io_uring_prep_epoll_wait(3)

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)