---
name: "io_uring_prep_readv"
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_readv"
---

# io\_uring\_prep\_readv(3)

prepare vector I/O read request

## NAME

io\_uring\_prep\_readv - prepare vector I/O read request

## SYNOPSIS

```
#include <sys/uio.h>
#include <liburing.h>
```

**void io\_uring\_prep\_readv(struct io\_uring\_sqe \****sqe***,**                          **int** *fd***,**                          **const struct iovec \****iovecs***,**                          **unsigned** *nr\_vecs***,**                          **\_\_u64** *offset***);**

## DESCRIPTION

The [**io\_uring\_prep\_readv**(3)](/io_uring_prep_readv/3.md) prepares a vectored IO read request. The submission queue entry *sqe* is setup to use the file descriptor *fd* to start reading *nr\_vecs* into the *iovecs* array at the specified *offset*.

On files that support seeking, if the offset is set to **-1**, the read operation commences at the file offset, and the file offset is incremented by the number of bytes read. See [**read**(2)](/read/2.md) for more details. Note that for an async API, reading and updating the current file offset may result in unpredictable behavior, unless access to the file is serialized. It is not encouraged to use this feature, if it's possible to provide the desired IO offset from the application or library.

On files that are not capable of seeking, the offset must be 0 or -1.

After the read has been prepared it can be submitted with one of the submit functions.

## 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.

## NOTES

Unless an application explicitly needs to pass in more than one iovec, it is more efficient to use [**io\_uring\_prep\_read**(3)](/io_uring_prep_read/3.md) rather than this function, as no state has to be maintained for a non-vectored IO request. As with any request that passes in data in a struct, that data must remain valid until the request has been successfully submitted. It need not remain valid until completion. Once a request has been submitted, the in-kernel state is stable. Very early kernels (5.4 and earlier) required state to be stable until the completion occurred. Applications can test for this behavior by inspecting the **IORING\_FEAT\_SUBMIT\_STABLE** flag passed back from [**io\_uring\_queue\_init\_params**(3)](/io_uring_queue_init_params/3.md).

This function accepts an array of iovec's with a size\_t number of bytes each, but io\_uring\_cqe's result code is an \_\_s32 value, so in theory a short read with a large enough iov\_len value could generate an ambiguous return. But the number of bytes actually transferred has the same limit as [**read**(2)](/read/2.md) so this cannot happen in practice.

## SEE ALSO

[**io\_uring\_get\_sqe**(3)](/io_uring_get_sqe/3.md), [**io\_uring\_prep\_read**(3)](/io_uring_prep_read/3.md), [**io\_uring\_prep\_readv2**(3)](/io_uring_prep_readv2/3.md), [**io\_uring\_submit**(3)](/io_uring_submit/3.md)