Vfrdtyky

I'm reading "Practical File System Design with the Be File System", in the BeFS, the "data stream" part of the inode struct looks like this:

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;

}

Then this book begin a calculation of the minimum and maximum file size, let's see the minimum one: each direct block_run maps 1 block
and each indirect maps at least 4K space (512 block_run's), and each double indirect maps at least 4K space (512 block_run's), and each block with 1KB size, the minimum file size ends at:

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)

I do confused about the double-indirect blocks mapped space, doesn't it should be:

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

Hmm,I figured it out after read that chapter many times.The double-indirect block contains a block_run which contains block address,it does NOT contains indirect block address.So the calculation is correct.