Re: [Qemu-devel] [PULL 00/54] Kconfig conversion, excluding ARM and MIPS

[Philippe Mathieu-Daudé]

On 3/5/19 9:08 PM, Eric Blake wrote:
> On 3/5/19 1:45 PM, Thomas Huth wrote:
> 
>>> If there are special instructions for what to do with
>>> build trees over the transition to kconfig, the pullreq
>>> cover letter would be a good place to mention them :-)
>>
>> I think you've got to do a "make distclean" inbetween... that's the old
>> problem when a default-configs/*.mak file gets added or erased - we do
>> not properly re-generate the dependencies in that case.
> 
> As in this?
> 
> upgrade path:
> build old commit
> make distclean
> git pull/branch/...

make distclean again?

> build new commit
> 
> downgrade path (when bisecting, backporting, ...)
> build new commit
> make distclean
> git branch/reset/...

make distclean again?

> build old commit
> 
> We obviously can't fix old commits to recognize when we are downgrading
> from a new commit, but is there anything we can do when upgrading to a
> newer commit to more gracefully inform the user if they forgot a 'make
> distclean' (or even better, to not make a 'make distclean' on upgrade
> mandatory)?  In particular, once this patch series lands, developers
> doing a blind 'git pull' will end up in the situation:
> 
> build old commit
> git pull
> build new commit # oops
> 
> but may not realize that they first have to reset back to the old commit
> prior to 'make distclean' to guarantee that it will work. Unless I'm
> mistaken and 'make distclean' on an incremental build will work in spite
> of the missing dependencies on *.mak files even when you forgot to clean
> before upgrading.
> 
> 'make distclean' is a heavy hammer, is there anything smaller in scope
> that will fix the problem without nuking everything, such as a strategic
> touch or rm of one particular file?
>