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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | SEE ALSO | COLOPHON |
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io_uring_prep_send(3) liburing Manual io_uring_prep_send(3)
io_uring_prep_send - prepare a send request
#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);
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.
None
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),
io_uring_buf_ring_init(3), io_uring_buf_ring_add(3), send(2)
sendto(2)
This page is part of the liburing (A library for io_uring)
project. Information about the project can be found at
⟨https://github.com/axboe/liburing⟩. If you have a bug report for
this manual page, send it to io-uring@vger.kernel.org. This page
was obtained from the project's upstream Git repository
⟨https://github.com/axboe/liburing⟩ on 2025-02-02. (At that time,
the date of the most recent commit that was found in the
repository was 2025-01-22.) 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
man-pages@man7.org
liburing-2.2 March 12, 2022 io_uring_prep_send(3)
Pages that refer to this page: io_uring_setup(2)
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HTML rendering created 2025-02-02 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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