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 "kernel/system.h"
  12 #include "kernel/vm.h"
  13 #include <signal.h>
  14 #include <string.h>
  15 #include <assert.h>
  16
  17 #include <minix/endpoint.h>
  18
  19 #if USE_FORK
  20
  21 /*===========================================================================*
  22  *                              do_fork                                      *
  23  *===========================================================================*/
  24 PUBLIC int do_fork(struct proc * caller, message * m_ptr)
  25 {
  26 /* Handle sys_fork().  PR_ENDPT has forked.  The child is PR_SLOT. */
  27 #if (_MINIX_CHIP == _CHIP_INTEL)
  28   reg_t old_ldt_sel;
  29   void *old_fpu_save_area_p;
  30 #endif
  31   register struct proc *rpc;            /* child process pointer */
  32   struct proc *rpp;                     /* parent process pointer */
  33   struct mem_map *map_ptr;      /* virtual address of map inside caller (PM) */
  34   int gen, r;
  35   int p_proc;
  36
  37   if(!isokendpt(m_ptr->PR_ENDPT, &p_proc))
  38         return EINVAL;
  39
  40   rpp = proc_addr(p_proc);
  41   rpc = proc_addr(m_ptr->PR_SLOT);
  42   if (isemptyp(rpp) || ! isemptyp(rpc)) return(EINVAL);
  43
  44   assert(!(rpp->p_misc_flags & MF_DELIVERMSG));
  45
  46   /* needs to be receiving so we know where the message buffer is */
  47   if(!RTS_ISSET(rpp, RTS_RECEIVING)) {
  48         printf("kernel: fork not done synchronously?\n");
  49         return EINVAL;
  50   }
  51
  52   map_ptr= (struct mem_map *) m_ptr->PR_MEM_PTR;
  53
  54   /* Copy parent 'proc' struct to child. And reinitialize some fields. */
  55   gen = _ENDPOINT_G(rpc->p_endpoint);
  56 #if (_MINIX_CHIP == _CHIP_INTEL)
  57   old_ldt_sel = rpc->p_seg.p_ldt_sel;   /* backup local descriptors */
  58   old_fpu_save_area_p = rpc->p_fpu_state.fpu_save_area_p;
  59 #endif
  60   *rpc = *rpp;                          /* copy 'proc' struct */
  61 #if (_MINIX_CHIP == _CHIP_INTEL)
  62   rpc->p_seg.p_ldt_sel = old_ldt_sel;   /* restore descriptors */
  63   rpc->p_fpu_state.fpu_save_area_p = old_fpu_save_area_p;
  64   if(rpp->p_misc_flags & MF_FPU_INITIALIZED)
  65         memcpy(rpc->p_fpu_state.fpu_save_area_p,
  66                rpp->p_fpu_state.fpu_save_area_p,
  67                FPU_XFP_SIZE);
  68 #endif
  69   if(++gen >= _ENDPOINT_MAX_GENERATION) /* increase generation */
  70         gen = 1;                        /* generation number wraparound */
  71   rpc->p_nr = m_ptr->PR_SLOT;           /* this was obliterated by copy */
  72   rpc->p_endpoint = _ENDPOINT(gen, rpc->p_nr);  /* new endpoint of slot */
  73
  74   rpc->p_reg.retreg = 0;        /* child sees pid = 0 to know it is child */
  75   rpc->p_user_time = 0;         /* set all the accounting times to 0 */
  76   rpc->p_sys_time = 0;
  77
  78   rpc->p_reg.psw &= ~TRACEBIT;          /* clear trace bit */
  79   rpc->p_misc_flags &= ~(MF_VIRT_TIMER | MF_PROF_TIMER | MF_SC_TRACE);
  80   rpc->p_virt_left = 0;         /* disable, clear the process-virtual timers */
  81   rpc->p_prof_left = 0;
  82
  83   /*
  84    * if the child process inherited a scheduler, the child process is not
  85    * runnable until it's scheduled. Otherwise the default kernel policy applies.
  86    * This is only the case of system servers, drivers and similar sensitive
  87    * processes
  88    */
  89   if (rpc->p_scheduler)
  90           RTS_SET(rpc, RTS_NO_QUANTUM);
  91
  92   /* If the parent is a privileged process, take away the privileges from the
  93    * child process and inhibit it from running by setting the NO_PRIV flag.
  94    * The caller should explicitely set the new privileges before executing.
  95    */
  96   if (priv(rpp)->s_flags & SYS_PROC) {
  97       rpc->p_priv = priv_addr(USER_PRIV_ID);
  98       rpc->p_rts_flags |= RTS_NO_PRIV;
  99   }
 100
 101   /* Calculate endpoint identifier, so caller knows what it is. */
 102   m_ptr->PR_ENDPT = rpc->p_endpoint;
 103   m_ptr->PR_FORK_MSGADDR = (char *) rpp->p_delivermsg_vir;
 104
 105   /* Install new map */
 106   r = newmap(caller, rpc, map_ptr);
 107   FIXLINMSG(rpc);
 108
 109   /* Don't schedule process in VM mode until it has a new pagetable. */
 110   if(m_ptr->PR_FORK_FLAGS & PFF_VMINHIBIT) {
 111         RTS_SET(rpc, RTS_VMINHIBIT);
 112   }
 113
 114   /*
 115    * Only one in group should have RTS_SIGNALED, child doesn't inherit tracing.
 116    */
 117   RTS_UNSET(rpc, (RTS_SIGNALED | RTS_SIG_PENDING | RTS_P_STOP));
 118   sigemptyset(&rpc->p_pending);
 119
 120   rpc->p_seg.p_cr3 = 0;
 121   rpc->p_seg.p_cr3_v = NULL;
 122
 123   return r;
 124 }
 125
 126 #endif /* USE_FORK */
 127