kernel_sigaction
extern void kernel_sigaction(int, __sighandler_t);
kernel_sigaction(sig, SIG_KTHREAD);
kernel_sigaction(sig, SIG_KTHREAD_KERNEL);
kernel_sigaction(sig, SIG_IGN);
EXPORT_SYMBOL(kernel_sigaction);
kernel_sigaction(SIGCHLD, SIG_DFL);
kernel_sigaction(SIGCHLD, SIG_IGN);