linux-kernel - Re: [patch 1/4] Configure out AIO support

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Message-ID: <20080805182607.GA28513@shareable.org>
Date:	Tue, 5 Aug 2008 19:26:07 +0100
From:	Jamie Lokier <jamie@...reable.org>
To:	Adrian Bunk <bunk@...nel.org>
Cc:	Bernhard Fischer <rep.dot.nop@...il.com>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	linux-kernel@...r.kernel.org, linux-embedded@...r.kernel.org,
	michael@...e-electrons.com, Matt Mackall <mpm@...enic.com>,
	bcrl@...ck.org, linux-aio@...ck.org, akpm@...ux-foundation.org
Subject: Re: [patch 1/4] Configure out AIO support

Adrian Bunk wrote:
> On Fri, Aug 01, 2008 at 12:42:22AM +0200, Bernhard Fischer wrote:
> > On Thu, Jul 31, 2008 at 01:12:19PM +0300, Adrian Bunk wrote:
> > >On Thu, Jul 31, 2008 at 12:09:29PM +0200, Bernhard Fischer wrote:
> > >> On Thu, Jul 31, 2008 at 11:27:04AM +0200, Thomas Petazzoni wrote:
> > >> >This patchs adds the CONFIG_AIO option which allows to remove support
> > >> >for asynchronous I/O operations, that are not necessarly used by
> > >> >applications, particularly on embedded devices. As this is a
> > >> >size-reduction option, it depends on CONFIG_EMBEDDED. It allows to
> > >> >save ~7 kilobytes of kernel code/data:
> > >> 
> > >> Shouldn't this also make sure not to install aio_abi.h or at least an
> > >> empty aio_abi.h?
> > >
> > >The userspace headers are independent of any kernel configuration
> > >(except for the architecture).
> > 
> > I beg to disagree:
> > internals as exposed by e.g. aio_abi.h are impl dependent. Noone except
> > the impl and it's users are interrested in it.
> >...
> 
> That's utter bullshit.
> 
> The contents of aio_abi.h is a kernel<->userspace ABI that mustn't ever 
> change. [1]

Case in point:

I want to be able to compile an application for embedded Linux which
*can use* Linux-AIO, but can also run on a kernel which has Linux-AIO
removed by this patch.

I still want to compile the application with that capability, in case
it's run on another kernel with it enabled.

I shouldn't have to have a separate, special kernel with all options
enabled, just to compile applications that run on multiple kernels and
use run-time features when available.

Just like all the other kernel<->userspace interfaces, the header
files (including their presence) shouldn't depend on kernel
configuration at all.

-- Jamie
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