io\_uring\_prep\_write(3) liburing Manual io\_uring\_prep\_write(3)

# [NAME](#NAME)

io\_uring\_prep\_write - prepare I/O write request

# [SYNOPSIS](#SYNOPSIS)

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

```
void io_uring_prep_write(struct io_uring_sqe *sqe,
                         int fd,
                         const void *buf,
                         unsigned nbytes,
                         __u64 offset);
```

# [DESCRIPTION](#DESCRIPTION)

The [**io\_uring\_prep\_write**(3)](/man/os/liburing/io_uring_prep_write.3) prepares an IO write request. The submission queue entry *sqe* is setup to use the file descriptor *fd* to start writing *nbytes* from the buffer *buf* at the specified *offset*.

On files that support seeking, if the offset is set to **-1**, the write operation commences at the file offset, and the file offset is incremented by the number of bytes written. See [**write**(2)](/man/os/liburing/write.2) 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 write has been prepared, it can be submitted with one of the submit functions.

# [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.

# [NOTES](#NOTES)

Despite accepting an unsigned number of bytes, 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)

November 15, 2021 liburing-2.1

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