week 7 kernel programming Flashcards
write simplified structure of kernel
initialise data structures at boot time;
while (true) {
while (timer not gone off) {
assign CPU to suitable process;
execute process;
}
select next suitable process;
}
describe kernel programming
Kernel has access to all resources
Kernel programs not subject to any constraints for memory acces
or hardware access
⇒ faulty kernel programs can cause system crash
describe Interaction between kernel and user programs
Interaction between kernel and user programs
Kernel provides its functions only via special functions, called
system calls
standard C-library provides them
Have strict separation of kernel data and data for user programs
⇒ need explicit copying between user program and kernel
(copy_to_user(), copy_from_user())
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how does kernel provide functions
Kernel provides its functions only via special functions, called system calls
what library provides the system calls
stanard c libraray
does user and kernel programneed strict seperation
yes
describe interrupts in kernel
in addition, have interrupts:
kernel asks HW to perform certain action
HW sends interrupt to kernel which performs desired action
interrupts must be processed quickly
⇒ any code called from interrupts must not sleep
what are the two main modes in kernel structure for kernel code
proces context
interrupt context
what is process context
kernel code working for user programs by
executing a system call
have access to user data only in process context
Any code running in process context may be pre-empted at any
time by an interrupt
Interrupts have priority levels
Interrupt of lower priority are pre-empted by interrupts of higher
priority
wha is interrupt context
kernel code handling an interrupt (eg by a
device)
have access to user data only in process context
Any code running in process context may be pre-empted at any
time by an interrupt
Interrupts have priority levels
Interrupt of lower priority are pre-empted by interrupts of higher
priority
describe kernel modules
can add code to running kernel
useful for providing device drivers which are required only if
hardware present
modprobe inserts module into running kernel
rmmod removes module from running kernel (if unused)
lsmod lists currently running modules
what does modprobe do
inserts module into running kernel
what does rmmod do
removes module from running kernel (if unused)
what does lsmod do
lists currently running modules
describe concurrency in kernel
Correct handling concurrency in the kernel important:
Manipulation of data structures which are shared between
code running in process mode and code running in interrupt
mode
code running in interrupt mode
must happen only within critical regions
In multi-processor system even manipulation of data structures
shared between code running in process context must happen only
within critical sections
how to achieve mutual exclucion in kernel
Semaphores/Mutex
spinlocks
describe semaphores/mutexes
when entering critical section fails,
current process is put to sleep until critical region is available
⇒ only usable if all critical regions are in process context
Functions: DEFINE_MUTEX(), mutex_lock(),
mutex_unlock()
describe spinlocks
processor tries repeatedly to enter critical section
Usable anywhere
Disadvantage: Have busy waiting
Functions: spin_lock_init(), spin_lock(),
spin_unlock()
disadvantage of spin locks
Disadvantage: Have busy waiting
2 types of semaphores
Normal semaphores
Read-Write semaphores: useful if some critical regions only
read shared data structures, and this happens often
describe Programming data transfer between userspace and kernel
Linux maintains a directory called proc as interface between user space and kernel
Files in this directory do not exist on disk
Read-and write-operations on these files translated into kernel operations, together with data transfer between user space and kernel
Useful mechanism for information exchange between kernel and user space
where can we find device drivers in kernel
in the subdirectory drivers, sorted according
to category
where can we find file system in kernel
in the subdirectory fs
where can we find scheduling and process management in kernel
in the subdirectory kernel
where can we find memory managemen in kernel
in the subdirectory mm
where can we find architecture specific low-level code (including assembly code) in kernel
in the subdirectory arch
where can we find include-files in kernel
in the subdirectory include
where can we find networking code in kernel
in the subdirectory net
