On Wed 25-04-18 00:07:07, Holger Hoffstätte wrote:
> On 04/24/18 19:34, 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.
>
> The above line just gives parenthesis salad errors, so why not compromise
> on:
>
> if ((iocb->ki_flags & (IOCB_DSYNC | IOCB_SYNC)) == IOCB_DSYNC) {
>
> Unless my bit twiddling has completely left me I think this is what was
> intended, and it actually compiles too.
Yup, I agree this is what needs to happen.
Honza
--
Jan Kara <[email protected]>
SUSE Labs, CR
