io_uring_prep_send(3) — Linux manual page


io_uring_prep_send(3)        liburing Manual       io_uring_prep_send(3)

NAME         top

       io_uring_prep_send - prepare a send request

SYNOPSIS         top

       #include <liburing.h>

       void io_uring_prep_send(struct io_uring_sqe *sqe,
                               int sockfd,
                               const void *buf,
                               size_t len,
                               int flags);

       void io_uring_prep_sendto(struct io_uring_sqe *sqe,
                                 int sockfd,
                                 const void *buf,
                                 size_t len,
                                 int flags,
                                 const struct sockaddr *addr,
                                 socklen_t addrlen);

       void io_uring_prep_send_bundle(struct io_uring_sqe *sqe,
                                      int sockfd,
                                      size_t len,
                                      int flags);

DESCRIPTION         top

       The io_uring_prep_send(3) function prepares a send request. The
       submission queue entry sqe is setup to use the file descriptor
       sockfd to start sending the data from buf of size len bytes and
       with modifier flags flags.

       Note that using IOSQE_IO_LINK with this request type requires the
       setting of MSG_WAITALL in the flags argument, as a short send
       isn't a considered an error condition without that being set.

       This function prepares an async send(2) request. See that man
       page for details.

       The io_uring_prep_sendto(3) function prepares a sendto request.
       The submission queue entry sqe is setup to use the file
       descriptor sockfd to start sending the data from buf of size len
       bytes and with modifier flags flags.  The destination address is
       specified by addr and addrlen and must be a valid address for the
       socket type.

       This function prepares an async sendto(2) request. See that man
       page for details.

       Both of the above send variants may be used with provided
       buffers, where rather than pass a buffer in directly with the
       request, IOSQE_BUFFER_SELECT is set in the SQE flags field, and
       additionally a buffer group ID is set in the SQE buf_group field.
       By using provided buffers with send requests, the application can
       prevent any kind of reordering of the outgoing data which can
       otherwise occur if the application has more than one send request
       inflight for a single socket. This provides better pipelining of
       data, where previously the app needed to manually serialize

       The bundle version allows the application to issue a single send
       request, with a buffer group ID given in the SQE buf_group field,
       which keeps sending from that buffer group until it runs out of
       buffers.  As with any other request using provided buffers,
       IOSQE_BUFFER_SELECT must also be set in the SQE flags before
       submission. A single CQE is posted for the send, with the result
       being how many bytes were sent, on success. When used with
       provided buffers, send or send bundle will contain the starting
       buffer group ID in the CQE flags field. The number of bytes sent
       starts from there, and will be in contigious buffer IDs after
       that. Send bundle, and send with provided buffers in general, are
       available since kernel 6.10, and can be further identified by
       checking for the IORING_FEAT_SEND_BUF_SELECT flag returned in
       when using io_uring_init_queue_params(3) to setup the ring.

RETURN VALUE         top


ERRORS         top

       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

SEE ALSO         top

       io_uring_get_sqe(3), io_uring_submit(3),
       io_uring_buf_ring_init(3), io_uring_buf_ring_add(3), send(2)

COLOPHON         top

       This page is part of the liburing (A library for io_uring)
       project.  Information about the project can be found at 
       ⟨⟩.  If you have a bug report for
       this manual page, send it to  This page
       was obtained from the project's upstream Git repository
       ⟨⟩ on 2024-06-14.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2024-06-03.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to

liburing-2.2                 March 12, 2022        io_uring_prep_send(3)

Pages that refer to this page: io_uring_prep_send(3)io_uring_prep_send_bundle(3)io_uring_prep_send_set_addr(3)io_uring_prep_sendto(3)io_uring_prep_send_zc(3)io_uring_prep_send_zc_fixed(3)