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vfs: Implement proper O_SYNC semantics

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While Linux provided an O_SYNC flag basically since day 1, it took until
Linux 2.4.0-test12pre2 to actually get it implemented for filesystems,
since that day we had generic_osync_around with only minor changes and the
great "For now, when the user asks for O_SYNC, we'll actually give
O_DSYNC" comment.  This patch intends to actually give us real O_SYNC
semantics in addition to the O_DSYNC semantics.  After Jan's O_SYNC
patches which are required before this patch it's actually surprisingly
simple, we just need to figure out when to set the datasync flag to
vfs_fsync_range and when not.

This patch renames the existing O_SYNC flag to O_DSYNC while keeping it's
numerical value to keep binary compatibility, and adds a new real O_SYNC
flag.  To guarantee backwards compatiblity it is defined as expanding to
both the O_DSYNC and the new additional binary flag (__O_SYNC) to make
sure we are backwards-compatible when compiled against the new headers.

This also means that all places that don't care about the differences can
just check O_DSYNC and get the right behaviour for O_SYNC, too - only
places that actuall care need to check __O_SYNC in addition.  Drivers and
network filesystems have been updated in a fail safe way to always do the
full sync magic if O_DSYNC is set.  The few places setting O_SYNC for
lower layers are kept that way for now to stay failsafe.

We enforce that O_DSYNC is set when __O_SYNC is set early in the open path
to make sure we always get these sane options.

Note that parisc really screwed up their headers as they already define a
O_DSYNC that has always been a no-op.  We try to repair it by using it for
the new O_DSYNC and redefinining O_SYNC to send both the traditional
O_SYNC numerical value _and_ the O_DSYNC one.

Cc: Richard Henderson <rth@twiddle.net>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Grant Grundler <grundler@parisc-linux.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andreas Dilger <adilger@sun.com>
Acked-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: Kyle McMartin <kyle@mcmartin.ca>
Acked-by: Ulrich Drepper <drepper@redhat.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jan Kara <jack@suse.cz>
This commit is contained in:
Christoph Hellwig
2009-10-27 11:05:28 +01:00
committed by Jan Kara
parent 59bc055211
commit 6b2f3d1f76
24 changed files with 109 additions and 40 deletions
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17
arch/mips/include/asm/fcntl.h
View File

@@ -10,7 +10,7 @@
#define O_APPEND 0x0008
#define O_SYNC 0x0010
#define O_DSYNC 0x0010 /* used to be O_SYNC, see below */
#define O_NONBLOCK 0x0080
#define O_CREAT 0x0100 /* not fcntl */
#define O_TRUNC 0x0200 /* not fcntl */
@@ -18,6 +18,21 @@
#define O_NOCTTY 0x0800 /* not fcntl */
#define FASYNC 0x1000 /* fcntl, for BSD compatibility */
#define O_LARGEFILE 0x2000 /* allow large file opens */
/*
* Before Linux 2.6.32 only O_DSYNC semantics were implemented, but using
* the O_SYNC flag. We continue to use the existing numerical value
* for O_DSYNC semantics now, but using the correct symbolic name for it.
* This new value is used to request true Posix O_SYNC semantics. It is
* defined in this strange way to make sure applications compiled against
* new headers get at least O_DSYNC semantics on older kernels.
*
* This has the nice side-effect that we can simply test for O_DSYNC
* wherever we do not care if O_DSYNC or O_SYNC is used.
*
* Note: __O_SYNC must never be used directly.
*/
#define __O_SYNC 0x4000
#define O_SYNC (__O_SYNC|O_DSYNC)
#define O_DIRECT 0x8000 /* direct disk access hint */
#define F_GETLK 14