NAME

       vpoll_create,     vpoll_ctl,    vpoll_close    -    generate    synthetic    events    for
       poll/select/ppoll/pselect/epoll

SYNOPSIS

       #include *vpoll.h*

       int vpoll_create(uint32_t init_events, int flags);

       int vpoll_ctl(int fd, int op, uint32_t events);

       int vpoll_close(int fd);

DESCRIPTION

       This library permits one to create a vpoll file descriptor “vpollfd” that can be  used  in
       poll/select/ppoll/pselect/epoll(2)  system  calls.   The  events  reported  by  a  can  be
       controlled by vpoll_ctl.  vpoll encodes the events using the same flags EPOLL* defined  in
       epoll_ctl(2).

       The  library  uses  the vpoll extension for eventfd if the kernel provides it otherwise it
       (partially) emulates  the  feature  using  socketpair(2).   The  emulation  supports  only
       EPOLLIN, EPOLLOUT flags and a non standard version of EPOLLHUP/EPOLLRDHUP.

       vpoll_create
              This  function  creates  a  “vpollfd”.  The argument init_events is used to set the
              initial state of events.  The following value can be included in flags:

              FD_CLOEXEC: Set the close-on-exec  flag  on  the  new  file  descriptor.   See  the
              description of the O_CLOEXEC flag in open(2) for reasons why this may be useful.

       vpoll_ctl
              This  function  changes  the  set  of  pending events reported by a “vpollfd”.  The
              argument op can take the following values:

              VPOLL_CTL_ADDEVENTS: the events set in the argument events are added to the set  of
              pending events.

              VPOLL_CTL_DELEVENTS: the events set in the argument events are deleted from the set
              of pending events.

              VPOLL_CTL_SETEVENTS: the value of the argument events is assigned  to  the  set  of
              pending events.

       vpoll_close
              This function closes the vpoll file descritor.

RETURN VALUE

       vpoll_create  returns  the new file descriptor, or -1 if an error occurred (in which case,
       errno is set appropriately)

       vpoll_ctl and vpoll_close return zero in case of success.  On error, -1 is  returned,  and
       errno is set appropriately.

EXAMPLE

              #define _GNU_SOURCE
              #include *stdio.h*
              #include *stdlib.h*
              #include *unistd.h*
              #include *fcntl.h*
              #include *errno.h*
              #include *sys/epoll.h*
              #include *vpoll.h*

              int main(int argc, char *argv[]) {
                int vpollfd = vpoll_create(0, FD_CLOEXEC);
                int epfd = epoll_create1(EPOLL_CLOEXEC);
                struct epoll_event reqevents={EPOLLIN | EPOLLRDHUP | EPOLLERR |
                    EPOLLOUT | EPOLLHUP | EPOLLPRI};
                epoll_ctl(epfd,  EPOLL_CTL_ADD, vpollfd, &reqevents);
                switch (fork()) {
                    case 0:
                        sleep(3);
                        vpoll_ctl(vpollfd, VPOLL_CTL_ADDEVENTS,  EPOLLIN);
                        sleep(3);
                        vpoll_ctl(vpollfd, VPOLL_CTL_ADDEVENTS,  EPOLLIN);
                        sleep(3);
                        vpoll_ctl(vpollfd, VPOLL_CTL_ADDEVENTS,  EPOLLOUT);
                        sleep(3);
                        vpoll_ctl(vpollfd, VPOLL_CTL_ADDEVENTS,  EPOLLHUP);
                        sleep(3);
                        exit(0);
                    default:
                        while (1) {
                            struct epoll_event ev;
                            int n = epoll_wait(epfd, &ev, 1, 1000);
                            if (n * 0) {
                                perror("epoll_wait");
                                break;
                            }
                            if (n * 0) {
                                printf("GOT event %x\n", ev.events);
                                vpoll_ctl(vpollfd, VPOLL_CTL_DELEVENTS, ev.events);
                                if (ev.events & EPOLLHUP)
                                        break;
                            } else {
                                printf("timeout\n");
                            }
                        }
                        break;
                    case -1:
                        printf("fork error\n");
                }
                vpoll_close(vpollfd);
                close(epfd);
                return 0;
              }

       On a machine running a Linux Kernel providing eventfd/vpoll the output of this program is:

              timeout
              timeout
              GOT event 1
              timeout
              timeout
              GOT event 1
              timeout
              timeout
              GOT event 4
              timeout
              timeout
              GOT event 10

       Instead when the demo program runs using the emulation layer the output is:

              timeout
              timeout
              GOT event 1
              timeout
              timeout
              GOT event 1
              timeout
              timeout
              GOT event 4
              timeout
              timeout
              GOT event 2011

       In  fact,  the  emulator  uses a socketpair to generate the events.  Hangup is emulated by
       closing the other end of the socketpair: this generates EPOLLHUP as well  as  EPOLLIN  and
       EPOLLRDHUP.

AUTHOR

       VirtualSquare.  Project leader: Renzo Davoli.