Re: [PATCH] splice: report related fsnotify events

[Jens Axboe <axboe@kernel.dk>]

On 4/4/23 7:45?AM, Amir Goldstein wrote:
> On Tue, Apr 4, 2023 at 12:21?PM Jan Kara <jack@suse.cz> wrote:
>>
>> On Mon 03-04-23 11:23:25, Jens Axboe wrote:
>>> On 4/3/23 11:15?AM, Amir Goldstein wrote:
>>>>> On 4/3/23 11:00?AM, Amir Goldstein wrote:
>>>>> io_uring does do it for non-polled IO, I don't think there's much point
>>>>> in adding it to IOPOLL however. Not really seeing any use cases where
>>>>> that would make sense.
>>>>>
>>>>
>>>> Users subscribe to fsnotify because they want to be notified of changes/
>>>> access to a file.
>>>> Why do you think that polled IO should be exempt?
>>>
>>> Because it's a drastically different use case. If you're doing high
>>> performance polled IO, then you'd never rely on something as slow as
>>> fsnotify to tell you of any changes that happened to a device or file.
>>> That would be counter productive.
>>
>> Well, I guess Amir wanted to say that the application using fsnotify is not
>> necessarily the one doing high performance polled IO. You could have e.g.
>> data mirroring application A tracking files that need mirroring to another
>> host using fsnotify and if some application B uses high performance polled
>> IO to modify a file, application A could miss the modified file.
>>
>> That being said if I look at exact details, currently I don't see a very
>> realistic usecase that would have problems (people don't depend on
>> FS_MODIFY or FS_ACCESS events too much, usually they just use FS_OPEN /
>> FS_CLOSE), which is likely why nobody reported these issues yet :).
>>
> 
> I guess so.
> Our monitoring application also does not rely on FS_MODIFY/FS_ACCESS
> as they could be too noisy.
> 
> The thing that I find missing is being able to tell if a file was *actually*
> accessed/modified in between open and close.
> This information could be provided with FS_CLOSE event

Agree, it's not a good fit for a lot of common use cases.

-- 
Jens Axboe