.\" Copyright (C) 2022 Jens Axboe <axboe@kernel.dk>
.\"
.\" SPDX-License-Identifier: LGPL-2.0-or-later
.\"
.TH io_uring_prep_tee 3 "March 13, 2022" "liburing-2.2" "liburing Manual"
.SH NAME
io_uring_prep_tee \- prepare a tee request
.SH SYNOPSIS
.nf
.B #include <fcntl.h>
.B #include <liburing.h>
.PP
.BI "void io_uring_prep_tee(struct io_uring_sqe *" sqe ","
.BI "                       int " fd_in ","
.BI "                       int " fd_out ","
.BI "                       unsigned int " nbytes ","
.BI "                       unsigned int " splice_flags ");"
.fi
.SH DESCRIPTION
.PP
The
.BR io_uring_prep_tee (3)
function prepares a tee request. The submission queue entry
.I sqe
is setup to use as input the file descriptor
.I fd_in
and as output the file descriptor
.I fd_out
duplicating up to
.I nbytes
bytes worth of data.
.I splice_flags
are modifier flags for the operation. See
.BR tee (2)
for the generic splice flags.

If
.I fd_out
is a direct descriptor,
.B IOSQE_FIXED_FILE
can be set in the SQE to indicate that. For the input file, the io_uring
specific
.B SPLICE_F_FD_IN_FIXED
can be set and
.I fd_in
given as a registered file descriptor offset.

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

.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 NOTES
Despite accepting an unsigned number of bytes, this function can transfer at most
INT_MAX bytes per call (the maximum for the underlying syscall interface).
In practice, limits as low as 65536 have been observed (just like with
.BR tee (2)
itself).
.SH SEE ALSO
.BR io_uring_get_sqe (3),
.BR io_uring_submit (3),
.BR io_uring_register (2),
.BR splice (2),
.BR tee (2)