Re: [PATCH v3 4/4] io_uring: add support for zone-append

[Kanchan Joshi]

On Fri, Jul 10, 2020 at 7:21 PM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
>
> On Fri, Jul 10, 2020 at 02:49:32PM +0100, Christoph Hellwig wrote:
> > On Fri, Jul 10, 2020 at 02:48:24PM +0100, Matthew Wilcox wrote:
> > > If we're going to go the route of changing the CQE, how about:
> > >
> > >  struct io_uring_cqe {
> > >          __u64   user_data;      /* sqe->data submission passed back */
> > > -        __s32   res;            /* result code for this event */
> > > -        __u32   flags;
> > > +   union {
> > > +           struct {
> > > +                   __s32   res;            /* result code for this event */
> > > +                   __u32   flags;
> > > +           };
> > > +           __s64   res64;
> > > +   };
> > >  };
> > >
> > > then we don't need to change the CQE size and it just depends on the SQE
> > > whether the CQE for it uses res+flags or res64.
> >
> > How do you return a status code or short write when you just have
> > a u64 that is needed for the offset?
>
> it's an s64 not a u64 so you can return a negative errno.  i didn't
> think we allowed short writes for objects-which-have-a-pos.

If we are doing this for zone-append (and not general cases), "__s64
res64" should work -.
64 bits = 1 (sign) + 23 (bytes-copied: cqe->res) + 40
(written-location: chunk_sector bytes limit)

-- 
Joshi