minix/kernel/system/do_segctl.c

/* The system call implemented in this file:
 *   m_type:	SYS_SEGCTL
 *
 * The parameters for this system call are:
 *    m4_l3:	SEG_PHYS	(physical base address)
 *    m4_l4:	SEG_SIZE	(size of segment)
 *    m4_l1:	SEG_SELECT	(return segment selector here)
 *    m4_l2:	SEG_OFFSET	(return offset within segment here)
 *    m4_l5:	SEG_INDEX	(return index into remote memory map here)
 */
#include "../system.h"
#include "../protect.h"

#if USE_SEGCTL

/*===========================================================================*
 *			        do_segctl				     *
 *===========================================================================*/
PUBLIC int do_segctl(m_ptr)
register message *m_ptr;	/* pointer to request message */
{
/* Return a segment selector and offset that can be used to reach a physical
 * address, for use by a driver doing memory I/O in the A0000 - DFFFF range.
 */
  u16_t selector;
  vir_bytes offset;
  int i, index;
  register struct proc *rp;
  phys_bytes phys = (phys_bytes) m_ptr->SEG_PHYS;
  vir_bytes size = (vir_bytes) m_ptr->SEG_SIZE;
  int result;

  /* First check if there is a slot available for this segment. */
  rp = proc_addr(m_ptr->m_source);
  index = -1;
  for (i=0; i < NR_REMOTE_SEGS; i++) {
      if (! rp->p_priv->s_farmem[i].in_use) {
          index = i; 
          rp->p_priv->s_farmem[i].in_use = TRUE;
          rp->p_priv->s_farmem[i].mem_phys = phys;
          rp->p_priv->s_farmem[i].mem_len = size;
          break;
      }
  }
  if (index < 0) return(ENOSPC);

  if (! machine.protected) {
      selector = phys / HCLICK_SIZE;
      offset = phys % HCLICK_SIZE;
      result = OK;
  } else {
      /* Check if the segment size can be recorded in bytes, that is, check
       * if descriptor's limit field can delimited the allowed memory region
       * precisely. This works up to 1MB. If the size is larger, 4K pages
       * instead of bytes are used.
       */
      if (size < BYTE_GRAN_MAX) {
          init_dataseg(&rp->p_ldt[EXTRA_LDT_INDEX+i], phys, size, 
          	USER_PRIVILEGE);
          selector = ((EXTRA_LDT_INDEX+i)*0x08) | (1*0x04) | USER_PRIVILEGE;
          offset = 0;
          result = OK;
      } else {
          init_dataseg(&rp->p_ldt[EXTRA_LDT_INDEX+i], phys & ~0xFFFF, 0, 
          	USER_PRIVILEGE);
          selector = ((EXTRA_LDT_INDEX+i)*0x08) | (1*0x04) | USER_PRIVILEGE;
          offset = phys & 0xFFFF;
          result = OK;
      }
  }

  /* Request successfully done. Now return the result. */
  m_ptr->SEG_INDEX = index | REMOTE_SEG;
  m_ptr->SEG_SELECT = selector;
  m_ptr->SEG_OFFSET = offset;
  return(result);
}

#endif /* USE_SEGCTL */