kernel/system/do_fork.c

   1 /* The kernel call implemented in this file:
   2  *   m_type:    SYS_FORK
   3  *
   4  * The parameters for this kernel call are:
   5  *    m1_i1:    PR_ENDPT        (parent, process that forked)
   6  *    m1_i2:    PR_SLOT         (child's process table slot)
   7  *    m1_p1:    PR_MEM_PTR      (new memory map for the child)
   8  *    m1_i3:    PR_FORK_FLAGS   (fork flags)
   9  */
  10
  11 #include "../system.h"
  12 #include "../vm.h"
  13 #include <signal.h>
  14 #include <string.h>
  15
  16 #include <minix/endpoint.h>
  17
  18 #if USE_FORK
  19
  20 /*===========================================================================*
  21  *                              do_fork                                      *
  22  *===========================================================================*/
  23 PUBLIC int do_fork(struct proc * caller, message * m_ptr)
  24 {
  25 /* Handle sys_fork().  PR_ENDPT has forked.  The child is PR_SLOT. */
  26 #if (_MINIX_CHIP == _CHIP_INTEL)
  27   reg_t old_ldt_sel;
  28   void *old_fpu_save_area_p;
  29 #endif
  30   register struct proc *rpc;            /* child process pointer */
  31   struct proc *rpp;                     /* parent process pointer */
  32   struct mem_map *map_ptr;      /* virtual address of map inside caller (PM) */
  33   int gen, r;
  34   int p_proc;
  35
  36   if(!isokendpt(m_ptr->PR_ENDPT, &p_proc))
  37         return EINVAL;
  38
  39   rpp = proc_addr(p_proc);
  40   rpc = proc_addr(m_ptr->PR_SLOT);
  41   if (isemptyp(rpp) || ! isemptyp(rpc)) return(EINVAL);
  42
  43   vmassert(!(rpp->p_misc_flags & MF_DELIVERMSG));
  44
  45   /* needs to be receiving so we know where the message buffer is */
  46   if(!RTS_ISSET(rpp, RTS_RECEIVING)) {
  47         printf("kernel: fork not done synchronously?\n");
  48         return EINVAL;
  49   }
  50
  51   map_ptr= (struct mem_map *) m_ptr->PR_MEM_PTR;
  52
  53   /* Copy parent 'proc' struct to child. And reinitialize some fields. */
  54   gen = _ENDPOINT_G(rpc->p_endpoint);
  55 #if (_MINIX_CHIP == _CHIP_INTEL)
  56   old_ldt_sel = rpc->p_seg.p_ldt_sel;   /* backup local descriptors */
  57   old_fpu_save_area_p = rpc->p_fpu_state.fpu_save_area_p;
  58 #endif
  59   *rpc = *rpp;                          /* copy 'proc' struct */
  60 #if (_MINIX_CHIP == _CHIP_INTEL)
  61   rpc->p_seg.p_ldt_sel = old_ldt_sel;   /* restore descriptors */
  62   rpc->p_fpu_state.fpu_save_area_p = old_fpu_save_area_p;
  63   if(rpp->p_misc_flags & MF_FPU_INITIALIZED)
  64         memcpy(rpc->p_fpu_state.fpu_save_area_p,
  65                rpp->p_fpu_state.fpu_save_area_p,
  66                FPU_XFP_SIZE);
  67 #endif
  68   if(++gen >= _ENDPOINT_MAX_GENERATION) /* increase generation */
  69         gen = 1;                        /* generation number wraparound */
  70   rpc->p_nr = m_ptr->PR_SLOT;           /* this was obliterated by copy */
  71   rpc->p_endpoint = _ENDPOINT(gen, rpc->p_nr);  /* new endpoint of slot */
  72
  73   rpc->p_reg.retreg = 0;        /* child sees pid = 0 to know it is child */
  74   rpc->p_user_time = 0;         /* set all the accounting times to 0 */
  75   rpc->p_sys_time = 0;
  76
  77   rpc->p_reg.psw &= ~TRACEBIT;          /* clear trace bit */
  78   rpc->p_misc_flags &= ~(MF_VIRT_TIMER | MF_PROF_TIMER | MF_SC_TRACE);
  79   rpc->p_virt_left = 0;         /* disable, clear the process-virtual timers */
  80   rpc->p_prof_left = 0;
  81
  82   /* Parent and child have to share the quantum that the forked process had,
  83    * so that queued processes do not have to wait longer because of the fork.
  84    * If the time left is odd, the child gets an extra tick.
  85    */
  86   rpc->p_ticks_left = (rpc->p_ticks_left + 1) / 2;
  87   rpp->p_ticks_left =  rpp->p_ticks_left / 2;
  88
  89   /* If the parent is a privileged process, take away the privileges from the
  90    * child process and inhibit it from running by setting the NO_PRIV flag.
  91    * The caller should explicitely set the new privileges before executing.
  92    */
  93   if (priv(rpp)->s_flags & SYS_PROC) {
  94       rpc->p_priv = priv_addr(USER_PRIV_ID);
  95       rpc->p_rts_flags |= RTS_NO_PRIV;
  96   }
  97
  98   /* Calculate endpoint identifier, so caller knows what it is. */
  99   m_ptr->PR_ENDPT = rpc->p_endpoint;
 100   m_ptr->PR_FORK_MSGADDR = (char *) rpp->p_delivermsg_vir;
 101
 102   /* Install new map */
 103   r = newmap(caller, rpc, map_ptr);
 104   FIXLINMSG(rpc);
 105
 106   /* Don't schedule process in VM mode until it has a new pagetable. */
 107   if(m_ptr->PR_FORK_FLAGS & PFF_VMINHIBIT) {
 108         RTS_SET(rpc, RTS_VMINHIBIT);
 109   }
 110
 111   /*
 112    * Only one in group should have RTS_SIGNALED, child doesn't inherit tracing.
 113    */
 114   RTS_UNSET(rpc, (RTS_SIGNALED | RTS_SIG_PENDING | RTS_P_STOP));
 115   sigemptyset(&rpc->p_pending);
 116
 117   return r;
 118 }
 119
 120 #endif /* USE_FORK */
 121