c - siginfo 中的 si_int 是什么以及它如何影响信号传播

Question

作为向用户空间发送中断的一部分，我看到了以下代码片段，但我不明白 si_int 如何影响信号传播。

static int SendToUsrSpace(void) {
  struct siginfo info;
  struct task_struct *t;
  int ret;

  memset(&info, 0, sizeof(struct siginfo));
  info.si_signo = 44;
  info.si_code = SI_QUEUE;
  info.si_int = 1234; // WHY NOT 36 or any random number?
  [...]
  ret = send_sig_info(44, &info, t);
  [...]
}

Answer 1

我认为 explanation is in sigqueue(3) .来自文本:

       sigqueue() sends the signal specified in sig to the process whose PID
       is given in pid.  The permissions required to send a signal are the
       same as for kill(2).  As with kill(2), the null signal (0) can be
       used to check if a process with a given PID exists.

       The value argument is used to specify an accompanying item of data
       (either an integer or a pointer value) to be sent with the signal,
       and has the following type:

           union sigval {
               int   sival_int;
               void *sival_ptr;
           };

       If the receiving process has installed a handler for this signal
       using the SA_SIGINFO flag to sigaction(2), then it can obtain this
       data via the si_value field of the siginfo_t structure passed as the
       second argument to the handler.  Furthermore, the si_code field of
       that structure will be set to SI_QUEUE.

因此，1234 看起来像是一个进程可以提取的任意值(如果它有一个处理此信号的处理程序)。它看起来像是一种用信号发送数据的方法。

补充阅读:我从sigaction(2)到达sigqueue , 它列出了 siginfo_t 的数据类型。