131 lines
3.6 KiB
Groff
131 lines
3.6 KiB
Groff
.\" Copyright (c) 1983, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\" Copyright (c) 2016 The FreeBSD Foundation, Inc.
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.\" All rights reserved.
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.\"
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.\" Parts of this documentation were written by
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.\" Konstantin Belousov <kib@FreeBSD.org> under sponsorship
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.\" from the FreeBSD Foundation.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)fsync.2 8.1 (Berkeley) 6/4/93
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.\" $FreeBSD$
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.\"
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.Dd May 24, 2017
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.Dt FSYNC 2
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.Os
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.Sh NAME
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.Nm fdatasync, fsync
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.Nd "synchronise changes to a file"
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In unistd.h
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.Ft int
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.Fn fdatasync "int fd"
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.Ft int
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.Fn fsync "int fd"
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.Sh DESCRIPTION
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The
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.Fn fsync
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system call
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causes all modified data and attributes of the file referenced by
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the file descriptor
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.Fa fd
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to be moved to a permanent storage device.
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This normally results in all in-core modified copies
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of buffers for the associated file to be written to a disk.
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.Pp
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The
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.Fn fdatasync
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system call causes all modified data of
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.Fa fd
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to be moved to a permanent storage device.
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Unlike
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.Fn fsync ,
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the system call does not guarantee that file attributes or
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metadata necessary to access the file are committed to the permanent storage.
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.Pp
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The
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.Fn fsync
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system call
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should be used by programs that require a file to be
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in a known state, for example, in building a simple transaction
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facility.
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If the file metadata has already been committed, using
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.Fn fdatasync
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can be more efficient than
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.Fn fsync .
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.Pp
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Both
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.Fn fdatasync
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and
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.Fn fsync
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calls are cancellation points.
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.Sh RETURN VALUES
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.Rv -std fsync
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.Sh ERRORS
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The
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.Fn fsync
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and
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.Fn fdatasync
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calls fail if:
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.Bl -tag -width Er
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.It Bq Er EBADF
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The
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.Fa fd
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argument
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is not a valid descriptor.
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.It Bq Er EINVAL
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The
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.Fa fd
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argument
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refers to a socket, not to a file.
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.It Bq Er EIO
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An I/O error occurred while reading from or writing to the file system.
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.El
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.Sh SEE ALSO
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.Xr sync 2 ,
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.Xr syncer 4 ,
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.Xr sync 8
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.Sh HISTORY
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The
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.Fn fsync
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system call appeared in
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.Bx 4.2 .
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The
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.Fn fdatasync
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system call appeared in
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.Fx 11.1 .
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.Sh BUGS
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The
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.Fn fdatasync
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system call currently does not guarantee that enqueued
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.Xr aio 4
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requests for the file referenced by
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.Fa fd
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are completed before the syscall returns.
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