怎么理解把标准输入以ET模式加入epoll，监听EPOLLOUT事件时，epoll_wait多次返回?

k54765254

man手册上说 edge-triggered mode delivers events only when changes occur on the monitored file descriptor

但是我理解标准输入一直是可写的，按说应该只通知一次，为什么epoll_wait会每次都返回呢？具体的可运行代码如下：

#include <stdio.h>
#include <sys/epoll.h>
#include <string.h>
#include <fcntl.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <limits.h>
#define MAX_EVENTS 512

static char* get_epoll_events_str(uint32_t event);

int main(int argc, char *argv[]) {
    int i,nfds;
    struct epoll_event event;
    struct epoll_event events[MAX_EVENTS];
    int fd = STDIN_FILENO; 
    int epfd = epoll_create1(0);
    if (epfd == -1) {
        perror("epoll_create1");
        exit(EXIT_FAILURE);
    }

    event.events = EPOLLOUT | EPOLLET;
    event.data.u64 = 123;
    int ret = epoll_ctl(epfd, EPOLL_CTL_ADD, fd, &event);
    if (ret == -1) {
        perror("epoll_ctl");
        exit(EXIT_FAILURE);
    }
    while (1) {
        nfds = epoll_wait(epfd, events, MAX_EVENTS, -1);
        if (nfds == -1) {
            perror("epoll_wait");
            exit(EXIT_FAILURE);
        }
        printf("epoll_wait return %d\n", nfds);

        for (i = 0; i < nfds; i++) {
            char* str = get_epoll_events_str(events[i].events);
            printf("%dth fd's data.u64=%lu,event is %s\n",i,events[i].data.u64,str);
            free(str);
        }
        sleep(1);
    }
    return 0;
}

static char* get_epoll_events_str(uint32_t event) {
    char str[4096] = {0};

    if(event == 0)
    {
        return NULL;
    }

    if (event & EPOLLIN) strcat(str, "EPOLLIN,");
    if (event & EPOLLPRI) strcat(str, "EPOLLPRI,");
    if (event & EPOLLOUT) strcat(str, "EPOLLOUT,");
    if (event & EPOLLRDNORM) strcat(str, "EPOLLRDNORM,");
    if (event & EPOLLRDBAND) strcat(str, "EPOLLRDBAND,");
    if (event & EPOLLWRNORM) strcat(str, "EPOLLWRNORM,");
    if (event & EPOLLWRBAND) strcat(str, "EPOLLWRBAND,");
    if (event & EPOLLMSG) strcat(str, "EPOLLMSG,");
    if (event & EPOLLERR) strcat(str, "EPOLLERR,");
    if (event & EPOLLHUP) strcat(str, "EPOLLHUP,");
    if (event & EPOLLRDHUP) strcat(str, "EPOLLRDHUP,");
    if (event & EPOLLWAKEUP) strcat(str, "EPOLLWAKEUP,");
    if (event & EPOLLONESHOT) strcat(str, "EPOLLONESHOT,");
    if (event & EPOLLET) strcat(str, "EPOLLET,");
    
    if(strlen(str) == 0)
    {
        return NULL;
    }
    
    return strdup(str);
}

remus.clearwater

STDOUT_FILENO or EPOLLIN ?

On Fri, Jun 15, 2018 at 2:21 PM, 陈积利 <k547...@gmail.com> wrote:

man手册上说 edge-triggered mode delivers events only when changes occur on the monitored file descriptor
但是我理解标准输入一直是可写的，按说应该只通知一次，为什么epoll_wait会每次都返回呢？具体的可运行代码如下：

