I am new in Linux kernel development. I have implemented a system call say my_pid in linux kernel 2.6. I want to call getpid system call from my system call. How can I do it?
I want something like:
pid_t my_pid(){ return getpid(); }
Also from C in user-space I can call any system call using: syscall(); What is the generic way to do this in kernel mode?
There is no generic way of doing this.
If you are in kernel space, you should invoke kernel functions that implement the system call functionality directly instead of using syscall-type instructions, or use other means of extracting the desired information / affecting the desired action.
For the specific case of getpid(), you can simply use current->pid.
The kernel name current is always a pointer to the current task_struct, which is defined via <linux/sched.h> (search for struct task_struct). Code that accesses members of that usually gets inlined, i.e. there's not even a function call (and much less a system call) required to get these when your code is running as part of the kernel.
