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SubjectRe: [PATCH] checkpatch: Add a --strict test for structs with bool member definitions
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(Adding Julia Lawall)

On Wed, 2018-04-11 at 09:29 -0700, Andrew Morton wrote:
> We already have some 500 bools-in-structs

I got at least triple that only in include/
so I expect there are at probably an order
of magnitude more than 500 in the kernel.

I suppose some cocci script could count the
actual number of instances. A regex can not.

> and the owners of that code will
> be wondering whether they should change them, and whether they should
> apply those remove-bool-in-struct patches which someone sent them.

Which is why the warning is --strict only

> So... can we please get some clarity here?


> ...
>
> (ooh, https://lkml.org/lkml/2017/11/21/384 is working this morning)
>
> hm, Linus suggests that instead of using
>
> bool mybool;
>
> we should use
>
> unsigned mybool:1;
>
> However that introduces the risk that alterations of mybool will use
> nonatomic rmw operations.
>
> unsigned myboolA:1;
> unsigned myboolB:1;
>
> so
>
> foo->myboolA = 1;
>
> could scribble on concurrent alterations of foo->myboolB. I think.

Without barriers, that could happen anyway.

To me, the biggest problem with conversions
from bool to bitfield is logical. ie:

unsigned int.singlebitfield = 4;

is not the same result as

bool = 4;

because of implicit truncation vs boolean conversion
so a direct change of bool use in structs to unsigned
would also require logic analysis.

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