Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
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: <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>
 <b1c58211-496a-ed85-a9bb-0d0cc56e250c@kernel.dk>
 <20200708150240.GT25523@casper.infradead.org>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <33b9887b-eaba-c7be-5dfd-fc7e7d416f48@kernel.dk>
Date:   Wed, 8 Jul 2020 09:06:48 -0600
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101
 Thunderbird/68.8.0
MIME-Version: 1.0
In-Reply-To: <20200708150240.GT25523@casper.infradead.org>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 7/8/20 9:02 AM, Matthew Wilcox wrote:
> 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 ...

I just wanted to get clarification there, because to me it sounded like
you expected Kanchan to do it, and Kanchan assuming it "was sorted". I'd
consider that a prerequisite for the append series as far as io_uring is
concerned, hence _someone_ needs to actually do it ;-)

-- 
Jens Axboe