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[linuxjm/jm.git] / manual / LDP_man-pages / draft / man2 / fsync.2

.\" Hey Emacs! This file is -*- nroff -*- source.
.\"
.\" Copyright 1993 Rickard E. Faith (faith@cs.unc.edu) and
.\" and Copyright 2006 Michael Kerrisk <mtk.manpages@gmail.com>
.\"
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Permission is granted to copy and distribute modified versions of this
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one.
.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date.  The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" the use of the information contained herein.  The author(s) may not
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\"
.\" Modified 21 Aug 1994 by Michael Chastain <mec@shell.portal.com>:
.\"   Removed note about old libc (pre-4.5.26) translating to 'sync'.
.\" Modified 15 Apr 1995 by Michael Chastain <mec@shell.portal.com>:
.\"   Added `see also' section.
.\" Modified 13 Apr 1996 by Markus Kuhn <mskuhn@cip.informatik.uni-erlangen.de>
.\"   Added remarks about fdatasync.
.\" Modified Fri Jan 31 16:27:42 1997 by Eric S. Raymond <esr@thyrsus.com>
.\" Modified 31 Jan 1997 by Eric S. Raymond <esr@thyrsus.com>
.\" Modified 18 Apr 2001 by Andi Kleen
.\"   Fix description to describe what it really does; add a few caveats.
.\" 2006-04-28, mtk, substantial rewrite of various parts.
.\"
.\" Japanese Version Copyright (c) 1997 HANATAKA Shinya
.\"         all rights reserved.
.\" Translated 1997-02-22, HANATAKA Shinya <hanataka@abyss.rim.or.jp>
.\" Modified 2001-05-19, HANATAKA Shinya <hanataka@abyss.rim.or.jp>
.\" Updated 2005-09-06, Akihiro MOTOKI <amotoki@dd.iij4u.or.jp>
.\" Updated 2006-07-30, Kentaro Shirakata <argrath@ub32.org>
.\" Updated 2007-10-13, Akihiro MOTOKI <amotoki@dd.iij4u.or.jp>, LDP v2.65
.\"
.\"WORD:        core                    ¥á¥â¥ê
.\"WORD:        disk                    ¥Ç¥£¥¹¥¯
.\"WORD:        synchronize             Ʊ´ü¤µ¤»¤ë
..\"
.TH FSYNC 2 2008-11-07 "Linux" "Linux Programmer's Manual"
.\"O .SH NAME
.SH ̾Á°
.\"O fsync, fdatasync \- synchronize a file's in-core state with storage device
fsync \- ¥á¥â¥ê¾å¤Ë¤¢¤ë¥Õ¥¡¥¤¥ë¤ÎÆâÍƤò¥¹¥È¥ì¡¼¥¸¥Ç¥Ð¥¤¥¹¾å¤Î¤â¤Î¤ÈƱ´ü¤µ¤»¤ë
.\"O .SH SYNOPSIS
.SH ½ñ¼°
.B #include <unistd.h>
.sp
.BI "int fsync(int " fd );
.sp
.BI "int fdatasync(int " fd );
.sp
.in -4n
.\"O Feature Test Macro Requirements for glibc (see
.\"O .BR feature_test_macros (7)):
glibc ¸þ¤±¤Îµ¡Ç½¸¡ºº¥Þ¥¯¥í¤ÎÍ×·ï
.RB ( feature_test_macros (7)
»²¾È):
.in
.sp
.BR fsync ():
_BSD_SOURCE || _XOPEN_SOURCE
.br
.\"O          || /* since glibc 2.8: */ _POSIX_C_SOURCE\ >=\ 200112L
         || /* glibc 2.8 °Ê¹ß¤Ç¤Ï: */ _POSIX_C_SOURCE\ >=\ 200112L
.\"O .\" _POSIX_C_SOURCE\ >=\ 200112L only since glibc 2.8
.\" _POSIX_C_SOURCE\ >=\ 200112L ¤Ï glibc 2.8 °Ê¹ß¤Î¤ß
.br
.BR fdatasync ():
_POSIX_C_SOURCE\ >=\ 199309L || _XOPEN_SOURCE\ >=\ 500
.\"O .SH DESCRIPTION
.SH ÀâÌÀ
.\"O .BR fsync ()
.\"O transfers ("flushes") all modified in-core data of
.\"O (i.e., modified buffer cache pages for) the
.\"O file referred to by the file descriptor
.\"O .I fd
.\"O to the disk device (or other permanent storage device)
.\"O where that file resides.
