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

[Florian Weimer]

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.

Thanks,
Florian