[SOLVED] Can we use kernel interface in application programs?

ayyasprings · 01-11-2019, 02:46 AM

Hi,

Can we use kernel provided implementation interfaces in User space programs?

For example

Code:

#include <sys/sem.h>
int semctl(int sem_id, int sem_num, int command, ...);
int semget(key_t key, int num_sems, int sem_flags);
int semop(int sem_id, struct sembuf *sem_ops, size_t num_sem_ops);

were meant for user application development.

Instead can we use the following interfaces of kernel impementation of semaphore

Code:

#include<asm/semaphore.h>
void sem_init(struct semaphore *sem, int val);
void down(struct semaphore *sem);
int down_interruptible(struct semaphore *sem);
int down_trylock(struct semaphore *sem);
void up(struct semaphore * sem);

in user application program.

please reply. I am newbie to linux kernel.

berndbausch · 01-11-2019, 03:09 AM

The kernel has an interface for applications, documented in section 2 of the manual. The reasons for providing this interface is the same as for any other software that provides a service: The interface is stable, whereas internal implementation can change from release to release (or bug fix to bug fix), and you don't want to allow processes to mess around in the kernel, thereby affecting other processes.

You can't use internal kernel functions in your application because you have no library that implements them. If you want to link your application with the kernel's semaphore library, this library depends on other kernel code, and in the end you link your application with the entire kernel. In other words, you create a new kernel that includes your application. I don't think this is your goal.

The real question is: What do you want to achieve? Why do you think you need the kernel's internal semaphore code?

ehartman · 01-11-2019, 03:18 AM

Quote:

Originally Posted by ayyasprings

Can we use kernel provided implementation interfaces in User space programs?

Yes, but through the C library (2) calls only (see man 2 <function> for details.
As your program runs in user space and the kernel in kernel space, no direct calls are possible (they have two different address ranges), that's why the standard library has these interface functions implemented.
I.e. READ(2) is the low-level call under FREAD(3)
and UNLINK(2) is what will be used at the lowest level by the 'rm' program.