[PATCH] libio: Always use _IO_BUFSIZE for stream buffers [BZ #4099]

[Florian Weimer]

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.

Thanks,
Florian
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