My Notes on Linux Kernel

Hello there, I am making notes on Linux kernel I hate reading books and other people notes, well I am refering Linux Kernel Development by Robert Love, The art of Linux Kernel Design by Yang Lixiang, The Linux Kernel Primer by Claudia Sakzberg Rodriguez, The Linux Kernel Teaching, and their official documentation.

The Process:

Program executing in the system. Thread of execution(its a special process) has: Unique Program Counter Process Stack Set of Processors register

Process related system call

fork(): creates new child process done by clone() system call
exec(): create new address and loads the program into thoes addresses
wait(): enables a process to wait for termination of specific process.
exit(): Terminates the process, frees the resources.

Kernel internally calls a process Task

Process discriptor & Task struct:

Task struct-> task list & process discriptor process discriptor-> stores the information about a process that kernel needs. pid parent_pid open files process address space pending signals process state . . etc

Allocating Process discriptor (task_struct)

• allocated dynamically by “SLAB ALLOCATOR”-> it catches the process making it easy for kernel to use it. wihtout this “object_based_allocator”–> kernel will spend to much time allocating, initialisiing and freeing the same object.
• provides object reuse and cache coloring

struct thread_info

• lives at bottom (in stacks that grow down)
• lives at top (that stacks that grow up)

struct thread_info

• it has a pointer to process discriptor.
• has fixed address (easy for kernel to find)

Storing the Process discriptor:

• PID (type pid-t): usually an integer, can be changed at the boot time. maxvalue–> max value of processes that can live on the system concurrently.

• /proc/sys/kernel/pid_max :: (mine 4194304): in a working a system (not in a compiled kernel –> it is still untouched by any machine).

• wrap arround: pid’s will overlap when we increase the number of pid’s possible on a machime.
• current macro: masking out 13 LSB bits of kernel stack pointer to get current_thread_info() function.

visit :: /init/init_task.c –> /task_struct init_task :: first task to run on a system