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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 <[email protected]>
Cc: Ivan Kokshaysky <[email protected]>
Cc: Grant Grundler <[email protected]>
Cc: "David S. Miller" <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Al Viro <[email protected]>
Cc: Andreas Dilger <[email protected]>
Acked-by: Trond Myklebust <[email protected]>
Acked-by: Kyle McMartin <[email protected]>
Acked-by: Ulrich Drepper <[email protected]>
Signed-off-by: Christoph Hellwig <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Jan Kara <[email protected]>
This commit is contained in:
Christoph Hellwig 2009-10-27 11:05:28 +01:00 • committed by Jan Kara
commit 6b2f3d1f76
24 changed files with 109 additions and 40 deletions
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3
fs/cifs/dir.c
View file

@ -214,7 +214,8 @@ int cifs_posix_open(char *full_path, struct inode **pinode,
posix_flags |= SMB_O_EXCL;
if (oflags & O_TRUNC)
posix_flags |= SMB_O_TRUNC;
if (oflags & O_SYNC)
/* be safe and imply O_SYNC for O_DSYNC */
if (oflags & O_DSYNC)
posix_flags |= SMB_O_SYNC;
if (oflags & O_DIRECTORY)
posix_flags |= SMB_O_DIRECTORY;

6
fs/cifs/file.c
View file

@ -76,8 +76,10 @@ static inline fmode_t cifs_posix_convert_flags(unsigned int flags)
reopening a file. They had their effect on the original open */
if (flags & O_APPEND)
posix_flags |= (fmode_t)O_APPEND;
if (flags & O_SYNC)
posix_flags |= (fmode_t)O_SYNC;
if (flags & O_DSYNC)
posix_flags |= (fmode_t)O_DSYNC;
if (flags & __O_SYNC)
posix_flags |= (fmode_t)__O_SYNC;
if (flags & O_DIRECTORY)
posix_flags |= (fmode_t)O_DIRECTORY;
if (flags & O_NOFOLLOW)