On Tue, Apr 24, 2018 at 10:34:44AM -0700, Christoph Hellwig wrote:
> On Sat, Apr 21, 2018 at 02:54:05PM +0200, Jan Kara wrote:
> > > - if (iocb->ki_flags & IOCB_DSYNC)
> > > + if (iocb->ki_flags & IOCB_DSYNC) {
> > > dio->flags |= IOMAP_DIO_NEED_SYNC;
> > > + /*
> > > + * We optimistically try using FUA for this IO. Any
> > > + * non-FUA write that occurs will clear this flag, hence
> > > + * we know before completion whether a cache flush is
> > > + * necessary.
> > > + */
> > > + dio->flags |= IOMAP_DIO_WRITE_FUA;
> > > + }
> >
> > So I don't think this is quite correct. IOCB_DSYNC gets set also for O_SYNC
> > writes (in that case we also set IOCB_SYNC). And for those we cannot use
> > the FUA optimization AFAICT (definitely IOMAP_F_DIRTY isn't a safe
> > indicator of a need of full fsync for O_SYNC). Other than that the patch
> > looks good to me.
>
> Oops, good catch. I think the above if should just be
>
> if (iocb->ki_flags & (IOCB_DSYNC | IOCB_SYNC) == IOCB_DSYNC)) {
>
> and we are fine.
Ah, not exactly. IOMAP_DIO_NEED_SYNC needs to be set for either
DYSNC or SYNC writes, while IOMAP_DIO_WRITE_FUA should only be set
for DSYNC.
I'll fix this up appropriately.
Cheers,
Dave.
--
Dave Chinner
david@xxxxxxxxxxxxx