.BR fsync ()
¤Ï¡¢¥Õ¥¡¥¤¥ëµ­½Ò»Ò
.I fd
¤Ç»²¾È¤µ¤ì¤ë¥Õ¥¡¥¤¥ë¤ÎÆâÉô¤Ç»ý¤Ã¤Æ¤¤¤ë¥Ç¡¼¥¿
(¤Ä¤Þ¤ê¥Ð¥Ã¥Õ¥¡¥­¥ã¥Ã¥·¥å¥Ú¡¼¥¸) ¤Î¤¦¤Á½¤Àµ¤µ¤ì¤¿¥Ç¡¼¥¿¤ò¡¢
¤½¤Î¥Õ¥¡¥¤¥ë¤¬Â°¤¹¤ë¥Ç¥£¥¹¥¯¥Ç¥Ð¥¤¥¹ (¤Þ¤¿¤Ï¤½¤Î¾¤Î±Ê³¥¹¥È¥ì¡¼¥¸¥Ç¥Ð¥¤¥¹)
¤ËžÁ÷ (¡Ö¥Õ¥é¥Ã¥·¥å¡×) ¤¹¤ë¡£
.\"O The call blocks until the device reports that the transfer has completed.
.\"O It also flushes metadata information associated with the file (see
.\"O .BR stat (2)).
¤³¤Î¸Æ¤Ó½Ð¤·¤ÏžÁ÷¤¬½ª¤ï¤Ã¤¿¤È¥Ç¥Ð¥¤¥¹¤¬Êó¹ð¤¹¤ë¤Þ¤Ç¥Ö¥í¥Ã¥¯¤¹¤ë¡£
¤Þ¤¿¥Õ¥¡¥¤¥ë¤Ë·ë¤Ó¤Ä¤¤¤¿¥á¥¿¥Ç¡¼¥¿¾ðÊó
.RB ( stat (2)
»²¾È) ¤â¥Õ¥é¥Ã¥·¥å¤¹¤ë¡£

.\"O Calling
.\"O .BR fsync ()
.\"O does not necessarily ensure
.\"O that the entry in the directory containing the file has also reached disk.
.\"O For that an explicit
.\"O .BR fsync ()
.\"O on a file descriptor for the directory is also needed.
.BR fsync ()
¤Î¸Æ¤Ó½Ð¤·¤Ï¡¢¥Õ¥¡¥¤¥ë¤¬Â¸ºß¤·¤Æ¤¤¤ë¥Ç¥£¥ì¥¯¥È¥ê¤Î¥¨¥ó¥È¥ê¤¬¥Ç¥£¥¹¥¯¤Ø
½ñ¤­¹þ¤Þ¤ì¤¿¤³¤È¤òÊݾڤ¹¤ë¤ï¤±¤Ç¤Ï¤Ê¤¤¡£
Êݾڤ¹¤ë¤¿¤á¤Ë¤ÏÌÀ¼¨Åª¤Ë¤½¤Î¥Ç¥£¥ì¥¯¥È¥ê¤Î¥Õ¥¡¥¤¥ëµ­½Ò»Ò¤ËÂФ·¤Æ¤â
.BR fsync ()
¤¹¤ëɬÍפ¬¤¢¤ë¡£

.\"O .BR fdatasync ()
.\"O is similar to
.\"O .BR fsync (),
.\"O but does not flush modified metadata unless that metadata
.\"O is needed in order to allow a subsequent data retrieval to be
.\"O correctly handled.
.BR fdatasync ()
¤Ï
.BR fsync ()
¤ÈƱÍͤǤ¢¤ë¤¬¡¢¥á¥¿¥Ç¡¼¥¿¤Î°·¤¤¤¬°Û¤Ê¤ë¡£
.BR fdatasync ()
¤Ï¡¢¤½¤ì°Ê¹ß¤Î¥Ç¡¼¥¿Æɤ߹þ¤ß¤òÀµ¤·¤¯°·¤¦¤¿¤á¤Ë¤½¤Î¥á¥¿¥Ç¡¼¥¿¤¬É¬ÍפË
¤Ê¤é¤Ê¤¤¸Â¤ê¡¢Êѹ¹¤µ¤ì¤¿¥á¥¿¥Ç¡¼¥¿¤ò¥Õ¥é¥Ã¥·¥å¤·¤Ê¤¤¡£
.\"O For example, changes to
.\"O .I st_atime
.\"O or
.\"O .I st_mtime
.\"O (respectively, time of last access and
.\"O time of last modification; see
.\"O .BR stat (2))
.\"O do not require flushing because they are not necessary for
.\"O a subsequent data read to be handled correctly.
