---
name: "io_uring_prep_msg_ring_cqe_flags"
section: "3"
platform: "linux"
package: "liburing"
version: "2.15-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/io_uring_prep_msg_ring_cqe_flags"
---

# io\_uring\_prep\_msg\_ring\_cqe\_flags(3)

send a message to another ring

## NAME

io\_uring\_prep\_msg\_ring - send a message to another ring

## SYNOPSIS

```
#include <liburing.h>
```

**void io\_uring\_prep\_msg\_ring(struct io\_uring\_sqe \****sqe***,**                         **int** *fd***,**                         **unsigned int** *len***,**                         **\_\_u64** *data***,**                         **unsigned int** *flags***);**

**void io\_uring\_prep\_msg\_ring\_cqe\_flags(struct io\_uring\_sqe \****sqe***,**                         **int** *fd***,**                         **unsigned int** *len***,**                         **\_\_u64** *data***,**                         **unsigned int** *flags***,**                         **unsigned int** *cqe\_flags***);**

## DESCRIPTION

[**io\_uring\_prep\_msg\_ring**(3)](/io_uring_prep_msg_ring/3.md) prepares to send a CQE to an io\_uring file descriptor. The submission queue entry *sqe* is setup to use the file descriptor *fd*, which must identify a io\_uring context, to post a CQE on that ring where the target CQE **res** field will contain the content of *len* and the **user\_data** of *data* with the request modifier flags set by *flags*. Currently there are no valid flag modifiers, this field must contain **0**.

The targeted ring may be any ring that the user has access to, even the ring itself. This request can be used for simple message passing to another ring, allowing 32+64 bits of data to be transferred through the *len* and *data* fields. The use case may be anything from simply waking up someone waiting on the targeted ring, or it can be used to pass messages between the two rings.

[**io\_uring\_prep\_msg\_ring\_cqe\_flags**(3)](/io_uring_prep_msg_ring_cqe_flags/3.md) is similar to [**io\_uring\_prep\_msg\_ring**(3)](/io_uring_prep_msg_ring/3.md)**.** But has an addition *cqe\_flags* parameter, which is used to set *flags* field on CQE side. That way, you can set the CQE flags field *cqe-\>flags* when sending a message. Be aware that io\_uring could potentially set additional bits into this field.

## RETURN VALUE

None

## ERRORS

These are the errors that are reported in the CQE *res* field.

- **-ENOMEM**

  The kernel was unable to allocate memory for the request.

- **-EINVAL**

  One of the fields set in the SQE was invalid.

- **-EBADFD**

  The descriptor passed in *fd* does not refer to an io\_uring file descriptor, or the ring is in a disabled state.

- **-EOVERFLOW**

  The kernel was unable to fill a CQE on the target ring. This can happen if the target CQ ring is in an overflow state and the kernel wasn't able to allocate memory for a new CQE entry.