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Date:   Wed, 8 Jul 2020 16:02:40 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Jens Axboe <axboe@kernel.dk>
Cc:     Kanchan Joshi <joshi.k@samsung.com>, viro@zeniv.linux.org.uk,
        bcrl@kvack.org, hch@infradead.org, Damien.LeMoal@wdc.com,
        asml.silence@gmail.com, linux-fsdevel@vger.kernel.org,
        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
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On Wed, Jul 08, 2020 at 08:59:50AM -0600, Jens Axboe wrote:
> On 7/8/20 8:58 AM, Matthew Wilcox wrote:
> > On Wed, Jul 08, 2020 at 08:54:07AM -0600, Jens Axboe wrote:
> >> On 7/8/20 6:58 AM, Kanchan Joshi wrote:
> >>>>> +#define IOCB_NO_CMPL		(15 << 28)
> >>>>>
> >>>>>  struct kiocb {
> >>>>> [...]
> >>>>> -	void (*ki_complete)(struct kiocb *iocb, long ret, long ret2);
> >>>>> +	loff_t __user *ki_uposp;
> >>>>> -	int			ki_flags;
> >>>>> +	unsigned int		ki_flags;
> >>>>>
> >>>>> +typedef void ki_cmpl(struct kiocb *, long ret, long ret2);
> >>>>> +static ki_cmpl * const ki_cmpls[15];
> >>>>>
> >>>>> +void ki_complete(struct kiocb *iocb, long ret, long ret2)
> >>>>> +{
> >>>>> +	unsigned int id = iocb->ki_flags >> 28;
> >>>>> +
> >>>>> +	if (id < 15)
> >>>>> +		ki_cmpls[id](iocb, ret, ret2);
> >>>>> +}
> >>>>>
> >>>>> +int kiocb_cmpl_register(void (*cb)(struct kiocb *, long, long))
> >>>>> +{
> >>>>> +	for (i = 0; i < 15; i++) {
> >>>>> +		if (ki_cmpls[id])
> >>>>> +			continue;
> >>>>> +		ki_cmpls[id] = cb;
> >>>>> +		return id;
> >>>>> +	}
> >>>>> +	WARN();
> >>>>> +	return -1;
> >>>>> +}
> >>>>
> >>>> That could work, we don't really have a lot of different completion
> >>>> types in the kernel.
> >>>
> >>> Thanks, this looks sorted.
> >>
> >> Not really, someone still needs to do that work. I took a quick look, and
> >> most of it looks straight forward. The only potential complication is
> >> ocfs2, which does a swap of the completion for the kiocb. That would just
> >> turn into an upper flag swap. And potential sync kiocb with NULL
> >> ki_complete. The latter should be fine, I think we just need to reserve
> >> completion nr 0 for being that.
> > 
> > I was reserving completion 15 for that ;-)
> > 
> > +#define IOCB_NO_CMPL		(15 << 28)
> > ...
> > +	if (id < 15)
> > +		ki_cmpls[id](iocb, ret, ret2);
> > 
> > Saves us one pointer in the array ...
> 
> That works. Are you going to turn this into an actual series of patches,
> adding the functionality and converting users?

I was under the impression Kanchan was going to do that, but I can run it
off quickly ...