156 lines
4.3 KiB
Groff
156 lines
4.3 KiB
Groff
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.\" $NetBSD: fsync.2,v 1.17 2010/05/17 12:38:04 jruoho Exp $
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.\"
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.\" Copyright (c) 1983, 1993
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.\" The Regents of the University of California. All rights reserved.
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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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.\"
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.Dd May 17, 2010
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.Dt FSYNC 2
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.Os
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.Sh NAME
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.Nm fsync ,
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.Nm fsync_range
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.Nd "synchronize a file's in-core state with that on disk"
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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 fsync "int fd"
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.Ft int
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.Fn fsync_range "int fd" "int how" "off_t start" "off_t length"
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.Sh DESCRIPTION
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.Fn fsync
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causes all modified data and attributes of
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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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.Fn fsync
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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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.Pp
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.Fn fsync_range
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causes all modified data starting at
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.Fa start
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for length
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.Fa length
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of
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.Fa fd
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to be written to permanent storage.
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Note that
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.Fn fsync_range
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requires that the file
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.Fa fd
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must be open for writing.
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.Pp
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.Fn fsync_range
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may flush the file data in one of two manners:
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.Bl -tag -width FDATASYNC -offset indent
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.It Dv FDATASYNC
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Synchronize the file data and sufficient meta-data to retrieve the
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data for the specified range.
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.It Dv FFILESYNC
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Synchronize all modified file data and meta-data for the specified range.
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.El
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.Pp
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By default,
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.Fn fsync_range
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does not flush disk caches, assuming that storage media are able to ensure
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completed writes are transfered to media.
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The
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.Dv FDISKSYNC
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flag may be included in the
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.Fa how
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parameter to trigger flushing of all disk caches for the file.
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.Pp
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If the
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.Fa length
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parameter is zero,
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.Fn fsync_range
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will synchronize all of the file data.
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.Sh RETURN VALUES
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A 0 value is returned on success.
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A \-1 value indicates an error.
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.Sh ERRORS
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.Fn fsync
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or
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.Fn fsync_range
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fail if:
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.Bl -tag -width Er
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.It Bq Er EBADF
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.Fa fd
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is not a valid descriptor.
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.It Bq Er EINVAL
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.Fa fd
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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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.Pp
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Additionally,
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.Fn fsync_range
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fails if:
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.Bl -tag -width Er
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.It Bq Er EBADF
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.Fa fd
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is not open for writing.
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.It Bq Er EINVAL
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.Fa start
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+
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.Fa length
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is less than
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.Fa start .
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.El
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.Sh NOTES
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For optimal efficiency, the
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.Fn fsync_range
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call requires that the file system containing the file referenced by
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.Fa fd
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support partial synchronization of file data.
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For file systems which do
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not support partial synchronization, the entire file will be synchronized
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and the call will be the equivalent of calling
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.Fn fsync .
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.Sh SEE ALSO
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.Xr sync 2 ,
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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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function call appeared in
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.Bx 4.2 .
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.Pp
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The
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.Fn fsync_range
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function call first appeared in
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.Nx 2.0
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and is modeled after the function available in AIX.
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