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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Fri, 10 Jul 2020 16:54:11 -0700
Message-ID: <CAHk-=wipXqemHbVnK1kQsFzGOOZ8FUXn3PKrZb5WC=KkgAjRRw@mail.gmail.com>
Subject: Re: Linux kernel in-tree Rust support
To:     Josh Triplett <josh@joshtriplett.org>
Cc:     Christian Brauner <christian.brauner@ubuntu.com>,
        Nick Desaulniers <ndesaulniers@google.com>,
        alex.gaynor@gmail.com, Greg KH <gregkh@linuxfoundation.org>,
        geofft@ldpreload.com, jbaublitz@redhat.com,
        Masahiro Yamada <masahiroy@kernel.org>,
        Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        LKML <linux-kernel@vger.kernel.org>,
        clang-built-linux <clang-built-linux@googlegroups.com>,
        Kees Cook <keescook@chromium.org>
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On Fri, Jul 10, 2020 at 3:59 PM Josh Triplett <josh@joshtriplett.org> wrote:
>
> As I recall, Greg's biggest condition for initial introduction of this
> was to do the same kind of "turn this Kconfig option on and turn an
> option under it off" trick that LTO uses, so that neither "make
> allnoconfig" nor "make allyesconfig" would require Rust until we've had
> plenty of time to experiment with it.

No, please make it a "is rust available" automatic config option. The
exact same way we already do the compiler versions and check for
various availability of compiler flags at config time.

See init/Kconfig for things like

  config LD_IS_LLD
          def_bool $(success,$(LD) -v | head -n 1 | grep -q LLD)

and the rust support should be similar. Something like

  config RUST_IS_AVAILABLE
          def_bool $(success,$(RUST) ..sometest..)

because I _don't_ want us to be in the situation where any new rust
support isn't even build-tested by default.

Quite the reverse. I'd want the first rust driver (or whatever) to be
introduced in such a simple format that failures will be obvious and
simple.

The _worst_ situation to be in is that s (small) group of people start
testing their very special situation, and do bad and crazy things
because "nobody else cares, it's hidden".

No, thank you.

             Linus