Re: adding proper O_SYNC/O_DSYNC, was Re: O_DIRECT and barriers

From: Jamie Lokier
Date: Fri Aug 28 2009 - 20:59:43 EST

Jamie Lokier wrote:
> Ulrich Drepper wrote:
> > > - O_RSYNC basically means we need to commit atime updates before a
> > > read returns, right?
> >
> > No, that's not it.
> >
> > O_RSYNC on its own just means the data is successfully transferred to
> > the calling process (always the case).
> >
> > O_RSYNC|O_DSYNC means that if a read request hits data that is currently
> > in a cache and not yet on the medium, then the write to medium is
> > successful before the read succeeds.
> >
> > O_RSYNC|O_SYNC means the same plus the integrity of file meta
> > information (access time etc).
> On several unixes, O_RSYNC means it will send the read to the
> hardware, not relying on the cache. This can be used to verify the
> data which was written earlier, whether by O_DSYNC or fdatasync.

I'm sure I read that in a couple of OS man pages, but I can't find it
again. Maybe it was something more obscure than the mainstream
unices; maybe I imagined it. Ho hum. For now, forget I said anythng.

-- Jamie
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