Re: [HPDD-discuss] [PATCH] nfsd: add a new EXPORT_OP_NOWCC flag to struct export_operations

["bfields@fieldses.org" <bfields@fieldses.org>]

On Wed, Sep 16, 2015 at 01:18:29PM -0400, Jeff Layton wrote:
> On Mon, 14 Sep 2015 12:10:15 -0400
> "bfields@fieldses.org" <bfields@fieldses.org> wrote:
> 
> > On Sat, Sep 12, 2015 at 06:24:54AM -0400, Jeff Layton wrote:
> > > I don't think it matters, at least not on x86_64. bools and chars both
> > > require a byte. pahole does show this adding a new hole, but that's
> > > just because this brings the code up to 5 flags and the next field
> > > (fh_pre_size) needs to be aligned.
> > > 
> > > I do agree that replacing those other unsigned chars with bools is more
> > > clear however. Maybe we should even replace them all with a single
> > > unsigned int and use bitops to set flags in there. That would be more
> > > space efficient now that we're at 5 flags.
> > 
> > Makes sense to me.--b.
> 
> I played around with this a little today, and it turns out not to make
> a lot of difference. Here's what pahole says about the existing code
> (once I moved fh_maxsize to snuggle up to fh_handle to plug a hole):
...
> I used an unsigned long for fh_flags since we might as well. Making it
> smaller just adds a hole in there since the compiler wants to align the
> fh_pre_size. Moving it around doesn't help either as it just moves the
> hole around. Note that this is x86_64. It might look different on a
> 32-bit arch, but I doubt it really matters much in the big scheme of
> things.
> 
> Bruce, I'll send out the patches that change this if you like, but I'm
> inclined to just leave this alone since it doesn't seem to have a
> tangible benefit.

Unless more flags are imminent I guess it's just a question of which is
more readable.  Arguably there's some value to making it more obvious
that these are each just a bit.  I'll accept your judgement on that
question.

--b.