O_DSYNC flag for open

O_DSYNC flag for open

[Denis Perchine]

Hello,

one small question... Will O_DSYNC flag be available in Linux?
It is available at least on AIX, and HP-UX. The difference with O_SYNC is the 
same as between fsync and fdatasync.

Any comments?

-- 
Sincerely Yours,
Denis Perchine

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Re: O_DSYNC flag for open

[Tom Vier]

fdatasync() is the same as fsync(), in linux. until fdatasync() is
implimented (ie, syncs the data only), there's no reason to define O_DSYNC.
just use:

#ifndef O_DSYNC
# define O_DSYNC O_SYNC
#endif

On Sat, Mar 10, 2001 at 01:03:57PM +0600, Denis Perchine wrote:
> one small question... Will O_DSYNC flag be available in Linux?
> It is available at least on AIX, and HP-UX. The difference with O_SYNC is the 
> same as between fsync and fdatasync.

-- 
Tom Vier <thomassr@erols.com>
DSA Key id 0x27371A2C

Re: O_DSYNC flag for open

[Stephen C. Tweedie]

Hi,

On Wed, Mar 14, 2001 at 10:26:42PM -0500, Tom Vier wrote:
> fdatasync() is the same as fsync(), in linux.

No, in 2.4 fdatasync does the right thing and skips the inode flush if
only the timestamps have changed.

> until fdatasync() is
> implimented (ie, syncs the data only)

fdatasync is required to sync more than just the data: it has to sync
the inode too if any fields other than the timestamps have changed.
So, for appending to files or writing new files from scratch, fsync ==
fdatasync (because each write also changes the inode size).  Only for
updating existing files in place does fdatasync behave differently.

> #ifndef O_DSYNC
> # define O_DSYNC O_SYNC
> #endif

2.4's O_SYNC actually does a fdatasync internally.  This is also the
default behaviour of HPUX, which requires you to set a sysctl variable
if you want O_SYNC to flush timestamp changes to disk.

Cheers,
 Stephen