Free Files and disks lessonsFiles and disks · Stage 0 · Files · Step 3

Inodes

See how a Unix file's record holds direct and indirect pointers, and work out the largest file it can describe. About 14 minutes.

Quick check

With 4 KB blocks and 4-byte pointers, how many data blocks can a single-indirect block reach?

A1,024
B12
C4,096

Show the answer

1,024. 4096 ÷ 4 = 1024 pointers fit in one block.

Your problem

Largest file size

An inode has directCount direct pointers, then single, double and triple indirect pointers, of which only the first indirectLevels are used (0 to 3: for 0 none, for 1 only single, for 2 single and double, and for 3 all three). Blocks are blockBytes bytes and pointers are pointerBytes bytes. Return the largest file size in bytes: the total number of addressable data blocks times blockBytes.

Example

blockBytes = 4096, pointerBytes = 4, directCount = 12, indirectLevels = 3 → 4402345721856

512 ≤ blockBytes ≤ 65536 powers of two · pointerBytes a power of two, at most 8 · 0 ≤ directCount ≤ 16 · 0 ≤ indirectLevels ≤ 3

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