Merge pull request #154 from hangpark/iss/153

[#153] Implement file extension

src/filesys/free-map.c

@@ -82,3 +82,52 @@ free_map_create (void)
   if (!bitmap_write (free_map, free_map_file))
     PANIC ("can't write free map");
 }
+
+/* Allocates consecutive sectors from the free map. This can be
+   used for recursive jobs.
+
+   Desired number of sectors to allocate from now is set by *CNTP.
+   But, kernel may not be able to allocate *CNTP consecutive sectors.
+   Then it decreases SIZE by half until (decreased) SIZE consecutive
+   sectors becomes available to be allocated.
+
+   After allocating n consecutive sectors, this method decrease
+   *CNTP by n so that desired number of sector reduced which can be
+   allocated in the next loop.
+
+   This returns the number of consecutive allocated sectors.
+
+   Example usage:
+
+   size_t cnt = 100; // Number of sectors to allocate.
+   size_t size = cnt;
+
+   while (cnt > 0)
+    {
+      size = free_map_allocate_r (&cnt, size, &sector);
+      if (size == 0)
+        goto fail; // Cannot allocate.
+
+      // Do whatever with size and sector.
+    }
+*/
+size_t
+free_map_allocate_r (size_t *cntp, size_t size, disk_sector_t *sectorp)
+{
+  ASSERT (cntp != NULL);
+  ASSERT (sectorp != NULL);
+
+  if (size > *cntp)
+    size = *cntp;
+
+  while (size > 0)
+    {
+      if (free_map_allocate (size, sectorp))
+        break;
+      size = size >> 1;
+    }
+
+  *cntp -= size;
+
+  return size;
+}

src/filesys/free-map.h

@@ -14,4 +14,6 @@ void free_map_close (void);
 bool free_map_allocate (size_t, disk_sector_t *);
 void free_map_release (disk_sector_t, size_t);
 
+size_t free_map_allocate_r (size_t *, size_t, disk_sector_t *);
+
 #endif /* filesys/free-map.h */