add a param to task_struct to record process schedule

taskstruct.c

// include/linux/sched.h

struct task_struct {
	int ctx;
	volatile long state;	/* -1 unrunnable, 0 runnable, >0 stopped */
	void *stack;
	atomic_t usage;
	unsigned int flags;	/* per process flags, defined below */
	unsigned int ptrace;
  //...
}

// include/linux/init_task.h
/*
 *  INIT_TASK is used to set up the first task table, touch at
 * your own risk!. Base=0, limit=0x1fffff (=2MB)
 */
#define INIT_TASK(tsk)	\
{									\
	.ctx		= 0,						\
	.state		= 0,						\
	.stack		= &init_thread_info,
	//...
}

// kernel/sched/core.c
static void __sched notrace __schedule(bool preempt)
{
	struct task_struct *prev, *next;
	unsigned long *switch_count;
	struct rq *rq;
	int cpu;

	cpu = smp_processor_id();
	rq = cpu_rq(cpu);
	rcu_note_context_switch();
	prev = rq->curr;

	prev->ctx++;
  //...
}

// fs/proc/base.c
static const struct pid_entry tgid_base_stuff[] = {
	DIR("task",       S_IRUGO|S_IXUGO, proc_task_inode_operations, proc_task_operations),
	//...
	ONE("ctx",	S_IRUSR, proc_pid_my_ctx),
	//...
}

static int proc_pid_my_ctx(struct seq_file *m, struct pid_namespace *ns,
			struct pid *pid, struct task_struct *task)
{
	seq_printf(m,"%d\n",task->ctx);
	return 0;
}