C- EPOLL事件不会提高Sigio

Question

根据我的研究，您可以将epoll文件描述符添加到民意调查，选择或其他epoll，如果可用事件，它将返回花粉蛋白。根据Epoll（7）：

   Q3  Is the epoll file descriptor itself poll/epoll/selectable?
   A3  Yes.  If an epoll file descriptor has events waiting, then it  will
       indicate as being readable.

这在我的测试中起作用。但是，我现在正在尝试将O_ASYNC应用于我的epoll FD，以便在事件准备就绪时会增加Sigio：

//Epoll setup code - trySc runs perror on the string and exits if the function returns -1
int epollFd = epoll_create1(EPOLL_CLOEXEC);
trySc(epollFd, "epoll_create1");
trySc(fcntl(epollFd, F_SETOWN, getpid()), "fcntl F_SETOWN");
trySc(fcntl(epollFd, F_SETSIG, SIGIO), "fcntl F_SETSIG");
int oldFlags = fcntl(epollFd, F_GETFL, 0);
trySc(oldFlags, "fcntl F_GETFL");
trySc(fcntl(epollFd, F_SETFL, oldFlags | O_ASYNC), "fcntl F_SETFL");
//Set up SIGIO and get a socket fd, you don't need to see this
//All my handler does is exit - it's a definite method of knowing SIGIO was raised
struct epoll_event event = {
        .events = EPOLLIN | EPOLLET,
        .data.fd = socketFd
};
trySc(epoll_ctl(epollFd, EPOLL_CTL_ADD, socketFd, &event), "epoll_ctl");
//Then connect
while(1){
        struct pollfd pfd = {
                .fd = epollFd,
                .events = POLLIN
        };
        //This blocks until I write something to the socket. Then it enters an infinite loop.
        printf("Returning to main(), poll = %dn", poll(&pfd, 1, -1));
}

当我这样做时，它不会为Epoll中的新事件引起Sigio。民意调查表明，EpollFD中已经准备好事件，但它应该提高Sigio（只需检查事件是否在Epollfd和退出中）。我知道我可以将O_ASYNC应用于插座（我也尝试过），但我希望将数据包含在我的事件中。epoll让我这样做。

这是我的完整代码：

#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/epoll.h>
#include <fcntl.h>
#include <netdb.h>
#include <poll.h>
#include <signal.h>
#include <errno.h>
void handleSIGIO(int, siginfo_t *, void *);
const struct sigaction saSIGIO = {
    .sa_sigaction = handleSIGIO,
    .sa_flags = SA_SIGINFO
};
const struct addrinfo hints = {
    .ai_flags = AI_PASSIVE,
    .ai_family = AF_INET,
    .ai_socktype = SOCK_STREAM
};
void trySc(int err, const char *msg){
    if(err != -1) return;
    perror(msg);
    exit(errno);
}
int main(){
    signal(SIGPIPE, SIG_IGN);
    trySc(sigaction(SIGIO, &saSIGIO, NULL), "sigaction");
    int epollFd = epoll_create1(EPOLL_CLOEXEC);
    trySc(epollFd, "epoll_create1");
    trySc(fcntl(epollFd, F_SETOWN, getpid()), "fcntl F_SETOWN");
    trySc(fcntl(epollFd, F_SETSIG, SIGIO), "fcntl F_SETSIG");
    int oldFlags = fcntl(epollFd, F_GETFL, 0);
    trySc(oldFlags, "fcntl F_GETFL");
    trySc(fcntl(epollFd, F_SETFL, oldFlags | O_ASYNC), "fcntl F_SETFL");
    int socketFd = socket(AF_INET, SOCK_STREAM, 0);
    trySc(socketFd, "socket");
    struct addrinfo *servinfo;
    trySc(getaddrinfo("127.0.0.1", "5000", &hints, &servinfo),
        "getaddrinfo");
    struct epoll_event event = {
        .events = EPOLLIN | EPOLLET,
        .data.fd = socketFd
    };
    trySc(epoll_ctl(epollFd, EPOLL_CTL_ADD, socketFd, &event), "epoll_ctl");
    trySc(connect(socketFd, servinfo->ai_addr, servinfo->ai_addrlen),
        "connect");
    printf("Connectedn");
    while(1){
        struct pollfd pfd = {
            .fd = epollFd,
            .events = POLLIN
        };
        printf("Returning to main(), poll = %dn", poll(&pfd, 1, -1));
    }
}
void handleSIGIO(int sn, siginfo_t *info, void *ctx){
    printf("SIGIO calledn");
    struct epoll_event event;
    if(epoll_wait(info->si_fd, &event, 1, 0) != 1){
        printf("Warning: no event availablen");
        return;
    }
    printf("Event raised for fd %dn", event.data.fd);
    exit(0);
}

编辑：根据本网站，我要做的应该有效：

Note that an epoll set descriptor can be used much like a regular file 
descriptor. That is, it can be made to generate SIGIO (or another signal)
when input (i.e. events) is available on it; likewise it can be used with 
poll() and can even be stored inside another epoll set.

Answer 1

进行更多研究后，我发现这是不可能的。根据open(2)

o_async

启用信号驱动的i/o：生成一个信号（默认情况下为sigio，但是当输入或输出 在此文件描述符上可能会有可能。此功能是 仅适用于终端，伪terminals，插座和 （由于Linux 2.6）管道和FIFOS。请参阅FCNTL（2） 细节。另请参见下面的错误。

我真的很希望我可以将Epoll与Sigio一起使用。我会找到我可以做的其他事情。

我找到了解决此问题的解决方案：将O_ASYNC应用于每个插座，在您的Sigio处理程序中，在您的Epoll FD上调用epoll_wait。然后处理epoll的事件。它也无法与不支持Sigio的FD一起使用，即使它们支持Epoll，但它可以与插座和管道一起使用，这可能是最常见的异步IO的使用。