+/*
+ * Allocate a block in the file system.
+ *
+ * The size of the requested block is given, which must be some
+ * multiple of fs_fsize and <= fs_bsize.
+ * A preference may be optionally specified. If a preference is given
+ * the following hierarchy is used to allocate a block:
+ * 1) allocate the requested block.
+ * 2) allocate a rotationally optimal block in the same cylinder.
+ * 3) allocate a block in the same cylinder group.
+ * 4) quadradically rehash into other cylinder groups, until an
+ * available block is located.
+ * If no block preference is given the following heirarchy is used
+ * to allocate a block:
+ * 1) allocate a block in the cylinder group that contains the
+ * inode for the file.
+ * 2) quadradically rehash into other cylinder groups, until an
+ * available block is located.
+ */