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Solutions for the First Quiz

This document provides answers to short-answer questions related to various topics in COSC 6360 Fall 2014, including mapped files, cylinder groups, FFS metadata updates, UNIX set-userid bit, file access control lists, and file system blocks.

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Solutions for the First Quiz

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  1. Solutions for the First Quiz COSC 6360 Fall 2014

  2. Questions with short answers • What is the main advantage of mapped files?

  3. Questions with short answers • What is the main advantage of mapped files? • Mapped files reduce the number of context switches in the file subsystem.

  4. Questions with short answers • What is the main advantage of cylinder groups?

  5. Questions with short answers • What is the main advantage of cylinder groups? • Since each cylinder group can contain both i-nodes and data blocks, the contents of most files can be located in the same cylinder group as their i-node.

  6. Questions with short answers • Why does FFS use blocking writes for all its metadata updates?

  7. Questions with short answers • Why does FFS use blocking writes for all its metadata updates? • To ensure that all metadata updates are written to disk in the right order.

  8. Questions with short answers • In MACH, what should be the inheritance attribute of an address range that contains a mapped file?

  9. Questions with short answers • In MACH, what should be the inheritance attribute of an address range that contains a mapped file? • Shared

  10. Questions with short answers • What does the UNIX set-userid bit allow?

  11. Questions with short answers • What does the UNIX set-userid bit allow? • It allows a program to be executed with the rights of its owner rather than with the rights of the user executing it.

  12. Questions with short answers • Where does UNIX store file access control lists?Hint: you probably know them under a different name.

  13. Questions with short answers • Where does UNIX store file access control lists?Hint: you probably know them under a different name. • In the i-node of each file

  14. File system • A 32-bit UNIX file system has 8 kilobyte blocks and i-nodes with 15 block addresses. How many file blocks can be accessed (4×5 points) • Directly from the i-node? • With one level of indirection? • With two levels of indirections? • With three levels of indirections?

  15. File System Other stuff 0 2 11 12 13 … … … … 15 block addresses 1 1 3 14 … Not needed 12 direct block addresses … … 2,048 indirect block addresses … … Block size =8 KB32-bit addresses 1,0241,024 double indirect block addresses but we only use 512K – 2,048 – 12 of them

  16. File system • A 32-bit UNIX file system has 8 kilobyte blocks and i-nodes with 15 block addresses. How many file blocks can be accessed (4×5 points) • Directly from the i-node? 12blocks • With one level of indirection? • With two levels of indirections? • With three levels of indirections?

  17. File system • A 32-bit UNIX file system has 8 kilobyte blocks and i-nodes with 15 block addresses. How many file blocks can be accessed (4×5 points) • Directly from the i-node? 12blocks • With one level of indirection? 2,048 blocks • With two levels of indirections? • With three levels of indirections?

  18. File system • A 32-bit UNIX file system has 8 kilobyte blocks and i-nodes with 15 block addresses. How many file blocks can be accessed (4×5 points) • Directly from the i-node? 12blocks • With one level of indirection? 2,048 blocks • With two levels of indirections?512K – 2K – 12blocks • With three levels of indirections?

  19. File system • A 32-bit UNIX file system has 8 kilobyte blocks and i-nodes with 15 block addresses. How many file blocks can be accessed (4×5 points) • Directly from the i-node? 12blocks • With one level of indirection? 2,048 blocks • With two levels of indirections?512K – 2K – 12blocks • With three levels of indirections? 0 blocks

  20. Virtual memory • Consider the Two-Handed Clock policy of Berkeley UNIX, where the page-referenced bit is simulated by software. • What is the function of the first hand of that clock? (5 easy points)

  21. Virtual memory • Consider the Two-Handed Clock policy of Berkeley UNIX, where the page-referenced bit is simulated by software. • What is the function of the first hand of that clock? (5 easy points) • It invalidates all the pages it touches.

  22. Virtual memory • Consider the Two-Handed Clock policy of Berkeley UNIX, where the page-referenced bit is simulated by software. • What is the function of the second hand of the clock? (5 easy points)

  23. Virtual memory • Consider the Two-Handed Clock policy of Berkeley UNIX, where the page-referenced bit is simulated by software. • What is the function of the second hand of the clock? (5 easy points) • It expels from memory all the invalid pages it touches.

  24. Virtual memory • Consider the Two-Handed Clock policy of Berkeley UNIX, where the page-referenced bit is simulated by software. • What would happen if the second hand follows too closely the first one? (5 points)

  25. Virtual memory • Consider the Two-Handed Clock policy of Berkeley UNIX, where the page-referenced bit is simulated by software. • What would happen if the second hand follows too closely the first one? (5 points) • Pages would be expelled too quickly • There will be too many page faults

  26. Virtual memory • Consider the Two-Handed Clock policy of Berkeley UNIX, where the page-referenced bit is simulated by software. • What would happen if the second hand is too far apart from the first one? (5 points)

  27. Virtual memory • Consider the Two-Handed Clock policy of Berkeley UNIX, where the page-referenced bit is simulated by software. • What would happen if the second hand is too far apart from the first one? (5 points) • Pages would remain too long in main memory after their last access. • It would be more difficult to find free page frames.

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