[Buildroot] [PATCH 05/16 v5] core/legal-info: ensure legal-info works in off-line mode

[Thomas Petazzoni <thomas.petazzoni@free-electrons.com>]

Hello,

On Fri, 11 Mar 2016 18:49:18 +0100, Yann E. MORIN wrote:
> Almost all packages which are saved for legal-info have their source
> archives downloaded as part of 'make source', which makes an off-line
> build completely possible [0].
> 
> However, for the pre-configured external toolchains, the source tarball
> is different, as the main tarball is a binary package. And that source
> tarball is only downloaded during the legal-info phase, which makes it
> inconvenient for full off-line builds.
> 
> We fix that by adding a new rule, $(1)-legal-source which only
> $(1)-all-source depends on, so that we only download it for a top-level
> 'make source', not as part of the standard download mechanism (i.e. only
> what is really needed to build).
> 
> This new rule depends, like the normal download mechanism, on a stamp
> file, so that we do not emit a spurious hash-check message on successive
> runs of 'make source'.
> 
> This way, we can do a complete [0] off-line build and are still able to
> generate legal-info, while at the same time we do not incur any download
> overhead during a simple build.

I am wondering what is the motivation for making "make legal-info"
absolutely executable off-line, after a "make source". I was about to
apply this patch, so my opinion is definitely not firm on this, but
I have some concern:

 * Now "make source" is downloading more stuff than is actually needed
   to do the build. And potentially a *lot* more this is going to
   download the source code for the toolchain, which you absolutely
   don't care about. So for a CodeSoucery ARM toolchain, instead of
   download just the 97 MB of the toolchain, you would download 97 MB +
   278 MB of source code. You're basically quadrupling the data to be
   downloaded for the toolchain itself.

 * Now, after a successful build, "make source" will no longer be a
   no-op operation, because "make source" will also download the files
   needed for legal-info. This is IMO rather unexpected.

Now whether those two concerns are really sufficient to justify a
different implementation can be discussed. One possible solution is to
have a "make legal-info-source", which would download whatever
legal-info needs to be executed offline.

That being said, we're really talking about a few corner cases, because
essentially, only the external toolchains currently make use of
<pkg>_ACTUAL_SOURCE.

Thomas
-- 
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com