1/* $NetBSD: dup2_pass_on_exec.c,v 1.2 2022/10/08 16:12:50 christos Exp $ */ 2 3/*++ 4/* NAME 5/* dup2_pass_on_exec 1 6/* SUMMARY 7/* dup2 close-on-exec behavior test program 8/* SYNOPSIS 9/* dup2_pass_on_exec 10/* DESCRIPTION 11/* dup2_pass_on_exec sets the close-on-exec flag on its 12/* standard input and then dup2() to duplicate it. 13/* Posix-1003.1 specifies in section 6.2.1.2 that dup2(o,n) should behave 14/* as: close(n); n = fcntl(o, F_DUPFD, n); as long as o is a valid 15/* file-descriptor, n!=o, and 0<=n<=[OPEN_MAX]. 16/* Section 6.5.2.2 states that the close-on-exec flag of the result of a 17/* successful fcntl(o, F_DUPFD, n) is cleared. 18/* 19/* At least Ultrix4.3a does not clear the close-on-exec flag of n on 20/* dup2(o, n). 21/* DIAGNOSTICS 22/* Problems are reported to the standard error stream. 23/* LICENSE 24/* .ad 25/* .fi 26/* The Secure Mailer license must be distributed with this software. 27/* AUTHOR(S) 28/* Christian von Roques <roques@pond.sub.org> 29/* Forststrasse 71 30/* 76131 Karlsruhe, GERMANY 31/*--*/ 32 33#include <stdio.h> 34#include <fcntl.h> 35#include <unistd.h> 36#include <stdlib.h> 37 38#define DO(s) if (s < 0) { perror(#s); exit(1); } 39 40int main(int unused_argc, char **unused_argv) 41{ 42 int res; 43 44 printf("Setting the close-on-exec flag of file-descriptor 0.\n"); 45 DO(fcntl(0, F_SETFD, 1)); 46 47 printf("Duplicating file-descriptor 0 to 3.\n"); 48 DO(dup2(0, 3)); 49 50 printf("Testing if the close-on-exec flag of file-descriptor 3 is set.\n"); 51 DO((res = fcntl(3, F_GETFD, 0))); 52 if (res & 1) 53 printf( 54"Yes, a newly dup2()ed file-descriptor has the close-on-exec \ 55flag cloned.\n\ 56THIS VIOLATES Posix1003.1 section 6.2.1.2 or 6.5.2.2!\n\ 57You should #define DUP2_DUPS_CLOSE_ON_EXEC in sys_defs.h \ 58for your OS.\n"); 59 else 60 printf( 61"No, a newly dup2()ed file-descriptor has the close-on-exec \ 62flag cleared.\n\ 63This complies with Posix1003.1 section 6.2.1.2 and 6.5.2.2!\n"); 64 65 return 0; 66} 67