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在ext2文件系统中，存储间接块（一次，二次，三次）的数据结构是什么，对他们的操作在哪个源文件里能找到，谢谢。 can u read the 17.6.3 Data Blocks Addressing of ULK. it is very clear there.---------------c&p here-----------------------------------------------------
The i_block field in the disk inode is an array of EXT2_N_BLOCKS components that contain logical block numbers. In the following discussion, we assume that EXT2_N_BLOCKS has the default value, namely 15. The array represents the initial part of a larger data structure, which is illustrated in Figure 17-5. As can be seen in the figure, the 15 components of the array are of 4 different types: · The first 12 components yield the logical block numbers corresponding to the first 12 blocks of the file—to the blocks that have file block numbers from 0 to 11. · The component at index 12 contains the logical block number of a block that represents a second-order array of logical block numbers. They correspond to the file block numbers ranging from 12 to b/4+11, where b is the filesystem's block size (each logical block number is stored in 4 bytes, so we divide by 4 in the formula). Therefore, the kernel must look in this component for a pointer to a block, and then look in that block for another pointer to the ultimate block that contains the file contents. · The component at index 13 contains the logical block number of a block containing a second-order array of logical block numbers; in turn, the entries of this second-order array point to third-order arrays, which store the logical block numbers that correspond to the file block numbers ranging from b/4+12 to (b/4)2+(b/4)+11. · Finally, the component at index 14 uses triple indirection: the fourth-order arrays store the logical block numbers corresponding to the file block numbers ranging from (b/4)2+(b/4)+12 to (b/4)3+(b/4)2+(b/4)+11 upward.
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