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.\" Copyright (C) 2022 Stefan Roesch <shr@fb.com>
.\"
.\" SPDX-License-Identifier: LGPL-2.0-or-later
.\"
.TH io_uring_sqe_set_flags "January 25, 2022" "liburing-2.1" "liburing Manual"
.SH NAME
io_uring_sqe_set_flags \- set flags for submission queue entry
.SH SYNOPSIS
.nf
.B #include <liburing.h>
.PP
.BI "void io_uring_sqe_set_flags(struct io_uring_sqe *" sqe ","
.BI " unsigned " flags ");"
.fi
.SH DESCRIPTION
.PP
The
.BR io_uring_sqe_set_flags (3)
function allows the caller to change the behavior of the submission queue entry
by specifying flags. It enables the
.I flags
belonging to the
.I sqe
submission queue entry param.
.I flags
is a bit mask of 0 or more of the following values ORed together:
.TP
.B IOSQE_FIXED_FILE
The file descriptor in the SQE refers to the index of a previously registered
file or direct file descriptor, not a normal file descriptor.
.TP
.B IOSQE_ASYNC
Normal operation for io_uring is to try and issue an sqe as non-blocking first,
and if that fails, execute it in an async manner. To support more efficient
overlapped operation of requests that the application knows/assumes will
always (or most of the time) block, the application can ask for an sqe to be
issued async from the start.
.TP
.B IOSQE_IO_LINK
When this flag is specified, the SQE forms a link with the next SQE in the
submission ring. That next SQE will not be started before the previous request
completes. This, in effect, forms a chain of SQEs, which can be arbitrarily
long. The tail of the chain is denoted by the first SQE that does not have this
flag set. Chains are not supported across submission boundaries. Even if the
last SQE in a submission has this flag set, it will still terminate the current
chain. This flag has no effect on previous SQE submissions, nor does it impact
SQEs that are outside of the chain tail. This means that multiple chains can be
executing in parallel, or chains and individual SQEs. Only members inside the
chain are serialized. A chain of SQEs will be broken if any request in that
chain ends in error.
.TP
.B IOSQE_IO_DRAIN
When this flag is specified, the SQE will not be started before previously
submitted SQEs have completed, and new SQEs will not be started before this
one completes.
.SH RETURN VALUE
None
.SH SEE ALSO
.BR io_uring_submit (3),
.BR io_uring_register (3)
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