provided code

src/filesys/free-map.c

@@ -0,0 +1,85 @@
+#include "filesys/free-map.h"
+#include <bitmap.h>
+#include <debug.h>
+#include "filesys/file.h"
+#include "filesys/filesys.h"
+#include "filesys/inode.h"
+
+static struct file *free_map_file;   /* Free map file. */
+static struct bitmap *free_map;      /* Free map, one bit per sector. */
+
+/* Initializes the free map. */
+void
+free_map_init (void) 
+{
+  free_map = bitmap_create (block_size (fs_device));
+  if (free_map == NULL)
+    PANIC ("bitmap creation failed--file system device is too large");
+  bitmap_mark (free_map, FREE_MAP_SECTOR);
+  bitmap_mark (free_map, ROOT_DIR_SECTOR);
+}
+
+/* Allocates CNT consecutive sectors from the free map and stores
+   the first into *SECTORP.
+   Returns true if successful, false if not enough consecutive
+   sectors were available or if the free_map file could not be
+   written. */
+bool
+free_map_allocate (size_t cnt, block_sector_t *sectorp)
+{
+  block_sector_t sector = bitmap_scan_and_flip (free_map, 0, cnt, false);
+  if (sector != BITMAP_ERROR
+      && free_map_file != NULL
+      && !bitmap_write (free_map, free_map_file))
+    {
+      bitmap_set_multiple (free_map, sector, cnt, false); 
+      sector = BITMAP_ERROR;
+    }
+  if (sector != BITMAP_ERROR)
+    *sectorp = sector;
+  return sector != BITMAP_ERROR;
+}
+
+/* Makes CNT sectors starting at SECTOR available for use. */
+void
+free_map_release (block_sector_t sector, size_t cnt)
+{
+  ASSERT (bitmap_all (free_map, sector, cnt));
+  bitmap_set_multiple (free_map, sector, cnt, false);
+  bitmap_write (free_map, free_map_file);
+}
+
+/* Opens the free map file and reads it from disk. */
+void
+free_map_open (void) 
+{
+  free_map_file = file_open (inode_open (FREE_MAP_SECTOR));
+  if (free_map_file == NULL)
+    PANIC ("can't open free map");
+  if (!bitmap_read (free_map, free_map_file))
+    PANIC ("can't read free map");
+}
+
+/* Writes the free map to disk and closes the free map file. */
+void
+free_map_close (void) 
+{
+  file_close (free_map_file);
+}
+
+/* Creates a new free map file on disk and writes the free map to
+   it. */
+void
+free_map_create (void) 
+{
+  /* Create inode. */
+  if (!inode_create (FREE_MAP_SECTOR, bitmap_file_size (free_map)))
+    PANIC ("free map creation failed");
+
+  /* Write bitmap to file. */
+  free_map_file = file_open (inode_open (FREE_MAP_SECTOR));
+  if (free_map_file == NULL)
+    PANIC ("can't open free map");
+  if (!bitmap_write (free_map, free_map_file))
+    PANIC ("can't write free map");
+}