io_uring_prep_write(3) liburing Manual io_uring_prep_write(3)

io_uring_prep_write - prepare I/O write request

#include <liburing.h>
void io_uring_prep_write(struct io_uring_sqe *sqe,
                         int fd,
                         const void *buf,
                         unsigned nbytes,
                         __u64 offset);

The 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) 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.


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.

io_uring_get_sqe(3), io_uring_submit(3)

November 15, 2021 liburing-2.1