Re: [PATCH v5 1/2] Return bytes transferred for partial direct I/O

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On 01/23/2018 12:35 AM, Matthew Wilcox wrote:
> On Mon, Jan 22, 2018 at 08:28:54PM -0700, Jens Axboe wrote:
>> On 1/22/18 8:18 PM, Goldwyn Rodrigues wrote:
>>>> that their application was "already broken". I'd hate for a kernel
>>>> upgrade to break them.
>>>>
>>>> I do wish we could make the change, and maybe we can. But it probably
>>>> needs some safe guard proc entry to toggle the behavior, something we
>>>> can drop in a few years when we're confident it won't break real
>>>> applications.
>>>
>>> Assuming we call it /proc/sys/fs/dio_short_writes(better names/paths?),
>>> should it be enabled or disabled by default?
>>
>> I'd enable it by default, if not, you are never going to be able to
>> remove it because you'll have no confidence that anyone actually flipped
>> the switch and ran with it enabled. The point of having it there and on
>> by default would be that if something does break, people have the option
>> of turning it off and restoring the previous behavior, without having to
>> change the kernel.
> 
> I think it's an opt-in prctl that's something like PRCTL_SHORT_WRITES_ALLOWED.
> 

I cannot decide where to stick this bit in the task_struct.
current->flags/PF_* does not seem right. Don't want to start a new
fs_flags field. Suggestions?

-- 
Goldwyn



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