Truncating An Inode's Data Blocks

This function is used both when deleting the inode, and when a user invokes a "truncate" operation (with a given offset) on a file, so it uses the inode's size field in order to know where to start truncating from:

• Read the inode's block index from disk.
• Calculate the entry of this index, from which we need to fully truncate blocks.
• Scan the index from that point until its end, freeing each block (possibly adding it to the free list), and mark the entry as empty.
• Update accounting data (e.g. number of blocks used by the inode).
• Note: when we support files with data, we will need to get back to this function.

Originally written by guy keren