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

From: Matthew Wilcox <willy@infradead.org>
To: Christoph Hellwig <hch@infradead.org>
Cc: Kanchan Joshi <joshiiitr@gmail.com>, 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>
Subject: Re: [PATCH v3 4/4] io_uring: add support for zone-append
Date: Fri, 10 Jul 2020 14:51:19 +0100	[thread overview]
Message-ID: <20200710135119.GL12769@casper.infradead.org> (raw)
In-Reply-To: <20200710134932.GA16257@infradead.org>

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.