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.