#include <stdio.h> #include <sys/epoll.h> #include <string.h> #include <fcntl.h> #include <stdlib.h> #include <unistd.h> #include <errno.h> #include <limits.h> #define MAX_EVENTS 512 static char* get_epoll_events_str(uint32_t event); int main(int argc, char *argv[]) { int i,nfds; struct epoll_event event; struct epoll_event events[MAX_EVENTS]; int fd = STDIN_FILENO; int epfd = epoll_create1(0); if (epfd == -1) { perror("epoll_create1"); exit(EXIT_FAILURE); } event.events = EPOLLOUT | EPOLLET; event.data.u64 = 123; int ret = epoll_ctl(epfd, EPOLL_CTL_ADD, fd, &event); if (ret == -1) { perror("epoll_ctl"); exit(EXIT_FAILURE); } while (1) { nfds = epoll_wait(epfd, events, MAX_EVENTS, -1); if (nfds == -1) { perror("epoll_wait"); exit(EXIT_FAILURE); } printf("epoll_wait return %d\n", nfds); for (i = 0; i < nfds; i++) { char* str = get_epoll_events_str(events[i].events); printf("%dth fd's data.u64=%lu,event is %s\n",i,events[i].data.u64,str); free(str); } sleep(1); } return 0; } static char* get_epoll_events_str(uint32_t event) { char str[4096] = {0}; if(event == 0) { return NULL; } if (event & EPOLLIN) strcat(str, "EPOLLIN,"); if (event & EPOLLPRI) strcat(str, "EPOLLPRI,"); if (event & EPOLLOUT) strcat(str, "EPOLLOUT,"); if (event & EPOLLRDNORM) strcat(str, "EPOLLRDNORM,"); if (event & EPOLLRDBAND) strcat(str, "EPOLLRDBAND,"); if (event & EPOLLWRNORM) strcat(str, "EPOLLWRNORM,"); if (event & EPOLLWRBAND) strcat(str, "EPOLLWRBAND,"); if (event & EPOLLMSG) strcat(str, "EPOLLMSG,"); if (event & EPOLLERR) strcat(str, "EPOLLERR,"); if (event & EPOLLHUP) strcat(str, "EPOLLHUP,"); if (event & EPOLLRDHUP) strcat(str, "EPOLLRDHUP,"); if (event & EPOLLWAKEUP) strcat(str, "EPOLLWAKEUP,"); if (event & EPOLLONESHOT) strcat(str, "EPOLLONESHOT,"); if (event & EPOLLET) strcat(str, "EPOLLET,"); if(strlen(str) == 0) { return NULL; } return strdup(str); }

--

remus.clearwater

$man 2 pipe

正常情况下，pipe的读端是不能写的（EBADF），epoll的设计思路应该是，立即返回让你去写它，

一旦用户空间写这个fd就会触发用户空间的错误处理流程以彻底消费掉这个事件，比如close(fd)。

这种情况应该是undefined的行为，严谨的说在一开始，epoll_ctl就应该是失败的；建议不要用

这种非确定性的东西。

On Fri, Jun 15, 2018 at 10:16 PM, Remus Clearwater <remus.c...@gmail.com> wrote:

STDOUT_FILENO or EPOLLIN ?

On Fri, Jun 15, 2018 at 2:21 PM, 陈积利 <k547...@gmail.com> wrote:
man手册上说 edge-triggered mode delivers events only when changes occur on the monitored file descriptor
但是我理解标准输入一直是可写的，按说应该只通知一次，为什么epoll_wait会每次都返回呢？具体的可运行代码如下：

#include <stdio.h> #include <sys/epoll.h> #include <string.h> #include <fcntl.h> #include <stdlib.h> #include <unistd.h> #include <errno.h> #include <limits.h> #define MAX_EVENTS 512 static char* get_epoll_events_str(uint32_t event); int main(int argc, char *argv[]) { int i,nfds; struct epoll_event event; struct epoll_event events[MAX_EVENTS]; int fd = STDIN_FILENO; int epfd = epoll_create1(0); if (epfd == -1) { perror("epoll_create1"); exit(EXIT_FAILURE); } event.events = EPOLLOUT | EPOLLET; event.data.u64 = 123; int ret = epoll_ctl(epfd, EPOLL_CTL_ADD, fd, &event); if (ret == -1) { perror("epoll_ctl"); exit(EXIT_FAILURE); } while (1) { nfds = epoll_wait(epfd, events, MAX_EVENTS, -1); if (nfds == -1) { perror("epoll_wait"); exit(EXIT_FAILURE); } printf("epoll_wait return %d\n", nfds); for (i = 0; i < nfds; i++) { char* str = get_epoll_events_str(events[i].events); printf("%dth fd's data.u64=%lu,event is %s\n",i,events[i].data.u64,str); free(str); } sleep(1); } return 0; } static char* get_epoll_events_str(uint32_t event) { char str[4096] = {0}; if(event == 0) { return NULL; } if (event & EPOLLIN) strcat(str, "EPOLLIN,"); if (event & EPOLLPRI) strcat(str, "EPOLLPRI,"); if (event & EPOLLOUT) strcat(str, "EPOLLOUT,"); if (event & EPOLLRDNORM) strcat(str, "EPOLLRDNORM,"); if (event & EPOLLRDBAND) strcat(str, "EPOLLRDBAND,"); if (event & EPOLLWRNORM) strcat(str, "EPOLLWRNORM,"); if (event & EPOLLWRBAND) strcat(str, "EPOLLWRBAND,"); if (event & EPOLLMSG) strcat(str, "EPOLLMSG,"); if (event & EPOLLERR) strcat(str, "EPOLLERR,"); if (event & EPOLLHUP) strcat(str, "EPOLLHUP,"); if (event & EPOLLRDHUP) strcat(str, "EPOLLRDHUP,"); if (event & EPOLLWAKEUP) strcat(str, "EPOLLWAKEUP,"); if (event & EPOLLONESHOT) strcat(str, "EPOLLONESHOT,"); if (event & EPOLLET) strcat(str, "EPOLLET,"); if(strlen(str) == 0) { return NULL; } return strdup(str); }

