// test_task_struct.c
#include <stdio.h>
#include <stddef.h> // for offsetof

#define container_of(ptr, type, member) ({ \
    const typeof(((type*)0)->member)* __mptr = (ptr); \
    (type*)((char*)__mptr - offsetof(type, member)); })

// Minimal doubly linked list
struct list_head {
    struct list_head *next, *prev;
};

static inline void INIT_LIST_HEAD(struct list_head *list)
{
    list->next = list;
    list->prev = list;
}

static inline void __list_add(struct list_head *new,
                              struct list_head *prev,
                              struct list_head *next)
{
    next->prev = new;
    new->next = next;
    new->prev = prev;
    prev->next = new;
}

static inline void list_add(struct list_head *new, struct list_head *head)
{
    __list_add(new, head, head->next);
}

static inline void list_add_tail(struct list_head *new, struct list_head *head)
{
    __list_add(new, head->prev, head);
}

#define list_entry(ptr, type, member) \
    container_of(ptr, type, member)

#define list_for_each(pos, head) \
    for (pos = (head)->next; pos != (head); pos = pos->next)

// A small struct like the Linux kernel's task_struct
struct task_struct {
    int pid;
    const char *comm;
    struct list_head tasks;  // linkage for global task list
} __attribute__((slr));

int main(void)
{
    struct list_head task_list;
    INIT_LIST_HEAD(&task_list);

    struct task_struct t1 = { .pid = 1, .comm = "init" };
    struct task_struct t2 = { .pid = 2, .comm = "kthreadd" };
    struct task_struct t3 = { .pid = 3, .comm = "worker" };

    INIT_LIST_HEAD(&t1.tasks);
    INIT_LIST_HEAD(&t2.tasks);
    INIT_LIST_HEAD(&t3.tasks);

    list_add_tail(&t1.tasks, &task_list);
    list_add_tail(&t2.tasks, &task_list);
    list_add_tail(&t3.tasks, &task_list);

    printf("Task list:\n");

    struct list_head *pos;
    list_for_each(pos, &task_list) {
        struct task_struct *task = list_entry(pos, struct task_struct, tasks);
        printf("  pid=%d, comm=%s\n", task->pid, task->comm);
    }

    return 0;
}