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From:   Masahiro Yamada <masahiroy@kernel.org>
Date:   Sun, 18 Apr 2021 04:35:15 +0900
Message-ID: <CAK7LNASpjUP+MvnUed68a074H2EPVeD5+KLzecAuFxxi_72eZw@mail.gmail.com>
Subject: Re: [PATCH 04/13] Kbuild: Rust support
To:     Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Cc:     Nick Desaulniers <ndesaulniers@google.com>,
        Miguel Ojeda <ojeda@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        rust-for-linux@vger.kernel.org,
        Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        Linux Doc Mailing List <linux-doc@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Alex Gaynor <alex.gaynor@gmail.com>,
        Geoffrey Thomas <geofft@ldpreload.com>,
        Finn Behrens <me@kloenk.de>,
        Adam Bratschi-Kaye <ark.email@gmail.com>,
        Wedson Almeida Filho <wedsonaf@google.com>,
        Michael Ellerman <mpe@ellerman.id.au>
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On Thu, Apr 15, 2021 at 9:43 AM Miguel Ojeda
<miguel.ojeda.sandonis@gmail.com> wrote:
>
> On Thu, Apr 15, 2021 at 1:19 AM Nick Desaulniers
> <ndesaulniers@google.com> wrote:
> >
> > Rather than check the origin (yikes, are we intentionally avoiding env
> > vars?), can this simply be
> > ifneq ($(CLIPPY),)
> >   KBUILD_CLIPPY := $(CLIPPY)
> > endif
> >
> > Then you can specify whatever value you want, support command line or
> > env vars, etc.?
>
> I was following the other existing cases like `V`. Masahiro can
> probably answer why they are done like this.

You are asking about this code:

ifeq ("$(origin V)", "command line")
  KBUILD_VERBOSE = $(V)
endif


You can pass V=1 from the Make command line,
but not from the environment.


KBUILD_VERBOSE is intended as an environment variable,
but you can use it from the Make command line.


Work:
 - make V=1
 - make KBUILD_VERBOSE=1
 - KBUILD_VERBOSE=1 make

Not work:
 - V=1 make


The behavior is like that before I became the maintainer.
In my best guess, the reason is,
V=1 is a useful shorthand of KBUILD_VERBOSE=1,
but it is too short. It should not accidentally
pick up an unintended environment variable.


-- 
Best Regards
Masahiro Yamada