--

spacewanderlzx

我本机测试的结果，只会返回一次 EPOLLHUP，没有多次返回的情况。我的操作系统 是：
 ￥ uname -a
Linux lzx-HP-ENVY-x360-Convertible-15-bp1xx 4.13.0-36-generic
#40-Ubuntu SMP Fri Feb 16 20:07:48 UTC 2018 x86_64 x86_64 x86_64
GNU/Linux

2018-06-15 14:21 GMT+08:00 陈积利 <k547...@gmail.com>:
> man手册上说 edge-triggered mode delivers events only when changes occur on the
> monitored file descriptor
>
> 但是我理解标准输入一直是可写的， 按说应该只通知一次，为什么epoll_wait会每次都返回呢？ 具体的可运行代码如下：
>
>
> #include <stdio.h>
> #include <sys/epoll.h>
> #include <string.h>
> #include <fcntl.h>
> #include <stdlib.h>
> #include <unistd.h>
> #include <errno.h>
> #include <limits.h>
> #define MAX_EVENTS 512
>
> static char* get_epoll_events_str(uint32_t event);
>
> int main(int argc, char *argv[]) {
>     int i,nfds;
>     struct epoll_event event;
>     struct epoll_event events[MAX_EVENTS];
>     int fd = STDIN_FILENO;
>     int epfd = epoll_create1(0);
>     if (epfd == -1) {
>         perror("epoll_create1");
>         exit(EXIT_FAILURE);
>     }
>
>     event.events = EPOLLOUT | EPOLLET;
>     event.data.u64 = 123;
>     int ret = epoll_ctl(epfd, EPOLL_CTL_ADD, fd, &event);
>     if (ret == -1) {
>         perror("epoll_ctl");
>         exit(EXIT_FAILURE);
>     }
>     while (1) {
>         nfds = epoll_wait(epfd, events, MAX_EVENTS, -1);
>         if (nfds == -1) {
>             perror("epoll_wait");
>             exit(EXIT_FAILURE);
>         }
>         printf("epoll_wait return %d\n", nfds);
>
>         for (i = 0; i < nfds; i++) {
>             char* str = get_epoll_events_str(events[i].events);
>             printf("%dth fd's data.u64=%lu,event is
> %s\n",i,events[i].data.u64,str);
>             free(str);
>         }
>         sleep(1);
>     }
>     return 0;
> }
>
> static char* get_epoll_events_str(uint32_t event) {
>     char str[4096] = {0};
>
>     if(event == 0)
>     {
>         return NULL;
>     }
>
>     if (event & EPOLLIN) strcat(str, "EPOLLIN,");
>     if (event & EPOLLPRI) strcat(str, "EPOLLPRI,");
>     if (event & EPOLLOUT) strcat(str, "EPOLLOUT,");
>     if (event & EPOLLRDNORM) strcat(str, "EPOLLRDNORM,");
>     if (event & EPOLLRDBAND) strcat(str, "EPOLLRDBAND,");
>     if (event & EPOLLWRNORM) strcat(str, "EPOLLWRNORM,");
>     if (event & EPOLLWRBAND) strcat(str, "EPOLLWRBAND,");
>     if (event & EPOLLMSG) strcat(str, "EPOLLMSG,");
>     if (event & EPOLLERR) strcat(str, "EPOLLERR,");
>     if (event & EPOLLHUP) strcat(str, "EPOLLHUP,");
>     if (event & EPOLLRDHUP) strcat(str, "EPOLLRDHUP,");
>     if (event & EPOLLWAKEUP) strcat(str, "EPOLLWAKEUP,");
>     if (event & EPOLLONESHOT) strcat(str, "EPOLLONESHOT,");
>     if (event & EPOLLET) strcat(str, "EPOLLET,");
>
>     if(strlen(str) == 0)
>     {
>         return NULL;
>     }
>
>     return strdup(str);
> }
>
>
>
>
> --
>

