--- /dev/null
+#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 disk sector. */
+
+/* Initializes the free map. */
+void
+free_map_init (void)
+{
+ free_map = bitmap_create (disk_size (filesys_disk));
+ if (free_map == NULL)
+ PANIC ("bitmap creation failed--disk 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 all sectors were
+ available. */
+bool
+free_map_allocate (size_t cnt, disk_sector_t *sectorp)
+{
+ disk_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 (disk_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");
+}