Re: [Qemu-devel] [PATCH v2 1/1] configure: dtc: Probe for libfdt_env.h

[David Gibson <david@gibson.dropbear.id.au>]

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On Wed, May 29, 2013 at 10:14:19AM +0100, Peter Maydell wrote:
> On 29 May 2013 09:18, David Gibson <david@gibson.dropbear.id.au> wrote:
> > On Mon, May 27, 2013 at 02:20:57PM +1000, peter.crosthwaite@xilinx.com wrote:
> >> From: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
> >> Currently QEMU provides a local clone of the file libfdt_env.h in
> >> /include. This file is supposed to come with the libfdt package and is
> >
> > So, this patch might be the right thing anyway, but the statement
> > above is entirely false.  libfdt_env.h is explicitly intended to be
> > supplied by the build environment embedding libfdt.  The version
> > provided in the libfdt package is a example version which will do
> > (although it might not be ideal) for userspace builds with a
> > sufficiently normal C library.
> 
> (You're upstream for libfdt, yes?)

More or less, yes.

> If you're expecting that build environments provide a libfdt_env.h
> then shouldn't you be avoiding making breaking changes to libfdt
> that require build environments to fix their libfdt_env.h?
> This came up in the first place because we no longer build with
> new libfdt...

I missed that discussion, what exactly was the problem?  It's possible
we did something silly in libfdt.  Then again, although we certainly
want to keep changes which require updates to libfdt_env.h rare, I'm
not going to rule out extensions to libfdt which add new (minor)
external dependencies, and therefore changes to libfdt_env.h.

That said, I did put my correction a bit too strongly.  While
libfdt_env.h is notionally always provided by the surrounding
environment, if the packaged one works for your environment, it's
probably a good idea to use it.  That should be the case for almost
all userspace builds - providing a custom libfdt_env.h is more
intended for kernels, bootloaders and other build environments with
peculiar constraints.

> (conversely, if we're supposed to update our libfdt_env.h as we
> go along, is there a changelog that documents needed changes
> and what needs to be present for compatibility with older versions
> of libfdt?)

Heh.  There definitely should be a document covering what needs to be
provided by libfdt_env.h, but alas there is not.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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