servers/vm/break.c

   1 /* The MINIX model of memory allocation reserves a fixed amount of memory for
   2  * the combined text, data, and stack segments.  The amount used for a child
   3  * process created by FORK is the same as the parent had.  If the child does
   4  * an EXEC later, the new size is taken from the header of the file EXEC'ed.
   5  *
   6  * The layout in memory consists of the text segment, followed by the data
   7  * segment, followed by a gap (unused memory), followed by the stack segment.
   8  * The data segment grows upward and the stack grows downward, so each can
   9  * take memory from the gap.  If they meet, the process must be killed.  The
  10  * procedures in this file deal with the growth of the data and stack segments.
  11  *
  12  * The entry points into this file are:
  13  *   do_brk:      BRK/SBRK system calls to grow or shrink the data segment
  14  */
  15
  16 #define _SYSTEM 1
  17
  18 #include <minix/callnr.h>
  19 #include <minix/com.h>
  20 #include <minix/config.h>
  21 #include <minix/const.h>
  22 #include <minix/ds.h>
  23 #include <minix/endpoint.h>
  24 #include <minix/keymap.h>
  25 #include <minix/minlib.h>
  26 #include <minix/type.h>
  27 #include <minix/ipc.h>
  28 #include <minix/sysutil.h>
  29 #include <minix/syslib.h>
  30 #include <minix/bitmap.h>
  31
  32 #include <errno.h>
  33 #include <env.h>
  34
  35 #include "glo.h"
  36 #include "vm.h"
  37 #include "proto.h"
  38 #include "util.h"
  39
  40 #define DATA_CHANGED       1    /* flag value when data segment size changed */
  41 #define STACK_CHANGED      2    /* flag value when stack size changed */
  42
  43 /*===========================================================================*
  44  *                              do_brk                                       *
  45  *===========================================================================*/
  46 int do_brk(message *msg)
  47 {
  48 /* Perform the brk(addr) system call.
  49  * The parameter, 'addr' is the new virtual address in D space.
  50  */
  51         int proc;
  52
  53         if(vm_isokendpt(msg->VMB_ENDPOINT, &proc) != OK) {
  54                 printf("VM: bogus endpoint VM_BRK %d\n", msg->VMB_ENDPOINT);
  55                 return EINVAL;
  56         }
  57
  58         return real_brk(&vmproc[proc], (vir_bytes) msg->VMB_ADDR);
  59 }
  60
  61 /*===========================================================================*
  62  *                              real_brk                                     *
  63  *===========================================================================*/
  64 int real_brk(vmp, v)
  65 struct vmproc *vmp;
  66 vir_bytes v;
  67 {
  68         if(map_region_extend_upto_v(vmp, v) == OK)
  69                 return OK;
  70
  71         return(ENOMEM);
  72 }