Re: [PATCH 6/7] md/raid10, LLVM: get rid of variable length array

[Michael Davidson]

On Fri, Mar 17, 2017 at 5:44 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
> Be that as it may; what you construct above is disgusting. Surely the
> code can be refactored to not look like dog vomit?
>
> Also; its not immediately obvious conf->copies is 'small' and this
> doesn't blow up the stack; I feel that deserves a comment somewhere.
>

I agree that the code is horrible.

It is, in fact, exactly the same solution that was used to remove
variable length arrays in structs from several of the crypto drivers a
few years ago - see the definition of SHASH_DESC_ON_STACK() in
"crypto/hash.h" - I did not, however, hide the horrors in a macro
preferring to leave the implementation visible as a warning to whoever
might touch the code next.

I believe that the actual stack usage is exactly the same as it was previously.

I can certainly wrap this  up in a macro and add comments with
appropriately dire warnings in it if you feel that is both necessary
and sufficient.