Linux Filesystem

Hey all,
The following are the probable questions related to Linux Filesystem that can be discussed.

1. What is the need for Virtual Memory ?
2. What is the difference between the term 'Virtual Memory' and 'Virtual Address Space' ?
3. Can an user space application view the physical address Or Can an user space application access the physical address space ?
4. Is it possible for two different application to have a same virtual address but point to different physical memory ?
5. What are the functionalities performed by _start ?
6. What is the difference between Code section, Data section, ro Data section & BSS section ?
7. What is the expansion of BSS and What is the need for BSS ?
8. What is the size of the Kernel space and that of User space ? Who decides the size of it . Is it dependent/done by Processor or MMU ?
9. Tell one of the etry point to kernel ?
10. Explain the system call mechanism such that the flow is from User space to Kernel space & returning back to User space ?
11. What is the use of SYSENTER ? Does it get executed in Userspace ?
12. What is the use of SYSEXIT ? Does it get executed in Kernelspace ?
13. What is the role of __sys_open ?
14. What is the use of ABI (Application Binary Interface) document ? Who provides that manual ?
15. How do you see the size of an executable file in Linux ?
16. What is the probable size of normal vmlinux ? What kind of sizes have you come across in normal linux and embedded linux scenarios ?
17. What is vmlinux.lds ?
18. Why do you find all addresses to start after '0xC0000000' if you do 'readelf -a vmlinux' ? Can you access those addresses ?
19. What is a FDT (File Descriptor Table) ?
20. Explain the relation between File Descriptor table, Symbol File table, iNode table and harddrive/phy memory ?
21. What command is used to setup/create the relation between the device and inode ?
22. What command/API is used to create an inode for a file ?
23. What is the use of 'file_operations' ? How have you used it ?
24. What is the use of /proc/PID/maps ?
25. What is task_struct ?
26. Explain the relation between file struct,File Descriptor Table(FDT), task_struct, MM_struct, vm_area_struct, Heap, Page Global Directory(PGD), Page table(PT) & user page .
27. What is the use of ioctl fuction ?
28. Explain one level page table address translation between VA and PA with an example ?
29. Explain multi level page table address translation between VA and PA with an example ?
30. Is it better to have less level of page table address translation or more levels of page table address translation ? What is the impact on performance w.r.t memory size and memory access ?
31. What is the difference between malloc and vmalloc ?
32. What is PAE (Physical Address Extension) ?
33. What is Dual Mapping ? Can a user virtual address and kernel virtual address map to the same physical address ?

Flash Memory

The below set of queries can be used for discussion on Flash Memory.

1. Why is serial flash memory preferred in embedded systems ?

2. Flash Memory is costlier than byte programmable EEPROM - True / False ?

3. MiniSD, MemoryStick are of NAND flash memory type - True / False ?

4. Flash memory's read access time is less than that of DRAM memory 's read access time - True / False ?

5. Flash memory has infinite number of erase-write cycles - True / False ?

6. NOR flash memory's usage is for random access read - True / False ?

7. NOR flash memory is preferred for XIP - True / False ?

8. NOR flash memory is more expensive than NAND flash memory - True/False ?

9. NAND flash memory's usage is for replacing the HDD and also to save space - True/False ?

10. NAND requires copying of memory contents into memory mapped RAM - True / False ?

11. A completely erased flash memory will have all corresponding bits set to 1 - True / False ?

12. Flash memory erases in both NOR and NAND flash memory is block basis - True / False ?

13. NAND flash memroy is not suitable for micrprocessor/microcontroller ROM - True / False ?

14. NOR memory is suitable for BIOS as it gives random access read/program - True/False ?

15. Why is NAND flash memory not suitable for ROM/Program memory of Microprocessor/Microcontroller ?

16. Erasure time of NOR flash memory is more than that of NAND flash memory - True/False ?

17. Write time of NOR flash memory is more than that of NAND flash memory - True/False ?

18. Why is blockwise erasure faster than that of bytewise erasure ?

19. Flash memory is a specific type of EEPROM - True / False ?

20. NAND flash memory is used for filesystems - True / False ? Why ?

21. In general, Flash Memory erase operation is slower than program operation . And the program operation is slower than read operation - True / False ?

22. In general, SPI interface is used by serial flash memory - True / False ?

23. What are the main areas of application of serial flash in embedded systems ?

24. NAND flash memory has greater storage density and lower cost per bit than NOR flash - True / False ?

25. What is XIP ? Where is it useful ?

26. What are the common Flash Memory problems ?

27. How will you test a Flash Memory ? Have you written any power on self test ?

How will you perform the following test procedures for flash memory -

a. Address bus test

b. Data bus test

c. Control signal test

d. Missing memory device test

28. Is writing to a flash memory straightforward ? How will you set/clear a particular bit of flash memory ?

29. How do you expand program memory space using Bank Switching/Code Banking ? Consider for 8051.

30. What are the disadvantages of Bank switching/Code Banking ? Consider for 8051.

31. Any alternative method to overcome drawbacks of Bank switching ?

32. What is the use of Common area in Code Banking ?

33. What is Overlaying ? Why is it popular in embedded systems ?

Knowing the answers for the above flash memory based interview questions will be definitely helpful to you for an embedded interview . Cheers :-) All the Best !