Prepare a poll request
# DESCRIPTION
The [io_uring_prep_poll_add] function prepares a poll request. The
submission queue entry *sqe* is setup to use the file descriptor *fd*
that should get polled, with the events desired specified in the
*poll_mask* argument.
The default behavior is a single-shot poll request. When the specified
event has triggered, a completion CQE is posted and no more events will
be generated by the poll request. [io_uring_prep_poll_multishot]
behaves identically in terms of events, but it persists across
notifications and will repeatedly post notifications for the same
registration. A CQE posted from a multishot poll request will have
**IORING_CQE_F_MORE** set in the CQE *flags* member, indicating that the
application should expect more completions from this request. If the
multishot poll request gets terminated or experiences an error, this
flag will not be set in the CQE. If this happens, the application should
not expect further CQEs from the original request and must reissue a new
one if it still wishes to get notifications on this file descriptor.
# RETURN VALUE
None
# ERRORS
The CQE *res* field will contain the result of the operation, which is a
bitmask of the events notified. See the [poll](https://man7.org/linux/man-pages/man2/poll.2.html) man page for
details. 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], [io_uring_submit], [poll](https://man7.org/linux/man-pages/man2/poll.2.html),
[epoll_ctl](https://man7.org/linux/man-pages/man2/epoll_ctl.2.html)