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

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Date:   Fri, 10 Jul 2020 14:51:19 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Kanchan Joshi <joshiiitr@...il.com>, Jens Axboe <axboe@...nel.dk>,
        Kanchan Joshi <joshi.k@...sung.com>, viro@...iv.linux.org.uk,
        bcrl@...ck.org, Damien.LeMoal@....com, asml.silence@...il.com,
        linux-fsdevel@...r.kernel.org, Matias Bj??rling <mb@...htnvm.io>,
        linux-kernel@...r.kernel.org, linux-aio@...ck.org,
        io-uring@...r.kernel.org, linux-block@...r.kernel.org,
        Selvakumar S <selvakuma.s1@...sung.com>,
        Nitesh Shetty <nj.shetty@...sung.com>,
        Javier Gonzalez <javier.gonz@...sung.com>
Subject: Re: [PATCH v3 4/4] io_uring: add support for zone-append

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.