---
name: "io_uring_prep_fallocate"
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_fallocate"
---

# io\_uring\_prep\_fallocate(3)

prepare a fallocate request

## NAME

io\_uring\_prep\_fallocate - prepare a fallocate request

## SYNOPSIS

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

**void io\_uring\_prep\_fallocate(struct io\_uring\_sqe \****sqe***,**                              **int** *fd***,**                              **int** *mode***,**                              **\_\_u64** *offset***,**                              **\_\_u64** *len***);**

## DESCRIPTION

The [**io\_uring\_prep\_fallocate**(3)](/io_uring_prep_fallocate/3.md) function prepares a fallocate request. The submission queue entry *sqe* is setup to use the file descriptor pointed to by *fd* to start a fallocate operation described by *mode* at offset *offset* and *len* length in bytes.

This function prepares an async [**fallocate**(2)](/fallocate/2.md) request. See that man page for details.

## 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_get_sqe/3.md), [**io\_uring\_submit**(3)](/io_uring_submit/3.md), [**fallocate**(2)](/fallocate/2.md)