NAME

       io_uring_prep_epoll_wait - prepare an epoll wait request

SYNOPSIS

       #include <sys/epoll.h>
       #include <liburing.h>

       void io_uring_prep_epoll_wait(struct io_uring_sqe *sqe,
                                     int fd,
                                     struct epoll_event *events,
                                     int maxevents,
                                     unsigned flags );"

DESCRIPTION

       The  io_uring_prep_epoll_wait(3)  function prepares an epoll_wait request. The submission queue entry sqe
       is setup to wait on a maximum of maxevents events on the epoll  file  descriptor  indicated  by  fd,  and
       filling the received events into the memory pointed to by events.

       This  function  prepares  an  async epoll_wait(2) request. See that man page for details. The use case is
       mostly for legacy event loops, where certain file descriptors may still  be  using  epoll  for  readiness
       notifications. Normally this would necessitate using epoll_wait with the io_uring fd added to that set as
       well, which is suboptimal as epoll doesn't provide the same kind of fine grained batch control and wakeup
       reductions  that  io_uring  does.  By using io_uring to read epoll events, the event loop can be entirely
       switched to io_uring, and reap the benefits of batch waiting and context switch reductions.

RETURN VALUE

       None

ERRORS

       The CQE res field will contain the result of the operation. See the  related  man  page  for  details  on
       possible  values. Note that where synchronous system calls will return -1 on failure and set errno to the
       actual error value, io_uring never uses errno.  Instead it returns the negated errno directly in the  CQE
       res field.

SEE ALSO

       io_uring_get_sqe(3), io_uring_submit(3), epoll_wait(2)

liburing-2.10                                     March 6, 2025                      io_uring_prep_epoll_wait(3)