Sys.c中的具体实现

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陈品维 14051409

SYSCALL_DEFINE0(mycall)
{
        printk("cpw is Here!\n");
        return 0;
}
SYSCALL_DEFINE3(mysetnice, int, pid, int, flag, int, nicevalue)
{
    // set_one_prio
    // set_user_nice
    struct task_struct *g, *p;
    struct user_struct *user;
    const struct cred *cred = current_cred();
    long niceval, retval = -ESRCH;
    struct pid *pgrp;
    kuid_t uid;
    // set 
    int error = -EINVAL;
    niceval = (long)nicevalue;
    // hook
    int which = PRIO_PROCESS;
    int who = pid;
    printk("Aklis's SysCall!\n");
    if (which > PRIO_USER || which < PRIO_PROCESS)
        return -EINVAL;
    error = -ESRCH;
    if (flag == 1) {
        if (niceval < MIN_NICE)
            niceval = MIN_NICE;
        if (niceval > MAX_NICE)
            niceval = MAX_NICE;
    }
    rcu_read_lock();  // 上锁
    read_lock(&tasklist_lock); // 上锁
    if (flag == 1) {
        switch (which) {
            case PRIO_PROCESS:
                if (who)
                    p = find_task_by_vpid(who);
                else 
                    p = current;
                if (p)
                    error = set_one_prio(p, niceval, error);
                break;
        }
        read_unlock(&tasklist_lock); // 解锁
        rcu_read_unlock();
        return error;
    }else if (flag == 0){
        printk("Aklis want to get the nice!\n");
        switch (which) {
        case PRIO_PROCESS:
            if (who)
                p = find_task_by_vpid(who);
            else
                p = current;
            if (p) {
                niceval = (task_nice(p));
                if (niceval >= MIN_NICE)
                    retval = niceval;
            }
            break;
        }
    }
    read_unlock(&tasklist_lock); // 解锁
    rcu_read_unlock();
    return retval;
}