Re: [PATCH v7 06/15] iomap: Return error code from iomap_write_iter()

Matthew Wilcox
2022-06-06T19:18:31Z

On Mon, Jun 06, 2022 at 09:39:03AM -0700, Stefan Roesch wrote:
>
>
> On 6/2/22 5:38 AM, Matthew Wilcox wrote:
> > On Wed, Jun 01, 2022 at 02:01:32PM -0700, Stefan Roesch wrote:
> >> Change the signature of iomap_write_iter() to return an error code. In
> >> case we cannot allocate a page in iomap_write_begin(), we will not retry
> >> the memory alloction in iomap_write_begin().
> >
> > loff_t can already represent an error code. And it's already used like
> > that.
> >
> >> @@ -829,7 +830,8 @@ static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
> >> length -= status;
> >> } while (iov_iter_count(i) && length);
> >>
> >> - return written ? written : status;
> >> + *processed = written ? written : error;
> >> + return error;
> >
> > I think the change you really want is:
> >
> > if (status == -EAGAIN)
> > return -EAGAIN;
> > if (written)
> > return written;
> > return status;
> >
>
> I think the change needs to be:
>
> - return written ? written : status;
> + if (status == -EAGAIN) {
> + iov_iter_revert(i, written);
> + return -EAGAIN;
> + }
> + if (written)
> + return written;
> + return status;

Ah yes, I think you're right.

Does it work to leave everything the way it is, call back into the
iomap_write_iter() after having done a short write, get the -EAGAIN at
that point and pass the already-advanced iterator to the worker thread?
I haven't looked into the details of how that works, so maybe you just
can't do that.