Try to explain how the first level file index structure, level two file index structure is constructed.

First-level file index (direct index) structure: There is a set of table entries in the File catalog table entry for indexing, and each table entry is registered with the disk block number where the logical record resides. The logical record is equal to the size of the disk block number, which is 512B.

Level two file index (primary indirect index) structure: There is a set of table entries in the file directory whose contents are registered with the block number of the first level index block. The index table in the first-level indexed table block registers the disk block number where the logical record of the file resides.

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Level three file index (level two indirect index) structure: There is a set of table entries in the file directory entry whose contents are registered as the block number of the second-level indexed table block. The Index table entry in the second-level index table block registers the block number of the first-level indexed table block, and the first-level index table entry registers the disk block number where the logical record of the file resides.

Try to explain how the first level file index structure, level two file index structure is constructed.