minix/kernel/system/do_fork.c

/* The kernel call implemented in this file:
 *   m_type:	SYS_FORK
 *
 * The parameters for this kernel call are:
 *    m1_i1:	PR_ENDPT	(parent, process that forked)
 *    m1_i2:	PR_SLOT		(child's process table slot)
 *    m1_p1:	PR_MEM_PTR	(new memory map for the child)
 *    m1_i3:	PR_FORK_FLAGS	(fork flags)
 */

#include "../system.h"
#include "../vm.h"
#include <signal.h>

#include <minix/endpoint.h>

#if USE_FORK

/*===========================================================================*
 *				do_fork					     *
 *===========================================================================*/
PUBLIC int do_fork(m_ptr)
register message *m_ptr;	/* pointer to request message */
{
/* Handle sys_fork().  PR_ENDPT has forked.  The child is PR_SLOT. */
#if (_MINIX_CHIP == _CHIP_INTEL)
  reg_t old_ldt_sel;
#endif
  register struct proc *rpc;		/* child process pointer */
  struct proc *rpp;			/* parent process pointer */
  struct mem_map *map_ptr;	/* virtual address of map inside caller (PM) */
  int i, gen, r;
  int p_proc;

  if(!isokendpt(m_ptr->PR_ENDPT, &p_proc))
	return EINVAL;

  rpp = proc_addr(p_proc);
  rpc = proc_addr(m_ptr->PR_SLOT);
  if (isemptyp(rpp) || ! isemptyp(rpc)) return(EINVAL);

  vmassert(!(rpp->p_misc_flags & MF_DELIVERMSG));

  /* needs to be receiving so we know where the message buffer is */
  if(!RTS_ISSET(rpp, RECEIVING)) {
	printf("kernel: fork not done synchronously?\n");
	return EINVAL;
  }

  /* memory becomes readonly */
  if (priv(rpp)->s_asynsize > 0) {
	printf("kernel: process with waiting asynsend table can't fork\n");
	return EINVAL;
  }

  map_ptr= (struct mem_map *) m_ptr->PR_MEM_PTR;

  /* Copy parent 'proc' struct to child. And reinitialize some fields. */
  gen = _ENDPOINT_G(rpc->p_endpoint);
#if (_MINIX_CHIP == _CHIP_INTEL)
  old_ldt_sel = rpc->p_seg.p_ldt_sel;	/* backup local descriptors */
#endif
  *rpc = *rpp;				/* copy 'proc' struct */
#if (_MINIX_CHIP == _CHIP_INTEL)
  rpc->p_seg.p_ldt_sel = old_ldt_sel;	/* restore descriptors */
#endif
  if(++gen >= _ENDPOINT_MAX_GENERATION)	/* increase generation */
	gen = 1;			/* generation number wraparound */
  rpc->p_nr = m_ptr->PR_SLOT;		/* this was obliterated by copy */
  rpc->p_endpoint = _ENDPOINT(gen, rpc->p_nr);	/* new endpoint of slot */

  rpc->p_reg.retreg = 0;	/* child sees pid = 0 to know it is child */
  rpc->p_user_time = 0;		/* set all the accounting times to 0 */
  rpc->p_sys_time = 0;

  rpc->p_reg.psw &= ~TRACEBIT;		/* clear trace bit */
  rpc->p_misc_flags &= ~(MF_VIRT_TIMER | MF_PROF_TIMER | MF_SC_TRACE);
  rpc->p_virt_left = 0;		/* disable, clear the process-virtual timers */
  rpc->p_prof_left = 0;

  /* Parent and child have to share the quantum that the forked process had,
   * so that queued processes do not have to wait longer because of the fork.
   * If the time left is odd, the child gets an extra tick.
   */
  rpc->p_ticks_left = (rpc->p_ticks_left + 1) / 2;
  rpp->p_ticks_left =  rpp->p_ticks_left / 2;	

  /* If the parent is a privileged process, take away the privileges from the 
   * child process and inhibit it from running by setting the NO_PRIV flag.
   * The caller should explicitely set the new privileges before executing.
   */
  if (priv(rpp)->s_flags & SYS_PROC) {
      rpc->p_priv = priv_addr(USER_PRIV_ID);
      rpc->p_rts_flags |= NO_PRIV;
  }

  /* Calculate endpoint identifier, so caller knows what it is. */
  m_ptr->PR_ENDPT = rpc->p_endpoint;
  m_ptr->PR_FORK_MSGADDR = (char *) rpp->p_delivermsg_vir;

  /* Install new map */
  r = newmap(rpc, map_ptr);
  FIXLINMSG(rpc);

  /* Don't schedule process in VM mode until it has a new pagetable. */
  if(m_ptr->PR_FORK_FLAGS & PFF_VMINHIBIT) {
  	RTS_LOCK_SET(rpc, VMINHIBIT);
  }

  /* Only one in group should have SIGNALED, child doesn't inherit tracing. */
  RTS_LOCK_UNSET(rpc, (SIGNALED | SIG_PENDING | P_STOP));
  sigemptyset(&rpc->p_pending);

  return r;
}

#endif /* USE_FORK */