remus.clearwater

不过我这儿确实是复现了。

1529105510.942205 epoll_wait(3, [{EPOLLOUT, {u32=123, u64=123}}], 512, -1) = 1 <0.000013>

1529105510.942242 write(1, "epoll_wait return 1\n", 20epoll_wait return 1

) = 20 <0.000014>

1529105510.942281 write(1, "0th fd's data.u64=123,event is EPOLLOUT,\n", 410th fd's data.u64=123,event is EPOLLOUT,

) = 41 <0.000017>

1529105510.942320 epoll_wait(3, [{EPOLLOUT, {u32=123, u64=123}}], 512, -1) = 1 <0.000013>

1529105510.942357 write(1, "epoll_wait return 1\n", 20epoll_wait return 1

) = 20 <0.000014>

1529105510.942396 write(1, "0th fd's data.u64=123,event is EPOLLOUT,\n", 410th fd's data.u64=123,event is EPOLLOUT,

) = 41 <0.000037>

1529105510.942461 epoll_wait(3, [{EPOLLOUT, {u32=123, u64=123}}], 512, -1) = 1 <0.000013>

1529105510.942501 write(1, "epoll_wait return 1\n", 20epoll_wait return 1

) = 20 <0.000014>

1529105510.942538 write(1, "0th fd's data.u64=123,event is EPOLLOUT,\n", 410th fd's data.u64=123,event is EPOLLOUT,

) = 41 <0.000015>

Linux 4.15.10-1.el7.elrepo.x86_64 #1 SMP Thu Mar 15 10:05:52 EDT 2018 x86_64 x86_64 x86_64 GNU/Linux

On Fri, Jun 15, 2018 at 11:30 PM, Zexuan Luo <spacew...@gmail.com> wrote:

我本机测试的结果，只会返回一次 EPOLLHUP，没有多次返回的情况。我的操作系统是：
￥ uname -a
Linux lzx-HP-ENVY-x360-Convertible-15-bp1xx 4.13.0-36-generic
#40-Ubuntu SMP Fri Feb 16 20:07:48 UTC 2018 x86_64 x86_64 x86_64
GNU/Linux

2018-06-15 14:21 GMT+08:00 陈积利 <k547...@gmail.com>:
> man手册上说 edge-triggered mode delivers events only when changes occur on the
> monitored file descriptor
>
> 但是我理解标准输入一直是可写的，按说应该只通知一次，为什么epoll_wait会每次都返回呢？具体的可运行代码如下：
>
>
> #include <stdio.h>
> #include <sys/epoll.h>
> #include <string.h>
> #include <fcntl.h>
> #include <stdlib.h>
> #include <unistd.h>
> #include <errno.h>
> #include <limits.h>
> #define MAX_EVENTS 512
>
> static char* get_epoll_events_str(uint32_t event);
>
> int main(int argc, char *argv[]) {
> int i,nfds;
> struct epoll_event event;
> struct epoll_event events[MAX_EVENTS];
> int fd = STDIN_FILENO;
> int epfd = epoll_create1(0);
> if (epfd == -1) {
> perror("epoll_create1");
> exit(EXIT_FAILURE);
> }
>
> event.events = EPOLLOUT | EPOLLET;
> event.data.u64 = 123;
> int ret = epoll_ctl(epfd, EPOLL_CTL_ADD, fd, &event);
> if (ret == -1) {
> perror("epoll_ctl");
> exit(EXIT_FAILURE);
> }
> while (1) {
> nfds = epoll_wait(epfd, events, MAX_EVENTS, -1);
> if (nfds == -1) {
> perror("epoll_wait");
> exit(EXIT_FAILURE);
> }
> printf("epoll_wait return %d\n", nfds);
>
> for (i = 0; i < nfds; i++) {
> char* str = get_epoll_events_str(events[i].events);
> printf("%dth fd's data.u64=%lu,event is
> %s\n",i,events[i].data.u64,str);
> free(str);
> }
> sleep(1);
> }
> return 0;
> }
>
> static char* get_epoll_events_str(uint32_t event) {
> char str[4096] = {0};
>
> if(event == 0)
> {
> return NULL;
> }
>
> if (event & EPOLLIN) strcat(str, "EPOLLIN,");
> if (event & EPOLLPRI) strcat(str, "EPOLLPRI,");
> if (event & EPOLLOUT) strcat(str, "EPOLLOUT,");
> if (event & EPOLLRDNORM) strcat(str, "EPOLLRDNORM,");
> if (event & EPOLLRDBAND) strcat(str, "EPOLLRDBAND,");
> if (event & EPOLLWRNORM) strcat(str, "EPOLLWRNORM,");
> if (event & EPOLLWRBAND) strcat(str, "EPOLLWRBAND,");
> if (event & EPOLLMSG) strcat(str, "EPOLLMSG,");
> if (event & EPOLLERR) strcat(str, "EPOLLERR,");
> if (event & EPOLLHUP) strcat(str, "EPOLLHUP,");
> if (event & EPOLLRDHUP) strcat(str, "EPOLLRDHUP,");
> if (event & EPOLLWAKEUP) strcat(str, "EPOLLWAKEUP,");
> if (event & EPOLLONESHOT) strcat(str, "EPOLLONESHOT,");
> if (event & EPOLLET) strcat(str, "EPOLLET,");
>
> if(strlen(str) == 0)
> {
> return NULL;
> }
>
> return strdup(str);
> }
>
>
>
>
> --
>
--

