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From:   Kanchan Joshi <joshiiitr@gmail.com>
Date:   Fri, 10 Jul 2020 19:41:19 +0530
Message-ID: <CA+1E3rKOZUz7oZ_DGW6xZPQaDu+T5iEKXctd+gsJw05VwpGQSQ@mail.gmail.com>
Subject: Re: [PATCH v3 4/4] io_uring: add support for zone-append
To:     Matthew Wilcox <willy@infradead.org>
Cc:     Christoph Hellwig <hch@infradead.org>,
        Jens Axboe <axboe@kernel.dk>,
        Kanchan Joshi <joshi.k@samsung.com>, viro@zeniv.linux.org.uk,
        bcrl@kvack.org, Damien.LeMoal@wdc.com, asml.silence@gmail.com,
        linux-fsdevel@vger.kernel.org, "Matias Bj??rling" <mb@lightnvm.io>,
        linux-kernel@vger.kernel.org, linux-aio@kvack.org,
        io-uring@vger.kernel.org, linux-block@vger.kernel.org,
        Selvakumar S <selvakuma.s1@samsung.com>,
        Nitesh Shetty <nj.shetty@samsung.com>,
        Javier Gonzalez <javier.gonz@samsung.com>
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Sender: linux-kernel-owner@vger.kernel.org
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On Fri, Jul 10, 2020 at 7:21 PM Matthew Wilcox <willy@infradead.org> 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