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 #include <minix/u64.h>
  19
  20 #if USE_FORK
  21
  22 /*===========================================================================*
  23  *                              do_fork                                      *
  24  *===========================================================================*/
  25 int do_fork(struct proc * caller, message * m_ptr)
  26 {
  27 /* Handle sys_fork().  PR_ENDPT has forked.  The child is PR_SLOT. */
  28 #if defined(__i386__)
  29   char *old_fpu_save_area_p;
  30 #endif
  31   register struct proc *rpc;            /* child process pointer */
  32   struct proc *rpp;                     /* parent process pointer */
  33   int gen;
  34   int p_proc;
  35   int namelen;
  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   /* make sure that the FPU context is saved in parent before copy */
  53   save_fpu(rpp);
  54   /* Copy parent 'proc' struct to child. And reinitialize some fields. */
  55   gen = _ENDPOINT_G(rpc->p_endpoint);
  56 #if defined(__i386__)
  57   old_fpu_save_area_p = rpc->p_seg.fpu_state;
  58 #endif
  59   *rpc = *rpp;                          /* copy 'proc' struct */
  60 #if defined(__i386__)
  61   rpc->p_seg.fpu_state = old_fpu_save_area_p;
  62   if(proc_used_fpu(rpp))
  63         memcpy(rpc->p_seg.fpu_state, rpp->p_seg.fpu_state, FPU_XFP_SIZE);
  64 #endif
  65   if(++gen >= _ENDPOINT_MAX_GENERATION) /* increase generation */
  66         gen = 1;                        /* generation number wraparound */
  67   rpc->p_nr = m_ptr->PR_SLOT;           /* this was obliterated by copy */
  68   rpc->p_endpoint = _ENDPOINT(gen, rpc->p_nr);  /* new endpoint of slot */
  69
  70   rpc->p_reg.retreg = 0;        /* child sees pid = 0 to know it is child */
  71   rpc->p_user_time = 0;         /* set all the accounting times to 0 */
  72   rpc->p_sys_time = 0;
  73
  74 #if defined(__i386__)
  75   rpc->p_reg.psw &= ~TRACEBIT;          /* clear trace bit */
  76 #endif
  77   rpc->p_misc_flags &=
  78         ~(MF_VIRT_TIMER | MF_PROF_TIMER | MF_SC_TRACE | MF_SPROF_SEEN);
  79   rpc->p_virt_left = 0;         /* disable, clear the process-virtual timers */
  80   rpc->p_prof_left = 0;
  81
  82   /* Mark process name as being a forked copy */
  83   namelen = strlen(rpc->p_name);
  84 #define FORKSTR "*F"
  85   if(namelen+strlen(FORKSTR) < sizeof(rpc->p_name))
  86         strcat(rpc->p_name, FORKSTR);
  87
  88   /* the child process is not runnable until it's scheduled. */
  89   RTS_SET(rpc, RTS_NO_QUANTUM);
  90   reset_proc_accounting(rpc);
  91
  92   make_zero64(rpc->p_cpu_time_left);
  93   make_zero64(rpc->p_cycles);
  94   make_zero64(rpc->p_kcall_cycles);
  95   make_zero64(rpc->p_kipc_cycles);
  96
  97   /* If the parent is a privileged process, take away the privileges from the
  98    * child process and inhibit it from running by setting the NO_PRIV flag.
  99    * The caller should explicitely set the new privileges before executing.
 100    */
 101   if (priv(rpp)->s_flags & SYS_PROC) {
 102       rpc->p_priv = priv_addr(USER_PRIV_ID);
 103       rpc->p_rts_flags |= RTS_NO_PRIV;
 104   }
 105
 106   /* Calculate endpoint identifier, so caller knows what it is. */
 107   m_ptr->PR_ENDPT = rpc->p_endpoint;
 108   m_ptr->PR_FORK_MSGADDR = (char *) rpp->p_delivermsg_vir;
 109
 110   /* Don't schedule process in VM mode until it has a new pagetable. */
 111   if(m_ptr->PR_FORK_FLAGS & PFF_VMINHIBIT) {
 112         RTS_SET(rpc, RTS_VMINHIBIT);
 113   }
 114
 115   /*
 116    * Only one in group should have RTS_SIGNALED, child doesn't inherit tracing.
 117    */
 118   RTS_UNSET(rpc, (RTS_SIGNALED | RTS_SIG_PENDING | RTS_P_STOP));
 119   (void) sigemptyset(&rpc->p_pending);
 120
 121 #if defined(__i386__)
 122   rpc->p_seg.p_cr3 = 0;
 123   rpc->p_seg.p_cr3_v = NULL;
 124 #elif defined(__arm__)
 125   rpc->p_seg.p_ttbr = 0;
 126   rpc->p_seg.p_ttbr_v = NULL;
 127 #endif
 128
 129   return OK;
 130 }
 131
 132 #endif /* USE_FORK */
 133