diff options
author | Christoph Hellwig <hch@lst.de> | 2009-10-27 06:05:28 -0400 |
---|---|---|
committer | Jan Kara <jack@suse.cz> | 2009-12-10 09:02:50 -0500 |
commit | 6b2f3d1f769be5779b479c37800229d9a4809fc3 (patch) | |
tree | 046ef6736ec6c25ab1c68741ba715d13645af336 /fs/namei.c | |
parent | 59bc055211b8d266ab6089158058bf8268e02006 (diff) |
vfs: Implement proper O_SYNC semantics
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>
Diffstat (limited to 'fs/namei.c')
-rw-r--r-- | fs/namei.c | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/fs/namei.c b/fs/namei.c index d11f404667e..b83d38f614f 100644 --- a/fs/namei.c +++ b/fs/namei.c | |||
@@ -1678,6 +1678,15 @@ struct file *do_filp_open(int dfd, const char *pathname, | |||
1678 | int will_write; | 1678 | int will_write; |
1679 | int flag = open_to_namei_flags(open_flag); | 1679 | int flag = open_to_namei_flags(open_flag); |
1680 | 1680 | ||
1681 | /* | ||
1682 | * O_SYNC is implemented as __O_SYNC|O_DSYNC. As many places only | ||
1683 | * check for O_DSYNC if the need any syncing at all we enforce it's | ||
1684 | * always set instead of having to deal with possibly weird behaviour | ||
1685 | * for malicious applications setting only __O_SYNC. | ||
1686 | */ | ||
1687 | if (open_flag & __O_SYNC) | ||
1688 | open_flag |= O_DSYNC; | ||
1689 | |||
1681 | if (!acc_mode) | 1690 | if (!acc_mode) |
1682 | acc_mode = MAY_OPEN | ACC_MODE(flag); | 1691 | acc_mode = MAY_OPEN | ACC_MODE(flag); |
1683 | 1692 | ||