io\_uring\_prep\_epoll\_wait(3) liburing Manual io\_uring\_prep\_epoll\_wait(3)

# [NAME](#NAME)

io\_uring\_prep\_epoll\_wait - prepare an epoll wait request

# [SYNOPSIS](#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](#DESCRIPTION)

The [**io\_uring\_prep\_epoll\_wait**(3)](/man/os/liburing/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)](/man/os/liburing/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](#RETURN_VALUE)

None

# [ERRORS](#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](#SEE_ALSO)

[**io\_uring\_get\_sqe**(3)](/man/os/liburing/io_uring_get_sqe.3), [**io\_uring\_submit**(3)](/man/os/liburing/io_uring_submit.3), [**epoll\_wait**(2)](/man/os/liburing/epoll_wait.2)

March 6, 2025 liburing-2.10

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Document: io_uring_prep_epoll_wait(3) from liburing 2.15-r4 (Chainguard OS)
Source: https://github.com/axboe/liburing.git