asmlinkage int sys_mycall(int arg) 
{
        return 0; 
}

if (signal_pending()) 
        return -ERESTARTSYS;

if (current->need_resched)
        schedule(); /* Will sleep */ 

printk(KERN_INFO "i = %u\n", i);

__u32 ipaddress;
printk(KERN_INFO "my ip: %d.%d.%d.%d\n", NIPQUAD(ipaddress));

참고: 당신이 사용자 모드의 프로그램에서 printf() 대신 printk() 를 사용하고 있음을 알게될 때, 진정한 커널 해커가 되었음을 느끼게 될 것이다.

참고: 또한, 원래 Unix Version 6 의 소스에는 printf() 함수 위편에 다음과 같은 주석이 달려 있다. "printf() 는 잡담을 위해 사용되서는 안된다." 이를 명심하기 바란다.

/* THIS IS BAD */
foo_open (...)
{
        stuff..
        if (fail)
                return -EBUSY;
        sleep.. (might get unloaded here)
        stuff..
        MOD_INC_USE_COUNT;
        return 0;
}

/* THIS IS GOOD /
foo_open (...)
{
        MOD_INC_USE_COUNT;
        stuff..
        if (fail) {
                MOD_DEC_USE_COUNT;
                return -EBUSY;
        }
        sleep.. (safe now)
        stuff..
        return 0;
}

EXPORT_NO_SYMBOLS;

static struct block_device_operations opt_fops = {
        .open               = opt_open,
        .release            = opt_release,
        .ioctl              = opt_ioctl,
        .check_media_change = opt_media_change,
};

extern inline void br_read_lock (enum brlock_indices idx)
{
        /*
         * This causes a link-time bug message if an
         * invalid index is used:
         */
        if (idx >= __BR_END)
                __br_lock_usage_bug();

        read_lock(&__brlock_array[smp_processor_id()][idx]);
}

/*
 * Kernel pointers have redundant information, so we can use a
 * scheme where we can return either an error code or a dentry
 * pointer with the same return value.
 *
 * This should be a per-architecture thing, to allow different
 * error and pointer decisions.
 */
 #define ERR_PTR(err)    ((void *)((long)(err)))
 #define PTR_ERR(ptr)    ((long)(ptr))
 #define IS_ERR(ptr)     ((unsigned long)(ptr) > (unsigned long)(-1000))

#define copy_to_user(to,from,n)                         \
        (__builtin_constant_p(n) ?                      \
         __constant_copy_to_user((to),(from),(n)) :     \
         __generic_copy_to_user((to),(from),(n)))

/*
 * Sun people can't spell worth damn. "compatability" indeed.
 * At least we *know* we can't spell, and use a spell-checker.
 */

/* Uh, actually Linus it is I who cannot spell. Too much murky
 * Sparc assembly will do this to ya.
 */
C_LABEL(cputypvar):
        .asciz "compatability"

/* Tested on SS-5, SS-10. Probably someone at Sun applied a spell-checker. */
        .align 4
C_LABEL(cputypvar_sun4m):
        .asciz "compatible"

/* Sun, you just can't beat me, you just can't.  Stop trying,
         * give up.  I'm serious, I am going to kick the living shit
         * out of you, game over, lights out.
         */