.\" Copyright (C) 2022 Jens Axboe <axboe@kernel.dk>
.\"
.\" SPDX-License-Identifier: LGPL-2.0-or-later
.\"
.TH io_uring_prep_send_zc 3 "September 6, 2022" "liburing-2.3" "liburing Manual"
.SH NAME
io_uring_prep_send_zc \- prepare a zerocopy send request
.SH SYNOPSIS
.nf
.B #include <liburing.h>
.PP
.BI "void io_uring_prep_send_zc(struct io_uring_sqe *" sqe ","
.BI "                           int " sockfd ","
.BI "                           const void *" buf ","
.BI "                           size_t " len ","
.BI "                           int " flags ","
.BI "                           unsigned " zc_flags ");"
.PP
.BI "void io_uring_prep_send_zc_fixed(struct io_uring_sqe *" sqe ","
.BI "                                 int " sockfd ","
.BI "                                 const void *" buf ","
.BI "                                 size_t " len ","
.BI "                                 int " flags ","
.BI "                                 unsigned " zc_flags ");"
.BI "                                 unsigned " buf_index ");"
.fi
.SH DESCRIPTION
.PP
The
.BR io_uring_prep_send_zc (3)
function prepares a zerocopy send request. The submission queue entry
.I sqe
is setup to use the file descriptor
.I sockfd
to start sending the data from
.I buf
of size
.I len
bytes with send modifier flags
.I flags
and zerocopy modifier flags
.IR zc_flags .

The 
.BR io_uring_prep_send_zc_fixed (3)
works just like
.BR io_uring_prep_send_zc (3)
except it requires the use of buffers that have been registered with 
.BR io_uring_register_buffers (3).
The
.I buf
and
.I len
arguments must fall within a region specified by
.I buf_index
in the previously registered buffer. The buffer need not be aligned with the 
start of the registered buffer.

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

These functions prepare an async zerocopy
.BR send (2)
request. See that man page for details. For details on the zerocopy nature
of it, see
.BR io_uring_enter (2) .

.SH RETURN VALUE
None
.SH ERRORS
The CQE
.I 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
.B -1
on failure and set
.I errno
to the actual error value, io_uring never uses
.IR errno .
Instead it returns the negated
.I errno
directly in the CQE
.I res
field.
.SH SEE ALSO
.BR io_uring_get_sqe (3),
.BR io_uring_submit (3),
.BR io_uring_prep_send (3),
.BR io_uring_enter (2),
.BR send (2)