Week 6: System Calls + Kernel

Question 1

What are some of the services system calls provide?

Answer 1

File manipulation.
Process control.
Device management.
Information maintenance.
Communications.

Question 2

What are the file manipulation modes?

Answer 2

Read: 4
Write: 2
Execute: 1

Read + Execute = 5

Question 3

What are the four groups found in permission?

Answer 3

OUGO
O: Special flag
U: User
G: User group
O: Other users

Question 4

What are the two system calls for opening and closing files?

Answer 4

int open(char * path, int flags, mode u mode): Opens/creates file
int close(fd):

Question 5

What type of OS is Linux?

Answer 5

Monolithic, meaning entire OS (drivers, file system and application IPC) is working in kernel space.
And modular.

Question 6

What are the two main modes for kernel code?

Answer 6

Process Context: Working for user programs by executing a system call.
Interrupt Context: Handling an interrupt, preempted by higher priority interrupt.

Question 7

What are the main functions of the Linux kernel?

Answer 7

Device drivers.
File systems.
Scheduling and process management.
Memory management.
Networking.
Architecture specific, low level code (e.g. assembly).
Include-files.

Question 8

What is the proc file system?

Answer 8

A virtual file system that provides a way to interact with kernel space from user space.

Question 9

What are the advantages of kernel modules?

Answer 9

Save memory.
Error in module does not affect kernel.
Faster to maintain and debug.
Easier to maintain multiple machines on a single code base.

Question 10

What are the disadvantages of kernel modules?

Answer 10

Size: Consumes unpagable memory.

Security.

Question 11

What are the types of module in the kernel?

Answer 11

In-Source Tree: Present in source code.

Out-of-Tree: Not present in source code.

Question 12

What two functions are needed for every module?

Answer 12

Initialize: Module loaded into kernel.
Cleanup: Just before module is removed.