Î㤨¤Ð¡¢
st_atime ¤ä st_mtime
(¤½¤ì¤¾¤ìºÇ½ª¥¢¥¯¥»¥¹»þ¹ï¡¢ºÇ½ª½¤Àµ»þ¹ï;
.BR stat (2)
»²¾È) ¤ÎÊѹ¹¤Ï¥Õ¥é¥Ã¥·¥å¤òɬÍפȤ·¤Ê¤¤¡£
¤Ê¤¼¤Ê¤é¤³¤ì¤é¤Ï¤½¤ì°Ê¹ß¤Î¥Ç¡¼¥¿Æɤ߹þ¤ß¤òÀµ¤·¤¯°·¤¦¤¿¤á¤Ë
ɬÍפǤϤʤ¤¤«¤é¤Ç¤¢¤ë¡£
.\"O On the other hand, a change to the file size
.\"O .RI ( st_size ,
.\"O as made by say
.\"O .BR ftruncate (2)),
.\"O would require a metadata flush.
°ìÊý¡¢¥Õ¥¡¥¤¥ë¥µ¥¤¥º
.RB ( ftruncate (2)
¤Ç¤Ï
.IR st_size )
¤ÎÊѹ¹¤Ï¥á¥¿¥Ç¡¼¥¿¤Î¥Õ¥é¥Ã¥·¥å¤¬É¬ÍפǤ¢¤ë¡£
.\"O The aim of
.\"O .BR fdatasync ()
.\"O is to reduce disk activity for applications that do not
.\"O require all metadata to be synchronized with the disk.
.BR fdatasync ()
¤ÎÁÀ¤¤¤Ï¡¢Á´¤Æ¤Î¥á¥¿¥Ç¡¼¥¿¤ò¥Ç¥£¥¹¥¯¤ÈƱ´ü¤¹¤ëɬÍפΤʤ¤
¥¢¥×¥ê¥±¡¼¥·¥ç¥ó¤ËÂФ·¤Æ¡¢¥Ç¥£¥¹¥¯¥¢¥¯¥»¥¹¤ò¸º¤é¤¹¤³¤È¤Ç¤¢¤ë¡£
.\"O .SH "RETURN VALUE"
.SH ÊÖ¤êÃÍ
.\"O On success, these system calls return zero.
.\"O On error, \-1 is returned, and
.\"O .I errno
.\"O is set appropriately.
À®¸ù¤·¤¿¾ì¹ç¡¢¤³¤ì¤é¤Î¥·¥¹¥Æ¥à¥³¡¼¥ë¤Ï¥¼¥í¤òÊÖ¤¹¡£
¥¨¥é¡¼¤Î¾ì¹ç¡¢\-1 ¤¬ÊÖ¤µ¤ì¡¢
.I errno
¤¬Å¬ÀÚ¤ËÀßÄꤵ¤ì¤ë¡£
.\"O .SH ERRORS
.SH ¥¨¥é¡¼
.TP
.B EBADF
.\"O .I fd
.\"O is not a valid file descriptor open for writing.
.I fd
¤¬½ñ¤­¹þ¤ß¤Î¤¿¤á¤Ë¥ª¡¼¥×¥ó¤µ¤ì¤¿¥Õ¥¡¥¤¥ëµ­½Ò»Ò¤Ç¤Ê¤¤¡£
.TP
.B EIO
.\"O An error occurred during synchronization.
Ʊ´üÁàºî¤Î´Ö¤Ë¥¨¥é¡¼¤¬È¯À¸¤·¤¿¡£
.TP
.BR EROFS ", " EINVAL
.\"O .I fd
.\"O is bound to a special file which does not support synchronization.
