/* Default pager for GNU Hurd.
   Copyright (C) 1996 Free Software Foundation, Inc.
   Written by Thomas Bushnell, n/BSG.

   This file is part of the GNU Hurd.

   The GNU Hurd is free software; you can redistribute it and/or
   modify it under the terms of the GNU General Public License as
   published by the Free Software Foundation; either version 2, or (at
   your option) any later version.

   The GNU Hurd is distributed in the hope that it will be useful, but
   WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. */


#include <hurd/pager.h>
#include <hurd/store.h>

struct user_pager_info 
{
  /* Size of the object */
  vm_size_t size;

  /* One entry for each page of the object. */
  off_t *map;
};

/* Expand the P->map as necessary to handle an incoming request of the
   page at ADDR. */
static inline void
expand_map (struct user_pager_info *p, vm_offset_t addr)
{
  /* See if this is beyond the current extent */
  if (page >= pager->size)
    {
      off_t *newmap;
      vm_size_t newsize;

      newsize = page + vm_page_size;
      newmap = realloc (pager->map, size / vm_page_size * sizeof (off_t));

      bzero (pager->map + pager->size / vm_page_size * sizeof (off_t),
	     (newsize - pager->size) / vm_page_size * sizeof (off_t));
      pager->size = newsize;
      pager->map = newmap;
    }
}

error_t
pager_read_page (struct user_pager_info *pager,
		 vm_offset_t page,
		 vm_address_t *buf,
		 int *write_lock)
{
  int pfn = page / vm_page_size;
  size_t nread;
  
  /* We never request write locks. */
  *write_lock = 0;

  expand_map (pager, page);

  if (!pager->map[pfn])
    vm_allocate (mach_task_self (), buf, vm_page_size, 1);
  else
    {
      store_read (backing_store, pager->map[pfn], vm_page_size, 
		  (void **)buf, &nread);
      if (nread != vm_page_size)
	{
	  munmap ((caddr_t) *buf, nread);
	  return EIO;
	}
    }
  return 0;
}

      
error_t
pager_write_page (struct user_pager_info *pager,
		  vm_offset_t page,
		  vm_address_t buf)
{
  int pfn = page / vm_page_size;
  size_t nwritten;
  
  expand_map (pager, page);
  
  if (!pager->map[pfn])
    pager->map[pfn] = allocate_backing_page ();
  
  /* No more backing store.  Oh dear. */
  if (!pager->map[pfn])
    return EIO;
  
  err = store_write (backing_store, pager->map[pfn], (void *) buf, 
		     vm_page_size, &nwritten);
  if (!err && nwritten != vm_page_size)
    err = EIO;
  return err;
}

error_t
pager_unlock_page (struct user_pager_info *pager,
		   vm_offset_t address)
{
  return 0;
}

error_t
pager_report_extent (struct user_pager_info *pager,
		     vm_address_t *offset,
		     vm_size_t *size)
{
  *offset = 0;
  *size = pager->size;
  return 0;
}

void
pager_clear_user_data (struct user_pager_info *pager)
{
  return_backing_pages (pager->map, pager->size / vm_page_size);
  free (pager->map);
}

void
pager_dropweak (struct user_pager_info *pager)
{
}