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From: Jens Axboe <[email protected]>
To: Matthew Wilcox <[email protected]>
Cc: Kanchan Joshi <[email protected]>,
	[email protected], [email protected], [email protected],
	[email protected], [email protected],
	[email protected], [email protected],
	[email protected], [email protected],
	[email protected], [email protected],
	Selvakumar S <[email protected]>,
	Nitesh Shetty <[email protected]>,
	Javier Gonzalez <[email protected]>
Subject: Re: [PATCH v3 4/4] io_uring: add support for zone-append
Date: Mon, 6 Jul 2020 08:33:39 -0600	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

On 7/6/20 8:32 AM, Matthew Wilcox wrote:
> On Mon, Jul 06, 2020 at 08:27:17AM -0600, Jens Axboe wrote:
>> On 7/6/20 8:10 AM, Matthew Wilcox wrote:
>>> On Sun, Jul 05, 2020 at 03:12:50PM -0600, Jens Axboe wrote:
>>>> On 7/5/20 3:09 PM, Matthew Wilcox wrote:
>>>>> On Sun, Jul 05, 2020 at 03:00:47PM -0600, Jens Axboe wrote:
>>>>>> On 7/5/20 12:47 PM, Kanchan Joshi wrote:
>>>>>>> From: Selvakumar S <[email protected]>
>>>>>>>
>>>>>>> For zone-append, block-layer will return zone-relative offset via ret2
>>>>>>> of ki_complete interface. Make changes to collect it, and send to
>>>>>>> user-space using cqe->flags.
>>>
>>>>> I'm surprised you aren't more upset by the abuse of cqe->flags for the
>>>>> address.
>>>>
>>>> Yeah, it's not great either, but we have less leeway there in terms of
>>>> how much space is available to pass back extra data.
>>>>
>>>>> What do you think to my idea of interpreting the user_data as being a
>>>>> pointer to somewhere to store the address?  Obviously other things
>>>>> can be stored after the address in the user_data.
>>>>
>>>> I don't like that at all, as all other commands just pass user_data
>>>> through. This means the application would have to treat this very
>>>> differently, and potentially not have a way to store any data for
>>>> locating the original command on the user side.
>>>
>>> I think you misunderstood me.  You seem to have thought I meant
>>> "use the user_data field to return the address" when I actually meant
>>> "interpret the user_data field as a pointer to where userspace
>>> wants the address stored".
>>
>> It's still somewhat weird to have user_data have special meaning, you're
>> now having the kernel interpret it while every other command it's just
>> an opaque that is passed through.
>>
>> But it could of course work, and the app could embed the necessary
>> u32/u64 in some other structure that's persistent across IO. If it
>> doesn't have that, then it'd need to now have one allocated and freed
>> across the lifetime of the IO.
>>
>> If we're going that route, it'd be better to define the write such that
>> you're passing in the necessary information upfront. In syscall terms,
>> then that'd be something ala:
>>
>> ssize_t my_append_write(int fd, const struct iovec *iov, int iovcnt,
>> 			off_t *offset, int flags);
>>
>> where *offset is copied out when the write completes. That removes the
>> need to abuse user_data, with just providing the storage pointer for the
>> offset upfront.
> 
> That works for me!  In io_uring terms, would you like to see that done
> as adding:
> 
>         union {
>                 __u64   off;    /* offset into file */
> +		__u64   *offp;	/* appending writes */
>                 __u64   addr2;
>         };
> 

Either that, or just use addr2 for it directly. I consider the appending
writes a marginal enough use case that it doesn't really warrant adding
a specially named field for that.