.I fd
¤¬Æ±´üÁàºî¤ò¥µ¥Ý¡¼¥È¤·¤Æ¤Ê¤¤Æüì¤Ê¥Õ¥¡¥¤¥ë¤ò»²¾È¤·¤Æ¤¤¤ë¡£
.\"O .SH "CONFORMING TO"
.SH ½àµò
4.3BSD, POSIX.1-2001.
.\"O .SH AVAILABILITY
.SH ²ÄÍÑÀ­
.\"O On POSIX systems on which
.\"O .BR fdatasync ()
.\"O is available,
.\"O .B _POSIX_SYNCHRONIZED_IO
.\"O is defined in
.\"O .I <unistd.h>
.\"O to a value greater than 0.
.\"O (See also
.\"O .BR sysconf (3).)
.BR fdatasync ()
¤¬ÍøÍѲÄǽ¤Ê POSIX ¥·¥¹¥Æ¥à¤Ç¤Ï¡¢
.B _POSIX_SYNCHRONIZED_IO
¤¬
.I <unistd.h>
¤Ç 0 ¤è¤êÂ礭¤ÊÃͤËÄêµÁ¤µ¤ì¤ë
.RB ( sysconf (3)
»²¾È)¡£
.\" POSIX.1-2001: It shall be defined to -1 or 0 or 200112L.
.\" -1: unavailable, 0: ask using sysconf().
.\" glibc defines them to 1.
.\"O .SH NOTES
.SH Ãí°Õ
.\"O Applications that access databases or log files often write a tiny
.\"O data fragment (e.g., one line in a log file) and then call
.\"O .BR fsync ()
.\"O immediately in order to ensure that the written data is physically
.\"O stored on the harddisk.
.\"O Unfortunately,
.\"O .BR fsync ()
.\"O will always initiate two write operations: one for the newly written
.\"O data and another one in order to update the modification time stored
.\"O in the inode.
.\"O If the modification time is not a part of the transaction
.\"O concept
.\"O .BR fdatasync ()
.\"O can be used to avoid unnecessary inode disk write operations.
¥Ç¡¼¥¿¥Ù¡¼¥¹¤ä¥í¥°¥Õ¥¡¥¤¥ë¤Ë¥¢¥¯¥»¥¹¤¹¤ë¥¢¥×¥ê¥±¡¼¥·¥ç¥ó¤Ï¡¢
Èó¾ï¤Ë¾®¤µ¤Ê¥Ç¡¼¥¿¤ÎÃÇÊҤνñ¤­¹þ¤ß¤ò¹Ô¤¤¡¢¤½¤Î¸å¤¹¤°¤Ë
.BR fsync ()
¤ò¸Æ¤Ó½Ð¤·¤Æ¡¢½ñ¤­¹þ¤ó¤À¥Ç¡¼¥¿¤¬¥Ï¡¼¥É¥Ç¥£¥¹¥¯¤ËʪÍýŪ¤Ë
³Î¼Â¤Ë³ÊǼ¤µ¤ì¤ë¤è¤¦¤Ë¤¹¤ë¤³¤È¤¬Â¿¤¤¡£
»ÄÇ°¤Ê¤¬¤é¡¢
.BR fsync ()
¤Ï¾ï¤Ë 2¤Ä¤Î½ñ¤­¹þ¤ßÁàºî¤ò³«»Ï¤¹¤ë¡£
°ì¤Ä¤Ï¿·¤·¤¯½ñ¤­¹þ¤Þ¤ì¤¿¥Ç¡¼¥¿¤ËÂФ¹¤ë¤â¤Î¤Ç¤¢¤ê¡¢
¤â¤¦°ì¤Ä¤Ï inode ¤Ë³ÊǼ¤µ¤ì¤ë½¤Àµ»þ¹ï (modification time) ¤ò
¹¹¿·¤¹¤ë¤¿¤á¤Î¤â¤Î¤Ç¤¢¤ë¡£
½¤Àµ»þ¹ï¤Î¹¹¿·¤¬ÉÔ²Äʬ¤ÊÁàºî (¥È¥é¥ó¥¶¥¯¥·¥ç¥ó) ¤Î°ìÉô¤Ç¤Ï¤Ê¤¤¾ì¹ç¡¢
.BR fdatasync ()
¤ò»È¤¦¤³¤È¤Ç¡¢ÉÔɬÍ×¤Ê inode ¤Î¥Ç¥£¥¹¥¯½ñ¤­¹þ¤ßÁàºî¤òÈò¤±¤ë¤³¤È¤¬¤Ç¤­¤ë¡£

.\"O If the underlying hard disk has write caching enabled, then
.\"O the data may not really be on permanent storage when
.\"O .BR fsync ()
.\"O /
.\"O .BR fdatasync ()
.\"O return.
