[RFC 1/2] rust: Introduce atomic API helpers

[Mark Rutland]

On Thu, Jun 13, 2024 at 11:17:47AM +0200, Peter Zijlstra wrote:
> On Thu, Jun 13, 2024 at 07:38:51AM +0200, Greg Kroah-Hartman wrote:
> > On Wed, Jun 12, 2024 at 03:30:24PM -0700, Boqun Feng wrote:
> > > +// Generated by scripts/atomic/gen-rust-atomic-helpers.sh
> > > +// DO NOT MODIFY THIS FILE DIRECTLY
> > 
> > Why not just build this at build time and not check the file into the
> > tree if it is always automatically generated?  That way it never gets
> > out of sync.  We do this for other types of auto-generated files in the
> > kernel today already.
> 
> Part of the problem is, is that a *TON* of files depend on the atomic.h
> headers. If we'd generate it on every build, you'd basically get to
> rebuild the whole kernel every single time.
> 
> Also, these files don't change too often. And if you look, there's a
> hash in those files which is used to check if things somehow got stale.

That and:

1) The generation is currently slow (multiple seconds), which gets
   people angry if they have to wait for it for a clean build. Improving
   that would require changing the way we generate the headers (e.g.
   rewrite that in something else to avoid the subshell fork problem).

   Last I looked there wasn't an obvious better way to do this, because
   nice options ended up pulling in more build-time dependencies.

2) Linus wanted git grep to work, which meant checking in the generated
   files:

   https://lore.kernel.org/all/CA+55aFxjU0op8QLLu0n-RjHBs7gQsLvD8jcyedgw6jeZFN7B+Q@mail.gmail.com/

Mark.