Android kernel compile error - incompatible types when assigning to type ‘uid_t’ from type ‘kuid_t’

Question

I'm getting the following error when trying to compile an Android kernel and I'm not sure how to change this part of the code to solve the error.

  CC      net/netfilter/xt_IDLETIMER.o
net/netfilter/xt_IDLETIMER.c: In function ‘reset_timer’:
net/netfilter/xt_IDLETIMER.c:360:16: error: incompatible types when assigning to type ‘uid_t’ from type ‘kuid_t’
     timer->uid = sk->sk_socket->file->f_cred->uid;
                ^
scripts/Makefile.build:257: recipe for target 'net/netfilter/xt_IDLETIMER.o' failed
make[2]: *** [net/netfilter/xt_IDLETIMER.o] Error 1
scripts/Makefile.build:402: recipe for target 'net/netfilter' failed
make[1]: *** [net/netfilter] Error 2
Makefile:937: recipe for target 'net' failed
make: *** [net] Error 2

I'm using the 3.18 kernel from https://android.googlesource.com/kernel/common.git/+/android-3.18. I generated a default .config with make menuconfig and then I merged the Android base and recommended configs included in the android/configs folder. Upon doing a make bzImage I get the above error.

I'm building on a ARM machine (for ARM) running Ubuntu 14.10 and gcc 4.9.1.

The enclosing function's code is:

static void reset_timer(const struct idletimer_tg_info *info,
                        struct sk_buff *skb)
{
        unsigned long now = jiffies;
        struct idletimer_tg *timer = info->timer;
        bool timer_prev;

        spin_lock_bh(&timestamp_lock);
        timer_prev = timer->active;
        timer->active = true;
        /* timer_prev is used to guard overflow problem in time_before*/
        if (!timer_prev || time_before(timer->timer.expires, now)) {
                pr_debug("Starting Checkentry timer (Expired, Jiffies): %lu, %lu\n",
                                timer->timer.expires, now);

                /* Stores the uid resposible for waking up the radio */
                if (skb && (skb->sk)) {
                        struct sock *sk = skb->sk;
                        read_lock_bh(&sk->sk_callback_lock);
                        if ((sk->sk_socket) && (sk->sk_socket->file) &&
                    (sk->sk_socket->file->f_cred))
                                timer->uid = sk->sk_socket->file->f_cred->uid;
                        read_unlock_bh(&sk->sk_callback_lock);
                }

                /* checks if there is a pending inactive notification*/
                if (timer->work_pending)
                        timer->delayed_timer_trigger = timer->last_modified_timer;
                else {  
                        timer->work_pending = true;
                        schedule_work(&timer->work);
                }
        }

        get_monotonic_boottime(&timer->last_modified_timer);
        mod_timer(&timer->timer,
                        msecs_to_jiffies(info->timeout * 1000) + now);
        spin_unlock_bh(&timestamp_lock);
}

Answer 1

I think the following function will help you:

 static inline uid_t __kuid_val(kuid_t uid)
 {
         return uid.val;
 }

You can find it in include/linux/uidgid.h