Prepare an epoll_ctl request
# DESCRIPTION
The [io_uring_prep_epoll_ctl] function prepares an epoll control
request. The submission queue entry *sqe* is setup to use the epoll
instance referred to by *epfd*, performing the operation *op* on the
file descriptor *fd*. The *ev* argument points to an *epoll_event*
structure as defined in [epoll_ctl](https://man7.org/linux/man-pages/man2/epoll_ctl.2.html).
The *op* argument can be one of:
**EPOLL_CTL_ADD**\
Add *fd* to the epoll instance.
**EPOLL_CTL_MOD**\
Modify the settings for *fd*.
**EPOLL_CTL_DEL**\
Remove *fd* from the epoll instance. *ev* is ignored for this operation.
This function prepares an async [epoll_ctl](https://man7.org/linux/man-pages/man2/epoll_ctl.2.html) request. See that man
page for details.
# RETURN VALUE
None
# ERRORS
The CQE *res* field will contain the result of the operation, 0 on
success. On error, a negative errno value is returned. See
[epoll_ctl](https://man7.org/linux/man-pages/man2/epoll_ctl.2.html) for possible error values.
# SEE ALSO
[io_uring_get_sqe], [io_uring_submit],
[io_uring_prep_epoll_wait], [epoll_ctl](https://man7.org/linux/man-pages/man2/epoll_ctl.2.html)