.\"O .\" See
.\"O .\" .BR hdparm (8)
.\"O .\" for how to disable that cache for IDE disks.
¥Ç¡¼¥¿¤¬ÇÛÃÖ¤µ¤ì¤Æ¤¤¤ë¥Ï¡¼¥É¥Ç¥£¥¹¥¯¤Î½ñ¤­¹þ¤ß¥­¥ã¥Ã¥·¥å¤¬Í­¸ú¤Ë
¤Ê¤Ã¤Æ¤¤¤ë¾ì¹ç¡¢
.BR fsync ()
/
.BR fdatasync ()
¤«¤éÌá¤Ã¤Æ¤­¤¿¤È¤·¤Æ¤â¡¢¤½¤Î¥Ç¡¼¥¿¤Ï¼ÂºÝ¤Ë¤Ï±Ê³Ū¤Êµ­²±ÇÞÂΤË
³ÊǼ¤µ¤ì¤Æ¤¤¤Ê¤¤¤«¤â¤·¤ì¤Ê¤¤¡£
.\" IDE ¥Ç¥£¥¹¥¯¤Î¥­¥ã¥Ã¥·¥å¤ò̵¸ú¤Ë¤¹¤ëÊýË¡¤Ë¤Ä¤¤¤Æ¤Ï
.\" .BR hdparm (8)
.\" ¤ò»²¾È¤Î¤³¤È¡£
.LP
.\"O When an ext2 file system is mounted with the
.\"O .I sync
.\"O option, directory entries are also implicitly synced by
.\"O .BR fsync ().
ext2 ¥Õ¥¡¥¤¥ë¡¦¥·¥¹¥Æ¥à¤¬
.I sync
¥ª¥×¥·¥ç¥ó¤Ä¤­¤Ç¥Þ¥¦¥ó¥È¤µ¤ì¤Æ¤¤¤ë¾ì¹ç¡¢
.BR fsync ()
¤Ç¥Ç¥£¥ì¥¯¥È¥ê¡¦¥¨¥ó¥È¥ê¤â°ÅÌۤΤ¦¤Á¤ËƱ´ü¤¹¤ë¡£
.LP
.\"O On kernels before 2.4,
.\"O .BR fsync ()
.\"O on big files can be inefficient.
.\"O An alternative might be to use the
.\"O .B O_SYNC
.\"O flag to
.\"O .BR open (2).
2.4 ¤è¤êÁ°¤Î¥«¡¼¥Í¥ë¤Ç¤ÏµðÂç¤Ê¥Õ¥¡¥¤¥ë¤Ë
.BR fsync ()
¤ò»ÈÍѤ¹¤ë¤³¤È¤Ï¸úΨ¤¬°­¤¤¾ì¹ç¤¬¤¢¤ë¡£
Ê̤ÎÊýË¡¤È¤·¤Æ
.BR open (2)
¤ÎºÝ¤Ë
.B O_SYNC
¥Õ¥é¥°¤ò»ÈÍѤ¹¤ë¤Î¤¬Îɤ¤¤«¤â¤·¤ì¤Ê¤¤¡£

.\"O In Linux 2.2 and earlier,
.\"O .BR fdatasync ()
.\"O is equivalent to
.\"O .BR fsync (),
.\"O and so has no performance advantage.
Linux 2.2 °ÊÁ°¤Ç¤Ï¡¢
.BR fdatasync ()
¤Ï
.BR fsync ()
¤ÈÅù²Á¤Ç¤¢¤ê¡¢À­Ç½Ì̤ǤΥá¥ê¥Ã¥È¤Ï¤Ê¤¤¡£
.\"O .SH "SEE ALSO"
.SH ´ØÏ¢¹àÌÜ
.BR bdflush (2),
.BR open (2),
.BR sync (2),
.BR sync_file_range (2),
.BR hdparm (8),
.BR mount (8),
.BR sync (8),
.BR update (8)