1#include <signal.h>
2
3void (*sigset(int sig, void (*handler)(int)))(int)
4{
5	struct sigaction sa, sa_old;
6	sigset_t mask, mask_old;
7
8	sigemptyset(&mask);
9	if (sigaddset(&mask, sig) < 0)
10		return SIG_ERR;
11
12	if (handler == SIG_HOLD) {
13		if (sigaction(sig, 0, &sa_old) < 0)
14			return SIG_ERR;
15		if (sigprocmask(SIG_BLOCK, &mask, &mask_old) < 0)
16			return SIG_ERR;
17	} else {
18		sa.sa_handler = handler;
19		sa.sa_flags = 0;
20		sigemptyset(&sa.sa_mask);
21		if (sigaction(sig, &sa, &sa_old) < 0)
22			return SIG_ERR;
23		if (sigprocmask(SIG_UNBLOCK, &mask, &mask_old) < 0)
24			return SIG_ERR;
25	}
26	return sigismember(&mask_old, sig) ? SIG_HOLD : sa_old.sa_handler;
27}
28