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/* GNU Mailutils -- a suite of utilities for electronic mail
   Copyright (C) 1999-2021 Free Software Foundation, Inc.

   This library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 3 of the License, or (at your option) any later version.

   This library 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
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General
   Public License along with this library.  If not, see 
   <http://www.gnu.org/licenses/>. */

#if HAVE_CONFIG_H
# include <config.h>
#endif

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

/* See Advanced Programming in the UNIX Environment, Stevens,
 * program  10.20 for the rational for the signal handling. I
 * had to look it up, so if somebody else is curious, thats where
 * to find it.
 */
int 
mu_spawnvp (const char *prog, char *av[], int *stat)
{
  pid_t pid;
  int err = 0;
  int progstat;
  struct sigaction ignore;
  
  struct sigsave {
    int signo;
    void *handler;
    int saved;
    struct sigaction act;
  };

  static struct sigsave sigsave[] = {
    { SIGINT,  SIG_IGN, 0 },
    { SIGQUIT, SIG_IGN, 0 },
    { SIGCHLD, SIG_DFL, 0 }
  };
  static int nsigsave = sizeof (sigsave) / sizeof (sigsave[0]);

  int i;
  
  sigset_t chldmask;
  sigset_t savemask;

  if (!prog || !av)
    return EINVAL;

  ignore.sa_flags = 0;
  sigemptyset (&ignore.sa_mask);
  for (i = 0; i < nsigsave; i++)
    {
      ignore.sa_handler = sigsave[i].handler;
      if (sigaction (sigsave[i].signo, &ignore, &sigsave[i].act) < 0)
	{
	  err = errno;
	  break;
	}
      sigsave[i].saved = 1;
    }

  if (err == 0)
    {
      sigemptyset (&chldmask);	/* now block SIGCHLD */
      sigaddset (&chldmask, SIGCHLD);

      if (sigprocmask (SIG_BLOCK, &chldmask, &savemask) < 0)
	err = errno;
      else  
	{
	  pid = fork ();

	  if (pid < 0)
	    {
	      err = errno;
	    }
	  else if (pid == 0)
	    {				/* child */
	      for (i = 0; i < nsigsave; i++)
		{
		  sigaction (sigsave[i].signo, &sigsave[i].act, NULL);
		}
	      sigprocmask (SIG_SETMASK, &savemask, NULL);

	      execvp (prog, av);
	      _exit (127);		/* exec error */
	    }
	  else
	    {				/* parent */
	      while (waitpid (pid, &progstat, 0) < 0)
		if (errno != EINTR)
		  {
		    err = errno; /* error other than EINTR from waitpid() */
		    break;
		  }
	      if (err == 0 && stat)
		*stat = progstat;
	    }
	}
    }
  /* restore previous signal actions & reset signal mask */
  for (i = 0; i < nsigsave; i++)
    {
      if (!sigsave[i].saved)
	break;
      if (sigaction (sigsave[i].signo, &sigsave[i].act, NULL) < 0)
	err = err ? err : errno;
    }
  if (sigprocmask (SIG_SETMASK, &savemask, NULL) < 0)
    err = err ? err : errno;

  return err;
}

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