----- Original Message -----
> From: "Matthew Wilcox" <willy@xxxxxxxxxxxxxxx>
> To: "Mathieu Desnoyers" <mathieu.desnoyers@xxxxxxxxxxxx>
> Cc: "Matthew Wilcox" <matthew.r.wilcox@xxxxxxxxx>, linux-fsdevel@xxxxxxxxxxxxxxx, linux-mm@xxxxxxxxx,
> linux-kernel@xxxxxxxxxxxxxxx
> Sent: Friday, October 17, 2014 12:33:31 AM
> Subject: Re: [PATCH v11 07/21] dax,ext2: Replace XIP read and write with DAX I/O
>
> On Thu, Oct 16, 2014 at 03:51:12PM -0400, Matthew Wilcox wrote:
> > On Thu, Oct 16, 2014 at 11:50:27AM +0200, Mathieu Desnoyers wrote:
> > > > + if (rw == WRITE) {
> > > > + if (!buffer_mapped(bh)) {
> > > > + retval = -EIO;
> > > > + /* FIXME: fall back to buffered I/O */
> > >
> > > Fallback on buffered I/O would void guarantee about having data stored
> > > into persistent memory after write returns. Not sure we actually want
> > > that.
> >
> > Yeah, I think that comment is just stale. I can't see a way in which
> > buffered I/O would succeed after DAX I/O falis.
>
> On further consideration, I think the whole thing is just foolish.
> I don't see how get_block(create == 1) can return success *and* a buffer
> that is !mapped.
Perhaps a safe approach could be to put a BUG_ON() to check this assumption ?
Thanks,
Mathieu
>
> So I did this nice simplification:
>
> - if (rw == WRITE) {
> - if (!buffer_mapped(bh)) {
> - retval = -EIO;
> - /* FIXME: fall back to buffered I/O
> */
> - break;
> - }
> - hole = false;
> - } else {
> - hole = !buffer_written(bh);
> - }
> + hole = (rw != WRITE) && !buffer_written(bh);
>
> (compile-tested only; I'm going to run all the changes through xfstests
> next week when I'm back home before sending out a v12).
>
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
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