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/* ISC license. */
#include <sys/wait.h>
#include <unistd.h>
#include <errno.h>
#include <skalibs/uint64.h>
#include <skalibs/allreadwrite.h>
#include <skalibs/djbunix.h>
#include <skalibs/posixplz.h>
pid_t doublefork ()
{
char pack[8] ;
int fd[2] ;
pid_t child ;
if (pipe(fd) == -1) return -1 ;
child = fork() ;
switch (child)
{
case -1:
{
fd_close(fd[1]) ;
fd_close(fd[0]) ;
return -1 ;
}
case 0:
{
pid_t pid ;
fd_close(fd[0]) ;
pid = fork() ;
switch (pid)
{
case -1: _exit(errno) ;
case 0: fd_close(fd[1]) ; return 0 ;
}
uint64_pack_big(pack, pid) ;
_exit((allwrite(fd[1], pack, 8) < 8) ? errno : 0) ;
}
}
fd_close(fd[1]) ;
{
uint64_t grandchild = 0 ;
int wstat ;
if (allread(fd[0], pack, 8) < 8) grandchild = 1 ;
fd_close(fd[0]) ;
wait_pid(child, &wstat) ;
if (grandchild) return (errno = WIFSIGNALED(wstat) ? EINTR : WEXITSTATUS(wstat), -1) ;
uint64_unpack_big(pack, &grandchild) ;
return (pid_t)grandchild ;
}
}
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