1 files changed, 131 insertions, 0 deletions
diff --git a/defpager/backing.c b/defpager/backing.c
new file mode 100644
index 00000000..5e6fbb65
--- /dev/null
+++ b/defpager/backing.c
@@ -0,0 +1,131 @@
+/* Backing store management 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/store.h>
+
+const struct store_class *const permitted_classes[] = 
+{
+  &store_device_class, &store_ileave_class, &store_concat_class, 0
+};
+
+/* Allocation map, by PAGE.  */  
+/* If a bit is SET the corresponding PAGE is free. */
+char *bmap;
+
+/* Number of bytes in bmap */
+size_t bmap_len;
+
+/* Allocation rotor */
+char *bmap_rotor;
+
+struct mutex bmap_lock;
+
+error_t
+init_backing (char *name)
+{
+  error_t err;
+  int i;
+
+  err = store_open (name, STORE_NO_FILEIO, &permitted_classes, &backing_store);
+  if (err)
+    return err;
+  
+  bmap_len = backing_store->size / vm_page_size / NBBY;
+  bmap = malloc (bmap_len);
+  for (i = 0; i < bmap_len; i++)
+    bmap[i] = 0xff;
+  bmap_rotor = bmap;
+
+  /* Mark the very first page as occupied.  This makes sure we never
+     return zero offsets from allocate_backing_page (which
+     conventionally means that there is no space left.  It also makes
+     sure we don't tromp on the misfeature in Linux of using the first
+     page for permanent data. */
+  *bmap_rotor |= 1;
+}
+
+int
+allocate_backing_page ()
+{
+  int wrapped;
+  int bit;
+  int pfn;
+
+  mutex_lock (&bmap_lock);
+
+  wrapped = (bmap_rotor == bmap);
+
+  while (!wrapped || bmap_rotor < bmap + bmap_len)
+    {
+      if (bmap[bmap_rotor])
+	break;
+      bmap_rotor++;
+      if (bmap_rotor >= bmap + bmap_len)
+	wrapped++;
+    }
+  
+  if (wrapped == 2)
+    {
+      /* Didn't find one... */
+      mutex_unlock (&bmap_lock);
+      printf ("WARNING: Out of paging space; pageout failing.");
+      return 0;
+    }
+  
+  /* Find which bit */
+  bit = ffs (*bmap_rotor);
+  assert (bit);
+  bit--;
+  
+  /* Mark it */
+  *bmap_rotor |= 1 << bit;
+  
+  /* Return the correct offset */
+  pfn = (bmap_rotor - bmap) * 8 + bit;
+
+  mutex_unlock (&bmap_lock);
+  
+  return pfn * (vm_page_size / store->block_size);
+}
+
+
+void
+return_backing_pages (off_t *map, int maplen)
+{
+  int i;
+  
+  mutex_lock (&bmap_lock);
+  for (i = 0; i < maplen; i++)
+    {
+      int pfn;
+      char *b;
+      int bit;
+
+      pfn = map[i] / (vm_page_size / store->block_size);
+      b = bmap + pfn & ~7;
+      bit = pfn & 7;
+      
+      assert ((*b & (1 << bit)) == 0);
+      *b |= 1 << bit;
+    }
+  mutex_unlock (&bmap_lock);
+}
+