AnsweredAssumed Answered


Question asked by MarkBishop on Oct 3, 2012
Latest reply on Oct 4, 2012 by MarkBishop

I've tried all the examples in the man pages and several of my own version of using epoll on a '/sys/class/gpio/gpioXX/value' file and none of it seems to work.  I do have support compiled into my kernel.  Does anyone have a small working example for me to try?


    int n;

    int epfd = epoll_create(1);

    int fd = open("/sys/class/gpio/gpio56/value", O_RDONLY );//| O_NONBLOCK);

    printf("open returned %d: %s\n", fd, strerror(errno));

    if(fd > 0) {

        char buf = 0;

        struct epoll_event ev;

        struct epoll_event events; = EPOLLPRI; = fd;

        n = epoll_ctl(epfd, EPOLL_CTL_ADD, fd, &ev);

        printf("epoll_ctl returned %d: %s\n", n, strerror(errno));

        while(1) {

               n = epoll_wait(epfd, &events, 1, -1);

            printf("epoll returned %d: %s\n", n, strerror(errno));

            if(n > 0) {

                n = lseek(, 0, SEEK_SET);

                printf("seek %d bytes: %s\n", n, strerror(errno));

                while(n = read(, &buf, 1)){

                    printf("read %d bytes: %s\n", n, strerror(errno));

                    printf("buf = 0x%x\n", buf);


                printf("epoll_ctl returned %d: %s\n", n, strerror(errno));