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Subject: Re: [PATCH v3 4/4] io_uring: add support for zone-append
To:     Matthew Wilcox <willy@infradead.org>
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>
References: <20200706143208.GA25523@casper.infradead.org>
 <20200707151105.GA23395@test-zns>
 <20200707155237.GM25523@casper.infradead.org>
 <20200707202342.GA28364@test-zns>
 <7a44d9c6-bf7d-0666-fc29-32c3cba9d1d8@kernel.dk>
 <20200707221812.GN25523@casper.infradead.org>
 <CGME20200707223803epcas5p41814360c764d6b5f67fdbf173a8ba64e@epcas5p4.samsung.com>
 <145cc0ad-af86-2d6a-78b3-9ade007aae52@kernel.dk>
 <20200708125805.GA16495@test-zns>
 <2962cd68-de34-89be-0464-8b102a3f1d0e@kernel.dk>
 <20200708145826.GS25523@casper.infradead.org>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <b1c58211-496a-ed85-a9bb-0d0cc56e250c@kernel.dk>
Date:   Wed, 8 Jul 2020 08:59:50 -0600
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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?

-- 
Jens Axboe