Re: [Qemu-devel] [PATCH] replace O_SYNC with O_FSYNC

[Jamie Lokier <jamie@shareable.org>]

Christoph Hellwig wrote:
> On Fri, Jun 19, 2009 at 10:22:07PM -0400, m a wrote:
> > This patch replaces O_SYNC with O_FSYNC. These two flags do the same 
> > thing, but only O_FSYNC is available in Mac OS 10.3 and under. It only 
> > replaces O_SYNC if it doesn't exist. This patch allows the file 
> > block-raw-posix.c to compile on Mac OS 10.3. This is my first time 
> > submitting a patch, so there might have been a few mistakes made.
> 
> But O_SYNC is a standard posix flag, while O_FSYNC appears to be
> a BSD extension.  Also the actual code uses O_DSYNC anyway, which
> also is in Posix but not actually natively supported by some OSes,
> e.g. Linux (but still provided in libc there).

If O_FSYNC and O_SYNC do the same thing, and O_SYNC is used anywhere,
there's no harm in this for portability:

    #if !defined(O_SYNC) && defined(O_FSYNC)
    #define O_SYNC O_FSYNC
    #endif

The patch assumes O_FSYNC is defined if O_SYNC isn't, which is wrong.

> >  /* OS X does not have O_DSYNC */
> >  #ifndef O_DSYNC
> >  #define O_DSYNC O_SYNC
> 
> So if the code here is correct and Darwin is the only supported OS where
> O_DSYNC is missing we could just replace the O_SYNC in the last line
> with O_FSYNC.

I agree, though the comment might be misleading, if there's another
supported OS without O_DSYNC.

-- Jamie