spawn for Unix

Strange enough, but implementation of spawn() functionality, i.e. execute another program, wait for it's completion and return errno could be tricky for Unix (trickiest part is errno handling). Following is a program I wrote some time ago to do that.

#include <unistd.h>
#include <stdlib.h>
#include <fcntl.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>

#include <sys/types.h>
#include <sys/wait.h>

int spawn(int argc, char** argv) {
  int pipes[2];
  int status = 0;
  int pid;
  
  if (pipe(pipes) != 0) {
    perror("pipe");
    return -1;
  }  
  fcntl(pipes[1], F_SETFD, FD_CLOEXEC);


  if ((pid = fork()) == 0) {
    int err;
    close(pipes[0]);    
    execv(argv[0], argv);
    err = errno; // errno may be function in MT case
    write(pipes[1], &err, sizeof(int));
    exit(127);
  }

  close(pipes[1]);
  if (read(pipes[0], &status, sizeof(int)) == 0) {
    status = 0;
  }

  if (pid != -1) {
    waitpid(pid, NULL, 0);
  }  

  return status;
}

int main(int argc, char** argv) {
  int s;
  char* argv1[] =  { "/bin/ls", NULL } ;
  char* argv2[] =  { "/bin/lsa", NULL} ;
  

  s = spawn(1, argv1);
  printf("for OK: %d, %s\n", s, strerror(s));
  s = spawn(1, argv2 );
  printf("for BAD: %d, %s\n", s, strerror(s));
  return 0;
}

Posted at 09:49PM Jun 07, 2007 by nike in Sun  |  Comments[4]