Re: sparse feature request: nocast integer types

[Christoph Hellwig <hch@infradead.org>]

On Mon, Nov 27, 2023 at 03:51:05PM +0300, Dan Carpenter wrote:
> My plan was to go through the false positives and manually edit out
> stuff like this.  The problem is that it's a lot of work and I haven't
> done it.  I did a similar thing for tracking user data and that works
> pretty decently these days.  So it's doable.

Yes, doing it without specific annotations seems like a pain.  I did a
little prototype with the existing sparse __nocast for one xfs type that
is not very heavily used, and it actually worked pretty good.

The major painpoint is that 0 isn't treated special, but with that 
fixed the amount of churn is mangable.

The next big thing is our stupid 64-bit divison helpers (do_div & co),
which require helpers to do that case. I'm actually kinda tempted to
propose that we drop 32-bit support for xfs to get rid of that and a
lot of other ugly things because of do_div.  That is unless we can
finally agree that the libgcc division helpes might not be great but
good enough that we don't want to inflict do_div on folks unless they
want to optize that case, which would be even better.

Linus, any commens on that?

> I'd prefer an annotation that had the type of the unit built in.

Annotating the type seems really hard.  I think the sparse concept
of simply not alowing different of these types to be mixed is good
enough without needing to know the actual unit in the type system.