spawn(pid_t *pid, const char *path,
  const posix_spawn_file_actions_t *file_actions,
  const posix_spawnattr_t *attrp,
  char *const argv[], char *const envp[])
{
  short int flags;
  pid_t p;
  volatile int error;
  error = 0;
  flags = attrp ? attrp->posix_attr_flags : 0;
  if (file_actions == NULL && is_vfork_safe(flags))
    p = vfork();
  else
#ifdef THERE_IS_NO_FORK
    return ENOSYS;
#else
    p = fork();
#endif
  switch (p) {
  case -1:
    return errno;
  case 0:
    if (attrp) {
      error = posix_spawnattr_handle(attrp);
      if (error)
        _exit(127);
    }
    execve(path, argv, envp);
    error = errno;
    _exit(127);
  default:
    if (error != 0)
      waitpid(p, NULL, WNOHANG);
    else if (pid != NULL)
      *pid = p;
    return error;
  }
}

int
posix_spawnattr_init(posix_spawnattr_t *attr)
{
  memset(attr, 0, sizeof(*attr));
  attr->posix_attr_flags = 0;
  sigprocmask(0, NULL, &attr->posix_attr_sigmask);
  sigemptyset(&attr->posix_attr_sigdefault);
  return 0;
}

int
posix_spawnattr_setflags(posix_spawnattr_t *attr, short flags)
{
  attr->posix_attr_flags = flags;
  return 0;
}

int
posix_spawnattr_setsigmask(posix_spawnattr_t *attr, const sigset_t *sigmask)
{
  attr->posix_attr_sigmask = *sigmask;
  return 0;
}

int
posix_spawnattr_setsigdefault(posix_spawnattr_t *attr, const sigset_t *sigmask)
{
  attr->posix_attr_sigdefault = *sigmask;
  return 0;
}