.\" Copyright (C) 2022 Jens Axboe <axboe@kernel.dk>
.\"
.\" SPDX-License-Identifier: LGPL-2.0-or-later
.\"
.TH io_uring_prep_fsync 3 "March 12, 2022" "liburing-2.2" "liburing Manual"
.SH NAME
io_uring_prep_fsync \- prepare an fsync request
.SH SYNOPSIS
.nf
.B #include <liburing.h>
.PP
.BI "void io_uring_prep_fsync(struct io_uring_sqe *" sqe ","
.BI "                         int " fd ","
.BI "                         unsigned " flags ");"
.fi
.SH DESCRIPTION
.PP
The
.BR io_uring_prep_fsync (3)
function prepares an fsync request. The submission queue entry
.I sqe
is setup to use the file descriptor
.I fd
that should get synced, with the modifier flags indicated by the
.I flags
argument.

This function prepares an fsync request. It can act either like an
.BR fsync (2)
operation, which is the default behavior. If
.B IORING_FSYNC_DATASYNC
is set in the
.I flags
argument, then it behaves like
.BR fdatasync (2).
If no range is specified, the
.I fd
will be synced from 0 to end-of-file.

It's possible to specify a range to sync, if one is desired. If the
.I off
field of the SQE is set to non-zero, then that indicates the offset to
start syncing at. If
.I len
is set in the SQE, then that indicates the size in bytes to sync from the
offset. Note that these fields are not accepted by this helper, so they have
to be set manually in the SQE after calling this prep helper.

.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 fsync (2),
.BR fdatasync (2)