io\_uring\_prep\_writev\_fixed(3) liburing Manual io\_uring\_prep\_writev\_fixed(3)

# [NAME](#NAME)

io\_uring\_prep\_writev\_fixed - prepare a vectored write using fixed buffers

# [SYNOPSIS](#SYNOPSIS)

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

```
void io_uring_prep_writev_fixed(struct io_uring_sqe *sqe,
                                int fd,
                                const struct iovec *iovecs,
                                unsigned nr_vecs,
                                __u64 offset,
                                int flags,
                                int buf_index);
```

# [DESCRIPTION](#DESCRIPTION)

The [**io\_uring\_prep\_writev\_fixed**(3)](/man/os/liburing/io_uring_prep_writev_fixed.3) function prepares a vectored write request using fixed (registered) buffers. The submission queue entry *sqe* is setup to use the file descriptor *fd* to start writing *nr\_vecs* iovecs from the file position *offset*.

The *iovecs* argument points to an array of iovec structures describing the write buffers. All buffers must be part of the registered buffer set at index *buf\_index*, previously registered with [**io\_uring\_register\_buffers**(3)](/man/os/liburing/io_uring_register_buffers.3).

The *flags* argument can contain any per-request flags, such as **RWF\_APPEND** or other flags supported by [**pwritev2**(2)](/man/os/liburing/pwritev2.2).

Using fixed buffers avoids the overhead of mapping buffers for each I/O operation, improving performance for applications that reuse the same buffers.

# [RETURN VALUE](#RETURN_VALUE)

None

# [ERRORS](#ERRORS)

The CQE *res* field will contain the result of the operation, the number of bytes written on success. On error, a negative errno value is returned.

# [NOTES](#NOTES)

Despite accepting an array of iovec's with a size\_t number of bytes each, this function can transfer at most INT\_MAX bytes per call (the maximum for the underlying syscall interface).

# [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), [**io\_uring\_prep\_writev**(3)](/man/os/liburing/io_uring_prep_writev.3), [**io\_uring\_prep\_writev2**(3)](/man/os/liburing/io_uring_prep_writev2.3), [**io\_uring\_prep\_write\_fixed**(3)](/man/os/liburing/io_uring_prep_write_fixed.3), [**io\_uring\_prep\_readv\_fixed**(3)](/man/os/liburing/io_uring_prep_readv_fixed.3), [**io\_uring\_register\_buffers**(3)](/man/os/liburing/io_uring_register_buffers.3)

January 18, 2025 liburing-2.10

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Document: io_uring_prep_writev_fixed(3) from liburing 2.15-r5 (Chainguard OS)
Source: https://github.com/axboe/liburing.git