Where is PCB on Linux

Question

A PCB or process control block, is defined like this on Wikipedia

Process Control Block (PCB, also called Task Controlling Block,[1] Task Struct, or Switchframe) is a data structure in the operating system kernel containing the information needed to manage a particular process. The PCB is "the manifestation of a process in an operating system

and its duty is:

Process identification data
Processor state data
Process control data

So where can the PCB of a process be found?

Answer 1

In the Linux kernel, each process is represented by a task_struct in a doubly-linked list, the head of which is init_task (pid 0, not pid 1). This is commonly known as the process table.

In user mode, the process table is visible to normal users under /proc. Taking the headings for your question:

• Process identification data is the process ID (which is in the path /proc/<process-id>/...), the command line (cmd), and possibly other attributes depending on your definition of 'identification'.

• Process state data includes scheduling data (sched, stat and schedstat), what the process is currently waiting on (wchan), its environment (environ) etc.

• Process control data could be said to be its credentials (uid_map) and resource limits (limits).

So it all depends how you define your terms... but in general, all data about a process can be found in /proc.

Answer 2

PCB in linux is part of thread_info struct

struct thread_info {
struct pcb_struct   pcb;        /* palcode state */

struct task_struct  *task;      /* main task structure */
unsigned int        flags;      /* low level flags */
unsigned int        ieee_state; /* see fpu.h */

mm_segment_t        addr_limit; /* thread address space */
unsigned        cpu;        /* current CPU */
int         preempt_count; /* 0 => preemptable, <0 => BUG */
unsigned int        status;     /* thread-synchronous flags */

int bpt_nsaved;
unsigned long bpt_addr[2];      /* breakpoint handling  */
unsigned int bpt_insn[2];};


struct pcb_struct {
unsigned long ksp; - Kernel Stack Pointer
unsigned long usp; - User stack Pointer
unsigned long ptbr; - Page table address
unsigned int pcc;
unsigned int asn;
unsigned long unique;
unsigned long flags;
unsigned long res1, res2;};