NAME

       io_uring_prep_send - prepare a send request

SYNOPSIS

       #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

       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 sends.

       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. Currently len must be given as 0 otherwise the request will be errored with -EINVAL as
       the result code. Future versions may allow setting to limit the transfer size. 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 contiguous 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

       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.

SEE ALSO

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

liburing-2.2                                     March 12, 2022                            io_uring_prep_send(3)