-- 
Jens Axboe


  reply	other threads:[~2020-07-06 14:33 UTC|newest]

Thread overview: 61+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <CGME20200705185204epcas5p3adeb4fc3473c5fc0472a7396783c5267@epcas5p3.samsung.com>
2020-07-05 18:47 ` [PATCH v3 0/4] zone-append support in io-uring and aio Kanchan Joshi
     [not found]   ` <CGME20200705185211epcas5p4059d05d2fcedb91829300a7a7d03fda3@epcas5p4.samsung.com>
2020-07-05 18:47     ` [PATCH v3 1/4] fs: introduce FMODE_ZONE_APPEND and IOCB_ZONE_APPEND Kanchan Joshi
     [not found]   ` <CGME20200705185217epcas5p1cc12d4b892f057a1fe06d73a00869daa@epcas5p1.samsung.com>
2020-07-05 18:47     ` [PATCH v3 2/4] block: add zone append handling for direct I/O path Kanchan Joshi
     [not found]   ` <CGME20200705185221epcas5p28b6d060df829b751109265222285da0e@epcas5p2.samsung.com>
2020-07-05 18:47     ` [PATCH v3 3/4] block: enable zone-append for iov_iter of bvec type Kanchan Joshi
     [not found]   ` <CGME20200705185227epcas5p16fba3cb92561794b960184c89fdf2bb7@epcas5p1.samsung.com>
2020-07-05 18:47     ` [PATCH v3 4/4] io_uring: add support for zone-append Kanchan Joshi
2020-07-05 21:00       ` Jens Axboe
2020-07-05 21:09         ` Matthew Wilcox
2020-07-05 21:12           ` Jens Axboe
2020-07-06 14:10             ` Matthew Wilcox
2020-07-06 14:27               ` Jens Axboe
2020-07-06 14:32                 ` Matthew Wilcox
2020-07-06 14:33                   ` Jens Axboe [this message]
2020-07-07 15:11                   ` Kanchan Joshi
2020-07-07 15:52                     ` Matthew Wilcox
2020-07-07 16:00                       ` Christoph Hellwig
2020-07-07 20:23                       ` Kanchan Joshi
2020-07-07 20:40                         ` Jens Axboe
2020-07-07 22:18                           ` Matthew Wilcox
2020-07-07 22:37                             ` Jens Axboe
2020-07-08 12:58                               ` Kanchan Joshi
2020-07-08 14:22                                 ` Matthew Wilcox
2020-07-08 16:41                                   ` Kanchan Joshi
2020-07-08 14:54                                 ` Jens Axboe
2020-07-08 14:58                                   ` Matthew Wilcox
2020-07-08 14:59                                     ` Jens Axboe
2020-07-08 15:02                                       ` Matthew Wilcox
2020-07-08 15:06                                         ` Jens Axboe
2020-07-08 16:08                                           ` Javier González
2020-07-08 16:33                                             ` Matthew Wilcox
2020-07-08 16:38                                               ` Jens Axboe
2020-07-08 17:13                                                 ` Kanchan Joshi
2020-07-08 16:43                                               ` Javier González
2020-07-06 13:58         ` Kanchan Joshi
2020-07-09 10:15         ` Christoph Hellwig
2020-07-09 13:58           ` Jens Axboe
2020-07-09 14:00             ` Christoph Hellwig
2020-07-09 14:05               ` Jens Axboe
2020-07-09 18:36                 ` Kanchan Joshi
2020-07-09 18:50                   ` Pavel Begunkov
2020-07-09 18:53                     ` Pavel Begunkov
2020-07-09 18:50                   ` Jens Axboe
2020-07-09 19:05                     ` Kanchan Joshi
2020-07-10 13:10                       ` Christoph Hellwig
2020-07-10 13:48                         ` Matthew Wilcox
2020-07-10 13:49                           ` Christoph Hellwig
2020-07-10 13:51                             ` Matthew Wilcox
2020-07-10 14:11                               ` Kanchan Joshi
2020-07-20 16:49                                 ` Kanchan Joshi
2020-07-20 17:14                                   ` Matthew Wilcox
2020-07-20 20:17                                     ` Kanchan Joshi
2020-07-21  0:59                                       ` Damien Le Moal
2020-07-21  1:15                                         ` Matthew Wilcox
2020-07-21  1:29                                           ` Jens Axboe
2020-07-21  2:19                                           ` Damien Le Moal
2020-07-10 14:09                         ` Jens Axboe
2020-07-20 16:46                           ` Kanchan Joshi
2020-07-10 13:09                     ` Christoph Hellwig
2020-07-10 13:29                       ` Kanchan Joshi
2020-07-10 13:43                         ` Christoph Hellwig
2020-07-20 17:02                           ` Kanchan Joshi
2020-07-10 13:57                         ` Kanchan Joshi

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