计算 BeDS 支持的最大文件大小

Question

我正在阅读 “使用 Be 文件系统进行实用文件系统设计”，在 BeFS 中，inode 结构的“数据流”部分如下所示：

struct {
  // each block_run(8 byte) is a disk address space which maps from
  // at lease 1 block and 65536 block at most
  block_run direct[12];
  // points to a block which contains block_run of real data
  block_run indirect;
  // points to a block which contains block_run of indirect blocks
  block_run double_indirect;
}

然后这本书开始计算最小和最大文件大小，我们看最小的：每个直接block_run映射1块每个间接映射至少 4K space（512 block_run's），每个双间接映射至少 4K space（512 block_run's），每个块1KB 大小，最小文件大小结束于：

direct blocks = 12K

indirect blocks = 512K (4K indirect block maps 512 block_runs of 1K each)

double-indirect blocks = 1024MB (4K double-indirect page maps 512 indirect pages that map 512 block_runs of 4K each)

我确实对映射的双间接块感到困惑 space，它不应该是：

double-indirect blocks = 512 * 512KB (each indirect page maps 512K space?)

Answer 1

嗯，看了很多times.The double-indirect block contains a block_run which contains block address, it does NOT contains indirect block address.So 计算是正确的。

计算 BeDS 支持的最大文件大小

Calculation of max file size supported in BeFS

c

unix

filesystems

linux-kernel