[PING] Avoid excessive buffer size in libio

[Florian Weimer]

On 11/30/2016 02:15 PM, Carlos O'Donell wrote:
> On 11/29/2016 11:50 AM, Florian Weimer wrote:
>> On 06/24/2016 05:35 PM, Florian Weimer wrote:
>>> On 05/19/2016 04:57 PM, Florian Weimer wrote:
>>>> On 03/31/2016 12:14 PM, Florian Weimer wrote:
>>>>> On 03/18/2016 11:52 PM, Roland McGrath wrote:
>>>>>
>>>>>> Whatever the results, they would not IMHO be relevant here.
>>>>>>
>>>>>> POSIX specifies that st_blksize is the "preferred I/O block size for
>>>>>> this
>>>>>> object".  It's the kernel's responsibility to give userland good advice
>>>>>> through this channel.  If there are common buggy kernels that give bad
>>>>>> advice, that is a reason to apply upper and lower limits to the
>>>>>> advice from
>>>>>> the kernel.  But the expectation should be that the kernel gets
>>>>>> fixed to
>>>>>> give good advice, and the optimal thing to do with a good kernel is to
>>>>>> follow its advice.
>>>>>>
>>>>>> Since the recommended use of st_blksize in this way is a standard user
>>>>>> feature and not just what stdio's implementation happens to do, there
>>>>>> is an
>>>>>> argument to be made that the limiting of the value should be done in
>>>>>> the
>>>>>> *stat functions reported st_blksize values rather than in stdio's
>>>>>> use of
>>>>>> them.  (I'm ambivalent about this point.)
>>>>>
>>>>> That's a good point.  I'll try to get feedback from kernel file system
>>>>> developers on this matter.
>>>>
>>>> I wasn't able to get any feedback.  Based on Rich's point about random
>>>> I/O and Roland's earlier suggestion, I'm just capping the reported
>>>> buffer size to 8192 in the attached patch.
>>>
>>> Ping?
>>>
>>>   <https://sourceware.org/ml/libc-alpha/2016-05/msg00428.html>
>>
>> Ping?
>
> Just to confirm the user can still call stat themselves and adjust the
> buffer size up if they want?

They can still install their own buffer, yes.

> If that's the case then this looks good to me and users have a way
> to re-enable the old behaviour.

Thanks,
Florian