jinwik

你一直printf就一直会有数据啊，把输出指向个文件。

On Friday, June 15, 2018 at 2:21:53 PM UTC+8, chenstrace wrote:

man手册上说 edge-triggered mode delivers events only when changes occur on the monitored file descriptor
但是我理解标准输入一直是可写的，按说应该只通知一次，为什么epoll_wait会每次都返回呢？具体的可运行代码如下：

#include <stdio.h> #include <sys/epoll.h> #include <string.h> #include <fcntl.h> #include <stdlib.h> #include <unistd.h> #include <errno.h> #include <limits.h> #define MAX_EVENTS 512 static char* get_epoll_events_str(uint32_t event); int main(int argc, char *argv[]) { int i,nfds; struct epoll_event event; struct epoll_event events[MAX_EVENTS]; int fd = STDIN_FILENO; int epfd = epoll_create1(0); if (epfd == -1) { perror("epoll_create1"); exit(EXIT_FAILURE); } event.events = EPOLLOUT | EPOLLET; event.data.u64 = 123; int ret = epoll_ctl(epfd, EPOLL_CTL_ADD, fd, &event); if (ret == -1) { perror("epoll_ctl"); exit(EXIT_FAILURE); } while (1) { nfds = epoll_wait(epfd, events, MAX_EVENTS, -1); if (nfds == -1) { perror("epoll_wait"); exit(EXIT_FAILURE); } printf("epoll_wait return %d\n", nfds); for (i = 0; i < nfds; i++) { char* str = get_epoll_events_str(events[i].events); printf("%dth fd's data.u64=%lu,event is %s\n",i,events[i].data.u64,str); free(str); } sleep(1); } return 0; } static char* get_epoll_events_str(uint32_t event) { char str[4096] = {0}; if(event == 0) { return NULL; } if (event & EPOLLIN) strcat(str, "EPOLLIN,"); if (event & EPOLLPRI) strcat(str, "EPOLLPRI,"); if (event & EPOLLOUT) strcat(str, "EPOLLOUT,"); if (event & EPOLLRDNORM) strcat(str, "EPOLLRDNORM,"); if (event & EPOLLRDBAND) strcat(str, "EPOLLRDBAND,"); if (event & EPOLLWRNORM) strcat(str, "EPOLLWRNORM,"); if (event & EPOLLWRBAND) strcat(str, "EPOLLWRBAND,"); if (event & EPOLLMSG) strcat(str, "EPOLLMSG,"); if (event & EPOLLERR) strcat(str, "EPOLLERR,"); if (event & EPOLLHUP) strcat(str, "EPOLLHUP,"); if (event & EPOLLRDHUP) strcat(str, "EPOLLRDHUP,"); if (event & EPOLLWAKEUP) strcat(str, "EPOLLWAKEUP,"); if (event & EPOLLONESHOT) strcat(str, "EPOLLONESHOT,"); if (event & EPOLLET) strcat(str, "EPOLLET,"); if(strlen(str) == 0) { return NULL; } return strdup(str); }

remus.clearwater

> 你一直printf就一直会有数据啊，把输出指向个文件。

是的 :D 你是正确的这是个pts文件

应该这样：

$ sleep 10 | strace -tttT -s 100 ./t2

......

