Data Blocks

• The tail end of the inode records where the data is actually stored:

 /* include/linux/ext2_fs.h */
 struct ext2_inode {
 ...
 __u32 i_block[EXT2_N_BLOCKS];/* Pointers to blocks */
 ...
 };

• Data blocks are addressed by with 32-bit numbers starting from 0 within each block group

• The inode has room for 15 block addresses (that's EXT2_N_BLOCKS)

• Elements 0..11 store the addresses of the first 12 blocks in the file

• What if a file needs more than 12 blocks?

• Block 12 does not contain any file data itself

  • Instead, it is stuffed full of addresses for more data blocks

  • It's called an indirect block

  • This suffices for files up to 2060 blocks

• Block 13 is the double indirect block

• This suffices for files up to 2060 + 4194304 blocks = 34.376 Gb

• Block 14 is a triple indirect block