c - 分配给 sigaction 结构的 sa_mask 字段的正确值是什么

Question

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>

void sigint_handler(int sig) {
  write(0, "nice try\n", 10);
}
int main(void) {
  struct sigaction sa; // configure sigaction
  sa.sa_handler=sigint_handler;
  sa.sa_flags=0;
  sa.sa_mask=0;
  if (sigaction(SIGINT, & sa, NULL) == -1) { // set handler
    perror("sigaction");
    exit(1);
  }
  printf("You shall not exit!\n");
  while (1) {
    sleep(1);
  }
}

上面的代码用 g++ 编译时会报错：

sigaction.c:13:14: error: no match for ‘operator=’ (operand types are ‘__sigset_t’ and
 ‘int’)
   13 |   sa.sa_mask=0;
      |              ^
In file included from /usr/include/x86_64-linux-gnu/bits/types/sigset_t.h:4,
                 from /usr/include/x86_64-linux-gnu/sys/select.h:33,
                 from /usr/include/x86_64-linux-gnu/sys/types.h:179,
                 from /usr/include/stdlib.h:394,
                 from /usr/include/c++/9/cstdlib:75,
                 from /usr/include/c++/9/stdlib.h:36,
                 from sigaction.c:2:

在 sigaction 的手册页中，其定义为 sigset_t sa_mask；我不确定这个 sigset_t 到底是什么。它的可能值是什么。