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

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Message-ID: <b1c58211-496a-ed85-a9bb-0d0cc56e250c@kernel.dk>
Date:   Wed, 8 Jul 2020 08:59:50 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Kanchan Joshi <joshi.k@...sung.com>, viro@...iv.linux.org.uk,
        bcrl@...ck.org, hch@...radead.org, Damien.LeMoal@....com,
        asml.silence@...il.com, linux-fsdevel@...r.kernel.org,
        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 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