1529108685.108754 epoll_create1(0) = 3 <0.000017>

1529108685.108792 epoll_ctl(3, EPOLL_CTL_ADD, 0, {EPOLLOUT|EPOLLET, {u32=123, u64=123}}) = 0 <0.000015>

1529108685.108836 epoll_wait(3, [{EPOLLHUP, {u32=123, u64=123}}], 512, -1) = 1 <9.981705>

1529108695.090677 fstat(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 4), ...}) = 0 <0.000021>

1529108695.090751 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fddd0e67000 <0.000026>

1529108695.090826 write(1, "epoll_wait return 1\n", 20epoll_wait return 1

......

不过实验结果应该是，除非stdin pipe的写端close，否则pipe读端的写事件跳变一直都不会触发。

不过文档里面并没有写明这种情况将会发生什么事情。

所以，如果想监听的是pts应该事先确定一下fd的类型。

On Sat, Jun 16, 2018 at 7:51 AM, Tim kiwi <ji...@gmail.com> wrote:

你一直printf就一直会有数据啊，把输出指向个文件。

On Friday, June 15, 2018 at 2:21:53 PM UTC+8, chenstrace wrote:
man手册上说 edge-triggered mode delivers events only when changes occur on the monitored file descriptor
但是我理解标准输入一直是可写的，按说应该只通知一次，为什么epoll_wait会每次都返回呢？具体的可运行代码如下：

#include <stdio.h> #include <sys/epoll.h> #include <string.h> #include <fcntl.h> #include <stdlib.h> #include <unistd.h> #include <errno.h> #include <limits.h> #define MAX_EVENTS 512 static char* get_epoll_events_str(uint32_t event); int main(int argc, char *argv[]) { int i,nfds; struct epoll_event event; struct epoll_event events[MAX_EVENTS]; int fd = STDIN_FILENO; int epfd = epoll_create1(0); if (epfd == -1) { perror("epoll_create1"); exit(EXIT_FAILURE); } event.events = EPOLLOUT | EPOLLET; event.data.u64 = 123; int ret = epoll_ctl(epfd, EPOLL_CTL_ADD, fd, &event); if (ret == -1) { perror("epoll_ctl"); exit(EXIT_FAILURE); } while (1) { nfds = epoll_wait(epfd, events, MAX_EVENTS, -1); if (nfds == -1) { perror("epoll_wait"); exit(EXIT_FAILURE); } printf("epoll_wait return %d\n", nfds); for (i = 0; i < nfds; i++) { char* str = get_epoll_events_str(events[i].events); printf("%dth fd's data.u64=%lu,event is %s\n",i,events[i].data.u64,str); free(str); } sleep(1); } return 0; } static char* get_epoll_events_str(uint32_t event) { char str[4096] = {0}; if(event == 0) { return NULL; } if (event & EPOLLIN) strcat(str, "EPOLLIN,"); if (event & EPOLLPRI) strcat(str, "EPOLLPRI,"); if (event & EPOLLOUT) strcat(str, "EPOLLOUT,"); if (event & EPOLLRDNORM) strcat(str, "EPOLLRDNORM,"); if (event & EPOLLRDBAND) strcat(str, "EPOLLRDBAND,"); if (event & EPOLLWRNORM) strcat(str, "EPOLLWRNORM,"); if (event & EPOLLWRBAND) strcat(str, "EPOLLWRBAND,"); if (event & EPOLLMSG) strcat(str, "EPOLLMSG,"); if (event & EPOLLERR) strcat(str, "EPOLLERR,"); if (event & EPOLLHUP) strcat(str, "EPOLLHUP,"); if (event & EPOLLRDHUP) strcat(str, "EPOLLRDHUP,"); if (event & EPOLLWAKEUP) strcat(str, "EPOLLWAKEUP,"); if (event & EPOLLONESHOT) strcat(str, "EPOLLONESHOT,"); if (event & EPOLLET) strcat(str, "EPOLLET,"); if(strlen(str) == 0) { return NULL; } return strdup(str); }

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